progs/trivial/clear-fbo-scissor.c

   1 /*
   2  * Use scissor to clear the four quadrants of the FBO to different
   3  * colors.  Then draw a grey triangle in the middle.
   4  */
   5
   6
   7 #include <assert.h>
   8 #include <stdio.h>
   9 #include <stdlib.h>
  10 #include <math.h>
  11 #include <string.h>
  12 #include <GL/glew.h>
  13 #include <GL/glut.h>
  14 #include <GL/glu.h>
  15
  16
  17 static int Width = 512, Height = 512;
  18 static GLuint MyFB, MyRB;
  19 static GLboolean UseTex = GL_FALSE;
  20 static GLboolean UseCopyPix = GL_FALSE;
  21
  22
  23 #define CheckError() \
  24    do { \
  25       GLenum err = glGetError(); \
  26       if (err != GL_NO_ERROR) \
  27          printf("Error: %s\n", gluErrorString(err)); \
  28       assert(err == GL_NO_ERROR); \
  29    } while (0)
  30
  31
  32 static void
  33 Init(void)
  34 {
  35    GLenum status;
  36
  37    fprintf(stderr, "GL_RENDERER   = %s\n", (char *) glGetString(GL_RENDERER));
  38    fprintf(stderr, "GL_VERSION    = %s\n", (char *) glGetString(GL_VERSION));
  39    fprintf(stderr, "GL_VENDOR     = %s\n", (char *) glGetString(GL_VENDOR));
  40    fflush(stderr);
  41
  42    if (!glutExtensionSupported("GL_EXT_framebuffer_object")) {
  43       printf("GL_EXT_framebuffer_object not found!\n");
  44       exit(0);
  45    }
  46
  47    glGenFramebuffersEXT(1, &MyFB);
  48    glGenRenderbuffersEXT(1, &MyRB);
  49
  50    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, MyFB);
  51
  52    if (UseTex) {
  53       GLuint tex;
  54       glGenTextures(1, &tex);
  55       glBindTexture(GL_TEXTURE_2D, tex);
  56       glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, Width, Height, 0,
  57                    GL_RGBA, GL_UNSIGNED_BYTE, NULL);
  58       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  59       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  60       glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT,
  61                                 GL_COLOR_ATTACHMENT0_EXT,
  62                                 GL_TEXTURE_2D, tex, 0);
  63    }
  64    else {
  65       glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, MyRB);
  66
  67       glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT,
  68                                    GL_COLOR_ATTACHMENT0_EXT,
  69                                    GL_RENDERBUFFER_EXT, MyRB);
  70
  71       glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGB, Width, Height);
  72    }
  73
  74    status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
  75    if (status != GL_FRAMEBUFFER_COMPLETE_EXT) {
  76       fprintf(stderr, "Framebuffer object is incomplete (0x%x)!\n", status);
  77    }
  78
  79    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
  80 }
  81
  82
  83 static void
  84 Reshape(int width, int height)
  85 {
  86    glViewport(0, 0, width, height);
  87    glMatrixMode(GL_PROJECTION);
  88    glLoadIdentity();
  89    glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
  90    glMatrixMode(GL_MODELVIEW);
  91
  92    Width = width;
  93    Height = height;
  94    if (!UseTex) {
  95       glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGB, Width, Height);
  96    }
  97 }
  98
  99
 100 static void
 101 Key(unsigned char key, int x, int y)
 102 {
 103    if (key == 27) {
 104       exit(0);
 105    }
 106    glutPostRedisplay();
 107 }
 108
 109
 110 static void
 111 Draw(void)
 112 {
 113    GLboolean scissor = GL_TRUE;
 114
 115    /* draw to user framebuffer */
 116    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, MyFB);
 117    glDrawBuffer(GL_COLOR_ATTACHMENT0_EXT);
 118    glReadBuffer(GL_COLOR_ATTACHMENT0_EXT);
 119
 120    glViewport(0, 0, Width, Height);
 121    CheckError();
 122
 123    if (scissor) {
 124       glEnable(GL_SCISSOR_TEST);
 125
 126       /* lower-left = red */
 127       glClearColor(1, 0, 0, 0);
 128       glScissor(0, 0, Width / 2, Height / 2);
 129       glClear(GL_COLOR_BUFFER_BIT);
 130
 131       /* lower-right = green */
 132       glClearColor(0, 1, 0, 0);
 133       glScissor(Width / 2, 0, Width - Width / 2, Height / 2);
 134       glClear(GL_COLOR_BUFFER_BIT);
 135
 136       /* upper-left = blue */
 137       glClearColor(0, 0, 1, 0);
 138       glScissor(0, Height / 2, Width / 2, Height - Height / 2);
 139       glClear(GL_COLOR_BUFFER_BIT);
 140
 141       /* upper-right = white */
 142       glClearColor(1, 1, 1, 0);
 143       glScissor(Width / 2, Height / 2, Width - Width / 2, Height - Height / 2);
 144       glClear(GL_COLOR_BUFFER_BIT);
 145
 146       glDisable(GL_SCISSOR_TEST);
 147    }
 148    else {
 149       glClearColor(0, 1, 0, 0);
 150       glClear(GL_COLOR_BUFFER_BIT);
 151    }
 152
 153    CheckError();
 154
 155    /* gray triangle in middle, pointing up */
 156    glColor3f(0.5, 0.5, 0.5);
 157    glBegin(GL_TRIANGLES);
 158    glVertex2f(Width/4, Height/4);
 159    glVertex2f(Width*3/4, Height/4);
 160    glVertex2f(Width/2, Height*3/4);
 161    glVertex2f(-0.5, -0.5);
 162    glVertex2f(+0.5, -0.5);
 163    glVertex2f( 0.0, 0.7);
 164    glEnd();
 165
 166    CheckError();
 167
 168    /* copy fbo to window */
 169    glBindFramebufferEXT(GL_READ_FRAMEBUFFER_EXT, MyFB);
 170    glReadBuffer(GL_COLOR_ATTACHMENT0_EXT);
 171    glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER_EXT, 0);
 172    glDrawBuffer(GL_BACK);
 173
 174    if (UseCopyPix) {
 175       glWindowPos2i(0, 0);
 176       glCopyPixels(0, 0, Width, Height, GL_COLOR);
 177    }
 178    else {
 179       GLubyte *buffer = malloc(Width * Height * 4);
 180
 181       /* read from user framebuffer */
 182       glReadPixels(0, 0, Width, Height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
 183
 184       /* draw to window */
 185       glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
 186       glWindowPos2iARB(0, 0);
 187       glDrawPixels(Width, Height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
 188
 189       free(buffer);
 190    }
 191
 192    /* Bind normal framebuffer */
 193    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
 194
 195    glutSwapBuffers();
 196
 197    CheckError();
 198 }
 199
 200
 201 int
 202 main(int argc, char *argv[])
 203 {
 204    int i;
 205
 206    glutInit(&argc, argv);
 207    glutInitWindowPosition(100, 0);
 208    glutInitWindowSize(Width, Height);
 209    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
 210
 211    for (i = 1; i < argc; i++) {
 212       if (strcmp(argv[i], "-t") == 0)
 213          UseTex = GL_TRUE;
 214       else if (strcmp(argv[i], "-c") == 0)
 215          UseCopyPix = GL_TRUE;
 216    }
 217
 218    if (UseTex)
 219       printf("Using render to texture\n");
 220    else
 221       printf("Using user-created render buffer\n");
 222
 223    if (!glutCreateWindow(argv[0])) {
 224       exit(1);
 225    }
 226
 227    glewInit();
 228    Init();
 229    glutReshapeFunc(Reshape);
 230    glutKeyboardFunc(Key);
 231    glutDisplayFunc(Draw);
 232    glutMainLoop();
 233    return 0;
 234 }