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
  19 #include <algorithm>
  20 #include <memory>
  21
  22 #define BUFFER_OFFSET(i) ((char *)nullptr + (i))
  23
  24 using namespace std;
  25
  26 // Operating point 3 (10 Hz on CPU, excluding preprocessing).
  27 constexpr float patch_overlap_ratio = 0.75f;
  28 constexpr unsigned coarsest_level = 0;
  29 constexpr unsigned finest_level = 0;
  30 constexpr unsigned patch_size_pixels = 12;
  31
  32 string read_file(const string &filename)
  33 {
  34         FILE *fp = fopen(filename.c_str(), "r");
  35         if (fp == nullptr) {
  36                 perror(filename.c_str());
  37                 exit(1);
  38         }
  39
  40         int ret = fseek(fp, 0, SEEK_END);
  41         if (ret == -1) {
  42                 perror("fseek(SEEK_END)");
  43                 exit(1);
  44         }
  45
  46         int size = ftell(fp);
  47
  48         ret = fseek(fp, 0, SEEK_SET);
  49         if (ret == -1) {
  50                 perror("fseek(SEEK_SET)");
  51                 exit(1);
  52         }
  53
  54         string str;
  55         str.resize(size);
  56         ret = fread(&str[0], size, 1, fp);
  57         if (ret == -1) {
  58                 perror("fread");
  59                 exit(1);
  60         }
  61         if (ret == 0) {
  62                 fprintf(stderr, "Short read when trying to read %d bytes from %s\n",
  63                                 size, filename.c_str());
  64                 exit(1);
  65         }
  66         fclose(fp);
  67
  68         return str;
  69 }
  70
  71
  72 GLuint compile_shader(const string &shader_src, GLenum type)
  73 {
  74         GLuint obj = glCreateShader(type);
  75         const GLchar* source[] = { shader_src.data() };
  76         const GLint length[] = { (GLint)shader_src.size() };
  77         glShaderSource(obj, 1, source, length);
  78         glCompileShader(obj);
  79
  80         GLchar info_log[4096];
  81         GLsizei log_length = sizeof(info_log) - 1;
  82         glGetShaderInfoLog(obj, log_length, &log_length, info_log);
  83         info_log[log_length] = 0;
  84         if (strlen(info_log) > 0) {
  85                 fprintf(stderr, "Shader compile log: %s\n", info_log);
  86         }
  87
  88         GLint status;
  89         glGetShaderiv(obj, GL_COMPILE_STATUS, &status);
  90         if (status == GL_FALSE) {
  91                 // Add some line numbers to easier identify compile errors.
  92                 string src_with_lines = "/*   1 */ ";
  93                 size_t lineno = 1;
  94                 for (char ch : shader_src) {
  95                         src_with_lines.push_back(ch);
  96                         if (ch == '\n') {
  97                                 char buf[32];
  98                                 snprintf(buf, sizeof(buf), "/* %3zu */ ", ++lineno);
  99                                 src_with_lines += buf;
 100                         }
 101                 }
 102
 103                 fprintf(stderr, "Failed to compile shader:\n%s\n", src_with_lines.c_str());
 104                 exit(1);
 105         }
 106
 107         return obj;
 108 }
 109
 110
 111 GLuint load_texture(const char *filename, unsigned width, unsigned height)
 112 {
 113         FILE *fp = fopen(filename, "rb");
 114         if (fp == nullptr) {
 115                 perror(filename);
 116                 exit(1);
 117         }
 118         unique_ptr<uint8_t[]> pix(new uint8_t[width * height]);
 119         if (fread(pix.get(), width * height, 1, fp) != 1) {
 120                 fprintf(stderr, "Short read from %s\n", filename);
 121                 exit(1);
 122         }
 123         fclose(fp);
 124
 125         // Convert to bottom-left origin.
 126         for (unsigned y = 0; y < height / 2; ++y) {
 127                 unsigned y2 = height - 1 - y;
 128                 swap_ranges(&pix[y * width], &pix[y * width + width], &pix[y2 * width]);
 129         }
 130
 131         int levels = 1;
 132         for (int w = width, h = height; w > 1 || h > 1; ) {
 133                 w >>= 1;
 134                 h >>= 1;
 135                 ++levels;
 136         }
 137
 138         GLuint tex;
 139         glCreateTextures(GL_TEXTURE_2D, 1, &tex);
 140         glTextureStorage2D(tex, levels, GL_R8, width, height);
 141         glTextureSubImage2D(tex, 0, 0, 0, width, height, GL_RED, GL_UNSIGNED_BYTE, pix.get());
 142         glGenerateTextureMipmap(tex);
 143
 144         return tex;
 145 }
 146
 147 GLuint link_program(GLuint vs_obj, GLuint fs_obj)
 148 {
 149         GLuint program = glCreateProgram();
 150         glAttachShader(program, vs_obj);
 151         glAttachShader(program, fs_obj);
 152         glLinkProgram(program);
 153         GLint success;
 154         glGetProgramiv(program, GL_LINK_STATUS, &success);
 155         if (success == GL_FALSE) {
 156                 GLchar error_log[1024] = {0};
 157                 glGetProgramInfoLog(program, 1024, nullptr, error_log);
 158                 fprintf(stderr, "Error linking program: %s\n", error_log);
 159                 exit(1);
 160         }
 161         return program;
 162 }
 163
 164 GLuint generate_vbo(GLint size, GLsizeiptr data_size, const GLvoid *data)
 165 {
 166         GLuint vbo;
 167         glCreateBuffers(1, &vbo);
 168         glBufferData(GL_ARRAY_BUFFER, data_size, data, GL_STATIC_DRAW);
 169         glNamedBufferData(vbo, data_size, data, GL_STATIC_DRAW);
 170         return vbo;
 171 }
 172
 173 GLuint fill_vertex_attribute(GLuint vao, GLuint glsl_program_num, const string &attribute_name, GLint size, GLenum type, GLsizeiptr data_size, const GLvoid *data)
 174 {
 175         int attrib = glGetAttribLocation(glsl_program_num, attribute_name.c_str());
 176         if (attrib == -1) {
 177                 return -1;
 178         }
 179
 180         GLuint vbo = generate_vbo(size, data_size, data);
 181
 182         glBindBuffer(GL_ARRAY_BUFFER, vbo);
 183         glEnableVertexArrayAttrib(vao, attrib);
 184         glVertexAttribPointer(attrib, size, type, GL_FALSE, 0, BUFFER_OFFSET(0));
 185         glBindBuffer(GL_ARRAY_BUFFER, 0);
 186
 187         return vbo;
 188 }
 189
 190 void bind_sampler(GLuint program, const char *uniform_name, GLuint texture_unit, GLuint tex, GLuint sampler)
 191 {
 192         GLint location = glGetUniformLocation(program, uniform_name);
 193         if (location == -1) {
 194                 return;
 195         }
 196
 197         glBindTextureUnit(texture_unit, tex);
 198         glBindSampler(texture_unit, sampler);
 199         glProgramUniform1i(program, location, texture_unit);
 200 }
 201
 202 int main(void)
 203 {
 204         if (SDL_Init(SDL_INIT_EVERYTHING) == -1) {
 205                 fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
 206                 exit(1);
 207         }
 208         SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
 209         SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0);
 210         SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 0);
 211         SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
 212
 213         SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
 214         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
 215         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 5);
 216         // SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_DEBUG_FLAG);
 217         SDL_Window *window = SDL_CreateWindow("OpenGL window",
 218                         SDL_WINDOWPOS_UNDEFINED,
 219                         SDL_WINDOWPOS_UNDEFINED,
 220                         64, 64,
 221                         SDL_WINDOW_OPENGL);
 222         SDL_GLContext context = SDL_GL_CreateContext(window);
 223         assert(context != nullptr);
 224
 225         // Load pictures.
 226         GLuint tex0 = load_texture("test1499.pgm", WIDTH, HEIGHT);
 227         GLuint tex1 = load_texture("test1500.pgm", WIDTH, HEIGHT);
 228
 229         // Load shaders.
 230         GLuint motion_vs_obj = compile_shader(read_file("motion_search.vert"), GL_VERTEX_SHADER);
 231         GLuint motion_fs_obj = compile_shader(read_file("motion_search.frag"), GL_FRAGMENT_SHADER);
 232         GLuint motion_search_program = link_program(motion_vs_obj, motion_fs_obj);
 233
 234         GLuint sobel_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
 235         GLuint sobel_fs_obj = compile_shader(read_file("sobel.frag"), GL_FRAGMENT_SHADER);
 236         GLuint sobel_program = link_program(sobel_vs_obj, sobel_fs_obj);
 237
 238         GLuint densify_vs_obj = compile_shader(read_file("densify.vert"), GL_VERTEX_SHADER);
 239         GLuint densify_fs_obj = compile_shader(read_file("densify.frag"), GL_FRAGMENT_SHADER);
 240         GLuint densify_program = link_program(densify_vs_obj, densify_fs_obj);
 241
 242         // Make some samplers.
 243         GLuint nearest_sampler;
 244         glCreateSamplers(1, &nearest_sampler);
 245         glSamplerParameteri(nearest_sampler, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 246         glSamplerParameteri(nearest_sampler, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
 247         glSamplerParameteri(nearest_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 248         glSamplerParameteri(nearest_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 249
 250         GLuint linear_sampler;
 251         glCreateSamplers(1, &linear_sampler);
 252         glSamplerParameteri(linear_sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 253         glSamplerParameteri(linear_sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 254         glSamplerParameteri(linear_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 255         glSamplerParameteri(linear_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 256
 257         GLuint mipmap_sampler;
 258         glCreateSamplers(1, &mipmap_sampler);
 259         glSamplerParameteri(mipmap_sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
 260         glSamplerParameteri(mipmap_sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 261         glSamplerParameteri(mipmap_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 262         glSamplerParameteri(mipmap_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 263
 264         // Coarsest level.
 265         int level = coarsest_level;
 266         int level_width = WIDTH >> level;
 267         int level_height = HEIGHT >> level;
 268         float patch_spacing_pixels = patch_size_pixels * (1.0f - patch_overlap_ratio);
 269         int width_patches = 1 + lrintf((level_width - patch_size_pixels) / patch_spacing_pixels);
 270         int height_patches = 1 + lrintf((level_height - patch_size_pixels) / patch_spacing_pixels);
 271
 272         // Make sure we always read from the correct level; the chosen
 273         // mipmapping could otherwise be rather unpredictable, especially
 274         // during motion search.
 275         GLuint tex0_view, tex1_view;
 276         glGenTextures(1, &tex0_view);
 277         glTextureView(tex0_view, GL_TEXTURE_2D, tex0, GL_R8, level, 1, 0, 1);
 278         glGenTextures(1, &tex1_view);
 279         glTextureView(tex1_view, GL_TEXTURE_2D, tex1, GL_R8, level, 1, 0, 1);
 280
 281         // Compute gradients in every point, used for the motion search.
 282         // The DIS paper doesn't actually mention how these are computed,
 283         // but seemingly, a 3x3 Sobel operator is used here (at least in
 284         // later versions of the code), while a [1 -8 0 8 -1] kernel is
 285         // used for all the derivatives in the variational refinement part
 286         // (which borrows code from DeepFlow). This is inconsistent,
 287         // but I guess we're better off with staying with the original
 288         // decisions until we actually know having different ones would be better.
 289
 290         // Create a new texture; we could be fancy and render use a multi-level
 291         // texture, but meh.
 292         GLuint grad0_tex;
 293         glCreateTextures(GL_TEXTURE_2D, 1, &grad0_tex);
 294         glTextureStorage2D(grad0_tex, 1, GL_RG16F, level_width, level_height);
 295
 296         GLuint grad0_fbo;
 297         glCreateFramebuffers(1, &grad0_fbo);
 298         glNamedFramebufferTexture(grad0_fbo, GL_COLOR_ATTACHMENT0, grad0_tex, 0);
 299
 300         glUseProgram(sobel_program);
 301         glBindTextureUnit(0, tex0_view);
 302         glBindSampler(0, nearest_sampler);
 303         glProgramUniform1i(sobel_program, glGetUniformLocation(sobel_program, "tex"), 0);
 304         glProgramUniform1f(sobel_program, glGetUniformLocation(sobel_program, "inv_width"), 1.0f / level_width);
 305         glProgramUniform1f(sobel_program, glGetUniformLocation(sobel_program, "inv_height"), 1.0f / level_height);
 306
 307         // Set up the VAO containing all the required position/texcoord data.
 308         GLuint sobel_vao;
 309         glCreateVertexArrays(1, &sobel_vao);
 310         glBindVertexArray(sobel_vao);
 311         float vertices[] = {
 312                 0.0f, 1.0f,
 313                 0.0f, 0.0f,
 314                 1.0f, 1.0f,
 315                 1.0f, 0.0f,
 316         };
 317         GLuint vertex_vbo;
 318         glCreateBuffers(1, &vertex_vbo);
 319         glNamedBufferData(vertex_vbo, sizeof(vertices), vertices, GL_STATIC_DRAW);
 320         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 321
 322         int position_attrib = glGetAttribLocation(sobel_program, "position");
 323         glEnableVertexArrayAttrib(sobel_vao, position_attrib);
 324         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 325
 326         int texcoord_attrib = glGetAttribLocation(sobel_program, "texcoord");
 327         glEnableVertexArrayAttrib(sobel_vao, texcoord_attrib);
 328         glVertexAttribPointer(texcoord_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 329
 330         glBindBuffer(GL_ARRAY_BUFFER, 0);
 331
 332         // Now finally draw.
 333         glViewport(0, 0, level_width, level_height);
 334         glBindFramebuffer(GL_FRAMEBUFFER, grad0_fbo);
 335         glUseProgram(sobel_program);
 336         glDisable(GL_BLEND);
 337         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 338
 339         // Motion search to find the initial flow.
 340
 341         // Create a flow texture, initialized to zero.
 342         GLuint flow_tex;
 343         glCreateTextures(GL_TEXTURE_2D, 1, &flow_tex);
 344         glTextureStorage2D(flow_tex, 1, GL_RG16F, width_patches, height_patches);
 345
 346         // And an output flow texture. (Well, we could have used texture barriers,
 347         // but I don't feel lucky today.)
 348         GLuint flow_out_tex;
 349         glCreateTextures(GL_TEXTURE_2D, 1, &flow_out_tex);
 350         glTextureStorage2D(flow_out_tex, 1, GL_RG16F, width_patches, height_patches);
 351
 352         GLuint flow_fbo;
 353         glCreateFramebuffers(1, &flow_fbo);
 354         glNamedFramebufferTexture(flow_fbo, GL_COLOR_ATTACHMENT0, flow_out_tex, 0);
 355
 356         glUseProgram(motion_search_program);
 357
 358         bind_sampler(motion_search_program, "image0_tex", 0, tex0_view, nearest_sampler);
 359         bind_sampler(motion_search_program, "image1_tex", 1, tex1_view, linear_sampler);
 360         bind_sampler(motion_search_program, "grad0_tex", 2, grad0_tex, nearest_sampler);
 361         bind_sampler(motion_search_program, "flow_tex", 3, flow_tex, nearest_sampler);
 362
 363         glProgramUniform1f(motion_search_program, glGetUniformLocation(motion_search_program, "image_width"), level_width);
 364         glProgramUniform1f(motion_search_program, glGetUniformLocation(motion_search_program, "image_height"), level_height);
 365         glProgramUniform1f(motion_search_program, glGetUniformLocation(motion_search_program, "inv_image_width"), 1.0f / level_width);
 366         glProgramUniform1f(motion_search_program, glGetUniformLocation(motion_search_program, "inv_image_height"), 1.0f / level_height);
 367
 368 //      printf("%d x %d patches on this level\n", width_patches, height_patches);
 369
 370         // Set up the VAO containing all the required position/texcoord data.
 371         GLuint motion_search_vao;
 372         glCreateVertexArrays(1, &motion_search_vao);
 373         glBindVertexArray(motion_search_vao);
 374         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 375
 376         position_attrib = glGetAttribLocation(motion_search_program, "position");
 377         glEnableVertexArrayAttrib(motion_search_vao, position_attrib);
 378         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 379
 380         texcoord_attrib = glGetAttribLocation(motion_search_program, "texcoord");
 381         glEnableVertexArrayAttrib(motion_search_vao, texcoord_attrib);
 382         glVertexAttribPointer(texcoord_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 383
 384         glBindBuffer(GL_ARRAY_BUFFER, 0);
 385
 386         // And draw.
 387         glViewport(0, 0, width_patches, height_patches);
 388         glBindFramebuffer(GL_FRAMEBUFFER, flow_fbo);
 389         glUseProgram(motion_search_program);
 390         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 391
 392         // Do “densification”, ie., upsampling of the flow patches to the flow field
 393         // (the same size as the image at this level). We draw one quad per patch
 394         // over its entire covered area (using instancing in the vertex shader),
 395         // and then weight the contributions in the pixel shader by post-warp difference.
 396         // This is equation (3) in the paper.
 397         //
 398         // We accumulate the flow vectors in the R/G channels (for u/v) and the total
 399         // weight in the B channel. Dividing R and G by B gives the normalized values.
 400
 401         // Set up an output texture.
 402         GLuint dense_flow_tex;
 403         glCreateTextures(GL_TEXTURE_2D, 1, &dense_flow_tex);
 404         //glTextureStorage2D(dense_flow_tex, 1, GL_RGB16F, level_width, level_height);
 405         glTextureStorage2D(dense_flow_tex, 1, GL_RGBA32F, level_width, level_height);
 406
 407         GLuint dense_flow_fbo;
 408         glCreateFramebuffers(1, &dense_flow_fbo);
 409         glNamedFramebufferTexture(dense_flow_fbo, GL_COLOR_ATTACHMENT0, dense_flow_tex, 0);
 410
 411         glUseProgram(densify_program);
 412
 413         bind_sampler(densify_program, "image0_tex", 0, tex0_view, nearest_sampler);
 414         bind_sampler(densify_program, "image1_tex", 1, tex1_view, linear_sampler);
 415         bind_sampler(densify_program, "flow_tex", 2, flow_out_tex, nearest_sampler);
 416
 417         glProgramUniform1i(densify_program, glGetUniformLocation(densify_program, "width_patches"), width_patches);
 418         glProgramUniform2f(densify_program, glGetUniformLocation(densify_program, "patch_size"),
 419                 float(patch_size_pixels) / level_width,
 420                 float(patch_size_pixels) / level_height);
 421
 422         float patch_spacing_x = float(level_width - patch_size_pixels) / (width_patches - 1);
 423         float patch_spacing_y = float(level_height - patch_size_pixels) / (height_patches - 1);
 424         glProgramUniform2f(densify_program, glGetUniformLocation(densify_program, "patch_spacing"),
 425                 patch_spacing_x / level_width,
 426                 patch_spacing_y / level_height);
 427
 428         // Set up the VAO containing all the required position/texcoord data.
 429         GLuint densify_vao;
 430         glCreateVertexArrays(1, &densify_vao);
 431         glBindVertexArray(densify_vao);
 432         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 433
 434         position_attrib = glGetAttribLocation(densify_program, "position");
 435         glEnableVertexArrayAttrib(densify_vao, position_attrib);
 436         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 437
 438         glBindBuffer(GL_ARRAY_BUFFER, 0);
 439
 440         // And draw.
 441         glViewport(0, 0, level_width, level_height);
 442         glEnable(GL_BLEND);
 443         glBlendFunc(GL_ONE, GL_ONE);
 444         glBindFramebuffer(GL_FRAMEBUFFER, dense_flow_fbo);
 445         glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width_patches * height_patches);
 446
 447         // TODO: Variational refinement.
 448
 449         unique_ptr<float[]> dense_flow(new float[level_width * level_height * 3]);
 450         glGetTextureImage(dense_flow_tex, 0, GL_RGB, GL_FLOAT, level_width * level_height * 3 * sizeof(float), dense_flow.get());
 451
 452         FILE *fp = fopen("flow.ppm", "wb");
 453         fprintf(fp, "P6\n%d %d\n255\n", level_width, level_height);
 454         for (unsigned y = 0; y < level_height; ++y) {
 455                 for (unsigned x = 0; x < level_width; ++x) {
 456                         float du = dense_flow[(y * level_width + x) * 3 + 0];
 457                         float dv = dense_flow[(y * level_width + x) * 3 + 1];
 458                         float w = dense_flow[(y * level_width + x) * 3 + 2];
 459
 460                         du /= w;
 461                         dv /= w;
 462
 463                         float angle = atan2(dv, du);
 464                         float magnitude = min(hypot(du * level_width, dv * level_height) / 20.0, 1.0);
 465
 466                         // HSV to RGB (from Wikipedia). Saturation is 1.
 467                         float c = magnitude;
 468                         float h = angle * 6.0 / (2.0 * M_PI);
 469                         float X = c * (1.0 - (fmod(h, 2.0) - 1.0));
 470                         float r = 0.0f, g = 0.0f, b = 0.0f;
 471                         if (h < 1.0f) {
 472                                 r = c; g = X;
 473                         } else if (h < 2.0f) {
 474                                 r = X; g = c;
 475                         } else if (h < 3.0f) {
 476                                 g = c; b = X;
 477                         } else if (h < 4.0f) {
 478                                 g = X; b = c;
 479                         } else if (h < 5.0f) {
 480                                 r = X; b = c;
 481                         } else if (h < 6.0f) {
 482                                 r = c; b = X;
 483                         } else {
 484                                 // h is NaN, so black is fine.
 485                         }
 486                         float m = magnitude - c;
 487                         r += m, g += m, b += m;
 488                         r = max(min(r, 1.0f), 0.0f);
 489                         g = max(min(g, 1.0f), 0.0f);
 490                         b = max(min(b, 1.0f), 0.0f);
 491                         putc(lrintf(r * 255.0f), fp);
 492                         putc(lrintf(g * 255.0f), fp);
 493                         putc(lrintf(b * 255.0f), fp);
 494                 }
 495         }
 496         fclose(fp);
 497
 498         fprintf(stderr, "err = %d\n", glGetError());
 499 }