progs/demos/singlebuffer.c

   1 /*
   2  * Demo of (nearly) flicker-free drawing with a single color buffer.
   3  *
   4  * Basically, draw the scene into the Z buffer first, then draw the
   5  * scene into the color buffer.  Finally, "clear" the background by
   6  * setting the fragments we didn't hit earlier.
   7  *
   8  * This won't work if you need blending.  The technique works best
   9  * when the scene is relatively simple and can be rendered quickly
  10  * (i.e. with hardware), and when the objects don't move too much from
  11  * one frame to the next.
  12  *
  13  * Brian Paul
  14  * 25 August 2005
  15  *
  16  * See Mesa license for terms.
  17  */
  18
  19
  20 #include <stdio.h>
  21 #include <stdlib.h>
  22 #include <GL/glut.h>
  23
  24
  25 #define FLICKER 0
  26 #define NO_FLICKER 1
  27
  28 static GLint Mode = NO_FLICKER;
  29 static GLfloat Xrot = 0, Yrot = 0, Zrot = 0;
  30 static GLboolean Anim = GL_TRUE;
  31 static GLfloat ClearColor[4] = {0.2, 0.2, 0.9, 0.0};
  32 static GLfloat NearClip = 5.0, FarClip = 25.0, ViewDist = 7.0;
  33 static double PrevTime = -1;
  34
  35 struct box {
  36    float tx, ty, tz;
  37    float rx, ry, rz, ra;
  38    float sx, sy, sz;
  39    float color[4];
  40 };
  41
  42 #define NUM_BOXES 25
  43
  44 struct box Boxes[NUM_BOXES];
  45
  46
  47 /* Return random float in [0,1] */
  48 static float
  49 Random(void)
  50 {
  51    int i = rand();
  52    return (float) (i % 1000) / 1000.0;
  53 }
  54
  55
  56 static void
  57 MakeBoxes(void)
  58 {
  59    int i;
  60    for (i = 0; i < NUM_BOXES; i++) {
  61       Boxes[i].tx = -1.0 + 2.0 * Random();
  62       Boxes[i].ty = -1.0 + 2.0 * Random();
  63       Boxes[i].tz = -1.0 + 2.0 * Random();
  64       Boxes[i].sx = 0.1 + Random() * 0.4;
  65       Boxes[i].sy = 0.1 + Random() * 0.4;
  66       Boxes[i].sz = 0.1 + Random() * 0.4;
  67       Boxes[i].rx = Random();
  68       Boxes[i].ry = Random();
  69       Boxes[i].rz = Random();
  70       Boxes[i].ra = Random() * 360.0;
  71       Boxes[i].color[0] = Random();
  72       Boxes[i].color[1] = Random();
  73       Boxes[i].color[2] = Random();
  74       Boxes[i].color[3] = 1.0;
  75    }
  76 }
  77
  78
  79 static void
  80 DrawBoxes(void)
  81 {
  82    int i;
  83    for (i = 0; i < NUM_BOXES; i++) {
  84       glPushMatrix();
  85       glTranslatef(Boxes[i].tx, Boxes[i].ty, Boxes[i].tz);
  86       glRotatef(Boxes[i].ra, Boxes[i].rx, Boxes[i].ry, Boxes[i].rz);
  87       glScalef(Boxes[i].sx, Boxes[i].sy, Boxes[i].sz);
  88       glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, Boxes[i].color);
  89       glutSolidCube(1.0);
  90       glPopMatrix();
  91    }
  92 }
  93
  94
  95 static void
  96 Idle(void)
  97 {
  98    double dt, t = glutGet(GLUT_ELAPSED_TIME) * 0.001;
  99    if (PrevTime < 0.0)
 100       PrevTime = t;
 101    dt = t - PrevTime;
 102    PrevTime = t;
 103    Xrot += 16.0 * dt;
 104    Yrot += 12.0 * dt;
 105    Zrot += 8.0 * dt;
 106    glutPostRedisplay();
 107 }
 108
 109
 110 static void
 111 Draw(void)
 112 {
 113    if (Mode == FLICKER) {
 114       glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 115    }
 116    else {
 117       /* don't clear color buffer */
 118       glClear(GL_DEPTH_BUFFER_BIT);
 119       /* update Z buffer only */
 120       glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
 121    }
 122
 123    glPushMatrix();
 124    glRotatef(Xrot, 1, 0, 0);
 125    glRotatef(Yrot, 0, 1, 0);
 126    glRotatef(Zrot, 0, 0, 1);
 127
 128    DrawBoxes();
 129
 130    if (Mode == NO_FLICKER) {
 131       /* update color buffer now */
 132       glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
 133       glDepthFunc(GL_EQUAL);
 134       DrawBoxes();
 135       glDepthFunc(GL_LESS);
 136    }
 137
 138    glPopMatrix();
 139
 140    if (Mode == NO_FLICKER) {
 141       /* "clear" the untouched pixels now.
 142        * Note: if you comment-out this code you'll see something interesting.
 143        */
 144       GLfloat x = FarClip / NearClip;
 145       GLfloat z = -(FarClip - ViewDist - 1.0);
 146       glDisable(GL_LIGHTING);
 147       glColor4fv(ClearColor);
 148       glBegin(GL_POLYGON);
 149       glVertex3f(-x, -x, z);
 150       glVertex3f( x, -x, z);
 151       glVertex3f( x,  x, z);
 152       glVertex3f(-x,  x, z);
 153       glEnd();
 154       glEnable(GL_LIGHTING);
 155    }
 156
 157    /* This is where you'd normally do SwapBuffers */
 158    glFinish();
 159 }
 160
 161
 162 static void
 163 Reshape(int width, int height)
 164 {
 165    glViewport(0, 0, width, height);
 166    glMatrixMode(GL_PROJECTION);
 167    glLoadIdentity();
 168    glFrustum(-1.0, 1.0, -1.0, 1.0, NearClip, FarClip);
 169    glMatrixMode(GL_MODELVIEW);
 170    glLoadIdentity();
 171    glTranslatef(0.0, 0.0, -ViewDist);
 172 }
 173
 174
 175 static void
 176 Key(unsigned char key, int x, int y)
 177 {
 178    (void) x;
 179    (void) y;
 180    switch (key) {
 181       case 'a':
 182          Anim = !Anim;
 183          if (Anim)
 184             glutIdleFunc(Idle);
 185          else
 186             glutIdleFunc(NULL);
 187          PrevTime = -1;
 188          break;
 189       case 'm':
 190          Mode = !Mode;
 191          break;
 192       case 'b':
 193          MakeBoxes();
 194          break;
 195       case 27:
 196          exit(0);
 197          break;
 198    }
 199    glutPostRedisplay();
 200 }
 201
 202
 203 static void
 204 SpecialKey(int key, int x, int y)
 205 {
 206    const GLfloat step = 3.0;
 207    (void) x;
 208    (void) y;
 209    switch (key) {
 210       case GLUT_KEY_UP:
 211          Xrot -= step;
 212          break;
 213       case GLUT_KEY_DOWN:
 214          Xrot += step;
 215          break;
 216       case GLUT_KEY_LEFT:
 217          Yrot -= step;
 218          break;
 219       case GLUT_KEY_RIGHT:
 220          Yrot += step;
 221          break;
 222    }
 223    glutPostRedisplay();
 224 }
 225
 226
 227 static void
 228 Init(void)
 229 {
 230    glClearColor(ClearColor[0], ClearColor[1], ClearColor[2], ClearColor[3]);
 231    glEnable(GL_DEPTH_TEST);
 232    glEnable(GL_LIGHTING);
 233    glEnable(GL_LIGHT0);
 234    glEnable(GL_CULL_FACE);
 235    glEnable(GL_NORMALIZE);
 236    MakeBoxes();
 237 }
 238
 239
 240 static void
 241 Usage(void)
 242 {
 243    printf("Keys:\n");
 244    printf("  m       - toggle drawing mode (flicker vs. no flicker)\n");
 245    printf("  a       - toggle animation\n");
 246    printf("  b       - generate new boxes\n");
 247    printf("  ARROWS  - rotate scene\n");
 248    printf("  ESC     - exit\n");
 249 }
 250
 251
 252 int
 253 main(int argc, char *argv[])
 254 {
 255    glutInit(&argc, argv);
 256    glutInitWindowSize(800, 800);
 257    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE | GLUT_DEPTH);
 258    glutCreateWindow(argv[0]);
 259    glutReshapeFunc(Reshape);
 260    glutKeyboardFunc(Key);
 261    glutSpecialFunc(SpecialKey);
 262    glutDisplayFunc(Draw);
 263    if (Anim)
 264       glutIdleFunc(Idle);
 265    Init();
 266    Usage();
 267    glutMainLoop();
 268    return 0;
 269 }