]> git.sesse.net Git - nageru/blobdiff - flow.cpp
Put depth in 0..1; evidently even fp32 depth is clamped in the ARB version.
[nageru] / flow.cpp
index 001b14af8cd173068c36f4198211f4fc3dc648a5..6a9d0eeb74ce551455e2392fb963e211759aaab3 100644 (file)
--- a/flow.cpp
+++ b/flow.cpp
 #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;
@@ -35,15 +39,41 @@ 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.
-float vr_gamma = 10.0f, vr_delta = 5.0f, vr_alpha = 10.0f;
+// 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 enable_variational_refinement = true;  // Just for debugging.
+bool enable_interpolation = false;
 
 // Some global OpenGL objects.
 // TODO: These should really be part of DISComputeFlow.
-GLuint nearest_sampler, linear_sampler, smoothness_sampler;
+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");
@@ -122,7 +152,12 @@ GLuint compile_shader(const string &shader_src, GLenum type)
        return obj;
 }
 
-GLuint load_texture(const char *filename, unsigned *width_ret, unsigned *height_ret)
+enum MipmapPolicy {
+       WITHOUT_MIPMAPS,
+       WITH_MIPMAPS
+};
+
+GLuint load_texture(const char *filename, unsigned *width_ret, unsigned *height_ret, MipmapPolicy mipmaps)
 {
        SDL_Surface *surf = IMG_Load(filename);
        if (surf == nullptr) {
@@ -131,8 +166,8 @@ GLuint load_texture(const char *filename, unsigned *width_ret, unsigned *height_
        }
 
        // For whatever reason, SDL doesn't support converting to YUV surfaces
-       // nor grayscale, so we'll do it (slowly) ourselves.
-       SDL_Surface *rgb_surf = SDL_ConvertSurfaceFormat(surf, SDL_PIXELFORMAT_RGBA8888, /*flags=*/0);
+       // 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);
@@ -142,34 +177,25 @@ GLuint load_texture(const char *filename, unsigned *width_ret, unsigned *height_
 
        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]);
+       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;
-               for (unsigned x = 0; x < width; ++x) {
-                       uint8_t r = sptr[(y2 * width + x) * 4 + 3];
-                       uint8_t g = sptr[(y2 * width + x) * 4 + 2];
-                       uint8_t b = sptr[(y2 * width + x) * 4 + 1];
-
-                       // Rec. 709.
-                       pix[y * width + x] = lrintf(r * 0.2126f + g * 0.7152f + b * 0.0722f);
-               }
+               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;
@@ -283,6 +309,52 @@ void PersistentFBOSet<num_elements>::render_to(const array<GLuint, num_elements>
        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);
+       glUseProgram(gray_program);
+       glDisable(GL_BLEND);
+       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+}
+
 // Compute gradients in every point, used for the motion search.
 // The DIS paper doesn't actually mention how these are computed,
 // but seemingly, a 3x3 Sobel operator is used here (at least in
@@ -303,7 +375,7 @@ private:
        GLuint sobel_program;
        GLuint sobel_vao;
 
-       GLuint uniform_tex, uniform_image_size;
+       GLuint uniform_tex;
 };
 
 Sobel::Sobel()
@@ -326,9 +398,7 @@ Sobel::Sobel()
 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);
+       bind_sampler(sobel_program, uniform_tex, 0, tex0_view, nearest_sampler);
 
        glViewport(0, 0, level_width, level_height);
        fbos.render_to(grad0_tex);
@@ -352,7 +422,7 @@ private:
        GLuint motion_search_program;
        GLuint motion_search_vao;
 
-       GLuint uniform_image_size, uniform_inv_image_size, uniform_inv_prev_level_size;
+       GLuint uniform_inv_image_size, uniform_inv_prev_level_size;
        GLuint uniform_image0_tex, uniform_image1_tex, uniform_grad0_tex, uniform_flow_tex;
 };
 
@@ -371,7 +441,6 @@ MotionSearch::MotionSearch()
        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");
@@ -386,10 +455,9 @@ void MotionSearch::exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GL
 
        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, zero_border_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);
 
@@ -421,7 +489,7 @@ private:
        GLuint densify_program;
        GLuint densify_vao;
 
-       GLuint uniform_width_patches, uniform_patch_size, uniform_patch_spacing;
+       GLuint uniform_patch_size, uniform_patch_spacing;
        GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
 };
 
@@ -440,7 +508,6 @@ Densify::Densify()
        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");
@@ -456,7 +523,6 @@ 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);
@@ -499,7 +565,6 @@ private:
        GLuint prewarp_vao;
 
        GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
-       GLuint uniform_image_size;
 };
 
 Prewarp::Prewarp()
@@ -520,8 +585,6 @@ Prewarp::Prewarp()
        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)
@@ -532,8 +595,6 @@ 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);
-
        glViewport(0, 0, level_width, level_height);
        glDisable(GL_BLEND);
        glBindVertexArray(prewarp_vao);
@@ -728,8 +789,8 @@ 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);
+       bind_sampler(equations_program, uniform_smoothness_x_tex, 5, smoothness_x_tex, zero_border_sampler);
+       bind_sampler(equations_program, uniform_smoothness_y_tex, 6, smoothness_y_tex, zero_border_sampler);
        glProgramUniform1f(equations_program, uniform_delta, vr_delta);
        glProgramUniform1f(equations_program, uniform_gamma, vr_gamma);
 
@@ -760,11 +821,12 @@ private:
        GLuint uniform_diff_flow_tex;
        GLuint uniform_equation_tex;
        GLuint uniform_smoothness_x_tex, uniform_smoothness_y_tex;
+       GLuint uniform_phase;
 };
 
 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);
 
@@ -781,6 +843,7 @@ SOR::SOR()
        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_phase = glGetUniformLocation(sor_program, "phase");
 }
 
 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)
@@ -788,16 +851,24 @@ void SOR::exec(GLuint diff_flow_tex, GLuint equation_tex, GLuint smoothness_x_te
        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_smoothness_x_tex, 1, smoothness_x_tex, zero_border_sampler);
+       bind_sampler(sor_program, uniform_smoothness_y_tex, 2, smoothness_y_tex, zero_border_sampler);
        bind_sampler(sor_program, uniform_equation_tex, 3, equation_tex, nearest_sampler);
 
+       // 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);
-       fbos.render_to(diff_flow_tex);  // NOTE: Bind to same as we render from!
+       fbos.render_to(diff_flow_tex);
 
        for (int i = 0; i < num_iterations; ++i) {
+               glProgramUniform1i(sor_program, uniform_phase, 0);
+               glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+               glTextureBarrier();
+               glProgramUniform1i(sor_program, uniform_phase, 1);
                glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
                if (i != num_iterations - 1) {
                        glTextureBarrier();
@@ -993,18 +1064,42 @@ private:
        bool ended = false;
 };
 
+class TexturePool {
+public:
+       GLuint get_texture(GLenum format, GLuint width, GLuint height);
+       void release_texture(GLuint tex_num);
+
+private:
+       struct Texture {
+               GLuint tex_num;
+               GLenum format;
+               GLuint width, height;
+               bool in_use = false;
+       };
+       vector<Texture> textures;
+};
+
 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);
-       void release_texture(GLuint tex);
+       GLuint exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_strategy);
+
+       void release_texture(GLuint tex) {
+               pool.release_texture(tex);
+       }
 
 private:
        int width, height;
        GLuint initial_flow_tex;
+       TexturePool pool;
 
        // The various passes.
        Sobel sobel;
@@ -1017,16 +1112,6 @@ private:
        SOR sor;
        AddBaseFlow add_base_flow;
        ResizeFlow resize_flow;
-
-       struct Texture {
-               GLuint tex_num;
-               GLenum format;
-               GLuint width, height;
-               bool in_use = false;
-       };
-       vector<Texture> textures;
-
-       GLuint get_texture(GLenum format, GLuint width, GLuint height);
 };
 
 DISComputeFlow::DISComputeFlow(int width, int height)
@@ -1047,13 +1132,15 @@ DISComputeFlow::DISComputeFlow(int width, int height)
 
        // 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);
+       // 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_NEAREST);
+       glSamplerParameteri(zero_border_sampler, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+       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 };
-       glSamplerParameterfv(smoothness_sampler, GL_TEXTURE_BORDER_COLOR, zero);
+       glSamplerParameterfv(zero_border_sampler, GL_TEXTURE_BORDER_COLOR, zero);
 
        // Initial flow is zero, 1x1.
        glCreateTextures(GL_TEXTURE_2D, 1, &initial_flow_tex);
@@ -1061,12 +1148,8 @@ DISComputeFlow::DISComputeFlow(int width, int height)
        glClearTexImage(initial_flow_tex, 0, GL_RG, GL_FLOAT, nullptr);
 }
 
-GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1)
+GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_strategy)
 {
-       for (const Texture &tex : textures) {
-               assert(!tex.in_use);
-       }
-
        int prev_level_width = 1, prev_level_height = 1;
        GLuint prev_level_flow_tex = initial_flow_tex;
 
@@ -1081,13 +1164,17 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1)
                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);
@@ -1096,7 +1183,7 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1)
 
                // Create a new texture; we could be fancy and render use a multi-level
                // texture, but meh.
-               GLuint grad0_tex = get_texture(GL_RG16F, level_width, level_height);
+               GLuint grad0_tex = pool.get_texture(GL_RG16F, level_width, level_height);
 
                // Find the derivative.
                {
@@ -1108,19 +1195,19 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1)
                // level (sampled bilinearly; no fancy tricks) as a guide, then search from there.
 
                // Create an output flow texture.
-               GLuint flow_out_tex = get_texture(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);
                }
-               release_texture(grad0_tex);
+               pool.release_texture(grad0_tex);
 
                // Densification.
 
                // Set up an output texture (initially zero).
-               GLuint dense_flow_tex = get_texture(GL_RGB16F, level_width, level_height);
+               GLuint dense_flow_tex = pool.get_texture(GL_RGB16F, level_width, level_height);
                glClearTexImage(dense_flow_tex, 0, GL_RGB, GL_FLOAT, nullptr);
 
                // And draw.
@@ -1128,7 +1215,7 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1)
                        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);
                }
-               release_texture(flow_out_tex);
+               pool.release_texture(flow_out_tex);
 
                // Everything below here in the loop belongs to variational refinement.
                ScopedTimer varref_timer("Variational refinement", &level_timer);
@@ -1140,40 +1227,42 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1)
                // 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 = get_texture(GL_R16F, level_width, level_height);
-               GLuint I_t_tex = get_texture(GL_R16F, level_width, level_height);
-               GLuint base_flow_tex = get_texture(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);
                }
-               release_texture(dense_flow_tex);
+               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 = get_texture(GL_RG16F, level_width, level_height);
-               GLuint beta_0_tex = get_texture(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);
                }
-               release_texture(I_tex);
+               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 = get_texture(GL_RG16F, level_width, level_height);
+               GLuint du_dv_tex = pool.get_texture(GL_RG16F, level_width, level_height);
                glClearTexImage(du_dv_tex, 0, GL_RG, GL_FLOAT, nullptr);
 
                // And for smoothness.
-               GLuint smoothness_x_tex = get_texture(GL_R16F, level_width, level_height);
-               GLuint smoothness_y_tex = get_texture(GL_R16F, level_width, level_height);
+               GLuint smoothness_x_tex = pool.get_texture(GL_R16F, level_width, level_height);
+               GLuint smoothness_y_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 = get_texture(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,
@@ -1197,25 +1286,27 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1)
                        }
                }
 
-               release_texture(I_t_tex);
-               release_texture(I_x_y_tex);
-               release_texture(beta_0_tex);
-               release_texture(smoothness_x_tex);
-               release_texture(smoothness_y_tex);
-               release_texture(equation_tex);
+               pool.release_texture(I_t_tex);
+               pool.release_texture(I_x_y_tex);
+               pool.release_texture(beta_0_tex);
+               pool.release_texture(smoothness_x_tex);
+               pool.release_texture(smoothness_y_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 part 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);
                }
-               release_texture(du_dv_tex);
+               pool.release_texture(du_dv_tex);
 
                if (prev_level_flow_tex != initial_flow_tex) {
-                       release_texture(prev_level_flow_tex);
+                       pool.release_texture(prev_level_flow_tex);
                }
                prev_level_flow_tex = base_flow_tex;
                prev_level_width = level_width;
@@ -1226,17 +1317,228 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1)
        timers.print();
 
        // Scale up the flow to the final size (if needed).
-       if (finest_level == 0) {
+       if (finest_level == 0 || resize_strategy == DO_NOT_RESIZE_FLOW) {
                return prev_level_flow_tex;
        } else {
-               GLuint final_tex = get_texture(GL_RG16F, width, height);
+               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);
-               release_texture(prev_level_flow_tex);
+               pool.release_texture(prev_level_flow_tex);
                return final_tex;
        }
 }
 
-GLuint DISComputeFlow::get_texture(GLenum format, GLuint width, GLuint height)
+// 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:
+       PersistentFBOSet<2> fbos;
+
+       GLuint splat_vs_obj;
+       GLuint splat_fs_obj;
+       GLuint splat_program;
+       GLuint splat_vao;
+
+       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);
+
+       // Set up the VAO containing all the required position/texcoord data.
+       glCreateVertexArrays(1, &splat_vao);
+       glBindVertexArray(splat_vao);
+       glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
+
+       GLint position_attrib = glGetAttribLocation(splat_program, "position");
+       glEnableVertexArrayAttrib(splat_vao, position_attrib);
+       glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
+
+       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.
+       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.)
+       glBindVertexArray(splat_vao);
+
+       // FIXME: Get this into FBOSet, so we can reuse FBOs across frames.
+       GLuint fbo;
+       glCreateFramebuffers(1, &fbo);
+       glNamedFramebufferTexture(fbo, GL_COLOR_ATTACHMENT0, flow_tex, 0);
+       glNamedFramebufferTexture(fbo, GL_DEPTH_ATTACHMENT, depth_tex, 0);
+       glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+
+       // 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);
+
+       glDeleteFramebuffers(1, &fbo);
+}
+
+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 blend_vao;
+
+       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);
+
+       // Set up the VAO containing all the required position/texcoord data.
+       glCreateVertexArrays(1, &blend_vao);
+       glBindVertexArray(blend_vao);
+
+       GLint position_attrib = glGetAttribLocation(blend_program, "position");
+       glEnableVertexArrayAttrib(blend_vao, position_attrib);
+       glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
+
+       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);
+       //glProgramUniform1f(blend_program, uniform_flow_consistency_tolerance, 1.0f / 
+
+       glViewport(0, 0, level_width, level_height);
+       fbos.render_to(output_tex);
+       glBindVertexArray(blend_vao);
+       glUseProgram(blend_program);
+       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;
+       TexturePool pool;
+       Splat splat;
+       Blend blend;
+};
+
+Interpolate::Interpolate(int width, int height, int flow_level)
+       : width(width), height(height), flow_level(flow_level) {}
+
+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);
+
+       // 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("Clear", &total_timer);
+               glClearTexImage(flow_tex, 0, GL_RG, GL_FLOAT, nullptr);
+               float infinity = 1.0f;
+               glClearTexImage(depth_tex, 0, GL_DEPTH_COMPONENT, GL_FLOAT, &infinity);
+       }
+
+       //SDL_GL_SwapWindow(window);
+       {
+               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);
+       }
+       //SDL_GL_SwapWindow(window);
+       pool.release_texture(depth_tex);
+       glDeleteTextures(1, &tex0_view);
+       glDeleteTextures(1, &tex1_view);
+
+       GLuint output_tex = pool.get_texture(GL_RGB8, width, height);
+       {
+               ScopedTimer timer("Blend", &total_timer);
+               blend.exec(tex0, tex1, flow_tex, output_tex, width, height, alpha);
+       }
+       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 &&
@@ -1257,7 +1559,7 @@ GLuint DISComputeFlow::get_texture(GLenum format, GLuint width, GLuint height)
        return tex.tex_num;
 }
 
-void DISComputeFlow::release_texture(GLuint tex_num)
+void TexturePool::release_texture(GLuint tex_num)
 {
        for (Texture &tex : textures) {
                if (tex.tex_num == tex_num) {
@@ -1269,6 +1571,14 @@ void DISComputeFlow::release_texture(GLuint tex_num)
        assert(false);
 }
 
+// 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];
+       }
+}
+
 void write_flow(const char *filename, const float *dense_flow, unsigned width, unsigned height)
 {
        FILE *flowfp = fopen(filename, "wb");
@@ -1277,15 +1587,7 @@ void write_flow(const char *filename, const float *dense_flow, unsigned width, u
        fwrite(&height, 4, 1, flowfp);
        for (unsigned y = 0; y < 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];
-
-                       dv = -dv;
-
-                       fwrite(&du, 4, 1, flowfp);
-                       fwrite(&dv, 4, 1, flowfp);
-               }
+               fwrite(&dense_flow[yy * width * 2], width * 2 * sizeof(float), 1, flowfp);
        }
        fclose(flowfp);
 }
@@ -1300,8 +1602,6 @@ void write_ppm(const char *filename, const float *dense_flow, unsigned width, un
                        float du = dense_flow[(yy * width + x) * 2 + 0];
                        float dv = dense_flow[(yy * width + x) * 2 + 1];
 
-                       dv = -dv;
-
                        uint8_t r, g, b;
                        flow2rgb(du, dv, &r, &g, &b);
                        putc(r, fp);
@@ -1312,27 +1612,227 @@ void write_ppm(const char *filename, const float *dense_flow, unsigned width, un
        fclose(fp);
 }
 
+void finish_one_read(GLuint width, GLuint height)
+{
+       assert(!reads_in_progress.empty());
+       ReadInProgress read = reads_in_progress.front();
+       reads_in_progress.pop_front();
+
+       unique_ptr<float[]> flow(new float[width * height * 2]);
+       void *buf = glMapNamedBufferRange(read.pbo, 0, width * height * 2 * sizeof(float), GL_MAP_READ_BIT);  // Blocks if the read isn't done yet.
+       memcpy(flow.get(), buf, width * height * 2 * sizeof(float));
+       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);
+       }
+}
+
+void schedule_read(GLuint tex, GLuint width, GLuint height, const char *filename0, const char *filename1, const char *flow_filename, const char *ppm_filename)
+{
+       if (spare_pbos.empty()) {
+               finish_one_read(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, GL_RG, GL_FLOAT, width * height * 2 * sizeof(float), 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]);
+       }
+
+       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(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(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(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 * 2 * sizeof(float), nullptr, GL_STREAM_READ);
+               spare_pbos.push(pbos[i]);
+       }
+
+       DISComputeFlow compute_flow(width1, height1);
+       GrayscaleConversion gray;
+       Interpolate interpolate(width1, height1, finest_level);
+       //Interpolate interpolate(width1, height1, 0);
+
+       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) {
+               float alpha = frameno / 60.0f;
+               GLuint interpolated_tex = interpolate.exec(tex0, tex1, forward_flow_tex, backward_flow_tex, width1, height1, alpha);
+
+               unique_ptr<uint8_t[]> rgb(new uint8_t[width1 * height1 * 3]);
+               glGetTextureImage(interpolated_tex, 0, GL_RGB, GL_UNSIGNED_BYTE, width1 * height1 * 3, rgb.get());
+
+               char buf[256];
+               snprintf(buf, sizeof(buf), "interp%04d.ppm", frameno);
+               FILE *fp = fopen(buf, "wb");
+               fprintf(fp, "P6\n%d %d\n255\n", width1, height1);
+               for (unsigned y = 0; y < height1; ++y) {
+                       unsigned y2 = height1 - 1 - y;
+                       fwrite(rgb.get() + y2 * width1 * 3, width1 * 3, 1, fp);
+               }
+               fclose(fp);
+       }
+
+       //schedule_read(interpolated_tex, width1, height1, filename0, filename1, "", "halfflow.ppm");
+       //interpolate.release_texture(interpolated_tex);
+       //finish_one_read(width1, height1);
+}
+
 int main(int argc, char **argv)
 {
         static const option long_options[] = {
-                { "alpha", required_argument, 0, 'a' },
-                { "delta", required_argument, 0, 'd' },
-                { "gamma", required_argument, 0, 'g' },
-               { "disable-timing", no_argument, 0, 1000 }
+               { "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 },
+               { "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, "a:d:g:", long_options, &option_index);
+               int c = getopt_long(argc, argv, "s:i:g:", long_options, &option_index);
 
                if (c == -1) {
                        break;
                }
                switch (c) {
-               case 'a':
+               case 's':
                        vr_alpha = atof(optarg);
                        break;
-               case 'd':
+               case 'i':
                        vr_delta = atof(optarg);
                        break;
                case 'g':
@@ -1341,6 +1841,12 @@ int main(int argc, char **argv)
                case 1000:
                        enable_timing = false;
                        break;
+               case 1001:
+                       enable_variational_refinement = false;
+                       break;
+               case 1002:
+                       enable_interpolation = true;
+                       break;
                default:
                        fprintf(stderr, "Unknown option '%s'\n", argv[option_index]);
                        exit(1);
@@ -1360,30 +1866,14 @@ int main(int argc, char **argv)
        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);
+       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);
 
-       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";
-       fprintf(stderr, "%s %s -> %s\n", filename0, filename1, flow_filename);
-
-       // Load pictures.
-       unsigned width1, height1, width2, height2;
-       GLuint tex0 = load_texture(filename0, &width1, &height1);
-       GLuint tex1 = load_texture(filename1, &width2, &height2);
-
-       if (width1 != width2 || height1 != height2) {
-               fprintf(stderr, "Image dimensions don't match (%dx%d versus %dx%d)\n",
-                       width1, height1, width2, height2);
-               exit(1);
-       }
-
        // FIXME: Should be part of DISComputeFlow (but needs to be initialized
        // before all the render passes).
        float vertices[] = {
@@ -1396,52 +1886,9 @@ int main(int argc, char **argv)
        glNamedBufferData(vertex_vbo, sizeof(vertices), vertices, GL_STATIC_DRAW);
        glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 
-       DISComputeFlow compute_flow(width1, height1);
-       GLuint final_tex = compute_flow.exec(tex0, tex1);
-
-       unique_ptr<float[]> dense_flow(new float[width1 * height1 * 2]);
-       glGetTextureImage(final_tex, 0, GL_RG, GL_FLOAT, width1 * height1 * 2 * sizeof(float), dense_flow.get());
-
-       compute_flow.release_texture(final_tex);
-
-       write_flow(flow_filename, dense_flow.get(), width1, height1);
-       write_ppm("flow.ppm", dense_flow.get(), width1, height1);
-
-       dense_flow.reset();
-
-       // 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];
-               fprintf(stderr, "%s %s -> %s\n", filename0, filename1, flow_filename);
-
-               GLuint width, height;
-               GLuint tex0 = load_texture(filename0, &width, &height);
-               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);
-               }
-
-               GLuint tex1 = load_texture(filename1, &width, &height);
-               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);
-               }
-
-               GLuint final_tex = compute_flow.exec(tex0, tex1);
-
-               unique_ptr<float[]> dense_flow(new float[width * height * 2]);
-               glGetTextureImage(final_tex, 0, GL_RG, GL_FLOAT, width * height * 2 * sizeof(float), dense_flow.get());
-
-               compute_flow.release_texture(final_tex);
-
-               write_flow(flow_filename, dense_flow.get(), width, height);
+       if (enable_interpolation) {
+               interpolate_image(argc, argv, optind);
+       } else {
+               compute_flow_only(argc, argv, optind);
        }
-
-       fprintf(stderr, "err = %d\n", glGetError());
 }