git.sesse.net Git - nageru/blob - flow.cpp

   1 #define NO_SDL_GLEXT 1
   2
   3 #define WIDTH 1280
   4 #define HEIGHT 720
   5
   6 #include <epoxy/gl.h>
   7
   8 #include <SDL2/SDL.h>
   9 #include <SDL2/SDL_error.h>
  10 #include <SDL2/SDL_events.h>
  11 #include <SDL2/SDL_image.h>
  12 #include <SDL2/SDL_keyboard.h>
  13 #include <SDL2/SDL_mouse.h>
  14 #include <SDL2/SDL_video.h>
  15
  16 #include <assert.h>
  17 #include <stdio.h>
  18 #include <unistd.h>
  19
  20 #include "util.h"
  21
  22 #include <algorithm>
  23 #include <memory>
  24
  25 #define BUFFER_OFFSET(i) ((char *)nullptr + (i))
  26
  27 using namespace std;
  28
  29 // Operating point 3 (10 Hz on CPU, excluding preprocessing).
  30 constexpr float patch_overlap_ratio = 0.75f;
  31 constexpr unsigned coarsest_level = 5;
  32 constexpr unsigned finest_level = 1;
  33 constexpr unsigned patch_size_pixels = 12;
  34
  35 // Some global OpenGL objects.
  36 GLuint nearest_sampler, linear_sampler, smoothness_sampler;
  37 GLuint vertex_vbo;
  38
  39 string read_file(const string &filename)
  40 {
  41         FILE *fp = fopen(filename.c_str(), "r");
  42         if (fp == nullptr) {
  43                 perror(filename.c_str());
  44                 exit(1);
  45         }
  46
  47         int ret = fseek(fp, 0, SEEK_END);
  48         if (ret == -1) {
  49                 perror("fseek(SEEK_END)");
  50                 exit(1);
  51         }
  52
  53         int size = ftell(fp);
  54
  55         ret = fseek(fp, 0, SEEK_SET);
  56         if (ret == -1) {
  57                 perror("fseek(SEEK_SET)");
  58                 exit(1);
  59         }
  60
  61         string str;
  62         str.resize(size);
  63         ret = fread(&str[0], size, 1, fp);
  64         if (ret == -1) {
  65                 perror("fread");
  66                 exit(1);
  67         }
  68         if (ret == 0) {
  69                 fprintf(stderr, "Short read when trying to read %d bytes from %s\n",
  70                                 size, filename.c_str());
  71                 exit(1);
  72         }
  73         fclose(fp);
  74
  75         return str;
  76 }
  77
  78
  79 GLuint compile_shader(const string &shader_src, GLenum type)
  80 {
  81         GLuint obj = glCreateShader(type);
  82         const GLchar* source[] = { shader_src.data() };
  83         const GLint length[] = { (GLint)shader_src.size() };
  84         glShaderSource(obj, 1, source, length);
  85         glCompileShader(obj);
  86
  87         GLchar info_log[4096];
  88         GLsizei log_length = sizeof(info_log) - 1;
  89         glGetShaderInfoLog(obj, log_length, &log_length, info_log);
  90         info_log[log_length] = 0;
  91         if (strlen(info_log) > 0) {
  92                 fprintf(stderr, "Shader compile log: %s\n", info_log);
  93         }
  94
  95         GLint status;
  96         glGetShaderiv(obj, GL_COMPILE_STATUS, &status);
  97         if (status == GL_FALSE) {
  98                 // Add some line numbers to easier identify compile errors.
  99                 string src_with_lines = "/*   1 */ ";
 100                 size_t lineno = 1;
 101                 for (char ch : shader_src) {
 102                         src_with_lines.push_back(ch);
 103                         if (ch == '\n') {
 104                                 char buf[32];
 105                                 snprintf(buf, sizeof(buf), "/* %3zu */ ", ++lineno);
 106                                 src_with_lines += buf;
 107                         }
 108                 }
 109
 110                 fprintf(stderr, "Failed to compile shader:\n%s\n", src_with_lines.c_str());
 111                 exit(1);
 112         }
 113
 114         return obj;
 115 }
 116
 117
 118 GLuint load_texture(const char *filename, unsigned width, unsigned height)
 119 {
 120         FILE *fp = fopen(filename, "rb");
 121         if (fp == nullptr) {
 122                 perror(filename);
 123                 exit(1);
 124         }
 125         unique_ptr<uint8_t[]> pix(new uint8_t[width * height]);
 126         if (fread(pix.get(), width * height, 1, fp) != 1) {
 127                 fprintf(stderr, "Short read from %s\n", filename);
 128                 exit(1);
 129         }
 130         fclose(fp);
 131
 132         // Convert to bottom-left origin.
 133         for (unsigned y = 0; y < height / 2; ++y) {
 134                 unsigned y2 = height - 1 - y;
 135                 swap_ranges(&pix[y * width], &pix[y * width + width], &pix[y2 * width]);
 136         }
 137
 138         int levels = 1;
 139         for (int w = width, h = height; w > 1 || h > 1; ) {
 140                 w >>= 1;
 141                 h >>= 1;
 142                 ++levels;
 143         }
 144
 145         GLuint tex;
 146         glCreateTextures(GL_TEXTURE_2D, 1, &tex);
 147         glTextureStorage2D(tex, levels, GL_R8, width, height);
 148         glTextureSubImage2D(tex, 0, 0, 0, width, height, GL_RED, GL_UNSIGNED_BYTE, pix.get());
 149         glGenerateTextureMipmap(tex);
 150
 151         return tex;
 152 }
 153
 154 GLuint link_program(GLuint vs_obj, GLuint fs_obj)
 155 {
 156         GLuint program = glCreateProgram();
 157         glAttachShader(program, vs_obj);
 158         glAttachShader(program, fs_obj);
 159         glLinkProgram(program);
 160         GLint success;
 161         glGetProgramiv(program, GL_LINK_STATUS, &success);
 162         if (success == GL_FALSE) {
 163                 GLchar error_log[1024] = {0};
 164                 glGetProgramInfoLog(program, 1024, nullptr, error_log);
 165                 fprintf(stderr, "Error linking program: %s\n", error_log);
 166                 exit(1);
 167         }
 168         return program;
 169 }
 170
 171 GLuint generate_vbo(GLint size, GLsizeiptr data_size, const GLvoid *data)
 172 {
 173         GLuint vbo;
 174         glCreateBuffers(1, &vbo);
 175         glBufferData(GL_ARRAY_BUFFER, data_size, data, GL_STATIC_DRAW);
 176         glNamedBufferData(vbo, data_size, data, GL_STATIC_DRAW);
 177         return vbo;
 178 }
 179
 180 GLuint fill_vertex_attribute(GLuint vao, GLuint glsl_program_num, const string &attribute_name, GLint size, GLenum type, GLsizeiptr data_size, const GLvoid *data)
 181 {
 182         int attrib = glGetAttribLocation(glsl_program_num, attribute_name.c_str());
 183         if (attrib == -1) {
 184                 return -1;
 185         }
 186
 187         GLuint vbo = generate_vbo(size, data_size, data);
 188
 189         glBindBuffer(GL_ARRAY_BUFFER, vbo);
 190         glEnableVertexArrayAttrib(vao, attrib);
 191         glVertexAttribPointer(attrib, size, type, GL_FALSE, 0, BUFFER_OFFSET(0));
 192         glBindBuffer(GL_ARRAY_BUFFER, 0);
 193
 194         return vbo;
 195 }
 196
 197 void bind_sampler(GLuint program, GLint location, GLuint texture_unit, GLuint tex, GLuint sampler)
 198 {
 199         if (location == -1) {
 200                 return;
 201         }
 202
 203         glBindTextureUnit(texture_unit, tex);
 204         glBindSampler(texture_unit, sampler);
 205         glProgramUniform1i(program, location, texture_unit);
 206 }
 207
 208 // Compute gradients in every point, used for the motion search.
 209 // The DIS paper doesn't actually mention how these are computed,
 210 // but seemingly, a 3x3 Sobel operator is used here (at least in
 211 // later versions of the code), while a [1 -8 0 8 -1] kernel is
 212 // used for all the derivatives in the variational refinement part
 213 // (which borrows code from DeepFlow). This is inconsistent,
 214 // but I guess we're better off with staying with the original
 215 // decisions until we actually know having different ones would be better.
 216 class Sobel {
 217 public:
 218         Sobel();
 219         void exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_height);
 220
 221 private:
 222         GLuint sobel_vs_obj;
 223         GLuint sobel_fs_obj;
 224         GLuint sobel_program;
 225         GLuint sobel_vao;
 226
 227         GLuint uniform_tex, uniform_image_size;
 228 };
 229
 230 Sobel::Sobel()
 231 {
 232         sobel_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
 233         sobel_fs_obj = compile_shader(read_file("sobel.frag"), GL_FRAGMENT_SHADER);
 234         sobel_program = link_program(sobel_vs_obj, sobel_fs_obj);
 235
 236         // Set up the VAO containing all the required position/texcoord data.
 237         glCreateVertexArrays(1, &sobel_vao);
 238         glBindVertexArray(sobel_vao);
 239
 240         GLint position_attrib = glGetAttribLocation(sobel_program, "position");
 241         glEnableVertexArrayAttrib(sobel_vao, position_attrib);
 242         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 243
 244         uniform_tex = glGetUniformLocation(sobel_program, "tex");
 245 }
 246
 247 void Sobel::exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_height)
 248 {
 249         glUseProgram(sobel_program);
 250         glBindTextureUnit(0, tex0_view);
 251         glBindSampler(0, nearest_sampler);
 252         glProgramUniform1i(sobel_program, uniform_tex, 0);
 253
 254         GLuint grad0_fbo;  // TODO: cleanup
 255         glCreateFramebuffers(1, &grad0_fbo);
 256         glNamedFramebufferTexture(grad0_fbo, GL_COLOR_ATTACHMENT0, grad0_tex, 0);
 257
 258         glViewport(0, 0, level_width, level_height);
 259         glBindFramebuffer(GL_FRAMEBUFFER, grad0_fbo);
 260         glBindVertexArray(sobel_vao);
 261         glUseProgram(sobel_program);
 262         glDisable(GL_BLEND);
 263         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 264 }
 265
 266 // Motion search to find the initial flow. See motion_search.frag for documentation.
 267 class MotionSearch {
 268 public:
 269         MotionSearch();
 270         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);
 271
 272 private:
 273         GLuint motion_vs_obj;
 274         GLuint motion_fs_obj;
 275         GLuint motion_search_program;
 276         GLuint motion_search_vao;
 277
 278         GLuint uniform_image_size, uniform_inv_image_size;
 279         GLuint uniform_image0_tex, uniform_image1_tex, uniform_grad0_tex, uniform_flow_tex;
 280 };
 281
 282 MotionSearch::MotionSearch()
 283 {
 284         motion_vs_obj = compile_shader(read_file("motion_search.vert"), GL_VERTEX_SHADER);
 285         motion_fs_obj = compile_shader(read_file("motion_search.frag"), GL_FRAGMENT_SHADER);
 286         motion_search_program = link_program(motion_vs_obj, motion_fs_obj);
 287
 288         // Set up the VAO containing all the required position/texcoord data.
 289         glCreateVertexArrays(1, &motion_search_vao);
 290         glBindVertexArray(motion_search_vao);
 291         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 292
 293         GLint position_attrib = glGetAttribLocation(motion_search_program, "position");
 294         glEnableVertexArrayAttrib(motion_search_vao, position_attrib);
 295         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 296
 297         uniform_image_size = glGetUniformLocation(motion_search_program, "image_size");
 298         uniform_inv_image_size = glGetUniformLocation(motion_search_program, "inv_image_size");
 299         uniform_image0_tex = glGetUniformLocation(motion_search_program, "image0_tex");
 300         uniform_image1_tex = glGetUniformLocation(motion_search_program, "image1_tex");
 301         uniform_grad0_tex = glGetUniformLocation(motion_search_program, "grad0_tex");
 302         uniform_flow_tex = glGetUniformLocation(motion_search_program, "flow_tex");
 303 }
 304
 305 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)
 306 {
 307         glUseProgram(motion_search_program);
 308
 309         bind_sampler(motion_search_program, uniform_image0_tex, 0, tex0_view, nearest_sampler);
 310         bind_sampler(motion_search_program, uniform_image1_tex, 1, tex1_view, linear_sampler);
 311         bind_sampler(motion_search_program, uniform_grad0_tex, 2, grad0_tex, nearest_sampler);
 312         bind_sampler(motion_search_program, uniform_flow_tex, 3, flow_tex, linear_sampler);
 313
 314         glProgramUniform2f(motion_search_program, uniform_image_size, level_width, level_height);
 315         glProgramUniform2f(motion_search_program, uniform_inv_image_size, 1.0f / level_width, 1.0f / level_height);
 316
 317         GLuint flow_fbo;  // TODO: cleanup
 318         glCreateFramebuffers(1, &flow_fbo);
 319         glNamedFramebufferTexture(flow_fbo, GL_COLOR_ATTACHMENT0, flow_out_tex, 0);
 320
 321         glViewport(0, 0, width_patches, height_patches);
 322         glBindFramebuffer(GL_FRAMEBUFFER, flow_fbo);
 323         glBindVertexArray(motion_search_vao);
 324         glUseProgram(motion_search_program);
 325         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 326 }
 327
 328 // Do “densification”, ie., upsampling of the flow patches to the flow field
 329 // (the same size as the image at this level). We draw one quad per patch
 330 // over its entire covered area (using instancing in the vertex shader),
 331 // and then weight the contributions in the pixel shader by post-warp difference.
 332 // This is equation (3) in the paper.
 333 //
 334 // We accumulate the flow vectors in the R/G channels (for u/v) and the total
 335 // weight in the B channel. Dividing R and G by B gives the normalized values.
 336 class Densify {
 337 public:
 338         Densify();
 339         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);
 340
 341 private:
 342         GLuint densify_vs_obj;
 343         GLuint densify_fs_obj;
 344         GLuint densify_program;
 345         GLuint densify_vao;
 346
 347         GLuint uniform_width_patches, uniform_patch_size, uniform_patch_spacing;
 348         GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
 349 };
 350
 351 Densify::Densify()
 352 {
 353         densify_vs_obj = compile_shader(read_file("densify.vert"), GL_VERTEX_SHADER);
 354         densify_fs_obj = compile_shader(read_file("densify.frag"), GL_FRAGMENT_SHADER);
 355         densify_program = link_program(densify_vs_obj, densify_fs_obj);
 356
 357         // Set up the VAO containing all the required position/texcoord data.
 358         glCreateVertexArrays(1, &densify_vao);
 359         glBindVertexArray(densify_vao);
 360         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 361
 362         GLint position_attrib = glGetAttribLocation(densify_program, "position");
 363         glEnableVertexArrayAttrib(densify_vao, position_attrib);
 364         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 365
 366         uniform_width_patches = glGetUniformLocation(densify_program, "width_patches");
 367         uniform_patch_size = glGetUniformLocation(densify_program, "patch_size");
 368         uniform_patch_spacing = glGetUniformLocation(densify_program, "patch_spacing");
 369         uniform_image0_tex = glGetUniformLocation(densify_program, "image0_tex");
 370         uniform_image1_tex = glGetUniformLocation(densify_program, "image1_tex");
 371         uniform_flow_tex = glGetUniformLocation(densify_program, "flow_tex");
 372 }
 373
 374 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)
 375 {
 376         glUseProgram(densify_program);
 377
 378         bind_sampler(densify_program, uniform_image0_tex, 0, tex0_view, nearest_sampler);
 379         bind_sampler(densify_program, uniform_image1_tex, 1, tex1_view, linear_sampler);
 380         bind_sampler(densify_program, uniform_flow_tex, 2, flow_tex, nearest_sampler);
 381
 382         glProgramUniform1i(densify_program, uniform_width_patches, width_patches);
 383         glProgramUniform2f(densify_program, uniform_patch_size,
 384                 float(patch_size_pixels) / level_width,
 385                 float(patch_size_pixels) / level_height);
 386
 387         float patch_spacing_x = float(level_width - patch_size_pixels) / (width_patches - 1);
 388         float patch_spacing_y = float(level_height - patch_size_pixels) / (height_patches - 1);
 389         glProgramUniform2f(densify_program, uniform_patch_spacing,
 390                 patch_spacing_x / level_width,
 391                 patch_spacing_y / level_height);
 392
 393         GLuint dense_flow_fbo;  // TODO: cleanup
 394         glCreateFramebuffers(1, &dense_flow_fbo);
 395         glNamedFramebufferTexture(dense_flow_fbo, GL_COLOR_ATTACHMENT0, dense_flow_tex, 0);
 396
 397         glViewport(0, 0, level_width, level_height);
 398         glEnable(GL_BLEND);
 399         glBlendFunc(GL_ONE, GL_ONE);
 400         glBindVertexArray(densify_vao);
 401         glBindFramebuffer(GL_FRAMEBUFFER, dense_flow_fbo);
 402         glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width_patches * height_patches);
 403 }
 404
 405 // Warp I_1 to I_w, and then compute the mean (I) and difference (I_t) of
 406 // I_0 and I_w. The prewarping is what enables us to solve the variational
 407 // flow for du,dv instead of u,v.
 408 //
 409 // See variational_refinement.txt for more information.
 410 class Prewarp {
 411 public:
 412         Prewarp();
 413         void exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint I_tex, GLuint I_t_tex, int level_width, int level_height);
 414
 415 private:
 416         GLuint prewarp_vs_obj;
 417         GLuint prewarp_fs_obj;
 418         GLuint prewarp_program;
 419         GLuint prewarp_vao;
 420
 421         GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
 422 };
 423
 424 Prewarp::Prewarp()
 425 {
 426         prewarp_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
 427         prewarp_fs_obj = compile_shader(read_file("prewarp.frag"), GL_FRAGMENT_SHADER);
 428         prewarp_program = link_program(prewarp_vs_obj, prewarp_fs_obj);
 429
 430         // Set up the VAO containing all the required position/texcoord data.
 431         glCreateVertexArrays(1, &prewarp_vao);
 432         glBindVertexArray(prewarp_vao);
 433         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 434
 435         GLint position_attrib = glGetAttribLocation(prewarp_program, "position");
 436         glEnableVertexArrayAttrib(prewarp_vao, position_attrib);
 437         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 438
 439         uniform_image0_tex = glGetUniformLocation(prewarp_program, "image0_tex");
 440         uniform_image1_tex = glGetUniformLocation(prewarp_program, "image1_tex");
 441         uniform_flow_tex = glGetUniformLocation(prewarp_program, "flow_tex");
 442 }
 443
 444 void Prewarp::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint I_tex, GLuint I_t_tex, int level_width, int level_height)
 445 {
 446         glUseProgram(prewarp_program);
 447
 448         bind_sampler(prewarp_program, uniform_image0_tex, 0, tex0_view, nearest_sampler);
 449         bind_sampler(prewarp_program, uniform_image1_tex, 1, tex1_view, linear_sampler);
 450         bind_sampler(prewarp_program, uniform_flow_tex, 2, flow_tex, nearest_sampler);
 451
 452         GLuint prewarp_fbo;  // TODO: cleanup
 453         glCreateFramebuffers(1, &prewarp_fbo);
 454         GLenum bufs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
 455         glNamedFramebufferDrawBuffers(prewarp_fbo, 2, bufs);
 456         glNamedFramebufferTexture(prewarp_fbo, GL_COLOR_ATTACHMENT0, I_tex, 0);
 457         glNamedFramebufferTexture(prewarp_fbo, GL_COLOR_ATTACHMENT1, I_t_tex, 0);
 458
 459         glViewport(0, 0, level_width, level_height);
 460         glDisable(GL_BLEND);
 461         glBindVertexArray(prewarp_vao);
 462         glBindFramebuffer(GL_FRAMEBUFFER, prewarp_fbo);
 463         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 464 }
 465
 466 // From I, calculate the partial derivatives I_x and I_y. We use a four-tap
 467 // central difference filter, since apparently, that's tradition (I haven't
 468 // measured quality versus a more normal 0.5 (I[x+1] - I[x-1]).)
 469 // The coefficients come from
 470 //
 471 //   https://en.wikipedia.org/wiki/Finite_difference_coefficient
 472 //
 473 // Also computes β_0, since it depends only on I_x and I_y.
 474 class Derivatives {
 475 public:
 476         Derivatives();
 477         void exec(GLuint input_tex, GLuint I_x_y_tex, GLuint beta_0_tex, int level_width, int level_height);
 478
 479 private:
 480         GLuint derivatives_vs_obj;
 481         GLuint derivatives_fs_obj;
 482         GLuint derivatives_program;
 483         GLuint derivatives_vao;
 484
 485         GLuint uniform_tex;
 486 };
 487
 488 Derivatives::Derivatives()
 489 {
 490         derivatives_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
 491         derivatives_fs_obj = compile_shader(read_file("derivatives.frag"), GL_FRAGMENT_SHADER);
 492         derivatives_program = link_program(derivatives_vs_obj, derivatives_fs_obj);
 493
 494         // Set up the VAO containing all the required position/texcoord data.
 495         glCreateVertexArrays(1, &derivatives_vao);
 496         glBindVertexArray(derivatives_vao);
 497         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 498
 499         GLint position_attrib = glGetAttribLocation(derivatives_program, "position");
 500         glEnableVertexArrayAttrib(derivatives_vao, position_attrib);
 501         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 502
 503         uniform_tex = glGetUniformLocation(derivatives_program, "tex");
 504 }
 505
 506 void Derivatives::exec(GLuint input_tex, GLuint I_x_y_tex, GLuint beta_0_tex, int level_width, int level_height)
 507 {
 508         glUseProgram(derivatives_program);
 509
 510         bind_sampler(derivatives_program, uniform_tex, 0, input_tex, nearest_sampler);
 511
 512         GLuint derivatives_fbo;  // TODO: cleanup
 513         glCreateFramebuffers(1, &derivatives_fbo);
 514         GLenum bufs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
 515         glNamedFramebufferDrawBuffers(derivatives_fbo, 2, bufs);
 516         glNamedFramebufferTexture(derivatives_fbo, GL_COLOR_ATTACHMENT0, I_x_y_tex, 0);
 517         glNamedFramebufferTexture(derivatives_fbo, GL_COLOR_ATTACHMENT1, beta_0_tex, 0);
 518
 519         glViewport(0, 0, level_width, level_height);
 520         glDisable(GL_BLEND);
 521         glBindVertexArray(derivatives_vao);
 522         glBindFramebuffer(GL_FRAMEBUFFER, derivatives_fbo);
 523         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 524 }
 525
 526 // Calculate the smoothness constraints between neighboring pixels;
 527 // s_x(x,y) stores smoothness between pixel (x,y) and (x+1,y),
 528 // and s_y(x,y) stores between (x,y) and (x,y+1). We'll sample with
 529 // border color (0,0) later, so that there's zero diffusion out of
 530 // the border.
 531 //
 532 // See variational_refinement.txt for more information.
 533 class ComputeSmoothness {
 534 public:
 535         ComputeSmoothness();
 536         void exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, int level_width, int level_height);
 537
 538 private:
 539         GLuint smoothness_vs_obj;
 540         GLuint smoothness_fs_obj;
 541         GLuint smoothness_program;
 542         GLuint smoothness_vao;
 543
 544         GLuint uniform_flow_tex, uniform_diff_flow_tex;
 545 };
 546
 547 ComputeSmoothness::ComputeSmoothness()
 548 {
 549         smoothness_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
 550         smoothness_fs_obj = compile_shader(read_file("smoothness.frag"), GL_FRAGMENT_SHADER);
 551         smoothness_program = link_program(smoothness_vs_obj, smoothness_fs_obj);
 552
 553         // Set up the VAO containing all the required position/texcoord data.
 554         glCreateVertexArrays(1, &smoothness_vao);
 555         glBindVertexArray(smoothness_vao);
 556         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 557
 558         GLint position_attrib = glGetAttribLocation(smoothness_program, "position");
 559         glEnableVertexArrayAttrib(smoothness_vao, position_attrib);
 560         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 561
 562         uniform_flow_tex = glGetUniformLocation(smoothness_program, "flow_tex");
 563         uniform_diff_flow_tex = glGetUniformLocation(smoothness_program, "diff_flow_tex");
 564 }
 565
 566 void ComputeSmoothness::exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, int level_width, int level_height)
 567 {
 568         glUseProgram(smoothness_program);
 569
 570         bind_sampler(smoothness_program, uniform_flow_tex, 0, flow_tex, nearest_sampler);
 571         bind_sampler(smoothness_program, uniform_diff_flow_tex, 1, diff_flow_tex, nearest_sampler);
 572
 573         GLuint smoothness_fbo;  // TODO: cleanup
 574         glCreateFramebuffers(1, &smoothness_fbo);
 575         GLenum bufs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
 576         glNamedFramebufferDrawBuffers(smoothness_fbo, 2, bufs);
 577         glNamedFramebufferTexture(smoothness_fbo, GL_COLOR_ATTACHMENT0, smoothness_x_tex, 0);
 578         glNamedFramebufferTexture(smoothness_fbo, GL_COLOR_ATTACHMENT1, smoothness_y_tex, 0);
 579
 580         glViewport(0, 0, level_width, level_height);
 581
 582         // Make sure the smoothness on the right and upper borders is zero.
 583         // We could have done this by making a (W-1)x(H-1) texture instead
 584         // (we're sampling smoothness with all-zero border color), but we'd
 585         // have to adjust the sampling coordinates, which is annoying.
 586         glScissor(0, 0, level_width - 1, level_height - 1);
 587         glEnable(GL_SCISSOR_TEST);
 588
 589         glDisable(GL_BLEND);
 590         glBindVertexArray(smoothness_vao);
 591         glBindFramebuffer(GL_FRAMEBUFFER, smoothness_fbo);
 592         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 593
 594         glDisable(GL_SCISSOR_TEST);
 595 }
 596
 597 // Set up the equations set (two equations in two unknowns, per pixel).
 598 // We store five floats; the three non-redundant elements of the 2x2 matrix (A)
 599 // as 32-bit floats, and the two elements on the right-hand side (b) as 16-bit
 600 // floats. (Actually, we store the inverse of the diagonal elements, because
 601 // we only ever need to divide by them.) This fits into four u32 values;
 602 // R, G, B for the matrix (the last element is symmetric) and A for the two b values.
 603 // All the values of the energy term (E_I, E_G, E_S), except the smoothness
 604 // terms that depend on other pixels, are calculated in one pass.
 605 //
 606 // See variational_refinement.txt for more information.
 607 class SetupEquations {
 608 public:
 609         SetupEquations();
 610         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);
 611
 612 private:
 613         GLuint equations_vs_obj;
 614         GLuint equations_fs_obj;
 615         GLuint equations_program;
 616         GLuint equations_vao;
 617
 618         GLuint uniform_I_x_y_tex, uniform_I_t_tex;
 619         GLuint uniform_diff_flow_tex, uniform_flow_tex;
 620         GLuint uniform_beta_0_tex;
 621         GLuint uniform_smoothness_x_tex, uniform_smoothness_y_tex;
 622
 623 };
 624
 625 SetupEquations::SetupEquations()
 626 {
 627         equations_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
 628         equations_fs_obj = compile_shader(read_file("equations.frag"), GL_FRAGMENT_SHADER);
 629         equations_program = link_program(equations_vs_obj, equations_fs_obj);
 630
 631         // Set up the VAO containing all the required position/texcoord data.
 632         glCreateVertexArrays(1, &equations_vao);
 633         glBindVertexArray(equations_vao);
 634         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 635
 636         GLint position_attrib = glGetAttribLocation(equations_program, "position");
 637         glEnableVertexArrayAttrib(equations_vao, position_attrib);
 638         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 639
 640         uniform_I_x_y_tex = glGetUniformLocation(equations_program, "I_x_y_tex");
 641         uniform_I_t_tex = glGetUniformLocation(equations_program, "I_t_tex");
 642         uniform_diff_flow_tex = glGetUniformLocation(equations_program, "diff_flow_tex");
 643         uniform_flow_tex = glGetUniformLocation(equations_program, "flow_tex");
 644         uniform_beta_0_tex = glGetUniformLocation(equations_program, "beta_0_tex");
 645         uniform_smoothness_x_tex = glGetUniformLocation(equations_program, "smoothness_x_tex");
 646         uniform_smoothness_y_tex = glGetUniformLocation(equations_program, "smoothness_y_tex");
 647 }
 648
 649 void SetupEquations::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)
 650 {
 651         glUseProgram(equations_program);
 652
 653         bind_sampler(equations_program, uniform_I_x_y_tex, 0, I_x_y_tex, nearest_sampler);
 654         bind_sampler(equations_program, uniform_I_t_tex, 1, I_t_tex, nearest_sampler);
 655         bind_sampler(equations_program, uniform_diff_flow_tex, 2, diff_flow_tex, nearest_sampler);
 656         bind_sampler(equations_program, uniform_flow_tex, 3, flow_tex, nearest_sampler);
 657         bind_sampler(equations_program, uniform_beta_0_tex, 4, beta_0_tex, nearest_sampler);
 658         bind_sampler(equations_program, uniform_smoothness_x_tex, 5, smoothness_x_tex, smoothness_sampler);
 659         bind_sampler(equations_program, uniform_smoothness_y_tex, 6, smoothness_y_tex, smoothness_sampler);
 660
 661         GLuint equations_fbo;  // TODO: cleanup
 662         glCreateFramebuffers(1, &equations_fbo);
 663         glNamedFramebufferTexture(equations_fbo, GL_COLOR_ATTACHMENT0, equation_tex, 0);
 664
 665         glViewport(0, 0, level_width, level_height);
 666         glDisable(GL_BLEND);
 667         glBindVertexArray(equations_vao);
 668         glBindFramebuffer(GL_FRAMEBUFFER, equations_fbo);
 669         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 670 }
 671
 672 // Calculate the smoothness constraints between neighboring pixels;
 673 // s_x(x,y) stores smoothness between pixel (x,y) and (x+1,y),
 674 // and s_y(x,y) stores between (x,y) and (x,y+1). We'll sample with
 675 // border color (0,0) later, so that there's zero diffusion out of
 676 // the border.
 677 //
 678 // See variational_refinement.txt for more information.
 679 class SOR {
 680 public:
 681         SOR();
 682         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);
 683
 684 private:
 685         GLuint sor_vs_obj;
 686         GLuint sor_fs_obj;
 687         GLuint sor_program;
 688         GLuint sor_vao;
 689
 690         GLuint uniform_diff_flow_tex;
 691         GLuint uniform_equation_tex;
 692         GLuint uniform_smoothness_x_tex, uniform_smoothness_y_tex;
 693 };
 694
 695 SOR::SOR()
 696 {
 697         sor_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
 698         sor_fs_obj = compile_shader(read_file("sor.frag"), GL_FRAGMENT_SHADER);
 699         sor_program = link_program(sor_vs_obj, sor_fs_obj);
 700
 701         // Set up the VAO containing all the required position/texcoord data.
 702         glCreateVertexArrays(1, &sor_vao);
 703         glBindVertexArray(sor_vao);
 704         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 705
 706         GLint position_attrib = glGetAttribLocation(sor_program, "position");
 707         glEnableVertexArrayAttrib(sor_vao, position_attrib);
 708         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 709
 710         uniform_diff_flow_tex = glGetUniformLocation(sor_program, "diff_flow_tex");
 711         uniform_equation_tex = glGetUniformLocation(sor_program, "equation_tex");
 712 }
 713
 714 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)
 715 {
 716         glUseProgram(sor_program);
 717
 718         bind_sampler(sor_program, uniform_diff_flow_tex, 0, diff_flow_tex, nearest_sampler);
 719         bind_sampler(sor_program, uniform_smoothness_x_tex, 1, smoothness_x_tex, smoothness_sampler);
 720         bind_sampler(sor_program, uniform_smoothness_y_tex, 2, smoothness_y_tex, smoothness_sampler);
 721         bind_sampler(sor_program, uniform_equation_tex, 3, equation_tex, nearest_sampler);
 722
 723         GLuint sor_fbo;  // TODO: cleanup
 724         glCreateFramebuffers(1, &sor_fbo);
 725         glNamedFramebufferTexture(sor_fbo, GL_COLOR_ATTACHMENT0, diff_flow_tex, 0);  // NOTE: Bind to same as we render from!
 726
 727         glViewport(0, 0, level_width, level_height);
 728         glDisable(GL_BLEND);
 729         glBindVertexArray(sor_vao);
 730         glBindFramebuffer(GL_FRAMEBUFFER, sor_fbo);
 731
 732         for (int i = 0; i < num_iterations; ++i) {
 733                 glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 734                 if (i != num_iterations - 1) {
 735                         glTextureBarrier();
 736                 }
 737         }
 738 }
 739
 740 int main(void)
 741 {
 742         if (SDL_Init(SDL_INIT_EVERYTHING) == -1) {
 743                 fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
 744                 exit(1);
 745         }
 746         SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
 747         SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0);
 748         SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 0);
 749         SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
 750
 751         SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
 752         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
 753         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 5);
 754         // SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_DEBUG_FLAG);
 755         SDL_Window *window = SDL_CreateWindow("OpenGL window",
 756                         SDL_WINDOWPOS_UNDEFINED,
 757                         SDL_WINDOWPOS_UNDEFINED,
 758                         64, 64,
 759                         SDL_WINDOW_OPENGL);
 760         SDL_GLContext context = SDL_GL_CreateContext(window);
 761         assert(context != nullptr);
 762
 763         // Load pictures.
 764         GLuint tex0 = load_texture("test1499.pgm", WIDTH, HEIGHT);
 765         GLuint tex1 = load_texture("test1500.pgm", WIDTH, HEIGHT);
 766
 767         // Make some samplers.
 768         glCreateSamplers(1, &nearest_sampler);
 769         glSamplerParameteri(nearest_sampler, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 770         glSamplerParameteri(nearest_sampler, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
 771         glSamplerParameteri(nearest_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 772         glSamplerParameteri(nearest_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 773
 774         glCreateSamplers(1, &linear_sampler);
 775         glSamplerParameteri(linear_sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 776         glSamplerParameteri(linear_sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 777         glSamplerParameteri(linear_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 778         glSamplerParameteri(linear_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 779
 780         // The smoothness is sampled so that once we get to a smoothness involving
 781         // a value outside the border, the diffusivity between the two becomes zero.
 782         glCreateSamplers(1, &smoothness_sampler);
 783         glSamplerParameteri(smoothness_sampler, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 784         glSamplerParameteri(smoothness_sampler, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
 785         glSamplerParameteri(smoothness_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
 786         glSamplerParameteri(smoothness_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
 787         float zero[] = { 0.0f, 0.0f, 0.0f, 0.0f };
 788         glSamplerParameterfv(smoothness_sampler, GL_TEXTURE_BORDER_COLOR, zero);
 789
 790         float vertices[] = {
 791                 0.0f, 1.0f,
 792                 0.0f, 0.0f,
 793                 1.0f, 1.0f,
 794                 1.0f, 0.0f,
 795         };
 796         glCreateBuffers(1, &vertex_vbo);
 797         glNamedBufferData(vertex_vbo, sizeof(vertices), vertices, GL_STATIC_DRAW);
 798         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 799
 800         // Initial flow is zero, 1x1.
 801         GLuint initial_flow_tex;
 802         glCreateTextures(GL_TEXTURE_2D, 1, &initial_flow_tex);
 803         glTextureStorage2D(initial_flow_tex, 1, GL_RGB32F, 1, 1);
 804
 805         GLuint prev_level_flow_tex = initial_flow_tex;
 806
 807         Sobel sobel;
 808         MotionSearch motion_search;
 809         Densify densify;
 810         Prewarp prewarp;
 811         Derivatives derivatives;
 812         ComputeSmoothness compute_smoothness;
 813         SetupEquations setup_equations;
 814         SOR sor;
 815
 816         GLuint query;
 817         glGenQueries(1, &query);
 818         glBeginQuery(GL_TIME_ELAPSED, query);
 819
 820         for (int level = coarsest_level; level >= int(finest_level); --level) {
 821                 int level_width = WIDTH >> level;
 822                 int level_height = HEIGHT >> level;
 823                 float patch_spacing_pixels = patch_size_pixels * (1.0f - patch_overlap_ratio);
 824                 int width_patches = 1 + lrintf((level_width - patch_size_pixels) / patch_spacing_pixels);
 825                 int height_patches = 1 + lrintf((level_height - patch_size_pixels) / patch_spacing_pixels);
 826
 827                 // Make sure we always read from the correct level; the chosen
 828                 // mipmapping could otherwise be rather unpredictable, especially
 829                 // during motion search.
 830                 // TODO: create these beforehand, and stop leaking them.
 831                 GLuint tex0_view, tex1_view;
 832                 glGenTextures(1, &tex0_view);
 833                 glTextureView(tex0_view, GL_TEXTURE_2D, tex0, GL_R8, level, 1, 0, 1);
 834                 glGenTextures(1, &tex1_view);
 835                 glTextureView(tex1_view, GL_TEXTURE_2D, tex1, GL_R8, level, 1, 0, 1);
 836
 837                 // Create a new texture; we could be fancy and render use a multi-level
 838                 // texture, but meh.
 839                 GLuint grad0_tex;
 840                 glCreateTextures(GL_TEXTURE_2D, 1, &grad0_tex);
 841                 glTextureStorage2D(grad0_tex, 1, GL_RG16F, level_width, level_height);
 842
 843                 // Find the derivative.
 844                 sobel.exec(tex0_view, grad0_tex, level_width, level_height);
 845
 846                 // Motion search to find the initial flow. We use the flow from the previous
 847                 // level (sampled bilinearly; no fancy tricks) as a guide, then search from there.
 848
 849                 // Create an output flow texture.
 850                 GLuint flow_out_tex;
 851                 glCreateTextures(GL_TEXTURE_2D, 1, &flow_out_tex);
 852                 glTextureStorage2D(flow_out_tex, 1, GL_RGB16F, width_patches, height_patches);
 853
 854                 // And draw.
 855                 motion_search.exec(tex0_view, tex1_view, grad0_tex, prev_level_flow_tex, flow_out_tex, level_width, level_height, width_patches, height_patches);
 856
 857                 // Densification.
 858
 859                 // Set up an output texture (initially zero).
 860                 GLuint dense_flow_tex;
 861                 glCreateTextures(GL_TEXTURE_2D, 1, &dense_flow_tex);
 862                 glTextureStorage2D(dense_flow_tex, 1, GL_RGB16F, level_width, level_height);
 863
 864                 // And draw.
 865                 densify.exec(tex0_view, tex1_view, flow_out_tex, dense_flow_tex, level_width, level_height, width_patches, height_patches);
 866
 867                 // Everything below here in the loop belongs to variational refinement.
 868                 // It is not done yet.
 869
 870                 // Prewarping; create I and I_t.
 871                 GLuint I_tex, I_t_tex;
 872                 glCreateTextures(GL_TEXTURE_2D, 1, &I_tex);
 873                 glCreateTextures(GL_TEXTURE_2D, 1, &I_t_tex);
 874                 glTextureStorage2D(I_tex, 1, GL_R16F, level_width, level_height);
 875                 glTextureStorage2D(I_t_tex, 1, GL_R16F, level_width, level_height);
 876                 prewarp.exec(tex0_view, tex1_view, dense_flow_tex, I_tex, I_t_tex, level_width, level_height);
 877
 878                 // Calculate I_x and I_y. We're only calculating first derivatives;
 879                 // the others will be taken on-the-fly in order to sample from fewer
 880                 // textures overall, since sampling from the L1 cache is cheap.
 881                 // (TODO: Verify that this is indeed faster than making separate
 882                 // double-derivative textures.)
 883                 GLuint I_x_y_tex, beta_0_tex;
 884                 glCreateTextures(GL_TEXTURE_2D, 1, &I_x_y_tex);
 885                 glCreateTextures(GL_TEXTURE_2D, 1, &beta_0_tex);
 886                 glTextureStorage2D(I_x_y_tex, 1, GL_RG16F, level_width, level_height);
 887                 glTextureStorage2D(beta_0_tex, 1, GL_R16F, level_width, level_height);
 888                 derivatives.exec(I_tex, I_x_y_tex, beta_0_tex, level_width, level_height);
 889
 890                 // We need somewhere to store du and dv (the flow increment, relative
 891                 // to the non-refined base flow u0 and v0). It starts at zero.
 892                 GLuint du_dv_tex;
 893                 glCreateTextures(GL_TEXTURE_2D, 1, &du_dv_tex);
 894                 glTextureStorage2D(du_dv_tex, 1, GL_RG16F, level_width, level_height);
 895
 896                 // And for smoothness.
 897                 GLuint smoothness_x_tex, smoothness_y_tex;
 898                 glCreateTextures(GL_TEXTURE_2D, 1, &smoothness_x_tex);
 899                 glCreateTextures(GL_TEXTURE_2D, 1, &smoothness_y_tex);
 900                 glTextureStorage2D(smoothness_x_tex, 1, GL_R16F, level_width, level_height);
 901                 glTextureStorage2D(smoothness_y_tex, 1, GL_R16F, level_width, level_height);
 902
 903                 // And finally for the equation set. See SetupEquations for
 904                 // the storage format.
 905                 GLuint equation_tex;
 906                 glCreateTextures(GL_TEXTURE_2D, 1, &equation_tex);
 907                 glTextureStorage2D(equation_tex, 1, GL_RGBA32UI, level_width, level_height);
 908
 909                 for (int outer_idx = 0; outer_idx < level + 1; ++outer_idx) {
 910                         // Calculate the smoothness terms between the neighboring pixels,
 911                         // both in x and y direction.
 912                         compute_smoothness.exec(dense_flow_tex, du_dv_tex, smoothness_x_tex, smoothness_y_tex, level_width, level_height);
 913
 914                         // Set up the 2x2 equation system for each pixel.
 915                         setup_equations.exec(I_x_y_tex, I_t_tex, du_dv_tex, dense_flow_tex, beta_0_tex, smoothness_x_tex, smoothness_y_tex, equation_tex, level_width, level_height);
 916
 917                         // Run a few SOR (or quasi-SOR, since we're not really Jacobi) iterations.
 918                         // Note that these are to/from the same texture.
 919                         sor.exec(du_dv_tex, equation_tex, smoothness_x_tex, smoothness_y_tex, level_width, level_height, 5);
 920                 }
 921
 922                 prev_level_flow_tex = dense_flow_tex;
 923         }
 924         glEndQuery(GL_TIME_ELAPSED);
 925
 926         GLint available;
 927         do {
 928                 glGetQueryObjectiv(query, GL_QUERY_RESULT_AVAILABLE, &available);
 929                 usleep(1000);
 930         } while (!available);
 931         GLuint64 time_elapsed;
 932         glGetQueryObjectui64v(query, GL_QUERY_RESULT, &time_elapsed);
 933         fprintf(stderr, "GPU time used = %.1f ms\n", time_elapsed / 1e6);
 934
 935         int level_width = WIDTH >> finest_level;
 936         int level_height = HEIGHT >> finest_level;
 937         unique_ptr<float[]> dense_flow(new float[level_width * level_height * 3]);
 938         glGetTextureImage(prev_level_flow_tex, 0, GL_RGB, GL_FLOAT, level_width * level_height * 3 * sizeof(float), dense_flow.get());
 939
 940         FILE *fp = fopen("flow.ppm", "wb");
 941         FILE *flowfp = fopen("flow.flo", "wb");
 942         fprintf(fp, "P6\n%d %d\n255\n", level_width, level_height);
 943         fprintf(flowfp, "FEIH");
 944         fwrite(&level_width, 4, 1, flowfp);
 945         fwrite(&level_height, 4, 1, flowfp);
 946         for (unsigned y = 0; y < unsigned(level_height); ++y) {
 947                 int yy = level_height - y - 1;
 948                 for (unsigned x = 0; x < unsigned(level_width); ++x) {
 949                         float du = dense_flow[(yy * level_width + x) * 3 + 0];
 950                         float dv = dense_flow[(yy * level_width + x) * 3 + 1];
 951                         float w = dense_flow[(yy * level_width + x) * 3 + 2];
 952
 953                         du = (du / w) * level_width;
 954                         dv = (-dv / w) * level_height;
 955
 956                         fwrite(&du, 4, 1, flowfp);
 957                         fwrite(&dv, 4, 1, flowfp);
 958
 959                         uint8_t r, g, b;
 960                         flow2rgb(du, dv, &r, &g, &b);
 961                         putc(r, fp);
 962                         putc(g, fp);
 963                         putc(b, fp);
 964                 }
 965         }
 966         fclose(fp);
 967         fclose(flowfp);
 968
 969         fprintf(stderr, "err = %d\n", glGetError());
 970 }