Demo of how to do (nearly) flicker-free rendering with a single color buffer.
This commit is contained in:
Brian Paul
269
progs/demos/singlebuffer.c
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269
progs/demos/singlebuffer.c
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/*
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* Demo of (nearly) flicker-free drawing with a single color buffer.
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*
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* Basically, draw the scene into the Z buffer first, then draw the
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* scene into the color buffer. Finally, "clear" the background by
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* setting the fragments we didn't hit earlier.
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*
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* This won't work if you need blending. The technique works best
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* when the scene is relatively simple and can be rendered quickly
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* (i.e. with hardware), and when the objects don't move too much from
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* one frame to the next.
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*
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* Brian Paul
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* 25 August 2005
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*
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* See Mesa license for terms.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <GL/glut.h>
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#define FLICKER 0
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#define NO_FLICKER 1
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static GLint Mode = NO_FLICKER;
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static GLfloat Xrot = 0, Yrot = 0, Zrot = 0;
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static GLboolean Anim = GL_TRUE;
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static GLfloat ClearColor[4] = {0.2, 0.2, 0.9, 0.0};
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static GLfloat NearClip = 5.0, FarClip = 25.0, ViewDist = 7.0;
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static double PrevTime = -1;
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struct box {
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float tx, ty, tz;
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float rx, ry, rz, ra;
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float sx, sy, sz;
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float color[4];
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};
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#define NUM_BOXES 25
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struct box Boxes[NUM_BOXES];
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/* Return random float in [0,1] */
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static float
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Random(void)
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{
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int i = rand();
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return (float) (i % 1000) / 1000.0;
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}
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static void
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MakeBoxes(void)
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{
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int i;
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for (i = 0; i < NUM_BOXES; i++) {
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Boxes[i].tx = -1.0 + 2.0 * Random();
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Boxes[i].ty = -1.0 + 2.0 * Random();
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Boxes[i].tz = -1.0 + 2.0 * Random();
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Boxes[i].sx = 0.1 + Random() * 0.4;
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Boxes[i].sy = 0.1 + Random() * 0.4;
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Boxes[i].sz = 0.1 + Random() * 0.4;
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Boxes[i].rx = Random();
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Boxes[i].ry = Random();
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Boxes[i].rz = Random();
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Boxes[i].ra = Random() * 360.0;
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Boxes[i].color[0] = Random();
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Boxes[i].color[1] = Random();
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Boxes[i].color[2] = Random();
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Boxes[i].color[3] = 1.0;
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}
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}
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static void
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DrawBoxes(void)
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{
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int i;
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for (i = 0; i < NUM_BOXES; i++) {
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glPushMatrix();
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glTranslatef(Boxes[i].tx, Boxes[i].ty, Boxes[i].tz);
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glRotatef(Boxes[i].ra, Boxes[i].rx, Boxes[i].ry, Boxes[i].rz);
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glScalef(Boxes[i].sx, Boxes[i].sy, Boxes[i].sz);
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glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, Boxes[i].color);
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glutSolidCube(1.0);
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glPopMatrix();
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}
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}
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static void
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Idle(void)
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{
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double dt, t = glutGet(GLUT_ELAPSED_TIME) * 0.001;
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if (PrevTime < 0.0)
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PrevTime = t;
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dt = t - PrevTime;
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PrevTime = t;
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Xrot += 16.0 * dt;
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Yrot += 12.0 * dt;
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Zrot += 8.0 * dt;
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glutPostRedisplay();
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}
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static void
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Draw(void)
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{
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if (Mode == FLICKER) {
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glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
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}
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else {
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/* don't clear color buffer */
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glClear(GL_DEPTH_BUFFER_BIT);
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/* update Z buffer only */
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glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
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}
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glPushMatrix();
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glRotatef(Xrot, 1, 0, 0);
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glRotatef(Yrot, 0, 1, 0);
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glRotatef(Zrot, 0, 0, 1);
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DrawBoxes();
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if (Mode == NO_FLICKER) {
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/* update color buffer now */
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glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
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glDepthFunc(GL_EQUAL);
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DrawBoxes();
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glDepthFunc(GL_LESS);
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}
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glPopMatrix();
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if (Mode == NO_FLICKER) {
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/* "clear" the untouched pixels now.
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* Note: if you comment-out this code you'll see something interesting.
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*/
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GLfloat x = FarClip / NearClip;
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GLfloat z = -(FarClip - ViewDist - 1.0);
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glDisable(GL_LIGHTING);
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glColor4fv(ClearColor);
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glBegin(GL_POLYGON);
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glVertex3f(-x, -x, z);
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glVertex3f( x, -x, z);
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glVertex3f( x, x, z);
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glVertex3f(-x, x, z);
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glEnd();
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glEnable(GL_LIGHTING);
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}
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/* This is where you'd normally do SwapBuffers */
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glFinish();
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}
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static void
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Reshape(int width, int height)
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{
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glViewport(0, 0, width, height);
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glMatrixMode(GL_PROJECTION);
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glLoadIdentity();
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glFrustum(-1.0, 1.0, -1.0, 1.0, NearClip, FarClip);
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glMatrixMode(GL_MODELVIEW);
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glLoadIdentity();
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glTranslatef(0.0, 0.0, -ViewDist);
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}
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static void
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Key(unsigned char key, int x, int y)
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{
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(void) x;
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(void) y;
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switch (key) {
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case 'a':
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Anim = !Anim;
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if (Anim)
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glutIdleFunc(Idle);
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else
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glutIdleFunc(NULL);
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PrevTime = -1;
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break;
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case 'm':
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Mode = !Mode;
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break;
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case 'b':
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MakeBoxes();
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break;
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case 27:
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exit(0);
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break;
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}
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glutPostRedisplay();
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}
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static void
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SpecialKey(int key, int x, int y)
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{
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const GLfloat step = 3.0;
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(void) x;
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(void) y;
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switch (key) {
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case GLUT_KEY_UP:
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Xrot -= step;
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break;
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case GLUT_KEY_DOWN:
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Xrot += step;
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break;
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case GLUT_KEY_LEFT:
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Yrot -= step;
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break;
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case GLUT_KEY_RIGHT:
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Yrot += step;
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break;
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}
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glutPostRedisplay();
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}
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static void
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Init(void)
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{
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glClearColor(ClearColor[0], ClearColor[1], ClearColor[2], ClearColor[3]);
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glEnable(GL_DEPTH_TEST);
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glEnable(GL_LIGHTING);
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glEnable(GL_LIGHT0);
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glEnable(GL_CULL_FACE);
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glEnable(GL_NORMALIZE);
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MakeBoxes();
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}
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static void
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Usage(void)
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{
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printf("Keys:\n");
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printf(" m - toggle drawing mode (flicker vs. no flicker)\n");
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printf(" a - toggle animation\n");
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printf(" b - generate new boxes\n");
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printf(" ARROWS - rotate scene\n");
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printf(" ESC - exit\n");
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}
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int
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main(int argc, char *argv[])
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{
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glutInit(&argc, argv);
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glutInitWindowSize(800, 800);
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glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE | GLUT_DEPTH);
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glutCreateWindow(argv[0]);
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glutReshapeFunc(Reshape);
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glutKeyboardFunc(Key);
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glutSpecialFunc(SpecialKey);
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glutDisplayFunc(Draw);
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if (Anim)
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glutIdleFunc(Idle);
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Init();
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Usage();
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glutMainLoop();
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return 0;
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}
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