]> git.sesse.net Git - nageru/blobdiff - flow.cpp
Write a .flo file for easier evaluation.
[nageru] / flow.cpp
index f4fbb74d67903c5ee1d422977b93636ae3026a79..43daa787905c87584b9bbdc54cb31063733b05ac 100644 (file)
--- a/flow.cpp
+++ b/flow.cpp
@@ -16,6 +16,8 @@
 #include <assert.h>
 #include <stdio.h>
 
+#include "flow2rgb.h"
+
 #include <algorithm>
 #include <memory>
 
@@ -25,10 +27,14 @@ using namespace std;
 
 // Operating point 3 (10 Hz on CPU, excluding preprocessing).
 constexpr float patch_overlap_ratio = 0.75f;
-constexpr unsigned coarsest_level = 0;
-constexpr unsigned finest_level = 0;
+constexpr unsigned coarsest_level = 5;
+constexpr unsigned finest_level = 1;
 constexpr unsigned patch_size_pixels = 12;
 
+// Some global OpenGL objects.
+GLuint nearest_sampler, linear_sampler, mipmap_sampler;
+GLuint vertex_vbo;
+
 string read_file(const string &filename)
 {
        FILE *fp = fopen(filename.c_str(), "r");
@@ -199,6 +205,189 @@ void bind_sampler(GLuint program, const char *uniform_name, GLuint texture_unit,
        glProgramUniform1i(program, location, texture_unit);
 }
 
+// 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
+// later versions of the code), while a [1 -8 0 8 -1] kernel is
+// used for all the derivatives in the variational refinement part
+// (which borrows code from DeepFlow). This is inconsistent,
+// but I guess we're better off with staying with the original
+// decisions until we actually know having different ones would be better.
+class Sobel {
+public:
+       Sobel();
+       void exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_height);
+
+private:
+       GLuint sobel_vs_obj;
+       GLuint sobel_fs_obj;
+       GLuint sobel_program;
+       GLuint sobel_vao;
+};
+
+Sobel::Sobel()
+{
+       sobel_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
+       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));
+
+       GLint texcoord_attrib = glGetAttribLocation(sobel_program, "texcoord");
+       glEnableVertexArrayAttrib(sobel_vao, texcoord_attrib);
+       glVertexAttribPointer(texcoord_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
+}
+
+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, glGetUniformLocation(sobel_program, "tex"), 0);
+       glProgramUniform2f(sobel_program, glGetUniformLocation(sobel_program, "image_size"), level_width, level_height);
+       glProgramUniform2f(sobel_program, glGetUniformLocation(sobel_program, "inv_image_size"), 1.0f / level_width, 1.0f / level_height);
+
+       GLuint grad0_fbo;  // TODO: cleanup
+       glCreateFramebuffers(1, &grad0_fbo);
+       glNamedFramebufferTexture(grad0_fbo, GL_COLOR_ATTACHMENT0, grad0_tex, 0);
+
+       glViewport(0, 0, level_width, level_height);
+       glBindFramebuffer(GL_FRAMEBUFFER, grad0_fbo);
+        glBindVertexArray(sobel_vao);
+       glUseProgram(sobel_program);
+       glDisable(GL_BLEND);
+       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+}
+
+// Motion search to find the initial flow. See motion_search.frag for documentation.
+class MotionSearch {
+public:
+       MotionSearch();
+       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 width_patches, int height_patches);
+
+private:
+       GLuint motion_vs_obj;
+       GLuint motion_fs_obj;
+       GLuint motion_search_program;
+       GLuint motion_search_vao;
+};
+
+MotionSearch::MotionSearch()
+{
+       motion_vs_obj = compile_shader(read_file("motion_search.vert"), GL_VERTEX_SHADER);
+       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));
+
+       GLint texcoord_attrib = glGetAttribLocation(motion_search_program, "texcoord");
+       glEnableVertexArrayAttrib(motion_search_vao, texcoord_attrib);
+       glVertexAttribPointer(texcoord_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
+}
+
+void MotionSearch::exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GLuint flow_tex, GLuint flow_out_tex, int level_width, int level_height, int width_patches, int height_patches)
+{
+       glUseProgram(motion_search_program);
+
+       bind_sampler(motion_search_program, "image0_tex", 0, tex0_view, nearest_sampler);
+       bind_sampler(motion_search_program, "image1_tex", 1, tex1_view, linear_sampler);
+       bind_sampler(motion_search_program, "grad0_tex", 2, grad0_tex, nearest_sampler);
+       bind_sampler(motion_search_program, "flow_tex", 3, flow_tex, linear_sampler);
+
+       glProgramUniform2f(motion_search_program, glGetUniformLocation(motion_search_program, "image_size"), level_width, level_height);
+       glProgramUniform2f(motion_search_program, glGetUniformLocation(motion_search_program, "inv_image_size"), 1.0f / level_width, 1.0f / 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);
+       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+}
+
+// Do “densification”, ie., upsampling of the flow patches to the flow field
+// (the same size as the image at this level). We draw one quad per patch
+// over its entire covered area (using instancing in the vertex shader),
+// and then weight the contributions in the pixel shader by post-warp difference.
+// This is equation (3) in the paper.
+//
+// We accumulate the flow vectors in the R/G channels (for u/v) and the total
+// weight in the B channel. Dividing R and G by B gives the normalized values.
+class Densify {
+public:
+       Densify();
+       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:
+       GLuint densify_vs_obj;
+       GLuint densify_fs_obj;
+       GLuint densify_program;
+       GLuint densify_vao;
+};
+
+Densify::Densify()
+{
+       densify_vs_obj = compile_shader(read_file("densify.vert"), GL_VERTEX_SHADER);
+       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));
+}
+
+void Densify::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)
+{
+       glUseProgram(densify_program);
+
+       bind_sampler(densify_program, "image0_tex", 0, tex0_view, nearest_sampler);
+       bind_sampler(densify_program, "image1_tex", 1, tex1_view, linear_sampler);
+       bind_sampler(densify_program, "flow_tex", 2, flow_tex, nearest_sampler);
+
+       glProgramUniform1i(densify_program, glGetUniformLocation(densify_program, "width_patches"), width_patches);
+       glProgramUniform2f(densify_program, glGetUniformLocation(densify_program, "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);
+       glProgramUniform2f(densify_program, glGetUniformLocation(densify_program, "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);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width_patches * height_patches);
+}
+
 int main(void)
 {
        if (SDL_Init(SDL_INIT_EVERYTHING) == -1) {
@@ -226,163 +415,145 @@ int main(void)
        GLuint tex0 = load_texture("test1499.pgm", WIDTH, HEIGHT);
        GLuint tex1 = load_texture("test1500.pgm", WIDTH, HEIGHT);
 
-       // Load shaders.
-       GLuint motion_vs_obj = compile_shader(read_file("motion_search.vert"), GL_VERTEX_SHADER);
-       GLuint motion_fs_obj = compile_shader(read_file("motion_search.frag"), GL_FRAGMENT_SHADER);
-       GLuint motion_search_program = link_program(motion_vs_obj, motion_fs_obj);
-
-       GLuint sobel_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
-       GLuint sobel_fs_obj = compile_shader(read_file("sobel.frag"), GL_FRAGMENT_SHADER);
-       GLuint sobel_program = link_program(sobel_vs_obj, sobel_fs_obj);
-
        // Make some samplers.
-       GLuint nearest_sampler;
        glCreateSamplers(1, &nearest_sampler);
        glSamplerParameteri(nearest_sampler, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glSamplerParameteri(nearest_sampler, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glSamplerParameteri(nearest_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glSamplerParameteri(nearest_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 
-       GLuint linear_sampler;
        glCreateSamplers(1, &linear_sampler);
        glSamplerParameteri(linear_sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glSamplerParameteri(linear_sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glSamplerParameteri(linear_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glSamplerParameteri(linear_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 
-       GLuint mipmap_sampler;
        glCreateSamplers(1, &mipmap_sampler);
        glSamplerParameteri(mipmap_sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
        glSamplerParameteri(mipmap_sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glSamplerParameteri(mipmap_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glSamplerParameteri(mipmap_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 
-       // Coarsest level.
-       int level = coarsest_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 always read from the correct level; the chosen
-       // mipmapping could otherwise be rather unpredictable, especially
-       // during motion search.
-       GLuint tex0_view, tex1_view;
-       glGenTextures(1, &tex0_view);
-       glTextureView(tex0_view, GL_TEXTURE_2D, tex0, GL_R8, level, 1, 0, 1);
-       glGenTextures(1, &tex1_view);
-       glTextureView(tex1_view, GL_TEXTURE_2D, tex1, GL_R8, level, 1, 0, 1);
-
-       // 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
-       // later versions of the code), while a [1 -8 0 8 -1] kernel is
-       // used for all the derivatives in the variational refinement part
-       // (which borrows code from DeepFlow). This is inconsistent,
-       // but I guess we're better off with staying with the original
-       // decisions until we actually know having different ones would be better.
-
-       // 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_fbo;
-       glCreateFramebuffers(1, &grad0_fbo);
-       glNamedFramebufferTexture(grad0_fbo, GL_COLOR_ATTACHMENT0, grad0_tex, 0);
-
-       glUseProgram(sobel_program);
-       glBindTextureUnit(0, tex0_view);
-       glBindSampler(0, nearest_sampler);
-       glProgramUniform1i(sobel_program, glGetUniformLocation(sobel_program, "tex"), 0);
-       glProgramUniform1f(sobel_program, glGetUniformLocation(sobel_program, "inv_width"), 1.0f / level_width);
-       glProgramUniform1f(sobel_program, glGetUniformLocation(sobel_program, "inv_height"), 1.0f / level_height);
-
-       // Set up the VAO containing all the required position/texcoord data.
-       GLuint sobel_vao;
-        glCreateVertexArrays(1, &sobel_vao);
-        glBindVertexArray(sobel_vao);
        float vertices[] = {
                0.0f, 1.0f,
                0.0f, 0.0f,
                1.0f, 1.0f,
                1.0f, 0.0f,
        };
-       GLuint vertex_vbo;
        glCreateBuffers(1, &vertex_vbo);
        glNamedBufferData(vertex_vbo, sizeof(vertices), vertices, GL_STATIC_DRAW);
        glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 
-       int position_attrib = glGetAttribLocation(sobel_program, "position");
-       glEnableVertexArrayAttrib(sobel_vao, position_attrib);
-       glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
-
-       int texcoord_attrib = glGetAttribLocation(sobel_program, "texcoord");
-       glEnableVertexArrayAttrib(sobel_vao, texcoord_attrib);
-       glVertexAttribPointer(texcoord_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
+       // Initial flow is zero, 1x1.
+       GLuint initial_flow_tex;
+       glCreateTextures(GL_TEXTURE_2D, 1, &initial_flow_tex);
+       glTextureStorage2D(initial_flow_tex, 1, GL_RGB32F, 1, 1);
 
-       glBindBuffer(GL_ARRAY_BUFFER, 0);
+       GLuint prev_level_flow_tex = initial_flow_tex;
 
-       // Now finally draw.
-       glViewport(0, 0, level_width, level_height);
-       glBindFramebuffer(GL_FRAMEBUFFER, grad0_fbo);
-       glUseProgram(sobel_program);
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       Sobel sobel;
+       MotionSearch motion_search;
+       Densify densify;
 
-       // Motion search to find the initial flow.
+       GLuint query;
+       glGenQueries(1, &query);
+       glBeginQuery(GL_TIME_ELAPSED, query);
 
-       // Create a flow texture, initialized to zero.
-       GLuint flow_tex;
-       glCreateTextures(GL_TEXTURE_2D, 1, &flow_tex);
-       glTextureStorage2D(flow_tex, 1, GL_RG16F, width_patches, height_patches);
+       for (int level = coarsest_level; level >= int(finest_level); --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);
 
-       // And an output flow texture. (Well, we could have used texture barriers,
-       // but I don't feel lucky today.)
-       GLuint flow_out_tex;
-       glCreateTextures(GL_TEXTURE_2D, 1, &flow_out_tex);
-       glTextureStorage2D(flow_out_tex, 1, GL_RG16F, width_patches, height_patches);
+               // 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);
+               glGenTextures(1, &tex1_view);
+               glTextureView(tex1_view, GL_TEXTURE_2D, tex1, GL_R8, level, 1, 0, 1);
 
-       GLuint flow_fbo;
-       glCreateFramebuffers(1, &flow_fbo);
-       glNamedFramebufferTexture(flow_fbo, GL_COLOR_ATTACHMENT0, flow_out_tex, 0);
+               // 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);
 
-       glUseProgram(motion_search_program);
+               // Find the derivative.
+               sobel.exec(tex0_view, grad0_tex, level_width, level_height);
 
-       bind_sampler(motion_search_program, "image0_tex", 0, tex0_view, nearest_sampler);
-       bind_sampler(motion_search_program, "image1_tex", 1, tex1_view, linear_sampler);
-       bind_sampler(motion_search_program, "grad0_tex", 2, grad0_tex, nearest_sampler);
-       bind_sampler(motion_search_program, "flow_tex", 3, flow_tex, nearest_sampler);
+               // Motion search to find the initial flow. We use the flow from the previous
+               // level (sampled bilinearly; no fancy tricks) as a guide, then search from there.
 
-       glProgramUniform1f(motion_search_program, glGetUniformLocation(motion_search_program, "image_width"), level_width);
-       glProgramUniform1f(motion_search_program, glGetUniformLocation(motion_search_program, "image_height"), level_height);
-       glProgramUniform1f(motion_search_program, glGetUniformLocation(motion_search_program, "inv_image_width"), 1.0f / level_width);
-       glProgramUniform1f(motion_search_program, glGetUniformLocation(motion_search_program, "inv_image_height"), 1.0f / level_height);
+               // Create an output flow texture.
+               GLuint flow_out_tex;
+               glCreateTextures(GL_TEXTURE_2D, 1, &flow_out_tex);
+               glTextureStorage2D(flow_out_tex, 1, GL_RG16F, width_patches, height_patches);
 
-//     printf("%d x %d patches on this level\n", width_patches, height_patches);
+               // And draw.
+               motion_search.exec(tex0_view, tex1_view, grad0_tex, prev_level_flow_tex, flow_out_tex, level_width, level_height, width_patches, height_patches);
 
-       // Set up the VAO containing all the required position/texcoord data.
-       GLuint motion_search_vao;
-        glCreateVertexArrays(1, &motion_search_vao);
-        glBindVertexArray(motion_search_vao);
-       glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
+               // Densification.
 
-       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));
+               // 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);
+               glTextureStorage2D(dense_flow_tex, 1, GL_RGBA32F, level_width, level_height);
 
-       texcoord_attrib = glGetAttribLocation(motion_search_program, "texcoord");
-       glEnableVertexArrayAttrib(motion_search_vao, texcoord_attrib);
-       glVertexAttribPointer(texcoord_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
+               // And draw.
+               densify.exec(tex0_view, tex1_view, flow_out_tex, dense_flow_tex, level_width, level_height, width_patches, height_patches);
 
-       glBindBuffer(GL_ARRAY_BUFFER, 0);
+               // TODO: Variational refinement.
 
-       // And draw.
-       glViewport(0, 0, width_patches, height_patches);
-       glBindFramebuffer(GL_FRAMEBUFFER, flow_fbo);
-       glUseProgram(motion_search_program);
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+               prev_level_flow_tex = dense_flow_tex;
+       }
+       glEndQuery(GL_TIME_ELAPSED);
+
+       GLint available;
+       do {
+               glGetQueryObjectiv(query, GL_QUERY_RESULT_AVAILABLE, &available);
+       } while (!available);
+       GLuint64 time_elapsed;
+       glGetQueryObjectui64v(query, GL_QUERY_RESULT, &time_elapsed);
+       fprintf(stderr, "GPU time used = %.1f ms\n", time_elapsed / 1e6);
+
+       int level_width = WIDTH >> finest_level;
+       int level_height = HEIGHT >> finest_level;
+       unique_ptr<float[]> dense_flow(new float[level_width * level_height * 3]);
+       glGetTextureImage(prev_level_flow_tex, 0, GL_RGB, GL_FLOAT, level_width * level_height * 3 * sizeof(float), dense_flow.get());
+
+       FILE *fp = fopen("flow.ppm", "wb");
+       FILE *flowfp = fopen("flow.flo", "wb");
+       fprintf(fp, "P6\n%d %d\n255\n", level_width, level_height);
+       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) * 3 + 0];
+                       float dv = dense_flow[(yy * level_width + x) * 3 + 1];
+                       float w = dense_flow[(yy * level_width + x) * 3 + 2];
+
+                       du = (du / w) * level_width;
+                       dv = (-dv / w) * level_height;
+
+                       fwrite(&du, 4, 1, flowfp);
+                       fwrite(&dv, 4, 1, flowfp);
+
+                       uint8_t r, g, b;
+                       flow2rgb(du, dv, &r, &g, &b);
+                       putc(r, fp);
+                       putc(g, fp);
+                       putc(b, fp);
+               }
+       }
+       fclose(fp);
+       fclose(flowfp);
 
        fprintf(stderr, "err = %d\n", glGetError());
 }