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Added a simple GLSL example using SDL
author Sam Lantinga <slouken@libsdl.org>
date Tue, 08 Feb 2011 22:11:16 -0800
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children c7be6ca3a0b8
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5236:e82908c86c9c 5237:74bc160186a8
1 /* This is a simple example of using GLSL shaders with SDL */
2
3 #include "SDL.h"
4
5 #ifdef HAVE_OPENGL
6
7 #include "SDL_opengl.h"
8
9
10 static SDL_bool shaders_supported;
11 static int current_shader = 0;
12
13 enum {
14 SHADER_COLOR,
15 SHADER_TEXTURE,
16 SHADER_TEXCOORDS,
17 NUM_SHADERS
18 };
19
20 typedef struct {
21 GLuint program;
22 GLuint vert_shader;
23 GLuint frag_shader;
24 const char *vert_source;
25 const char *frag_source;
26 } ShaderData;
27
28 static ShaderData shaders[NUM_SHADERS] = {
29
30 /* SHADER_COLOR */
31 { 0, 0, 0,
32 /* vertex shader */
33 "varying vec4 v_color;\n"
34 "\n"
35 "void main()\n"
36 "{\n"
37 " gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
38 " v_color = gl_Color;\n"
39 "}",
40 /* fragment shader */
41 "varying vec4 v_color;\n"
42 "\n"
43 "void main()\n"
44 "{\n"
45 " gl_FragColor = v_color;\n"
46 "}"
47 },
48
49 /* SHADER_TEXTURE */
50 { 0, 0, 0,
51 /* vertex shader */
52 "varying vec4 v_color;\n"
53 "varying vec2 v_texCoord;\n"
54 "\n"
55 "void main()\n"
56 "{\n"
57 " gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
58 " v_color = gl_Color;\n"
59 " v_texCoord = vec2(gl_MultiTexCoord0);\n"
60 "}",
61 /* fragment shader */
62 "varying vec4 v_color;\n"
63 "varying vec2 v_texCoord;\n"
64 "uniform sampler2D tex0;\n"
65 "\n"
66 "void main()\n"
67 "{\n"
68 " gl_FragColor = texture2D(tex0, v_texCoord) * v_color;\n"
69 "}"
70 },
71
72 /* SHADER_TEXCOORDS */
73 { 0, 0, 0,
74 /* vertex shader */
75 "varying vec2 v_texCoord;\n"
76 "\n"
77 "void main()\n"
78 "{\n"
79 " gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
80 " v_texCoord = vec2(gl_MultiTexCoord0);\n"
81 "}",
82 /* fragment shader */
83 "varying vec2 v_texCoord;\n"
84 "\n"
85 "void main()\n"
86 "{\n"
87 " vec4 color;\n"
88 " vec2 delta;\n"
89 " float dist;\n"
90 "\n"
91 " delta = vec2(0.5, 0.5) - v_texCoord;\n"
92 " dist = dot(delta, delta);\n"
93 "\n"
94 " color.r = v_texCoord.x;\n"
95 " color.g = v_texCoord.x * v_texCoord.y;\n"
96 " color.b = v_texCoord.y;\n"
97 " color.a = 1.0 - (dist * 4.0);\n"
98 " gl_FragColor = color;\n"
99 "}"
100 },
101 };
102
103 static PFNGLATTACHOBJECTARBPROC glAttachObjectARB;
104 static PFNGLCOMPILESHADERARBPROC glCompileShaderARB;
105 static PFNGLCREATEPROGRAMOBJECTARBPROC glCreateProgramObjectARB;
106 static PFNGLCREATESHADEROBJECTARBPROC glCreateShaderObjectARB;
107 static PFNGLDELETEOBJECTARBPROC glDeleteObjectARB;
108 static PFNGLGETINFOLOGARBPROC glGetInfoLogARB;
109 static PFNGLGETOBJECTPARAMETERIVARBPROC glGetObjectParameterivARB;
110 static PFNGLGETUNIFORMLOCATIONARBPROC glGetUniformLocationARB;
111 static PFNGLLINKPROGRAMARBPROC glLinkProgramARB;
112 static PFNGLSHADERSOURCEARBPROC glShaderSourceARB;
113 static PFNGLUNIFORM1IARBPROC glUniform1iARB;
114 static PFNGLUSEPROGRAMOBJECTARBPROC glUseProgramObjectARB;
115
116 static SDL_bool CompileShader(GLenum shader, const char *source)
117 {
118 GLint status;
119
120 glShaderSourceARB(shader, 1, &source, NULL);
121 glCompileShaderARB(shader);
122 glGetObjectParameterivARB(shader, GL_OBJECT_COMPILE_STATUS_ARB, &status);
123 if (status == 0) {
124 GLint length;
125 char *info;
126
127 glGetObjectParameterivARB(shader, GL_OBJECT_INFO_LOG_LENGTH_ARB, &length);
128 info = SDL_stack_alloc(char, length+1);
129 glGetInfoLogARB(shader, length, NULL, info);
130 fprintf(stderr, "Failed to compile shader:\n%s\n%s", source, info);
131 SDL_stack_free(info);
132
133 return SDL_FALSE;
134 } else {
135 return SDL_TRUE;
136 }
137 }
138
139 static SDL_bool CompileShaderProgram(ShaderData *data)
140 {
141 const int num_tmus_bound = 4;
142 int i;
143 GLint location;
144
145 glGetError();
146
147 /* Create one program object to rule them all */
148 data->program = glCreateProgramObjectARB();
149
150 /* Create the vertex shader */
151 data->vert_shader = glCreateShaderObjectARB(GL_VERTEX_SHADER_ARB);
152 if (!CompileShader(data->vert_shader, data->vert_source)) {
153 return SDL_FALSE;
154 }
155
156 /* Create the fragment shader */
157 data->frag_shader = glCreateShaderObjectARB(GL_FRAGMENT_SHADER_ARB);
158 if (!CompileShader(data->frag_shader, data->frag_source)) {
159 return SDL_FALSE;
160 }
161
162 /* ... and in the darkness bind them */
163 glAttachObjectARB(data->program, data->vert_shader);
164 glAttachObjectARB(data->program, data->frag_shader);
165 glLinkProgramARB(data->program);
166
167 /* Set up some uniform variables */
168 glUseProgramObjectARB(data->program);
169 for (i = 0; i < num_tmus_bound; ++i) {
170 char tex_name[5];
171 SDL_snprintf(tex_name, SDL_arraysize(tex_name), "tex%d", i);
172 location = glGetUniformLocationARB(data->program, tex_name);
173 if (location >= 0) {
174 glUniform1iARB(location, i);
175 }
176 }
177 glUseProgramObjectARB(0);
178
179 return (glGetError() == GL_NO_ERROR);
180 }
181
182 static void DestroyShaderProgram(ShaderData *data)
183 {
184 glDeleteObjectARB(data->vert_shader);
185 glDeleteObjectARB(data->frag_shader);
186 glDeleteObjectARB(data->program);
187 }
188
189 static SDL_bool InitShaders()
190 {
191 int i;
192
193 /* Check for shader support */
194 shaders_supported = SDL_FALSE;
195 if (SDL_GL_ExtensionSupported("GL_ARB_shader_objects") &&
196 SDL_GL_ExtensionSupported("GL_ARB_shading_language_100") &&
197 SDL_GL_ExtensionSupported("GL_ARB_vertex_shader") &&
198 SDL_GL_ExtensionSupported("GL_ARB_fragment_shader")) {
199 glAttachObjectARB = (PFNGLATTACHOBJECTARBPROC) SDL_GL_GetProcAddress("glAttachObjectARB");
200 glCompileShaderARB = (PFNGLCOMPILESHADERARBPROC) SDL_GL_GetProcAddress("glCompileShaderARB");
201 glCreateProgramObjectARB = (PFNGLCREATEPROGRAMOBJECTARBPROC) SDL_GL_GetProcAddress("glCreateProgramObjectARB");
202 glCreateShaderObjectARB = (PFNGLCREATESHADEROBJECTARBPROC) SDL_GL_GetProcAddress("glCreateShaderObjectARB");
203 glDeleteObjectARB = (PFNGLDELETEOBJECTARBPROC) SDL_GL_GetProcAddress("glDeleteObjectARB");
204 glGetInfoLogARB = (PFNGLGETINFOLOGARBPROC) SDL_GL_GetProcAddress("glGetInfoLogARB");
205 glGetObjectParameterivARB = (PFNGLGETOBJECTPARAMETERIVARBPROC) SDL_GL_GetProcAddress("glGetObjectParameterivARB");
206 glGetUniformLocationARB = (PFNGLGETUNIFORMLOCATIONARBPROC) SDL_GL_GetProcAddress("glGetUniformLocationARB");
207 glLinkProgramARB = (PFNGLLINKPROGRAMARBPROC) SDL_GL_GetProcAddress("glLinkProgramARB");
208 glShaderSourceARB = (PFNGLSHADERSOURCEARBPROC) SDL_GL_GetProcAddress("glShaderSourceARB");
209 glUniform1iARB = (PFNGLUNIFORM1IARBPROC) SDL_GL_GetProcAddress("glUniform1iARB");
210 glUseProgramObjectARB = (PFNGLUSEPROGRAMOBJECTARBPROC) SDL_GL_GetProcAddress("glUseProgramObjectARB");
211 if (glAttachObjectARB &&
212 glCompileShaderARB &&
213 glCreateProgramObjectARB &&
214 glCreateShaderObjectARB &&
215 glDeleteObjectARB &&
216 glGetInfoLogARB &&
217 glGetObjectParameterivARB &&
218 glGetUniformLocationARB &&
219 glLinkProgramARB &&
220 glShaderSourceARB &&
221 glUniform1iARB &&
222 glUseProgramObjectARB) {
223 shaders_supported = SDL_TRUE;
224 }
225 }
226
227 if (!shaders_supported) {
228 return SDL_FALSE;
229 }
230
231 /* Compile all the shaders */
232 for (i = 0; i < NUM_SHADERS; ++i) {
233 if (!CompileShaderProgram(&shaders[i])) {
234 fprintf(stderr, "Unable to compile shader!\n");
235 return SDL_FALSE;
236 }
237 }
238
239 /* We're done! */
240 return SDL_TRUE;
241 }
242
243 static void QuitShaders()
244 {
245 int i;
246
247 for (i = 0; i < NUM_SHADERS; ++i) {
248 DestroyShaderProgram(&shaders[i]);
249 }
250 }
251
252 /* Quick utility function for texture creation */
253 static int
254 power_of_two(int input)
255 {
256 int value = 1;
257
258 while (value < input) {
259 value <<= 1;
260 }
261 return value;
262 }
263
264 GLuint
265 SDL_GL_LoadTexture(SDL_Surface * surface, GLfloat * texcoord)
266 {
267 GLuint texture;
268 int w, h;
269 SDL_Surface *image;
270 SDL_Rect area;
271 Uint32 saved_flags;
272 Uint8 saved_alpha;
273
274 /* Use the surface width and height expanded to powers of 2 */
275 w = power_of_two(surface->w);
276 h = power_of_two(surface->h);
277 texcoord[0] = 0.0f; /* Min X */
278 texcoord[1] = 0.0f; /* Min Y */
279 texcoord[2] = (GLfloat) surface->w / w; /* Max X */
280 texcoord[3] = (GLfloat) surface->h / h; /* Max Y */
281
282 image = SDL_CreateRGBSurface(SDL_SWSURFACE, w, h, 32,
283 #if SDL_BYTEORDER == SDL_LIL_ENDIAN /* OpenGL RGBA masks */
284 0x000000FF,
285 0x0000FF00, 0x00FF0000, 0xFF000000
286 #else
287 0xFF000000,
288 0x00FF0000, 0x0000FF00, 0x000000FF
289 #endif
290 );
291 if (image == NULL) {
292 return 0;
293 }
294
295 /* Save the alpha blending attributes */
296 saved_flags = surface->flags & (SDL_SRCALPHA | SDL_RLEACCELOK);
297 SDL_GetSurfaceAlphaMod(surface, &saved_alpha);
298 if ((saved_flags & SDL_SRCALPHA) == SDL_SRCALPHA) {
299 SDL_SetAlpha(surface, 0, 0);
300 }
301
302 /* Copy the surface into the GL texture image */
303 area.x = 0;
304 area.y = 0;
305 area.w = surface->w;
306 area.h = surface->h;
307 SDL_BlitSurface(surface, &area, image, &area);
308
309 /* Restore the alpha blending attributes */
310 if ((saved_flags & SDL_SRCALPHA) == SDL_SRCALPHA) {
311 SDL_SetAlpha(surface, saved_flags, saved_alpha);
312 }
313
314 /* Create an OpenGL texture for the image */
315 glGenTextures(1, &texture);
316 glBindTexture(GL_TEXTURE_2D, texture);
317 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
318 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
319 glTexImage2D(GL_TEXTURE_2D,
320 0,
321 GL_RGBA, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, image->pixels);
322 SDL_FreeSurface(image); /* No longer needed */
323
324 return texture;
325 }
326
327 /* A general OpenGL initialization function. Sets all of the initial parameters. */
328 void InitGL(int Width, int Height) // We call this right after our OpenGL window is created.
329 {
330 GLdouble aspect;
331
332 glViewport(0, 0, Width, Height);
333 glClearColor(0.0f, 0.0f, 0.0f, 0.0f); // This Will Clear The Background Color To Black
334 glClearDepth(1.0); // Enables Clearing Of The Depth Buffer
335 glDepthFunc(GL_LESS); // The Type Of Depth Test To Do
336 glEnable(GL_DEPTH_TEST); // Enables Depth Testing
337 glShadeModel(GL_SMOOTH); // Enables Smooth Color Shading
338
339 glMatrixMode(GL_PROJECTION);
340 glLoadIdentity(); // Reset The Projection Matrix
341
342 aspect = (GLdouble)Width / Height;
343 glOrtho(-3.0, 3.0, -3.0 / aspect, 3.0 / aspect, 0.0, 1.0);
344
345 glMatrixMode(GL_MODELVIEW);
346 }
347
348 /* The main drawing function. */
349 void DrawGLScene(GLuint texture, GLfloat * texcoord)
350 {
351 /* Texture coordinate lookup, to make it simple */
352 enum {
353 MINX,
354 MINY,
355 MAXX,
356 MAXY
357 };
358
359 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear The Screen And The Depth Buffer
360 glLoadIdentity(); // Reset The View
361
362 glTranslatef(-1.5f,0.0f,0.0f); // Move Left 1.5 Units
363
364 // draw a triangle (in smooth coloring mode)
365 glBegin(GL_POLYGON); // start drawing a polygon
366 glColor3f(1.0f,0.0f,0.0f); // Set The Color To Red
367 glVertex3f( 0.0f, 1.0f, 0.0f); // Top
368 glColor3f(0.0f,1.0f,0.0f); // Set The Color To Green
369 glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
370 glColor3f(0.0f,0.0f,1.0f); // Set The Color To Blue
371 glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
372 glEnd(); // we're done with the polygon (smooth color interpolation)
373
374 glTranslatef(3.0f,0.0f,0.0f); // Move Right 3 Units
375
376 // Enable blending
377 glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
378 glEnable(GL_BLEND);
379 glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
380
381 // draw a textured square (quadrilateral)
382 glEnable(GL_TEXTURE_2D);
383 glBindTexture(GL_TEXTURE_2D, texture);
384 glColor3f(1.0f,1.0f,1.0f);
385 if (shaders_supported) {
386 glUseProgramObjectARB(shaders[current_shader].program);
387 }
388
389 glBegin(GL_QUADS); // start drawing a polygon (4 sided)
390 glTexCoord2f(texcoord[MINX], texcoord[MINY]);
391 glVertex3f(-1.0f, 1.0f, 0.0f); // Top Left
392 glTexCoord2f(texcoord[MAXX], texcoord[MINY]);
393 glVertex3f( 1.0f, 1.0f, 0.0f); // Top Right
394 glTexCoord2f(texcoord[MAXX], texcoord[MAXY]);
395 glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
396 glTexCoord2f(texcoord[MINX], texcoord[MAXY]);
397 glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
398 glEnd(); // done with the polygon
399
400 if (shaders_supported) {
401 glUseProgramObjectARB(0);
402 }
403 glDisable(GL_TEXTURE_2D);
404
405 // swap buffers to display, since we're double buffered.
406 SDL_GL_SwapBuffers();
407 }
408
409 int main(int argc, char **argv)
410 {
411 int done;
412 SDL_Surface *surface;
413 GLuint texture;
414 GLfloat texcoords[4];
415
416 /* Initialize SDL for video output */
417 if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
418 fprintf(stderr, "Unable to initialize SDL: %s\n", SDL_GetError());
419 exit(1);
420 }
421
422 /* Create a 640x480 OpenGL screen */
423 if ( SDL_SetVideoMode(640, 480, 0, SDL_OPENGL) == NULL ) {
424 fprintf(stderr, "Unable to create OpenGL screen: %s\n", SDL_GetError());
425 SDL_Quit();
426 exit(2);
427 }
428
429 /* Set the title bar in environments that support it */
430 SDL_WM_SetCaption("Shader Demo", NULL);
431
432 surface = SDL_LoadBMP("icon.bmp");
433 if ( ! surface ) {
434 fprintf(stderr, "Unable to load icon.bmp: %s\n", SDL_GetError());
435 SDL_Quit();
436 exit(3);
437 }
438 texture = SDL_GL_LoadTexture(surface, texcoords);
439 SDL_FreeSurface(surface);
440
441 /* Loop, drawing and checking events */
442 InitGL(640, 480);
443 if (InitShaders()) {
444 printf("Shaders supported, press SPACE to cycle them.\n");
445 } else {
446 printf("Shaders not supported!\n");
447 }
448 done = 0;
449 while ( ! done ) {
450 DrawGLScene(texture, texcoords);
451
452 /* This could go in a separate function */
453 { SDL_Event event;
454 while ( SDL_PollEvent(&event) ) {
455 if ( event.type == SDL_QUIT ) {
456 done = 1;
457 }
458 if ( event.type == SDL_KEYDOWN ) {
459 if ( event.key.keysym.sym == SDLK_SPACE ) {
460 current_shader = (current_shader + 1) % NUM_SHADERS;
461 }
462 if ( event.key.keysym.sym == SDLK_ESCAPE ) {
463 done = 1;
464 }
465 }
466 }
467 }
468 }
469 QuitShaders();
470 SDL_Quit();
471 return 1;
472 }
473
474 #else /* HAVE_OPENGL */
475
476 int
477 main(int argc, char *argv[])
478 {
479 printf("No OpenGL support on this system\n");
480 return 1;
481 }
482
483 #endif /* HAVE_OPENGL */