X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=flow.cpp;h=3f3ff90ee6da46af401cf4ec636fc1581fd021bd;hb=d55856fef7b51604230ab3480f2930155d830ca8;hp=15161988eb77ddab0c9eaf070385763f40038584;hpb=c214d6919f05020b0695bccb8c948e6229c51375;p=nageru

diff --git a/flow.cpp b/flow.cpp
index 1516198..3f3ff90 100644
--- a/flow.cpp
+++ b/flow.cpp
@@ -1,8 +1,5 @@
 #define NO_SDL_GLEXT 1
 
-#define WIDTH 1280
-#define HEIGHT 720
-
 #include <epoxy/gl.h>
 
 #include <SDL2/SDL.h>
@@ -14,29 +11,71 @@
 #include <SDL2/SDL_video.h>
 
 #include <assert.h>
+#include <getopt.h>
 #include <stdio.h>
 #include <unistd.h>
 
+#include "gpu_timers.h"
 #include "util.h"
 
 #include <algorithm>
+#include <deque>
 #include <memory>
+#include <map>
+#include <stack>
 #include <vector>
 
 #define BUFFER_OFFSET(i) ((char *)nullptr + (i))
 
 using namespace std;
 
+SDL_Window *window;
+
 // Operating point 3 (10 Hz on CPU, excluding preprocessing).
 constexpr float patch_overlap_ratio = 0.75f;
 constexpr unsigned coarsest_level = 5;
 constexpr unsigned finest_level = 1;
 constexpr unsigned patch_size_pixels = 12;
 
+// Weighting constants for the different parts of the variational refinement.
+// These don't correspond 1:1 to the values given in the DIS paper,
+// since we have different normalizations and ranges in some cases.
+// These are found through a simple grid search on some MPI-Sintel data,
+// although the error (EPE) seems to be fairly insensitive to the precise values.
+// Only the relative values matter, so we fix alpha (the smoothness constant)
+// at unity and tweak the others.
+float vr_alpha = 1.0f, vr_delta = 0.25f, vr_gamma = 0.25f;
+
+bool enable_timing = true;
+bool detailed_timing = false;
+bool enable_variational_refinement = true;  // Just for debugging.
+bool enable_interpolation = false;
+
 // Some global OpenGL objects.
-GLuint nearest_sampler, linear_sampler, smoothness_sampler;
+// TODO: These should really be part of DISComputeFlow.
+GLuint nearest_sampler, linear_sampler, zero_border_sampler;
 GLuint vertex_vbo;
 
+// Structures for asynchronous readback. We assume everything is the same size (and GL_RG16F).
+struct ReadInProgress {
+	GLuint pbo;
+	string filename0, filename1;
+	string flow_filename, ppm_filename;  // Either may be empty for no write.
+};
+stack<GLuint> spare_pbos;
+deque<ReadInProgress> reads_in_progress;
+
+int find_num_levels(int width, int height)
+{
+	int levels = 1;
+	for (int w = width, h = height; w > 1 || h > 1; ) {
+		w >>= 1;
+		h >>= 1;
+		++levels;
+	}
+	return levels;
+}
+
 string read_file(const string &filename)
 {
 	FILE *fp = fopen(filename.c_str(), "r");
@@ -115,39 +154,53 @@ GLuint compile_shader(const string &shader_src, GLenum type)
 	return obj;
 }
 
+enum MipmapPolicy {
+	WITHOUT_MIPMAPS,
+	WITH_MIPMAPS
+};
 
-GLuint load_texture(const char *filename, unsigned width, unsigned height)
+GLuint load_texture(const char *filename, unsigned *width_ret, unsigned *height_ret, MipmapPolicy mipmaps)
 {
-	FILE *fp = fopen(filename, "rb");
-	if (fp == nullptr) {
-		perror(filename);
+	SDL_Surface *surf = IMG_Load(filename);
+	if (surf == nullptr) {
+		fprintf(stderr, "IMG_Load(%s): %s\n", filename, IMG_GetError());
 		exit(1);
 	}
-	unique_ptr<uint8_t[]> pix(new uint8_t[width * height]);
-	if (fread(pix.get(), width * height, 1, fp) != 1) {
-		fprintf(stderr, "Short read from %s\n", filename);
+
+	// For whatever reason, SDL doesn't support converting to YUV surfaces
+	// nor grayscale, so we'll do it ourselves.
+	SDL_Surface *rgb_surf = SDL_ConvertSurfaceFormat(surf, SDL_PIXELFORMAT_RGBA32, /*flags=*/0);
+	if (rgb_surf == nullptr) {
+		fprintf(stderr, "SDL_ConvertSurfaceFormat(%s): %s\n", filename, SDL_GetError());
 		exit(1);
 	}
-	fclose(fp);
 
-	// Convert to bottom-left origin.
-	for (unsigned y = 0; y < height / 2; ++y) {
+	SDL_FreeSurface(surf);
+
+	unsigned width = rgb_surf->w, height = rgb_surf->h;
+	const uint8_t *sptr = (uint8_t *)rgb_surf->pixels;
+	unique_ptr<uint8_t[]> pix(new uint8_t[width * height * 4]);
+
+	// Extract the Y component, and convert to bottom-left origin.
+	for (unsigned y = 0; y < height; ++y) {
 		unsigned y2 = height - 1 - y;
-		swap_ranges(&pix[y * width], &pix[y * width + width], &pix[y2 * width]);
+		memcpy(pix.get() + y * width * 4, sptr + y2 * rgb_surf->pitch, width * 4);
 	}
+	SDL_FreeSurface(rgb_surf);
 
-	int levels = 1;
-	for (int w = width, h = height; w > 1 || h > 1; ) {
-		w >>= 1;
-		h >>= 1;
-		++levels;
-	}
+	int num_levels = (mipmaps == WITH_MIPMAPS) ? find_num_levels(width, height) : 1;
 
 	GLuint tex;
 	glCreateTextures(GL_TEXTURE_2D, 1, &tex);
-	glTextureStorage2D(tex, levels, GL_R8, width, height);
-	glTextureSubImage2D(tex, 0, 0, 0, width, height, GL_RED, GL_UNSIGNED_BYTE, pix.get());
-	glGenerateTextureMipmap(tex);
+	glTextureStorage2D(tex, num_levels, GL_RGBA8, width, height);
+	glTextureSubImage2D(tex, 0, 0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pix.get());
+
+	if (mipmaps == WITH_MIPMAPS) {
+		glGenerateTextureMipmap(tex);
+	}
+
+	*width_ret = width;
+	*height_ret = height;
 
 	return tex;
 }
@@ -169,41 +222,165 @@ GLuint link_program(GLuint vs_obj, GLuint fs_obj)
 	return program;
 }
 
-GLuint generate_vbo(GLint size, GLsizeiptr data_size, const GLvoid *data)
+void bind_sampler(GLuint program, GLint location, GLuint texture_unit, GLuint tex, GLuint sampler)
 {
-	GLuint vbo;
-	glCreateBuffers(1, &vbo);
-	glBufferData(GL_ARRAY_BUFFER, data_size, data, GL_STATIC_DRAW);
-	glNamedBufferData(vbo, data_size, data, GL_STATIC_DRAW);
-	return vbo;
+	if (location == -1) {
+		return;
+	}
+
+	glBindTextureUnit(texture_unit, tex);
+	glBindSampler(texture_unit, sampler);
+	glProgramUniform1i(program, location, texture_unit);
 }
 
-GLuint fill_vertex_attribute(GLuint vao, GLuint glsl_program_num, const string &attribute_name, GLint size, GLenum type, GLsizeiptr data_size, const GLvoid *data)
-{
-	int attrib = glGetAttribLocation(glsl_program_num, attribute_name.c_str());
-	if (attrib == -1) {
-		return -1;
+// A class that caches FBOs that render to a given set of textures.
+// It never frees anything, so it is only suitable for rendering to
+// the same (small) set of textures over and over again.
+template<size_t num_elements>
+class PersistentFBOSet {
+public:
+	void render_to(const array<GLuint, num_elements> &textures);
+
+	// Convenience wrappers.
+	void render_to(GLuint texture0) {
+		render_to({{texture0}});
+	}
+
+	void render_to(GLuint texture0, GLuint texture1) {
+		render_to({{texture0, texture1}});
+	}
+
+	void render_to(GLuint texture0, GLuint texture1, GLuint texture2) {
+		render_to({{texture0, texture1, texture2}});
+	}
+
+	void render_to(GLuint texture0, GLuint texture1, GLuint texture2, GLuint texture3) {
+		render_to({{texture0, texture1, texture2, texture3}});
 	}
 
-	GLuint vbo = generate_vbo(size, data_size, data);
+private:
+	// TODO: Delete these on destruction.
+	map<array<GLuint, num_elements>, GLuint> fbos;
+};
+
+template<size_t num_elements>
+void PersistentFBOSet<num_elements>::render_to(const array<GLuint, num_elements> &textures)
+{
+	auto it = fbos.find(textures);
+	if (it != fbos.end()) {
+		glBindFramebuffer(GL_FRAMEBUFFER, it->second);
+		return;
+	}
 
-	glBindBuffer(GL_ARRAY_BUFFER, vbo);
-	glEnableVertexArrayAttrib(vao, attrib);
-	glVertexAttribPointer(attrib, size, type, GL_FALSE, 0, BUFFER_OFFSET(0));
-	glBindBuffer(GL_ARRAY_BUFFER, 0);
+	GLuint fbo;
+	glCreateFramebuffers(1, &fbo);
+	GLenum bufs[num_elements];
+	for (size_t i = 0; i < num_elements; ++i) {
+		glNamedFramebufferTexture(fbo, GL_COLOR_ATTACHMENT0 + i, textures[i], 0);
+		bufs[i] = GL_COLOR_ATTACHMENT0 + i;
+	}
+	glNamedFramebufferDrawBuffers(fbo, num_elements, bufs);
 
-	return vbo;
+	fbos[textures] = fbo;
+	glBindFramebuffer(GL_FRAMEBUFFER, fbo);
 }
 
-void bind_sampler(GLuint program, GLint location, GLuint texture_unit, GLuint tex, GLuint sampler)
+// Same, but with a depth texture.
+template<size_t num_elements>
+class PersistentFBOSetWithDepth {
+public:
+	void render_to(GLuint depth_tex, const array<GLuint, num_elements> &textures);
+
+	// Convenience wrappers.
+	void render_to(GLuint depth_tex, GLuint texture0) {
+		render_to(depth_tex, {{texture0}});
+	}
+
+	void render_to(GLuint depth_tex, GLuint texture0, GLuint texture1) {
+		render_to(depth_tex, {{texture0, texture1}});
+	}
+
+	void render_to(GLuint depth_tex, GLuint texture0, GLuint texture1, GLuint texture2) {
+		render_to(depth_tex, {{texture0, texture1, texture2}});
+	}
+
+	void render_to(GLuint depth_tex, GLuint texture0, GLuint texture1, GLuint texture2, GLuint texture3) {
+		render_to(depth_tex, {{texture0, texture1, texture2, texture3}});
+	}
+
+private:
+	// TODO: Delete these on destruction.
+	map<pair<GLuint, array<GLuint, num_elements>>, GLuint> fbos;
+};
+
+template<size_t num_elements>
+void PersistentFBOSetWithDepth<num_elements>::render_to(GLuint depth_tex, const array<GLuint, num_elements> &textures)
 {
-	if (location == -1) {
+	auto key = make_pair(depth_tex, textures);
+
+	auto it = fbos.find(key);
+	if (it != fbos.end()) {
+		glBindFramebuffer(GL_FRAMEBUFFER, it->second);
 		return;
 	}
 
-	glBindTextureUnit(texture_unit, tex);
-	glBindSampler(texture_unit, sampler);
-	glProgramUniform1i(program, location, texture_unit);
+	GLuint fbo;
+	glCreateFramebuffers(1, &fbo);
+	GLenum bufs[num_elements];
+	glNamedFramebufferTexture(fbo, GL_DEPTH_ATTACHMENT, depth_tex, 0);
+	for (size_t i = 0; i < num_elements; ++i) {
+		glNamedFramebufferTexture(fbo, GL_COLOR_ATTACHMENT0 + i, textures[i], 0);
+		bufs[i] = GL_COLOR_ATTACHMENT0 + i;
+	}
+	glNamedFramebufferDrawBuffers(fbo, num_elements, bufs);
+
+	fbos[key] = fbo;
+	glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+}
+
+// Convert RGB to grayscale, using Rec. 709 coefficients.
+class GrayscaleConversion {
+public:
+	GrayscaleConversion();
+	void exec(GLint tex, GLint gray_tex, int width, int height);
+
+private:
+	PersistentFBOSet<1> fbos;
+	GLuint gray_vs_obj;
+	GLuint gray_fs_obj;
+	GLuint gray_program;
+	GLuint gray_vao;
+
+	GLuint uniform_tex;
+};
+
+GrayscaleConversion::GrayscaleConversion()
+{
+	gray_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
+	gray_fs_obj = compile_shader(read_file("gray.frag"), GL_FRAGMENT_SHADER);
+	gray_program = link_program(gray_vs_obj, gray_fs_obj);
+
+	// Set up the VAO containing all the required position/texcoord data.
+	glCreateVertexArrays(1, &gray_vao);
+	glBindVertexArray(gray_vao);
+
+	GLint position_attrib = glGetAttribLocation(gray_program, "position");
+	glEnableVertexArrayAttrib(gray_vao, position_attrib);
+	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
+
+	uniform_tex = glGetUniformLocation(gray_program, "tex");
+}
+
+void GrayscaleConversion::exec(GLint tex, GLint gray_tex, int width, int height)
+{
+	glUseProgram(gray_program);
+	bind_sampler(gray_program, uniform_tex, 0, tex, nearest_sampler);
+
+	glViewport(0, 0, width, height);
+	fbos.render_to(gray_tex);
+	glBindVertexArray(gray_vao);
+	glDisable(GL_BLEND);
+	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
 // Compute gradients in every point, used for the motion search.
@@ -220,12 +397,12 @@ public:
 	void exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_height);
 
 private:
+	PersistentFBOSet<1> fbos;
 	GLuint sobel_vs_obj;
 	GLuint sobel_fs_obj;
 	GLuint sobel_program;
-	GLuint sobel_vao;
 
-	GLuint uniform_tex, uniform_image_size;
+	GLuint uniform_tex;
 };
 
 Sobel::Sobel()
@@ -234,32 +411,16 @@ Sobel::Sobel()
 	sobel_fs_obj = compile_shader(read_file("sobel.frag"), GL_FRAGMENT_SHADER);
 	sobel_program = link_program(sobel_vs_obj, sobel_fs_obj);
 
-	// Set up the VAO containing all the required position/texcoord data.
-	glCreateVertexArrays(1, &sobel_vao);
-	glBindVertexArray(sobel_vao);
-
-	GLint position_attrib = glGetAttribLocation(sobel_program, "position");
-	glEnableVertexArrayAttrib(sobel_vao, position_attrib);
-	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
 	uniform_tex = glGetUniformLocation(sobel_program, "tex");
 }
 
 void Sobel::exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_height)
 {
 	glUseProgram(sobel_program);
-	glBindTextureUnit(0, tex0_view);
-	glBindSampler(0, nearest_sampler);
-	glProgramUniform1i(sobel_program, uniform_tex, 0);
-
-	GLuint grad0_fbo;  // TODO: cleanup
-	glCreateFramebuffers(1, &grad0_fbo);
-	glNamedFramebufferTexture(grad0_fbo, GL_COLOR_ATTACHMENT0, grad0_tex, 0);
+	bind_sampler(sobel_program, uniform_tex, 0, tex0_view, nearest_sampler);
 
 	glViewport(0, 0, level_width, level_height);
-	glBindFramebuffer(GL_FRAMEBUFFER, grad0_fbo);
-	glBindVertexArray(sobel_vao);
-	glUseProgram(sobel_program);
+	fbos.render_to(grad0_tex);
 	glDisable(GL_BLEND);
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
@@ -271,13 +432,14 @@ public:
 	void exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GLuint flow_tex, GLuint flow_out_tex, int level_width, int level_height, int prev_level_width, int prev_level_height, int width_patches, int height_patches);
 
 private:
+	PersistentFBOSet<1> fbos;
+
 	GLuint motion_vs_obj;
 	GLuint motion_fs_obj;
 	GLuint motion_search_program;
-	GLuint motion_search_vao;
 
-	GLuint uniform_image_size, uniform_inv_image_size, uniform_inv_prev_level_size;
-	GLuint uniform_image0_tex, uniform_image1_tex, uniform_grad0_tex, uniform_flow_tex;
+	GLuint uniform_inv_image_size, uniform_inv_prev_level_size;
+	GLuint uniform_image1_tex, uniform_grad0_tex, uniform_flow_tex;
 };
 
 MotionSearch::MotionSearch()
@@ -286,19 +448,8 @@ MotionSearch::MotionSearch()
 	motion_fs_obj = compile_shader(read_file("motion_search.frag"), GL_FRAGMENT_SHADER);
 	motion_search_program = link_program(motion_vs_obj, motion_fs_obj);
 
-	// Set up the VAO containing all the required position/texcoord data.
-	glCreateVertexArrays(1, &motion_search_vao);
-	glBindVertexArray(motion_search_vao);
-	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
-
-	GLint position_attrib = glGetAttribLocation(motion_search_program, "position");
-	glEnableVertexArrayAttrib(motion_search_vao, position_attrib);
-	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
-	uniform_image_size = glGetUniformLocation(motion_search_program, "image_size");
 	uniform_inv_image_size = glGetUniformLocation(motion_search_program, "inv_image_size");
 	uniform_inv_prev_level_size = glGetUniformLocation(motion_search_program, "inv_prev_level_size");
-	uniform_image0_tex = glGetUniformLocation(motion_search_program, "image0_tex");
 	uniform_image1_tex = glGetUniformLocation(motion_search_program, "image1_tex");
 	uniform_grad0_tex = glGetUniformLocation(motion_search_program, "grad0_tex");
 	uniform_flow_tex = glGetUniformLocation(motion_search_program, "flow_tex");
@@ -308,23 +459,15 @@ void MotionSearch::exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GL
 {
 	glUseProgram(motion_search_program);
 
-	bind_sampler(motion_search_program, uniform_image0_tex, 0, tex0_view, nearest_sampler);
 	bind_sampler(motion_search_program, uniform_image1_tex, 1, tex1_view, linear_sampler);
-	bind_sampler(motion_search_program, uniform_grad0_tex, 2, grad0_tex, nearest_sampler);
+	bind_sampler(motion_search_program, uniform_grad0_tex, 2, grad0_tex, linear_sampler);
 	bind_sampler(motion_search_program, uniform_flow_tex, 3, flow_tex, linear_sampler);
 
-	glProgramUniform2f(motion_search_program, uniform_image_size, level_width, level_height);
 	glProgramUniform2f(motion_search_program, uniform_inv_image_size, 1.0f / level_width, 1.0f / level_height);
 	glProgramUniform2f(motion_search_program, uniform_inv_prev_level_size, 1.0f / prev_level_width, 1.0f / prev_level_height);
 
-	GLuint flow_fbo;  // TODO: cleanup
-	glCreateFramebuffers(1, &flow_fbo);
-	glNamedFramebufferTexture(flow_fbo, GL_COLOR_ATTACHMENT0, flow_out_tex, 0);
-
 	glViewport(0, 0, width_patches, height_patches);
-	glBindFramebuffer(GL_FRAMEBUFFER, flow_fbo);
-	glBindVertexArray(motion_search_vao);
-	glUseProgram(motion_search_program);
+	fbos.render_to(flow_out_tex);
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
@@ -342,12 +485,13 @@ public:
 	void exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint dense_flow_tex, int level_width, int level_height, int width_patches, int height_patches);
 
 private:
+	PersistentFBOSet<1> fbos;
+
 	GLuint densify_vs_obj;
 	GLuint densify_fs_obj;
 	GLuint densify_program;
-	GLuint densify_vao;
 
-	GLuint uniform_width_patches, uniform_patch_size, uniform_patch_spacing;
+	GLuint uniform_patch_size;
 	GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
 };
 
@@ -357,18 +501,7 @@ Densify::Densify()
 	densify_fs_obj = compile_shader(read_file("densify.frag"), GL_FRAGMENT_SHADER);
 	densify_program = link_program(densify_vs_obj, densify_fs_obj);
 
-	// Set up the VAO containing all the required position/texcoord data.
-	glCreateVertexArrays(1, &densify_vao);
-	glBindVertexArray(densify_vao);
-	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
-
-	GLint position_attrib = glGetAttribLocation(densify_program, "position");
-	glEnableVertexArrayAttrib(densify_vao, position_attrib);
-	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
-	uniform_width_patches = glGetUniformLocation(densify_program, "width_patches");
 	uniform_patch_size = glGetUniformLocation(densify_program, "patch_size");
-	uniform_patch_spacing = glGetUniformLocation(densify_program, "patch_spacing");
 	uniform_image0_tex = glGetUniformLocation(densify_program, "image0_tex");
 	uniform_image1_tex = glGetUniformLocation(densify_program, "image1_tex");
 	uniform_flow_tex = glGetUniformLocation(densify_program, "flow_tex");
@@ -382,28 +515,16 @@ void Densify::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint d
 	bind_sampler(densify_program, uniform_image1_tex, 1, tex1_view, linear_sampler);
 	bind_sampler(densify_program, uniform_flow_tex, 2, flow_tex, nearest_sampler);
 
-	glProgramUniform1i(densify_program, uniform_width_patches, width_patches);
 	glProgramUniform2f(densify_program, uniform_patch_size,
 		float(patch_size_pixels) / level_width,
 		float(patch_size_pixels) / level_height);
 
-	float patch_spacing_x = float(level_width - patch_size_pixels) / (width_patches - 1);
-	float patch_spacing_y = float(level_height - patch_size_pixels) / (height_patches - 1);
-	if (width_patches == 1) patch_spacing_x = 0.0f;  // Avoid infinities.
-	if (height_patches == 1) patch_spacing_y = 0.0f;
-	glProgramUniform2f(densify_program, uniform_patch_spacing,
-		patch_spacing_x / level_width,
-		patch_spacing_y / level_height);
-
-	GLuint dense_flow_fbo;  // TODO: cleanup
-	glCreateFramebuffers(1, &dense_flow_fbo);
-	glNamedFramebufferTexture(dense_flow_fbo, GL_COLOR_ATTACHMENT0, dense_flow_tex, 0);
-
 	glViewport(0, 0, level_width, level_height);
 	glEnable(GL_BLEND);
 	glBlendFunc(GL_ONE, GL_ONE);
-	glBindVertexArray(densify_vao);
-	glBindFramebuffer(GL_FRAMEBUFFER, dense_flow_fbo);
+	fbos.render_to(dense_flow_tex);
+	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
+	glClear(GL_COLOR_BUFFER_BIT);
 	glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width_patches * height_patches);
 }
 
@@ -421,13 +542,13 @@ public:
 	void exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint normalized_flow_tex, GLuint I_tex, GLuint I_t_tex, int level_width, int level_height);
 
 private:
+	PersistentFBOSet<3> fbos;
+
 	GLuint prewarp_vs_obj;
 	GLuint prewarp_fs_obj;
 	GLuint prewarp_program;
-	GLuint prewarp_vao;
 
 	GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
-	GLuint uniform_image_size;
 };
 
 Prewarp::Prewarp()
@@ -436,20 +557,9 @@ Prewarp::Prewarp()
 	prewarp_fs_obj = compile_shader(read_file("prewarp.frag"), GL_FRAGMENT_SHADER);
 	prewarp_program = link_program(prewarp_vs_obj, prewarp_fs_obj);
 
-	// Set up the VAO containing all the required position/texcoord data.
-	glCreateVertexArrays(1, &prewarp_vao);
-	glBindVertexArray(prewarp_vao);
-	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
-
-	GLint position_attrib = glGetAttribLocation(prewarp_program, "position");
-	glEnableVertexArrayAttrib(prewarp_vao, position_attrib);
-	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
 	uniform_image0_tex = glGetUniformLocation(prewarp_program, "image0_tex");
 	uniform_image1_tex = glGetUniformLocation(prewarp_program, "image1_tex");
 	uniform_flow_tex = glGetUniformLocation(prewarp_program, "flow_tex");
-
-	uniform_image_size = glGetUniformLocation(prewarp_program, "image_size");
 }
 
 void Prewarp::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint I_tex, GLuint I_t_tex, GLuint normalized_flow_tex, int level_width, int level_height)
@@ -460,20 +570,9 @@ void Prewarp::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint I
 	bind_sampler(prewarp_program, uniform_image1_tex, 1, tex1_view, linear_sampler);
 	bind_sampler(prewarp_program, uniform_flow_tex, 2, flow_tex, nearest_sampler);
 
-	glProgramUniform2f(prewarp_program, uniform_image_size, level_width, level_height);
-
-	GLuint prewarp_fbo;  // TODO: cleanup
-	glCreateFramebuffers(1, &prewarp_fbo);
-	GLenum bufs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2 };
-	glNamedFramebufferDrawBuffers(prewarp_fbo, 3, bufs);
-	glNamedFramebufferTexture(prewarp_fbo, GL_COLOR_ATTACHMENT0, I_tex, 0);
-	glNamedFramebufferTexture(prewarp_fbo, GL_COLOR_ATTACHMENT1, I_t_tex, 0);
-	glNamedFramebufferTexture(prewarp_fbo, GL_COLOR_ATTACHMENT2, normalized_flow_tex, 0);
-
 	glViewport(0, 0, level_width, level_height);
 	glDisable(GL_BLEND);
-	glBindVertexArray(prewarp_vao);
-	glBindFramebuffer(GL_FRAMEBUFFER, prewarp_fbo);
+	fbos.render_to(I_tex, I_t_tex, normalized_flow_tex);
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
@@ -491,10 +590,11 @@ public:
 	void exec(GLuint input_tex, GLuint I_x_y_tex, GLuint beta_0_tex, int level_width, int level_height);
 
 private:
+	PersistentFBOSet<2> fbos;
+
 	GLuint derivatives_vs_obj;
 	GLuint derivatives_fs_obj;
 	GLuint derivatives_program;
-	GLuint derivatives_vao;
 
 	GLuint uniform_tex;
 };
@@ -505,15 +605,6 @@ Derivatives::Derivatives()
 	derivatives_fs_obj = compile_shader(read_file("derivatives.frag"), GL_FRAGMENT_SHADER);
 	derivatives_program = link_program(derivatives_vs_obj, derivatives_fs_obj);
 
-	// Set up the VAO containing all the required position/texcoord data.
-	glCreateVertexArrays(1, &derivatives_vao);
-	glBindVertexArray(derivatives_vao);
-	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
-
-	GLint position_attrib = glGetAttribLocation(derivatives_program, "position");
-	glEnableVertexArrayAttrib(derivatives_vao, position_attrib);
-	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
 	uniform_tex = glGetUniformLocation(derivatives_program, "tex");
 }
 
@@ -523,87 +614,60 @@ void Derivatives::exec(GLuint input_tex, GLuint I_x_y_tex, GLuint beta_0_tex, in
 
 	bind_sampler(derivatives_program, uniform_tex, 0, input_tex, nearest_sampler);
 
-	GLuint derivatives_fbo;  // TODO: cleanup
-	glCreateFramebuffers(1, &derivatives_fbo);
-	GLenum bufs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
-	glNamedFramebufferDrawBuffers(derivatives_fbo, 2, bufs);
-	glNamedFramebufferTexture(derivatives_fbo, GL_COLOR_ATTACHMENT0, I_x_y_tex, 0);
-	glNamedFramebufferTexture(derivatives_fbo, GL_COLOR_ATTACHMENT1, beta_0_tex, 0);
-
 	glViewport(0, 0, level_width, level_height);
 	glDisable(GL_BLEND);
-	glBindVertexArray(derivatives_vao);
-	glBindFramebuffer(GL_FRAMEBUFFER, derivatives_fbo);
+	fbos.render_to(I_x_y_tex, beta_0_tex);
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
-// Calculate the smoothness constraints between neighboring pixels;
-// s_x(x,y) stores smoothness between pixel (x,y) and (x+1,y),
-// and s_y(x,y) stores between (x,y) and (x,y+1). We'll sample with
-// border color (0,0) later, so that there's zero diffusion out of
-// the border.
+// Calculate the diffusivity for each pixels, g(x,y). Smoothness (s) will
+// be calculated in the shaders on-the-fly by sampling in-between two
+// neighboring g(x,y) pixels, plus a border tweak to make sure we get
+// zero smoothness at the border.
 //
 // See variational_refinement.txt for more information.
-class ComputeSmoothness {
+class ComputeDiffusivity {
 public:
-	ComputeSmoothness();
-	void exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, int level_width, int level_height);
+	ComputeDiffusivity();
+	void exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint diffusivity_tex, int level_width, int level_height, bool zero_diff_flow);
 
 private:
-	GLuint smoothness_vs_obj;
-	GLuint smoothness_fs_obj;
-	GLuint smoothness_program;
-	GLuint smoothness_vao;
+	PersistentFBOSet<1> fbos;
+
+	GLuint diffusivity_vs_obj;
+	GLuint diffusivity_fs_obj;
+	GLuint diffusivity_program;
 
 	GLuint uniform_flow_tex, uniform_diff_flow_tex;
+	GLuint uniform_alpha, uniform_zero_diff_flow;
 };
 
-ComputeSmoothness::ComputeSmoothness()
+ComputeDiffusivity::ComputeDiffusivity()
 {
-	smoothness_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
-	smoothness_fs_obj = compile_shader(read_file("smoothness.frag"), GL_FRAGMENT_SHADER);
-	smoothness_program = link_program(smoothness_vs_obj, smoothness_fs_obj);
-
-	// Set up the VAO containing all the required position/texcoord data.
-	glCreateVertexArrays(1, &smoothness_vao);
-	glBindVertexArray(smoothness_vao);
-	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
-
-	GLint position_attrib = glGetAttribLocation(smoothness_program, "position");
-	glEnableVertexArrayAttrib(smoothness_vao, position_attrib);
-	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
-	uniform_flow_tex = glGetUniformLocation(smoothness_program, "flow_tex");
-	uniform_diff_flow_tex = glGetUniformLocation(smoothness_program, "diff_flow_tex");
+	diffusivity_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
+	diffusivity_fs_obj = compile_shader(read_file("diffusivity.frag"), GL_FRAGMENT_SHADER);
+	diffusivity_program = link_program(diffusivity_vs_obj, diffusivity_fs_obj);
+
+	uniform_flow_tex = glGetUniformLocation(diffusivity_program, "flow_tex");
+	uniform_diff_flow_tex = glGetUniformLocation(diffusivity_program, "diff_flow_tex");
+	uniform_alpha = glGetUniformLocation(diffusivity_program, "alpha");
+	uniform_zero_diff_flow = glGetUniformLocation(diffusivity_program, "zero_diff_flow");
 }
 
-void ComputeSmoothness::exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, int level_width, int level_height)
+void ComputeDiffusivity::exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint diffusivity_tex, int level_width, int level_height, bool zero_diff_flow)
 {
-	glUseProgram(smoothness_program);
+	glUseProgram(diffusivity_program);
 
-	bind_sampler(smoothness_program, uniform_flow_tex, 0, flow_tex, nearest_sampler);
-	bind_sampler(smoothness_program, uniform_diff_flow_tex, 1, diff_flow_tex, nearest_sampler);
-
-	GLuint smoothness_fbo;  // TODO: cleanup
-	glCreateFramebuffers(1, &smoothness_fbo);
-	GLenum bufs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
-	glNamedFramebufferDrawBuffers(smoothness_fbo, 2, bufs);
-	glNamedFramebufferTexture(smoothness_fbo, GL_COLOR_ATTACHMENT0, smoothness_x_tex, 0);
-	glNamedFramebufferTexture(smoothness_fbo, GL_COLOR_ATTACHMENT1, smoothness_y_tex, 0);
+	bind_sampler(diffusivity_program, uniform_flow_tex, 0, flow_tex, nearest_sampler);
+	bind_sampler(diffusivity_program, uniform_diff_flow_tex, 1, diff_flow_tex, nearest_sampler);
+	glProgramUniform1f(diffusivity_program, uniform_alpha, vr_alpha);
+	glProgramUniform1i(diffusivity_program, uniform_zero_diff_flow, zero_diff_flow);
 
 	glViewport(0, 0, level_width, level_height);
 
 	glDisable(GL_BLEND);
-	glBindVertexArray(smoothness_vao);
-	glBindFramebuffer(GL_FRAMEBUFFER, smoothness_fbo);
+	fbos.render_to(diffusivity_tex);
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
-
-	// Make sure the smoothness on the right and upper borders is zero.
-	// We could have done this by making (W-1)xH and Wx(H-1) textures instead
-	// (we're sampling smoothness with all-zero border color), but we'd
-	// have to adjust the sampling coordinates, which is annoying.
-	glClearTexSubImage(smoothness_x_tex, 0,  level_width - 1, 0, 0,   1, level_height, 1,  GL_RED, GL_FLOAT, nullptr);
-	glClearTexSubImage(smoothness_y_tex, 0,  0, level_height - 1, 0,  level_width, 1, 1,   GL_RED, GL_FLOAT, nullptr);
 }
 
 // Set up the equations set (two equations in two unknowns, per pixel).
@@ -619,45 +683,40 @@ void ComputeSmoothness::exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint smoot
 class SetupEquations {
 public:
 	SetupEquations();
-	void exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex, GLuint flow_tex, GLuint beta_0_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, GLuint equation_tex, int level_width, int level_height);
+	void exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex, GLuint flow_tex, GLuint beta_0_tex, GLuint diffusivity_tex, GLuint equation_tex, int level_width, int level_height, bool zero_diff_flow);
 
 private:
+	PersistentFBOSet<1> fbos;
+
 	GLuint equations_vs_obj;
 	GLuint equations_fs_obj;
 	GLuint equations_program;
-	GLuint equations_vao;
 
 	GLuint uniform_I_x_y_tex, uniform_I_t_tex;
 	GLuint uniform_diff_flow_tex, uniform_base_flow_tex;
 	GLuint uniform_beta_0_tex;
-	GLuint uniform_smoothness_x_tex, uniform_smoothness_y_tex;
+	GLuint uniform_diffusivity_tex;
+	GLuint uniform_gamma, uniform_delta, uniform_zero_diff_flow;
 };
 
 SetupEquations::SetupEquations()
 {
-	equations_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
+	equations_vs_obj = compile_shader(read_file("equations.vert"), GL_VERTEX_SHADER);
 	equations_fs_obj = compile_shader(read_file("equations.frag"), GL_FRAGMENT_SHADER);
 	equations_program = link_program(equations_vs_obj, equations_fs_obj);
 
-	// Set up the VAO containing all the required position/texcoord data.
-	glCreateVertexArrays(1, &equations_vao);
-	glBindVertexArray(equations_vao);
-	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
-
-	GLint position_attrib = glGetAttribLocation(equations_program, "position");
-	glEnableVertexArrayAttrib(equations_vao, position_attrib);
-	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
 	uniform_I_x_y_tex = glGetUniformLocation(equations_program, "I_x_y_tex");
 	uniform_I_t_tex = glGetUniformLocation(equations_program, "I_t_tex");
 	uniform_diff_flow_tex = glGetUniformLocation(equations_program, "diff_flow_tex");
 	uniform_base_flow_tex = glGetUniformLocation(equations_program, "base_flow_tex");
 	uniform_beta_0_tex = glGetUniformLocation(equations_program, "beta_0_tex");
-	uniform_smoothness_x_tex = glGetUniformLocation(equations_program, "smoothness_x_tex");
-	uniform_smoothness_y_tex = glGetUniformLocation(equations_program, "smoothness_y_tex");
+	uniform_diffusivity_tex = glGetUniformLocation(equations_program, "diffusivity_tex");
+	uniform_gamma = glGetUniformLocation(equations_program, "gamma");
+	uniform_delta = glGetUniformLocation(equations_program, "delta");
+	uniform_zero_diff_flow = glGetUniformLocation(equations_program, "zero_diff_flow");
 }
 
-void SetupEquations::exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex, GLuint base_flow_tex, GLuint beta_0_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, GLuint equation_tex, int level_width, int level_height)
+void SetupEquations::exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex, GLuint base_flow_tex, GLuint beta_0_tex, GLuint diffusivity_tex, GLuint equation_tex, int level_width, int level_height, bool zero_diff_flow)
 {
 	glUseProgram(equations_program);
 
@@ -666,87 +725,89 @@ void SetupEquations::exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex
 	bind_sampler(equations_program, uniform_diff_flow_tex, 2, diff_flow_tex, nearest_sampler);
 	bind_sampler(equations_program, uniform_base_flow_tex, 3, base_flow_tex, nearest_sampler);
 	bind_sampler(equations_program, uniform_beta_0_tex, 4, beta_0_tex, nearest_sampler);
-	bind_sampler(equations_program, uniform_smoothness_x_tex, 5, smoothness_x_tex, smoothness_sampler);
-	bind_sampler(equations_program, uniform_smoothness_y_tex, 6, smoothness_y_tex, smoothness_sampler);
-
-	GLuint equations_fbo;  // TODO: cleanup
-	glCreateFramebuffers(1, &equations_fbo);
-	glNamedFramebufferTexture(equations_fbo, GL_COLOR_ATTACHMENT0, equation_tex, 0);
+	bind_sampler(equations_program, uniform_diffusivity_tex, 5, diffusivity_tex, zero_border_sampler);
+	glProgramUniform1f(equations_program, uniform_delta, vr_delta);
+	glProgramUniform1f(equations_program, uniform_gamma, vr_gamma);
+	glProgramUniform1i(equations_program, uniform_zero_diff_flow, zero_diff_flow);
 
 	glViewport(0, 0, level_width, level_height);
 	glDisable(GL_BLEND);
-	glBindVertexArray(equations_vao);
-	glBindFramebuffer(GL_FRAMEBUFFER, equations_fbo);
+	fbos.render_to(equation_tex);
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
-// Calculate the smoothness constraints between neighboring pixels;
-// s_x(x,y) stores smoothness between pixel (x,y) and (x+1,y),
-// and s_y(x,y) stores between (x,y) and (x,y+1). We'll sample with
-// border color (0,0) later, so that there's zero diffusion out of
-// the border.
+// Actually solve the equation sets made by SetupEquations, by means of
+// successive over-relaxation (SOR).
 //
 // See variational_refinement.txt for more information.
 class SOR {
 public:
 	SOR();
-	void exec(GLuint diff_flow_tex, GLuint equation_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, int level_width, int level_height, int num_iterations);
+	void exec(GLuint diff_flow_tex, GLuint equation_tex, GLuint diffusivity_tex, int level_width, int level_height, int num_iterations, bool zero_diff_flow, ScopedTimer *sor_timer);
 
 private:
+	PersistentFBOSet<1> fbos;
+
 	GLuint sor_vs_obj;
 	GLuint sor_fs_obj;
 	GLuint sor_program;
-	GLuint sor_vao;
 
 	GLuint uniform_diff_flow_tex;
 	GLuint uniform_equation_tex;
-	GLuint uniform_smoothness_x_tex, uniform_smoothness_y_tex;
+	GLuint uniform_diffusivity_tex;
+	GLuint uniform_phase, uniform_zero_diff_flow;
 };
 
 SOR::SOR()
 {
-	sor_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
+	sor_vs_obj = compile_shader(read_file("sor.vert"), GL_VERTEX_SHADER);
 	sor_fs_obj = compile_shader(read_file("sor.frag"), GL_FRAGMENT_SHADER);
 	sor_program = link_program(sor_vs_obj, sor_fs_obj);
 
-	// Set up the VAO containing all the required position/texcoord data.
-	glCreateVertexArrays(1, &sor_vao);
-	glBindVertexArray(sor_vao);
-	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
-
-	GLint position_attrib = glGetAttribLocation(sor_program, "position");
-	glEnableVertexArrayAttrib(sor_vao, position_attrib);
-	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
 	uniform_diff_flow_tex = glGetUniformLocation(sor_program, "diff_flow_tex");
 	uniform_equation_tex = glGetUniformLocation(sor_program, "equation_tex");
-	uniform_smoothness_x_tex = glGetUniformLocation(sor_program, "smoothness_x_tex");
-	uniform_smoothness_y_tex = glGetUniformLocation(sor_program, "smoothness_y_tex");
+	uniform_diffusivity_tex = glGetUniformLocation(sor_program, "diffusivity_tex");
+	uniform_phase = glGetUniformLocation(sor_program, "phase");
+	uniform_zero_diff_flow = glGetUniformLocation(sor_program, "zero_diff_flow");
 }
 
-void SOR::exec(GLuint diff_flow_tex, GLuint equation_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, int level_width, int level_height, int num_iterations)
+void SOR::exec(GLuint diff_flow_tex, GLuint equation_tex, GLuint diffusivity_tex, int level_width, int level_height, int num_iterations, bool zero_diff_flow, ScopedTimer *sor_timer)
 {
 	glUseProgram(sor_program);
 
 	bind_sampler(sor_program, uniform_diff_flow_tex, 0, diff_flow_tex, nearest_sampler);
-	bind_sampler(sor_program, uniform_smoothness_x_tex, 1, smoothness_x_tex, smoothness_sampler);
-	bind_sampler(sor_program, uniform_smoothness_y_tex, 2, smoothness_y_tex, smoothness_sampler);
-	bind_sampler(sor_program, uniform_equation_tex, 3, equation_tex, nearest_sampler);
+	bind_sampler(sor_program, uniform_diffusivity_tex, 1, diffusivity_tex, zero_border_sampler);
+	bind_sampler(sor_program, uniform_equation_tex, 2, equation_tex, nearest_sampler);
 
-	GLuint sor_fbo;  // TODO: cleanup
-	glCreateFramebuffers(1, &sor_fbo);
-	glNamedFramebufferTexture(sor_fbo, GL_COLOR_ATTACHMENT0, diff_flow_tex, 0);  // NOTE: Bind to same as we render from!
+	glProgramUniform1i(sor_program, uniform_zero_diff_flow, zero_diff_flow);
 
+	// NOTE: We bind to the texture we are rendering from, but we never write any value
+	// that we read in the same shader pass (we call discard for red values when we compute
+	// black, and vice versa), and we have barriers between the passes, so we're fine
+	// as per the spec.
 	glViewport(0, 0, level_width, level_height);
 	glDisable(GL_BLEND);
-	glBindVertexArray(sor_vao);
-	glBindFramebuffer(GL_FRAMEBUFFER, sor_fbo);
+	fbos.render_to(diff_flow_tex);
 
 	for (int i = 0; i < num_iterations; ++i) {
-		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
-		if (i != num_iterations - 1) {
+		{
+			ScopedTimer timer("Red pass", sor_timer);
+			glProgramUniform1i(sor_program, uniform_phase, 0);
+			glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 			glTextureBarrier();
 		}
+		{
+			ScopedTimer timer("Black pass", sor_timer);
+			if (zero_diff_flow && i == 0) {
+				// Not zero anymore.
+				glProgramUniform1i(sor_program, uniform_zero_diff_flow, 0);
+			}
+			glProgramUniform1i(sor_program, uniform_phase, 1);
+			glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+			if (i != num_iterations - 1) {
+				glTextureBarrier();
+			}
+		}
 	}
 }
 
@@ -758,10 +819,11 @@ public:
 	void exec(GLuint base_flow_tex, GLuint diff_flow_tex, int level_width, int level_height);
 
 private:
+	PersistentFBOSet<1> fbos;
+
 	GLuint add_flow_vs_obj;
 	GLuint add_flow_fs_obj;
 	GLuint add_flow_program;
-	GLuint add_flow_vao;
 
 	GLuint uniform_diff_flow_tex;
 };
@@ -772,15 +834,6 @@ AddBaseFlow::AddBaseFlow()
 	add_flow_fs_obj = compile_shader(read_file("add_base_flow.frag"), GL_FRAGMENT_SHADER);
 	add_flow_program = link_program(add_flow_vs_obj, add_flow_fs_obj);
 
-	// Set up the VAO containing all the required position/texcoord data.
-	glCreateVertexArrays(1, &add_flow_vao);
-	glBindVertexArray(add_flow_vao);
-	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
-
-	GLint position_attrib = glGetAttribLocation(add_flow_program, "position");
-	glEnableVertexArrayAttrib(add_flow_vao, position_attrib);
-	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
 	uniform_diff_flow_tex = glGetUniformLocation(add_flow_program, "diff_flow_tex");
 }
 
@@ -790,126 +843,110 @@ void AddBaseFlow::exec(GLuint base_flow_tex, GLuint diff_flow_tex, int level_wid
 
 	bind_sampler(add_flow_program, uniform_diff_flow_tex, 0, diff_flow_tex, nearest_sampler);
 
-	GLuint add_flow_fbo;  // TODO: cleanup
-	glCreateFramebuffers(1, &add_flow_fbo);
-	glNamedFramebufferTexture(add_flow_fbo, GL_COLOR_ATTACHMENT0, base_flow_tex, 0);
-
 	glViewport(0, 0, level_width, level_height);
 	glEnable(GL_BLEND);
 	glBlendFunc(GL_ONE, GL_ONE);
-	glBindVertexArray(add_flow_vao);
-	glBindFramebuffer(GL_FRAMEBUFFER, add_flow_fbo);
+	fbos.render_to(base_flow_tex);
 
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
-class GPUTimers {
+// Take a copy of the flow, bilinearly interpolated and scaled up.
+class ResizeFlow {
 public:
-	void print();
-	pair<GLuint, GLuint> begin_timer(const string &name, int level);
+	ResizeFlow();
+	void exec(GLuint in_tex, GLuint out_tex, int input_width, int input_height, int output_width, int output_height);
 
 private:
-	struct Timer {
-		string name;
-		int level;
-		pair<GLuint, GLuint> query;
-	};
-	vector<Timer> timers;
+	PersistentFBOSet<1> fbos;
+
+	GLuint resize_flow_vs_obj;
+	GLuint resize_flow_fs_obj;
+	GLuint resize_flow_program;
+
+	GLuint uniform_flow_tex;
+	GLuint uniform_scale_factor;
 };
 
-pair<GLuint, GLuint> GPUTimers::begin_timer(const string &name, int level)
+ResizeFlow::ResizeFlow()
 {
-	GLuint queries[2];
-	glGenQueries(2, queries);
-	glQueryCounter(queries[0], GL_TIMESTAMP);
-
-	Timer timer;
-	timer.name = name;
-	timer.level = level;
-	timer.query.first = queries[0];
-	timer.query.second = queries[1];
-	timers.push_back(timer);
-	return timer.query;
+	resize_flow_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
+	resize_flow_fs_obj = compile_shader(read_file("resize_flow.frag"), GL_FRAGMENT_SHADER);
+	resize_flow_program = link_program(resize_flow_vs_obj, resize_flow_fs_obj);
+
+	uniform_flow_tex = glGetUniformLocation(resize_flow_program, "flow_tex");
+	uniform_scale_factor = glGetUniformLocation(resize_flow_program, "scale_factor");
 }
 
-void GPUTimers::print()
+void ResizeFlow::exec(GLuint flow_tex, GLuint out_tex, int input_width, int input_height, int output_width, int output_height)
 {
-	for (const Timer &timer : timers) {
-		// NOTE: This makes the CPU wait for the GPU.
-		GLuint64 time_start, time_end;
-		glGetQueryObjectui64v(timer.query.first, GL_QUERY_RESULT, &time_start);
-		glGetQueryObjectui64v(timer.query.second, GL_QUERY_RESULT, &time_end);
-		//fprintf(stderr, "GPU time used = %.1f ms\n", time_elapsed / 1e6);
-		for (int i = 0; i < timer.level * 2; ++i) {
-			fprintf(stderr, " ");
-		}
-		fprintf(stderr, "%-30s %4.1f ms\n", timer.name.c_str(), (time_end - time_start) / 1e6);
-	}
-}
+	glUseProgram(resize_flow_program);
 
-// A simple RAII class for timing until the end of the scope.
-class ScopedTimer {
-public:
-	ScopedTimer(const string &name, GPUTimers *timers)
-		: timers(timers), level(0)
-	{
-		query = timers->begin_timer(name, level);
-	}
+	bind_sampler(resize_flow_program, uniform_flow_tex, 0, flow_tex, nearest_sampler);
 
-	ScopedTimer(const string &name, ScopedTimer *parent_timer)
-		: timers(parent_timer->timers),
-		  level(parent_timer->level + 1)
-	{
-		query = timers->begin_timer(name, level);
-	}
+	glProgramUniform2f(resize_flow_program, uniform_scale_factor, float(output_width) / input_width, float(output_height) / input_height);
 
-	~ScopedTimer()
-	{
-		end();
-	}
+	glViewport(0, 0, output_width, output_height);
+	glDisable(GL_BLEND);
+	fbos.render_to(out_tex);
 
-	void end()
-	{
-		if (!ended) {
-			glQueryCounter(query.second, GL_TIMESTAMP);
-			ended = true;
-		}
-	}
+	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+}
+
+class TexturePool {
+public:
+	GLuint get_texture(GLenum format, GLuint width, GLuint height);
+	void release_texture(GLuint tex_num);
 
 private:
-	GPUTimers *timers;
-	int level;
-	pair<GLuint, GLuint> query;
-	bool ended = false;
+	struct Texture {
+		GLuint tex_num;
+		GLenum format;
+		GLuint width, height;
+		bool in_use = false;
+	};
+	vector<Texture> textures;
 };
 
-int main(void)
-{
-	if (SDL_Init(SDL_INIT_EVERYTHING) == -1) {
-		fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
-		exit(1);
+class DISComputeFlow {
+public:
+	DISComputeFlow(int width, int height);
+
+	enum ResizeStrategy {
+		DO_NOT_RESIZE_FLOW,
+		RESIZE_FLOW_TO_FULL_SIZE
+	};
+
+	// Returns a texture that must be released with release_texture()
+	// after use.
+	GLuint exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_strategy);
+
+	void release_texture(GLuint tex) {
+		pool.release_texture(tex);
 	}
-	SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
-	SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0);
-	SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 0);
-	SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
 
-	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
-	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
-	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 5);
-	// SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_DEBUG_FLAG);
-	SDL_Window *window = SDL_CreateWindow("OpenGL window",
-			SDL_WINDOWPOS_UNDEFINED,
-			SDL_WINDOWPOS_UNDEFINED,
-			64, 64,
-			SDL_WINDOW_OPENGL);
-	SDL_GLContext context = SDL_GL_CreateContext(window);
-	assert(context != nullptr);
+private:
+	int width, height;
+	GLuint initial_flow_tex;
+	GLuint vertex_vbo, vao;
+	TexturePool pool;
 
-	// Load pictures.
-	GLuint tex0 = load_texture("test1499.pgm", WIDTH, HEIGHT);
-	GLuint tex1 = load_texture("test1500.pgm", WIDTH, HEIGHT);
+	// The various passes.
+	Sobel sobel;
+	MotionSearch motion_search;
+	Densify densify;
+	Prewarp prewarp;
+	Derivatives derivatives;
+	ComputeDiffusivity compute_diffusivity;
+	SetupEquations setup_equations;
+	SOR sor;
+	AddBaseFlow add_base_flow;
+	ResizeFlow resize_flow;
+};
 
+DISComputeFlow::DISComputeFlow(int width, int height)
+	: width(width), height(height)
+{
 	// Make some samplers.
 	glCreateSamplers(1, &nearest_sampler);
 	glSamplerParameteri(nearest_sampler, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
@@ -925,14 +962,22 @@ int main(void)
 
 	// The smoothness is sampled so that once we get to a smoothness involving
 	// a value outside the border, the diffusivity between the two becomes zero.
-	glCreateSamplers(1, &smoothness_sampler);
-	glSamplerParameteri(smoothness_sampler, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
-	glSamplerParameteri(smoothness_sampler, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
-	glSamplerParameteri(smoothness_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
-	glSamplerParameteri(smoothness_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
-	float zero[] = { 0.0f, 0.0f, 0.0f, 0.0f };
-	glSamplerParameterfv(smoothness_sampler, GL_TEXTURE_BORDER_COLOR, zero);
+	// Similarly, gradients are zero outside the border, since the edge is taken
+	// to be constant.
+	glCreateSamplers(1, &zero_border_sampler);
+	glSamplerParameteri(zero_border_sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+	glSamplerParameteri(zero_border_sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+	glSamplerParameteri(zero_border_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
+	glSamplerParameteri(zero_border_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
+	float zero[] = { 0.0f, 0.0f, 0.0f, 0.0f };  // Note that zero alpha means we can also see whether we sampled outside the border or not.
+	glSamplerParameterfv(zero_border_sampler, GL_TEXTURE_BORDER_COLOR, zero);
+
+	// Initial flow is zero, 1x1.
+	glCreateTextures(GL_TEXTURE_2D, 1, &initial_flow_tex);
+	glTextureStorage2D(initial_flow_tex, 1, GL_RG16F, 1, 1);
+	glClearTexImage(initial_flow_tex, 0, GL_RG, GL_FLOAT, nullptr);
 
+	// Set up the vertex data that will be shared between all passes.
 	float vertices[] = {
 		0.0f, 1.0f,
 		0.0f, 0.0f,
@@ -941,48 +986,45 @@ int main(void)
 	};
 	glCreateBuffers(1, &vertex_vbo);
 	glNamedBufferData(vertex_vbo, sizeof(vertices), vertices, GL_STATIC_DRAW);
+
+	glCreateVertexArrays(1, &vao);
+	glBindVertexArray(vao);
 	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 
-	// Initial flow is zero, 1x1.
-	GLuint initial_flow_tex;
-	glCreateTextures(GL_TEXTURE_2D, 1, &initial_flow_tex);
-	glTextureStorage2D(initial_flow_tex, 1, GL_RG16F, 1, 1);
-	int prev_level_width = 1, prev_level_height = 1;
+	GLint position_attrib = 0;  // Hard-coded in every vertex shader.
+	glEnableVertexArrayAttrib(vao, position_attrib);
+	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
+}
 
+GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_strategy)
+{
+	int prev_level_width = 1, prev_level_height = 1;
 	GLuint prev_level_flow_tex = initial_flow_tex;
 
-	Sobel sobel;
-	MotionSearch motion_search;
-	Densify densify;
-	Prewarp prewarp;
-	Derivatives derivatives;
-	ComputeSmoothness compute_smoothness;
-	SetupEquations setup_equations;
-	SOR sor;
-	AddBaseFlow add_base_flow;
-
-	GLuint query;
-	glGenQueries(1, &query);
-	glBeginQuery(GL_TIME_ELAPSED, query);
-
 	GPUTimers timers;
 
+	glBindVertexArray(vao);
+
 	ScopedTimer total_timer("Total", &timers);
 	for (int level = coarsest_level; level >= int(finest_level); --level) {
 		char timer_name[256];
-		snprintf(timer_name, sizeof(timer_name), "Level %d", level);
+		snprintf(timer_name, sizeof(timer_name), "Level %d (%d x %d)", level, width >> level, height >> level);
 		ScopedTimer level_timer(timer_name, &total_timer);
 
-		int level_width = WIDTH >> level;
-		int level_height = HEIGHT >> level;
+		int level_width = width >> level;
+		int level_height = height >> level;
 		float patch_spacing_pixels = patch_size_pixels * (1.0f - patch_overlap_ratio);
-		int width_patches = 1 + lrintf((level_width - patch_size_pixels) / patch_spacing_pixels);
-		int height_patches = 1 + lrintf((level_height - patch_size_pixels) / patch_spacing_pixels);
+
+		// Make sure we have patches at least every Nth pixel, e.g. for width=9
+		// and patch_spacing=3 (the default), we put out patch centers in
+		// x=0, x=3, x=6, x=9, which is four patches. The fragment shader will
+		// lock all the centers to integer coordinates if needed.
+		int width_patches = 1 + ceil(level_width / patch_spacing_pixels);
+		int height_patches = 1 + ceil(level_height / patch_spacing_pixels);
 
 		// Make sure we always read from the correct level; the chosen
 		// mipmapping could otherwise be rather unpredictable, especially
 		// during motion search.
-		// TODO: create these beforehand, and stop leaking them.
 		GLuint tex0_view, tex1_view;
 		glGenTextures(1, &tex0_view);
 		glTextureView(tex0_view, GL_TEXTURE_2D, tex0, GL_R8, level, 1, 0, 1);
@@ -991,9 +1033,7 @@ int main(void)
 
 		// Create a new texture; we could be fancy and render use a multi-level
 		// texture, but meh.
-		GLuint grad0_tex;
-		glCreateTextures(GL_TEXTURE_2D, 1, &grad0_tex);
-		glTextureStorage2D(grad0_tex, 1, GL_RG16F, level_width, level_height);
+		GLuint grad0_tex = pool.get_texture(GL_R32UI, level_width, level_height);
 
 		// Find the derivative.
 		{
@@ -1005,29 +1045,26 @@ int main(void)
 		// level (sampled bilinearly; no fancy tricks) as a guide, then search from there.
 
 		// Create an output flow texture.
-		GLuint flow_out_tex;
-		glCreateTextures(GL_TEXTURE_2D, 1, &flow_out_tex);
-		glTextureStorage2D(flow_out_tex, 1, GL_RGB16F, width_patches, height_patches);
+		GLuint flow_out_tex = pool.get_texture(GL_RGB16F, width_patches, height_patches);
 
 		// And draw.
 		{
 			ScopedTimer timer("Motion search", &level_timer);
 			motion_search.exec(tex0_view, tex1_view, grad0_tex, prev_level_flow_tex, flow_out_tex, level_width, level_height, prev_level_width, prev_level_height, width_patches, height_patches);
 		}
+		pool.release_texture(grad0_tex);
 
 		// Densification.
 
-		// Set up an output texture (initially zero).
-		GLuint dense_flow_tex;
-		glCreateTextures(GL_TEXTURE_2D, 1, &dense_flow_tex);
-		glTextureStorage2D(dense_flow_tex, 1, GL_RGB16F, level_width, level_height);
-		glClearTexImage(dense_flow_tex, 0, GL_RGB, GL_FLOAT, nullptr);
+		// Set up an output texture (cleared in Densify).
+		GLuint dense_flow_tex = pool.get_texture(GL_RGB16F, level_width, level_height);
 
 		// And draw.
 		{
 			ScopedTimer timer("Densification", &level_timer);
 			densify.exec(tex0_view, tex1_view, flow_out_tex, dense_flow_tex, level_width, level_height, width_patches, height_patches);
 		}
+		pool.release_texture(flow_out_tex);
 
 		// Everything below here in the loop belongs to variational refinement.
 		ScopedTimer varref_timer("Variational refinement", &level_timer);
@@ -1039,84 +1076,84 @@ int main(void)
 		// in pixels, not 0..1 normalized OpenGL texture coordinates.
 		// This is because variational refinement depends so heavily on derivatives,
 		// which are measured in intensity levels per pixel.
-		GLuint I_tex, I_t_tex, base_flow_tex;
-		glCreateTextures(GL_TEXTURE_2D, 1, &I_tex);
-		glCreateTextures(GL_TEXTURE_2D, 1, &I_t_tex);
-		glCreateTextures(GL_TEXTURE_2D, 1, &base_flow_tex);
-		glTextureStorage2D(I_tex, 1, GL_R16F, level_width, level_height);
-		glTextureStorage2D(I_t_tex, 1, GL_R16F, level_width, level_height);
-		glTextureStorage2D(base_flow_tex, 1, GL_RG16F, level_width, level_height);
+		GLuint I_tex = pool.get_texture(GL_R16F, level_width, level_height);
+		GLuint I_t_tex = pool.get_texture(GL_R16F, level_width, level_height);
+		GLuint base_flow_tex = pool.get_texture(GL_RG16F, level_width, level_height);
 		{
 			ScopedTimer timer("Prewarping", &varref_timer);
 			prewarp.exec(tex0_view, tex1_view, dense_flow_tex, I_tex, I_t_tex, base_flow_tex, level_width, level_height);
 		}
+		pool.release_texture(dense_flow_tex);
+		glDeleteTextures(1, &tex0_view);
+		glDeleteTextures(1, &tex1_view);
 
 		// Calculate I_x and I_y. We're only calculating first derivatives;
 		// the others will be taken on-the-fly in order to sample from fewer
 		// textures overall, since sampling from the L1 cache is cheap.
 		// (TODO: Verify that this is indeed faster than making separate
 		// double-derivative textures.)
-		GLuint I_x_y_tex, beta_0_tex;
-		glCreateTextures(GL_TEXTURE_2D, 1, &I_x_y_tex);
-		glCreateTextures(GL_TEXTURE_2D, 1, &beta_0_tex);
-		glTextureStorage2D(I_x_y_tex, 1, GL_RG16F, level_width, level_height);
-		glTextureStorage2D(beta_0_tex, 1, GL_R16F, level_width, level_height);
+		GLuint I_x_y_tex = pool.get_texture(GL_RG16F, level_width, level_height);
+		GLuint beta_0_tex = pool.get_texture(GL_R16F, level_width, level_height);
 		{
 			ScopedTimer timer("First derivatives", &varref_timer);
 			derivatives.exec(I_tex, I_x_y_tex, beta_0_tex, level_width, level_height);
 		}
+		pool.release_texture(I_tex);
 
 		// We need somewhere to store du and dv (the flow increment, relative
-		// to the non-refined base flow u0 and v0). It starts at zero.
-		GLuint du_dv_tex;
-		glCreateTextures(GL_TEXTURE_2D, 1, &du_dv_tex);
-		glTextureStorage2D(du_dv_tex, 1, GL_RG16F, level_width, level_height);
-		glClearTexImage(du_dv_tex, 0, GL_RG, GL_FLOAT, nullptr);
-
-		// And for smoothness.
-		GLuint smoothness_x_tex, smoothness_y_tex;
-		glCreateTextures(GL_TEXTURE_2D, 1, &smoothness_x_tex);
-		glCreateTextures(GL_TEXTURE_2D, 1, &smoothness_y_tex);
-		glTextureStorage2D(smoothness_x_tex, 1, GL_R16F, level_width, level_height);
-		glTextureStorage2D(smoothness_y_tex, 1, GL_R16F, level_width, level_height);
+		// to the non-refined base flow u0 and v0). It's initially garbage,
+		// but not read until we've written something sane to it.
+		GLuint du_dv_tex = pool.get_texture(GL_RG16F, level_width, level_height);
+
+		// And for diffusivity.
+		GLuint diffusivity_tex = pool.get_texture(GL_R16F, level_width, level_height);
 
 		// And finally for the equation set. See SetupEquations for
 		// the storage format.
-		GLuint equation_tex;
-		glCreateTextures(GL_TEXTURE_2D, 1, &equation_tex);
-		glTextureStorage2D(equation_tex, 1, GL_RGBA32UI, level_width, level_height);
+		GLuint equation_tex = pool.get_texture(GL_RGBA32UI, level_width, level_height);
 
 		for (int outer_idx = 0; outer_idx < level + 1; ++outer_idx) {
-			// Calculate the smoothness terms between the neighboring pixels,
-			// both in x and y direction.
+			// Calculate the diffusivity term for each pixel.
 			{
-				ScopedTimer timer("Compute smoothness", &varref_timer);
-				compute_smoothness.exec(base_flow_tex, du_dv_tex, smoothness_x_tex, smoothness_y_tex, level_width, level_height);
+				ScopedTimer timer("Compute diffusivity", &varref_timer);
+				compute_diffusivity.exec(base_flow_tex, du_dv_tex, diffusivity_tex, level_width, level_height, outer_idx == 0);
 			}
 
 			// Set up the 2x2 equation system for each pixel.
 			{
 				ScopedTimer timer("Set up equations", &varref_timer);
-				setup_equations.exec(I_x_y_tex, I_t_tex, du_dv_tex, base_flow_tex, beta_0_tex, smoothness_x_tex, smoothness_y_tex, equation_tex, level_width, level_height);
+				setup_equations.exec(I_x_y_tex, I_t_tex, du_dv_tex, base_flow_tex, beta_0_tex, diffusivity_tex, equation_tex, level_width, level_height, outer_idx == 0);
 			}
 
 			// Run a few SOR (or quasi-SOR, since we're not really Jacobi) iterations.
 			// Note that these are to/from the same texture.
 			{
 				ScopedTimer timer("SOR", &varref_timer);
-				sor.exec(du_dv_tex, equation_tex, smoothness_x_tex, smoothness_y_tex, level_width, level_height, 5);
+				sor.exec(du_dv_tex, equation_tex, diffusivity_tex, level_width, level_height, 5, outer_idx == 0, &timer);
 			}
 		}
 
+		pool.release_texture(I_t_tex);
+		pool.release_texture(I_x_y_tex);
+		pool.release_texture(beta_0_tex);
+		pool.release_texture(diffusivity_tex);
+		pool.release_texture(equation_tex);
+
 		// Add the differential flow found by the variational refinement to the base flow,
 		// giving the final flow estimate for this level.
 		// The output is in diff_flow_tex; we don't need to make a new texture.
-		// You can comment out this prat if you wish to test disabling of the variational refinement.
-		{
+		//
+		// Disabling this doesn't save any time (although we could easily make it so that
+		// it is more efficient), but it helps debug the motion search.
+		if (enable_variational_refinement) {
 			ScopedTimer timer("Add differential flow", &varref_timer);
 			add_base_flow.exec(base_flow_tex, du_dv_tex, level_width, level_height);
 		}
+		pool.release_texture(du_dv_tex);
 
+		if (prev_level_flow_tex != initial_flow_tex) {
+			pool.release_texture(prev_level_flow_tex);
+		}
 		prev_level_flow_tex = base_flow_tex;
 		prev_level_width = level_width;
 		prev_level_height = level_height;
@@ -1125,27 +1162,466 @@ int main(void)
 
 	timers.print();
 
-	int level_width = WIDTH >> finest_level;
-	int level_height = HEIGHT >> finest_level;
-	unique_ptr<float[]> dense_flow(new float[level_width * level_height * 2]);
-	glGetTextureImage(prev_level_flow_tex, 0, GL_RG, GL_FLOAT, level_width * level_height * 2 * sizeof(float), dense_flow.get());
+	// Scale up the flow to the final size (if needed).
+	if (finest_level == 0 || resize_strategy == DO_NOT_RESIZE_FLOW) {
+		return prev_level_flow_tex;
+	} else {
+		GLuint final_tex = pool.get_texture(GL_RG16F, width, height);
+		resize_flow.exec(prev_level_flow_tex, final_tex, prev_level_width, prev_level_height, width, height);
+		pool.release_texture(prev_level_flow_tex);
+		return final_tex;
+	}
+}
+
+// Forward-warp the flow half-way (or rather, by alpha). A non-zero “splatting”
+// radius fills most of the holes.
+class Splat {
+public:
+	Splat();
+
+	// alpha is the time of the interpolated frame (0..1).
+	void exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLuint backward_flow_tex, GLuint flow_tex, GLuint depth_tex, int width, int height, float alpha);
+
+private:
+	PersistentFBOSetWithDepth<1> fbos;
+
+	GLuint splat_vs_obj;
+	GLuint splat_fs_obj;
+	GLuint splat_program;
+
+	GLuint uniform_invert_flow, uniform_splat_size, uniform_alpha;
+	GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
+	GLuint uniform_inv_flow_size;
+};
+
+Splat::Splat()
+{
+	splat_vs_obj = compile_shader(read_file("splat.vert"), GL_VERTEX_SHADER);
+	splat_fs_obj = compile_shader(read_file("splat.frag"), GL_FRAGMENT_SHADER);
+	splat_program = link_program(splat_vs_obj, splat_fs_obj);
+
+	uniform_invert_flow = glGetUniformLocation(splat_program, "invert_flow");
+	uniform_splat_size = glGetUniformLocation(splat_program, "splat_size");
+	uniform_alpha = glGetUniformLocation(splat_program, "alpha");
+	uniform_image0_tex = glGetUniformLocation(splat_program, "image0_tex");
+	uniform_image1_tex = glGetUniformLocation(splat_program, "image1_tex");
+	uniform_flow_tex = glGetUniformLocation(splat_program, "flow_tex");
+	uniform_inv_flow_size = glGetUniformLocation(splat_program, "inv_flow_size");
+}
+
+void Splat::exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLuint backward_flow_tex, GLuint flow_tex, GLuint depth_tex, int width, int height, float alpha)
+{
+	glUseProgram(splat_program);
+
+	bind_sampler(splat_program, uniform_image0_tex, 0, tex0, linear_sampler);
+	bind_sampler(splat_program, uniform_image1_tex, 1, tex1, linear_sampler);
+
+	// FIXME: This is set to 1.0 right now so not to trigger Haswell's “PMA stall”.
+	// Move to 2.0 later, or even 4.0.
+	// (Since we have hole filling, it's not critical, but larger values seem to do
+	// better than hole filling for large motion, blurs etc.)
+	float splat_size = 1.0f;  // 4x4 splat means 16x overdraw, 2x2 splat means 4x overdraw.
+	glProgramUniform2f(splat_program, uniform_splat_size, splat_size / width, splat_size / height);
+	glProgramUniform1f(splat_program, uniform_alpha, alpha);
+	glProgramUniform2f(splat_program, uniform_inv_flow_size, 1.0f / width, 1.0f / height);
+
+	glViewport(0, 0, width, height);
+	glDisable(GL_BLEND);
+	glEnable(GL_DEPTH_TEST);
+	glDepthFunc(GL_LESS);  // We store the difference between I_0 and I_1, where less difference is good. (Default 1.0 is effectively +inf, which always loses.)
+
+	fbos.render_to(depth_tex, flow_tex);
+
+	// Evidently NVIDIA doesn't use fast clears for glClearTexImage, so clear now that
+	// we've got it bound.
+	glClearColor(1000.0f, 1000.0f, 0.0f, 1.0f);  // Invalid flow.
+	glClearDepth(1.0f);  // Effectively infinity.
+	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+	// Do forward splatting.
+	bind_sampler(splat_program, uniform_flow_tex, 2, forward_flow_tex, nearest_sampler);
+	glProgramUniform1i(splat_program, uniform_invert_flow, 0);
+	glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width * height);
+
+	// Do backward splatting.
+	bind_sampler(splat_program, uniform_flow_tex, 2, backward_flow_tex, nearest_sampler);
+	glProgramUniform1i(splat_program, uniform_invert_flow, 1);
+	glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width * height);
+
+	glDisable(GL_DEPTH_TEST);
+}
+
+// Doing good and fast hole-filling on a GPU is nontrivial. We choose an option
+// that's fairly simple (given that most holes are really small) and also hopefully
+// cheap should the holes not be so small. Conceptually, we look for the first
+// non-hole to the left of us (ie., shoot a ray until we hit something), then
+// the first non-hole to the right of us, then up and down, and then average them
+// all together. It's going to create “stars” if the holes are big, but OK, that's
+// a tradeoff.
+//
+// Our implementation here is efficient assuming that the hierarchical Z-buffer is
+// on even for shaders that do discard (this typically kills early Z, but hopefully
+// not hierarchical Z); we set up Z so that only holes are written to, which means
+// that as soon as a hole is filled, the rasterizer should just skip it. Most of the
+// fullscreen quads should just be discarded outright, really.
+class HoleFill {
+public:
+	HoleFill();
+
+	// Output will be in flow_tex, temp_tex[0, 1, 2], representing the filling
+	// from the down, left, right and up, respectively. Use HoleBlend to merge
+	// them into one.
+	void exec(GLuint flow_tex, GLuint depth_tex, GLuint temp_tex[3], int width, int height);
+
+private:
+	PersistentFBOSetWithDepth<1> fbos;
+
+	GLuint fill_vs_obj;
+	GLuint fill_fs_obj;
+	GLuint fill_program;
+
+	GLuint uniform_tex;
+	GLuint uniform_z, uniform_sample_offset;
+};
+
+HoleFill::HoleFill()
+{
+	fill_vs_obj = compile_shader(read_file("hole_fill.vert"), GL_VERTEX_SHADER);
+	fill_fs_obj = compile_shader(read_file("hole_fill.frag"), GL_FRAGMENT_SHADER);
+	fill_program = link_program(fill_vs_obj, fill_fs_obj);
+
+	uniform_tex = glGetUniformLocation(fill_program, "tex");
+	uniform_z = glGetUniformLocation(fill_program, "z");
+	uniform_sample_offset = glGetUniformLocation(fill_program, "sample_offset");
+}
+
+void HoleFill::exec(GLuint flow_tex, GLuint depth_tex, GLuint temp_tex[3], int width, int height)
+{
+	glUseProgram(fill_program);
+
+	bind_sampler(fill_program, uniform_tex, 0, flow_tex, nearest_sampler);
+
+	glProgramUniform1f(fill_program, uniform_z, 1.0f - 1.0f / 1024.0f);
+
+	glViewport(0, 0, width, height);
+	glDisable(GL_BLEND);
+	glEnable(GL_DEPTH_TEST);
+	glDepthFunc(GL_LESS);  // Only update the values > 0.999f (ie., only invalid pixels).
+
+	fbos.render_to(depth_tex, flow_tex);  // NOTE: Reading and writing to the same texture.
+
+	// Fill holes from the left, by shifting 1, 2, 4, 8, etc. pixels to the right.
+	for (int offs = 1; offs < width; offs *= 2) {
+		glProgramUniform2f(fill_program, uniform_sample_offset, -offs / float(width), 0.0f);
+		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+		glTextureBarrier();
+	}
+	glCopyImageSubData(flow_tex, GL_TEXTURE_2D, 0, 0, 0, 0, temp_tex[0], GL_TEXTURE_2D, 0, 0, 0, 0, width, height, 1);
+
+	// Similar to the right; adjust Z a bit down, so that we re-fill the pixels that
+	// were overwritten in the last algorithm.
+	glProgramUniform1f(fill_program, uniform_z, 1.0f - 2.0f / 1024.0f);
+	for (int offs = 1; offs < width; offs *= 2) {
+		glProgramUniform2f(fill_program, uniform_sample_offset, offs / float(width), 0.0f);
+		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+		glTextureBarrier();
+	}
+	glCopyImageSubData(flow_tex, GL_TEXTURE_2D, 0, 0, 0, 0, temp_tex[1], GL_TEXTURE_2D, 0, 0, 0, 0, width, height, 1);
+
+	// Up.
+	glProgramUniform1f(fill_program, uniform_z, 1.0f - 3.0f / 1024.0f);
+	for (int offs = 1; offs < height; offs *= 2) {
+		glProgramUniform2f(fill_program, uniform_sample_offset, 0.0f, -offs / float(height));
+		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+		glTextureBarrier();
+	}
+	glCopyImageSubData(flow_tex, GL_TEXTURE_2D, 0, 0, 0, 0, temp_tex[2], GL_TEXTURE_2D, 0, 0, 0, 0, width, height, 1);
+
+	// Down.
+	glProgramUniform1f(fill_program, uniform_z, 1.0f - 4.0f / 1024.0f);
+	for (int offs = 1; offs < height; offs *= 2) {
+		glProgramUniform2f(fill_program, uniform_sample_offset, 0.0f, offs / float(height));
+		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+		glTextureBarrier();
+	}
+
+	glDisable(GL_DEPTH_TEST);
+}
+
+// Blend the four directions from HoleFill into one pixel, so that single-pixel
+// holes become the average of their four neighbors.
+class HoleBlend {
+public:
+	HoleBlend();
+
+	void exec(GLuint flow_tex, GLuint depth_tex, GLuint temp_tex[3], int width, int height);
+
+private:
+	PersistentFBOSetWithDepth<1> fbos;
+
+	GLuint blend_vs_obj;
+	GLuint blend_fs_obj;
+	GLuint blend_program;
+
+	GLuint uniform_left_tex, uniform_right_tex, uniform_up_tex, uniform_down_tex;
+	GLuint uniform_z, uniform_sample_offset;
+};
+
+HoleBlend::HoleBlend()
+{
+	blend_vs_obj = compile_shader(read_file("hole_fill.vert"), GL_VERTEX_SHADER);  // Reuse the vertex shader from the fill.
+	blend_fs_obj = compile_shader(read_file("hole_blend.frag"), GL_FRAGMENT_SHADER);
+	blend_program = link_program(blend_vs_obj, blend_fs_obj);
+
+	uniform_left_tex = glGetUniformLocation(blend_program, "left_tex");
+	uniform_right_tex = glGetUniformLocation(blend_program, "right_tex");
+	uniform_up_tex = glGetUniformLocation(blend_program, "up_tex");
+	uniform_down_tex = glGetUniformLocation(blend_program, "down_tex");
+	uniform_z = glGetUniformLocation(blend_program, "z");
+	uniform_sample_offset = glGetUniformLocation(blend_program, "sample_offset");
+}
+
+void HoleBlend::exec(GLuint flow_tex, GLuint depth_tex, GLuint temp_tex[3], int width, int height)
+{
+	glUseProgram(blend_program);
+
+	bind_sampler(blend_program, uniform_left_tex, 0, temp_tex[0], nearest_sampler);
+	bind_sampler(blend_program, uniform_right_tex, 1, temp_tex[1], nearest_sampler);
+	bind_sampler(blend_program, uniform_up_tex, 2, temp_tex[2], nearest_sampler);
+	bind_sampler(blend_program, uniform_down_tex, 3, flow_tex, nearest_sampler);
+
+	glProgramUniform1f(blend_program, uniform_z, 1.0f - 4.0f / 1024.0f);
+	glProgramUniform2f(blend_program, uniform_sample_offset, 0.0f, 0.0f);
+
+	glViewport(0, 0, width, height);
+	glDisable(GL_BLEND);
+	glEnable(GL_DEPTH_TEST);
+	glDepthFunc(GL_LEQUAL);  // Skip over all of the pixels that were never holes to begin with.
+
+	fbos.render_to(depth_tex, flow_tex);  // NOTE: Reading and writing to the same texture.
+
+	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+
+	glDisable(GL_DEPTH_TEST);
+}
+
+class Blend {
+public:
+	Blend();
+	void exec(GLuint tex0, GLuint tex1, GLuint flow_tex, GLuint output_tex, int width, int height, float alpha);
+
+private:
+	PersistentFBOSet<1> fbos;
+	GLuint blend_vs_obj;
+	GLuint blend_fs_obj;
+	GLuint blend_program;
+
+	GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
+	GLuint uniform_alpha, uniform_flow_consistency_tolerance;
+};
+
+Blend::Blend()
+{
+	blend_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
+	blend_fs_obj = compile_shader(read_file("blend.frag"), GL_FRAGMENT_SHADER);
+	blend_program = link_program(blend_vs_obj, blend_fs_obj);
+
+	uniform_image0_tex = glGetUniformLocation(blend_program, "image0_tex");
+	uniform_image1_tex = glGetUniformLocation(blend_program, "image1_tex");
+	uniform_flow_tex = glGetUniformLocation(blend_program, "flow_tex");
+	uniform_alpha = glGetUniformLocation(blend_program, "alpha");
+	uniform_flow_consistency_tolerance = glGetUniformLocation(blend_program, "flow_consistency_tolerance");
+}
+
+void Blend::exec(GLuint tex0, GLuint tex1, GLuint flow_tex, GLuint output_tex, int level_width, int level_height, float alpha)
+{
+	glUseProgram(blend_program);
+	bind_sampler(blend_program, uniform_image0_tex, 0, tex0, linear_sampler);
+	bind_sampler(blend_program, uniform_image1_tex, 1, tex1, linear_sampler);
+	bind_sampler(blend_program, uniform_flow_tex, 2, flow_tex, linear_sampler);  // May be upsampled.
+	glProgramUniform1f(blend_program, uniform_alpha, alpha);
+
+	glViewport(0, 0, level_width, level_height);
+	fbos.render_to(output_tex);
+	glDisable(GL_BLEND);  // A bit ironic, perhaps.
+	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+}
+
+class Interpolate {
+public:
+	Interpolate(int width, int height, int flow_level);
+
+	// Returns a texture that must be released with release_texture()
+	// after use. tex0 and tex1 must be RGBA8 textures with mipmaps
+	// (unless flow_level == 0).
+	GLuint exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLuint backward_flow_tex, GLuint width, GLuint height, float alpha);
+
+	void release_texture(GLuint tex) {
+		pool.release_texture(tex);
+	}
+
+private:
+	int width, height, flow_level;
+	GLuint vertex_vbo, vao;
+	TexturePool pool;
+
+	Splat splat;
+	HoleFill hole_fill;
+	HoleBlend hole_blend;
+	Blend blend;
+};
+
+Interpolate::Interpolate(int width, int height, int flow_level)
+	: width(width), height(height), flow_level(flow_level) {
+	// Set up the vertex data that will be shared between all passes.
+	float vertices[] = {
+		0.0f, 1.0f,
+		0.0f, 0.0f,
+		1.0f, 1.0f,
+		1.0f, 0.0f,
+	};
+	glCreateBuffers(1, &vertex_vbo);
+	glNamedBufferData(vertex_vbo, sizeof(vertices), vertices, GL_STATIC_DRAW);
+
+	glCreateVertexArrays(1, &vao);
+	glBindVertexArray(vao);
+	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
+
+	GLint position_attrib = 0;  // Hard-coded in every vertex shader.
+	glEnableVertexArrayAttrib(vao, position_attrib);
+	glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
+}
+
+GLuint Interpolate::exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLuint backward_flow_tex, GLuint width, GLuint height, float alpha)
+{
+	GPUTimers timers;
+
+	ScopedTimer total_timer("Total", &timers);
+
+	glBindVertexArray(vao);
+
+	// Pick out the right level to test splatting results on.
+	GLuint tex0_view, tex1_view;
+	glGenTextures(1, &tex0_view);
+	glTextureView(tex0_view, GL_TEXTURE_2D, tex0, GL_RGBA8, flow_level, 1, 0, 1);
+	glGenTextures(1, &tex1_view);
+	glTextureView(tex1_view, GL_TEXTURE_2D, tex1, GL_RGBA8, flow_level, 1, 0, 1);
+
+	int flow_width = width >> flow_level;
+	int flow_height = height >> flow_level;
+
+	GLuint flow_tex = pool.get_texture(GL_RG16F, flow_width, flow_height);
+	GLuint depth_tex = pool.get_texture(GL_DEPTH_COMPONENT32F, flow_width, flow_height);  // Used for ranking flows.
+
+	{
+		ScopedTimer timer("Splat", &total_timer);
+		splat.exec(tex0_view, tex1_view, forward_flow_tex, backward_flow_tex, flow_tex, depth_tex, flow_width, flow_height, alpha);
+	}
+	glDeleteTextures(1, &tex0_view);
+	glDeleteTextures(1, &tex1_view);
+
+	GLuint temp_tex[3];
+	temp_tex[0] = pool.get_texture(GL_RG16F, flow_width, flow_height);
+	temp_tex[1] = pool.get_texture(GL_RG16F, flow_width, flow_height);
+	temp_tex[2] = pool.get_texture(GL_RG16F, flow_width, flow_height);
+
+	{
+		ScopedTimer timer("Fill holes", &total_timer);
+		hole_fill.exec(flow_tex, depth_tex, temp_tex, flow_width, flow_height);
+		hole_blend.exec(flow_tex, depth_tex, temp_tex, flow_width, flow_height);
+	}
+
+	pool.release_texture(temp_tex[0]);
+	pool.release_texture(temp_tex[1]);
+	pool.release_texture(temp_tex[2]);
+	pool.release_texture(depth_tex);
+
+	GLuint output_tex = pool.get_texture(GL_RGBA8, width, height);
+	{
+		ScopedTimer timer("Blend", &total_timer);
+		blend.exec(tex0, tex1, flow_tex, output_tex, width, height, alpha);
+	}
+	pool.release_texture(flow_tex);
+	total_timer.end();
+	timers.print();
+
+	return output_tex;
+}
+
+GLuint TexturePool::get_texture(GLenum format, GLuint width, GLuint height)
+{
+	for (Texture &tex : textures) {
+		if (!tex.in_use && tex.format == format &&
+		    tex.width == width && tex.height == height) {
+			tex.in_use = true;
+			return tex.tex_num;
+		}
+	}
+
+	Texture tex;
+	glCreateTextures(GL_TEXTURE_2D, 1, &tex.tex_num);
+	glTextureStorage2D(tex.tex_num, 1, format, width, height);
+	tex.format = format;
+	tex.width = width;
+	tex.height = height;
+	tex.in_use = true;
+	textures.push_back(tex);
+	return tex.tex_num;
+}
+
+void TexturePool::release_texture(GLuint tex_num)
+{
+	for (Texture &tex : textures) {
+		if (tex.tex_num == tex_num) {
+			assert(tex.in_use);
+			tex.in_use = false;
+			return;
+		}
+	}
+	assert(false);
+}
 
-	FILE *fp = fopen("flow.ppm", "wb");
-	FILE *flowfp = fopen("flow.flo", "wb");
-	fprintf(fp, "P6\n%d %d\n255\n", level_width, level_height);
+// OpenGL uses a bottom-left coordinate system, .flo files use a top-left coordinate system.
+void flip_coordinate_system(float *dense_flow, unsigned width, unsigned height)
+{
+	for (unsigned i = 0; i < width * height; ++i) {
+		dense_flow[i * 2 + 1] = -dense_flow[i * 2 + 1];
+	}
+}
+
+// Not relevant for RGB.
+void flip_coordinate_system(uint8_t *dense_flow, unsigned width, unsigned height)
+{
+}
+
+void write_flow(const char *filename, const float *dense_flow, unsigned width, unsigned height)
+{
+	FILE *flowfp = fopen(filename, "wb");
 	fprintf(flowfp, "FEIH");
-	fwrite(&level_width, 4, 1, flowfp);
-	fwrite(&level_height, 4, 1, flowfp);
-	for (unsigned y = 0; y < unsigned(level_height); ++y) {
-		int yy = level_height - y - 1;
-		for (unsigned x = 0; x < unsigned(level_width); ++x) {
-			float du = dense_flow[(yy * level_width + x) * 2 + 0];
-			float dv = dense_flow[(yy * level_width + x) * 2 + 1];
+	fwrite(&width, 4, 1, flowfp);
+	fwrite(&height, 4, 1, flowfp);
+	for (unsigned y = 0; y < height; ++y) {
+		int yy = height - y - 1;
+		fwrite(&dense_flow[yy * width * 2], width * 2 * sizeof(float), 1, flowfp);
+	}
+	fclose(flowfp);
+}
 
-			dv = -dv;
+// Not relevant for RGB.
+void write_flow(const char *filename, const uint8_t *dense_flow, unsigned width, unsigned height)
+{
+	assert(false);
+}
 
-			fwrite(&du, 4, 1, flowfp);
-			fwrite(&dv, 4, 1, flowfp);
+void write_ppm(const char *filename, const float *dense_flow, unsigned width, unsigned height)
+{
+	FILE *fp = fopen(filename, "wb");
+	fprintf(fp, "P6\n%d %d\n255\n", width, height);
+	for (unsigned y = 0; y < unsigned(height); ++y) {
+		int yy = height - y - 1;
+		for (unsigned x = 0; x < unsigned(width); ++x) {
+			float du = dense_flow[(yy * width + x) * 2 + 0];
+			float dv = dense_flow[(yy * width + x) * 2 + 1];
 
 			uint8_t r, g, b;
 			flow2rgb(du, dv, &r, &g, &b);
@@ -1155,7 +1631,321 @@ int main(void)
 		}
 	}
 	fclose(fp);
-	fclose(flowfp);
+}
+
+void write_ppm(const char *filename, const uint8_t *rgba, unsigned width, unsigned height)
+{
+	unique_ptr<uint8_t[]> rgb_line(new uint8_t[width * 3 + 1]);
+
+	FILE *fp = fopen(filename, "wb");
+	fprintf(fp, "P6\n%d %d\n255\n", width, height);
+	for (unsigned y = 0; y < height; ++y) {
+		unsigned y2 = height - 1 - y;
+		for (size_t x = 0; x < width; ++x) {
+			memcpy(&rgb_line[x * 3], &rgba[(y2 * width + x) * 4], 4);
+		}
+		fwrite(rgb_line.get(), width * 3, 1, fp);
+	}
+	fclose(fp);
+}
+
+struct FlowType {
+	using type = float;
+	static constexpr GLenum gl_format = GL_RG;
+	static constexpr GLenum gl_type = GL_FLOAT;
+	static constexpr int num_channels = 2;
+};
+
+struct RGBAType {
+	using type = uint8_t;
+	static constexpr GLenum gl_format = GL_RGBA;
+	static constexpr GLenum gl_type = GL_UNSIGNED_BYTE;
+	static constexpr int num_channels = 4;
+};
+
+template <class Type>
+void finish_one_read(GLuint width, GLuint height)
+{
+	using T = typename Type::type;
+	constexpr int bytes_per_pixel = Type::num_channels * sizeof(T);
+
+	assert(!reads_in_progress.empty());
+	ReadInProgress read = reads_in_progress.front();
+	reads_in_progress.pop_front();
+
+	unique_ptr<T[]> flow(new typename Type::type[width * height * Type::num_channels]);
+	void *buf = glMapNamedBufferRange(read.pbo, 0, width * height * bytes_per_pixel, GL_MAP_READ_BIT);  // Blocks if the read isn't done yet.
+	memcpy(flow.get(), buf, width * height * bytes_per_pixel);  // TODO: Unneeded for RGBType, since flip_coordinate_system() does nothing.:
+	glUnmapNamedBuffer(read.pbo);
+	spare_pbos.push(read.pbo);
+
+	flip_coordinate_system(flow.get(), width, height);
+	if (!read.flow_filename.empty()) {
+		write_flow(read.flow_filename.c_str(), flow.get(), width, height);
+		fprintf(stderr, "%s %s -> %s\n", read.filename0.c_str(), read.filename1.c_str(), read.flow_filename.c_str());
+	}
+	if (!read.ppm_filename.empty()) {
+		write_ppm(read.ppm_filename.c_str(), flow.get(), width, height);
+	}
+}
+
+template <class Type>
+void schedule_read(GLuint tex, GLuint width, GLuint height, const char *filename0, const char *filename1, const char *flow_filename, const char *ppm_filename)
+{
+	using T = typename Type::type;
+	constexpr int bytes_per_pixel = Type::num_channels * sizeof(T);
+
+	if (spare_pbos.empty()) {
+		finish_one_read<Type>(width, height);
+	}
+	assert(!spare_pbos.empty());
+	reads_in_progress.emplace_back(ReadInProgress{ spare_pbos.top(), filename0, filename1, flow_filename, ppm_filename });
+	glBindBuffer(GL_PIXEL_PACK_BUFFER, spare_pbos.top());
+	spare_pbos.pop();
+	glGetTextureImage(tex, 0, Type::gl_format, Type::gl_type, width * height * bytes_per_pixel, nullptr);
+	glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
+}
+
+void compute_flow_only(int argc, char **argv, int optind)
+{
+	const char *filename0 = argc >= (optind + 1) ? argv[optind] : "test1499.png";
+	const char *filename1 = argc >= (optind + 2) ? argv[optind + 1] : "test1500.png";
+	const char *flow_filename = argc >= (optind + 3) ? argv[optind + 2] : "flow.flo";
+
+	// Load pictures.
+	unsigned width1, height1, width2, height2;
+	GLuint tex0 = load_texture(filename0, &width1, &height1, WITHOUT_MIPMAPS);
+	GLuint tex1 = load_texture(filename1, &width2, &height2, WITHOUT_MIPMAPS);
+
+	if (width1 != width2 || height1 != height2) {
+		fprintf(stderr, "Image dimensions don't match (%dx%d versus %dx%d)\n",
+			width1, height1, width2, height2);
+		exit(1);
+	}
+
+	// Set up some PBOs to do asynchronous readback.
+	GLuint pbos[5];
+	glCreateBuffers(5, pbos);
+	for (int i = 0; i < 5; ++i) {
+		glNamedBufferData(pbos[i], width1 * height1 * 2 * sizeof(float), nullptr, GL_STREAM_READ);
+		spare_pbos.push(pbos[i]);
+	}
 
-	fprintf(stderr, "err = %d\n", glGetError());
+	int levels = find_num_levels(width1, height1);
+	GLuint tex0_gray, tex1_gray;
+	glCreateTextures(GL_TEXTURE_2D, 1, &tex0_gray);
+	glCreateTextures(GL_TEXTURE_2D, 1, &tex1_gray);
+	glTextureStorage2D(tex0_gray, levels, GL_R8, width1, height1);
+	glTextureStorage2D(tex1_gray, levels, GL_R8, width1, height1);
+
+	GrayscaleConversion gray;
+	gray.exec(tex0, tex0_gray, width1, height1);
+	glDeleteTextures(1, &tex0);
+	glGenerateTextureMipmap(tex0_gray);
+
+	gray.exec(tex1, tex1_gray, width1, height1);
+	glDeleteTextures(1, &tex1);
+	glGenerateTextureMipmap(tex1_gray);
+
+	DISComputeFlow compute_flow(width1, height1);
+	GLuint final_tex = compute_flow.exec(tex0_gray, tex1_gray, DISComputeFlow::RESIZE_FLOW_TO_FULL_SIZE);
+
+	schedule_read<FlowType>(final_tex, width1, height1, filename0, filename1, flow_filename, "flow.ppm");
+	compute_flow.release_texture(final_tex);
+
+	// See if there are more flows on the command line (ie., more than three arguments),
+	// and if so, process them.
+	int num_flows = (argc - optind) / 3;
+	for (int i = 1; i < num_flows; ++i) {
+		const char *filename0 = argv[optind + i * 3 + 0];
+		const char *filename1 = argv[optind + i * 3 + 1];
+		const char *flow_filename = argv[optind + i * 3 + 2];
+		GLuint width, height;
+		GLuint tex0 = load_texture(filename0, &width, &height, WITHOUT_MIPMAPS);
+		if (width != width1 || height != height1) {
+			fprintf(stderr, "%s: Image dimensions don't match (%dx%d versus %dx%d)\n",
+				filename0, width, height, width1, height1);
+			exit(1);
+		}
+		gray.exec(tex0, tex0_gray, width, height);
+		glGenerateTextureMipmap(tex0_gray);
+		glDeleteTextures(1, &tex0);
+
+		GLuint tex1 = load_texture(filename1, &width, &height, WITHOUT_MIPMAPS);
+		if (width != width1 || height != height1) {
+			fprintf(stderr, "%s: Image dimensions don't match (%dx%d versus %dx%d)\n",
+				filename1, width, height, width1, height1);
+			exit(1);
+		}
+		gray.exec(tex1, tex1_gray, width, height);
+		glGenerateTextureMipmap(tex1_gray);
+		glDeleteTextures(1, &tex1);
+
+		GLuint final_tex = compute_flow.exec(tex0_gray, tex1_gray, DISComputeFlow::RESIZE_FLOW_TO_FULL_SIZE);
+
+		schedule_read<FlowType>(final_tex, width1, height1, filename0, filename1, flow_filename, "");
+		compute_flow.release_texture(final_tex);
+	}
+	glDeleteTextures(1, &tex0_gray);
+	glDeleteTextures(1, &tex1_gray);
+
+	while (!reads_in_progress.empty()) {
+		finish_one_read<FlowType>(width1, height1);
+	}
+}
+
+// Interpolate images based on
+//
+//   Herbst, Seitz, Baker: “Occlusion Reasoning for Temporal Interpolation
+//   Using Optical Flow”
+//
+// or at least a reasonable subset thereof. Unfinished.
+void interpolate_image(int argc, char **argv, int optind)
+{
+	const char *filename0 = argc >= (optind + 1) ? argv[optind] : "test1499.png";
+	const char *filename1 = argc >= (optind + 2) ? argv[optind + 1] : "test1500.png";
+	//const char *out_filename = argc >= (optind + 3) ? argv[optind + 2] : "interpolated.png";
+
+	// Load pictures.
+	unsigned width1, height1, width2, height2;
+	GLuint tex0 = load_texture(filename0, &width1, &height1, WITH_MIPMAPS);
+	GLuint tex1 = load_texture(filename1, &width2, &height2, WITH_MIPMAPS);
+
+	if (width1 != width2 || height1 != height2) {
+		fprintf(stderr, "Image dimensions don't match (%dx%d versus %dx%d)\n",
+			width1, height1, width2, height2);
+		exit(1);
+	}
+
+	// Set up some PBOs to do asynchronous readback.
+	GLuint pbos[5];
+	glCreateBuffers(5, pbos);
+	for (int i = 0; i < 5; ++i) {
+		glNamedBufferData(pbos[i], width1 * height1 * 4 * sizeof(uint8_t), nullptr, GL_STREAM_READ);
+		spare_pbos.push(pbos[i]);
+	}
+
+	DISComputeFlow compute_flow(width1, height1);
+	GrayscaleConversion gray;
+	Interpolate interpolate(width1, height1, finest_level);
+
+	int levels = find_num_levels(width1, height1);
+	GLuint tex0_gray, tex1_gray;
+	glCreateTextures(GL_TEXTURE_2D, 1, &tex0_gray);
+	glCreateTextures(GL_TEXTURE_2D, 1, &tex1_gray);
+	glTextureStorage2D(tex0_gray, levels, GL_R8, width1, height1);
+	glTextureStorage2D(tex1_gray, levels, GL_R8, width1, height1);
+
+	gray.exec(tex0, tex0_gray, width1, height1);
+	glGenerateTextureMipmap(tex0_gray);
+
+	gray.exec(tex1, tex1_gray, width1, height1);
+	glGenerateTextureMipmap(tex1_gray);
+
+	GLuint forward_flow_tex = compute_flow.exec(tex0_gray, tex1_gray, DISComputeFlow::DO_NOT_RESIZE_FLOW);
+	GLuint backward_flow_tex = compute_flow.exec(tex1_gray, tex0_gray, DISComputeFlow::DO_NOT_RESIZE_FLOW);
+
+	for (int frameno = 1; frameno < 60; ++frameno) {
+		char ppm_filename[256];
+		snprintf(ppm_filename, sizeof(ppm_filename), "interp%04d.ppm", frameno);
+
+		float alpha = frameno / 60.0f;
+		GLuint interpolated_tex = interpolate.exec(tex0, tex1, forward_flow_tex, backward_flow_tex, width1, height1, alpha);
+
+		schedule_read<RGBAType>(interpolated_tex, width1, height1, filename0, filename1, "", ppm_filename);
+		interpolate.release_texture(interpolated_tex);
+	}
+
+	while (!reads_in_progress.empty()) {
+		finish_one_read<RGBAType>(width1, height1);
+	}
+}
+
+int main(int argc, char **argv)
+{
+        static const option long_options[] = {
+		{ "smoothness-relative-weight", required_argument, 0, 's' },  // alpha.
+		{ "intensity-relative-weight", required_argument, 0, 'i' },  // delta.
+		{ "gradient-relative-weight", required_argument, 0, 'g' },  // gamma.
+		{ "disable-timing", no_argument, 0, 1000 },
+		{ "detailed-timing", no_argument, 0, 1003 },
+		{ "ignore-variational-refinement", no_argument, 0, 1001 },  // Still calculates it, just doesn't apply it.
+		{ "interpolate", no_argument, 0, 1002 }
+	};
+
+	for ( ;; ) {
+		int option_index = 0;
+		int c = getopt_long(argc, argv, "s:i:g:", long_options, &option_index);
+
+		if (c == -1) {
+			break;
+		}
+		switch (c) {
+		case 's':
+			vr_alpha = atof(optarg);
+			break;
+		case 'i':
+			vr_delta = atof(optarg);
+			break;
+		case 'g':
+			vr_gamma = atof(optarg);
+			break;
+		case 1000:
+			enable_timing = false;
+			break;
+		case 1001:
+			enable_variational_refinement = false;
+			break;
+		case 1002:
+			enable_interpolation = true;
+			break;
+		case 1003:
+			detailed_timing = true;
+			break;
+		default:
+			fprintf(stderr, "Unknown option '%s'\n", argv[option_index]);
+			exit(1);
+		};
+	}
+
+	if (SDL_Init(SDL_INIT_EVERYTHING) == -1) {
+		fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
+		exit(1);
+	}
+	SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
+	SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0);
+	SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 0);
+	SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
+
+	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
+	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
+	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 5);
+	// SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_DEBUG_FLAG);
+	window = SDL_CreateWindow("OpenGL window",
+		SDL_WINDOWPOS_UNDEFINED,
+		SDL_WINDOWPOS_UNDEFINED,
+		64, 64,
+		SDL_WINDOW_OPENGL | SDL_WINDOW_HIDDEN);
+	SDL_GLContext context = SDL_GL_CreateContext(window);
+	assert(context != nullptr);
+
+	glDisable(GL_DITHER);
+
+	// FIXME: Should be part of DISComputeFlow (but needs to be initialized
+	// before all the render passes).
+	float vertices[] = {
+		0.0f, 1.0f,
+		0.0f, 0.0f,
+		1.0f, 1.0f,
+		1.0f, 0.0f,
+	};
+	glCreateBuffers(1, &vertex_vbo);
+	glNamedBufferData(vertex_vbo, sizeof(vertices), vertices, GL_STATIC_DRAW);
+	glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
+
+	if (enable_interpolation) {
+		interpolate_image(argc, argv, optind);
+	} else {
+		compute_flow_only(argc, argv, optind);
+	}
 }