/* dissolve.c - by Tom McReynolds, SGI *//* An Example of dissolve, using stencil *//* Drag with left mouse button to dissolve to the 3D background,   Drag with middle mouse button to dissolve to checkerboard, and   use right button for menu to clear stencil. */#include "glut.h"#include <stdlib.h>#include <string.h>#include <math.h>#include <stdio.h>#ifdef WIN32#define random rand#endifint winWidth = 512;int winHeight = 512;/* Create a single component texture map */GLfloat *make_texture(int maxs, int maxt){  int s, t;  static GLfloat *texture;  texture = (GLfloat *) malloc(maxs * maxt * sizeof(GLfloat));  for (t = 0; t < maxt; t++) {    for (s = 0; s < maxs; s++) {      texture[s + maxs * t] = ((s >> 4) & 0x1) ^ ((t >> 4) & 0x1);    }  }  return texture;}enum {  SPHERE = 1, CONE};GLfloat angle = 0.f;    /* angle of rotating object in  layer 0 */enum {  X, Y};GLboolean eraser = GL_FALSE;GLint layer = 1;GLint eraserpos[2] ={512 / 8, 512 / 12};/* draw eraser and erase what's underneath */GLubyte *eraserpix = 0;int erasersize = 0;voidmakeEraser(void){  int i, skip;  erasersize = 4 * winWidth / 4 * winHeight / 6;  eraserpix = (GLubyte *) realloc(eraserpix, erasersize * sizeof(GLubyte));  /* make it white */  (void) memset(eraserpix, 255, erasersize * sizeof(GLubyte));  skip = (int) (random() % 8);  for (i = 0; i < erasersize; i++) {    if (!skip) {      eraserpix[i] = 0;      eraserpix[i + 1] = 0;      eraserpix[i + 2] = 0;      eraserpix[i + 3] = 0;      skip = (int) (random() % 8);    } else      skip--;  }}/* ARGSUSED2 *//* left button, first layer, middle button, second layer */voidmouse(int button, int state, int x, int y){  if (state == GLUT_DOWN) {    eraser = GL_TRUE;    if (button == GLUT_LEFT_BUTTON)      layer = 1;    else                /* GLUT_MIDDLE: GLUT_RIGHT is for menu */      layer = 0;  } else {              /* GLUT_UP */    eraser = GL_FALSE;  }  glutPostRedisplay();}enum {  CLEAR};                      /* menu choices */GLboolean clearstencil = GL_TRUE;voidmenu(int choice){  switch (choice) {  case CLEAR:    clearstencil = GL_TRUE;    break;  }  glutPostRedisplay();}/* used to get current width and height of viewport */voidreshape(int wid, int ht){  glViewport(0, 0, wid, ht);  winWidth = wid;  winHeight = ht;  clearstencil = GL_TRUE;  makeEraser();  glutPostRedisplay();}voiddraweraser(void){  glMatrixMode(GL_PROJECTION);  glLoadIdentity();  gluOrtho2D(0, winWidth, 0, winHeight);  glMatrixMode(GL_MODELVIEW);  glLoadIdentity();  /* replace with this layer */  glStencilFunc(GL_ALWAYS, layer, 0);  glStencilOp(GL_KEEP, GL_REPLACE, GL_REPLACE);  glDisable(GL_LIGHTING);  glDisable(GL_DEPTH_TEST);  glEnable(GL_ALPHA_TEST);  glAlphaFunc(GL_NOTEQUAL, 0);  glRasterPos2i(eraserpos[X], eraserpos[Y]);  glBitmap(0, 0, 0.f, 0.f, -winWidth / 8.f, -winHeight / 12.f, 0);  glDrawPixels(winWidth / 4, winHeight / 6, GL_RGBA, GL_UNSIGNED_BYTE, eraserpix);  glDisable(GL_ALPHA_TEST);}voiddrawlayer2(void){  glMatrixMode(GL_PROJECTION);  glLoadIdentity();  gluOrtho2D(0, winWidth, 0, winHeight);  glMatrixMode(GL_MODELVIEW);  glLoadIdentity();  glDisable(GL_LIGHTING);  glDisable(GL_DEPTH_TEST);  glEnable(GL_TEXTURE_2D);  glBegin(GL_QUADS);  glTexCoord2i(0, 0);  glVertex2i(0, 0);  glTexCoord2i(1, 0);  glVertex2i(winWidth, 0);  glTexCoord2i(1, 1);  glVertex2i(winWidth, winHeight);  glTexCoord2i(0, 1);  glVertex2i(0, winHeight);  glEnd();  glDisable(GL_TEXTURE_2D);  if (glGetError())     /* to catch programming errors; should never happen */    printf("Oops! I screwed up my OpenGL calls somewhere\n");}voiddrawlayer1(void){  /* material properties for objects in scene */  static GLfloat wall_mat[] =  {1.f, 1.f, 1.f, 1.f};  static GLfloat lightpos[] =  {50.f, 50.f, -320.f, 1.f};  /* draw a perspective scene */  glMatrixMode(GL_PROJECTION);  glLoadIdentity();  glFrustum(-100., 100., -100., 100., 320., 640.);  glMatrixMode(GL_MODELVIEW);  glLoadIdentity();  /* turn on features */  glEnable(GL_DEPTH_TEST);  glEnable(GL_LIGHTING);  glEnable(GL_LIGHT0);  /* place light 0 in the right place */  glLightfv(GL_LIGHT0, GL_POSITION, lightpos);  /* remove back faces to speed things up */  glCullFace(GL_BACK);  /* Note: wall verticies are ordered so they are all front facing this lets     me do back face culling to speed things up.  */  glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, wall_mat);  /* floor */  /* make the floor textured */  glEnable(GL_TEXTURE_2D);  /* Since we want to turn texturing on for floor only, we have to make floor      a separate glBegin()/glEnd() sequence. You can't turn texturing on and     off between begin and end calls */  glBegin(GL_QUADS);  glNormal3f(0.f, 1.f, 0.f);  glTexCoord2i(0, 0);  glVertex3f(-100.f, -100.f, -320.f);  glTexCoord2i(1, 0);  glVertex3f(100.f, -100.f, -320.f);  glTexCoord2i(1, 1);  glVertex3f(100.f, -100.f, -520.f);  glTexCoord2i(0, 1);  glVertex3f(-100.f, -100.f, -520.f);  glEnd();  glDisable(GL_TEXTURE_2D);  /* walls */  glBegin(GL_QUADS);  /* left wall */  glNormal3f(1.f, 0.f, 0.f);  glVertex3f(-100.f, -100.f, -320.f);  glVertex3f(-100.f, -100.f, -520.f);  glVertex3f(-100.f, 100.f, -520.f);  glVertex3f(-100.f, 100.f, -320.f);  /* right wall */  glNormal3f(-1.f, 0.f, 0.f);  glVertex3f(100.f, -100.f, -320.f);  glVertex3f(100.f, 100.f, -320.f);  glVertex3f(100.f, 100.f, -520.f);  glVertex3f(100.f, -100.f, -520.f);  /* ceiling */  glNormal3f(0.f, -1.f, 0.f);  glVertex3f(-100.f, 100.f, -320.f);  glVertex3f(-100.f, 100.f, -520.f);  glVertex3f(100.f, 100.f, -520.f);  glVertex3f(100.f, 100.f, -320.f);  /* back wall */  glNormal3f(0.f, 0.f, 1.f);  glVertex3f(-100.f, -100.f, -520.f);  glVertex3f(100.f, -100.f, -520.f);  glVertex3f(100.f, 100.f, -520.f);  glVertex3f(-100.f, 100.f, -520.f);  glEnd();  glPushMatrix();  glTranslatef(-80.f, -80.f, -420.f);  glCallList(SPHERE);  glPopMatrix();  glPushMatrix();  glTranslatef(-20.f, -100.f, -500.f);  glCallList(CONE);  glPopMatrix();  if (glGetError())     /* to catch programming errors; should never happen */    printf("Oops! I screwed up my OpenGL calls somewhere\n");}voiddrawlayer0(void){  static GLfloat lightpos[] =  {50.f, 50.f, 0.f, 1.f};  glMatrixMode(GL_PROJECTION);  glLoadIdentity();  glOrtho(-50.f, 50.f, -50.f, 50.f, 0.f, 100.f);  glMatrixMode(GL_MODELVIEW);  glLoadIdentity();  glTranslatef(0.f, 0.f, -50.f);  glRotatef(angle, 0.f, 1.f, 0.f);  glRotatef(90.f, 0.f, 0.f, 1.f);  glTranslatef(0.f, -25.f, 0.f);  glEnable(GL_LIGHTING);  glEnable(GL_LIGHT0);  glLightfv(GL_LIGHT0, GL_POSITION, lightpos);  glCullFace(GL_BACK);  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);  glCallList(CONE);}voidredraw(void){  if (glutLayerGet(GLUT_NORMAL_DAMAGED) ||    clearstencil == GL_TRUE) {    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);    clearstencil = GL_FALSE;  } else    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);  glStencilFunc(GL_EQUAL, 2, ~0);  drawlayer2();  glStencilFunc(GL_EQUAL, 1, ~0);  drawlayer1();  glStencilFunc(GL_EQUAL, 0, ~0);  drawlayer0();  if (eraser)    draweraser();  glutSwapBuffers();}voididle(void){  angle += 1.f;  glutPostRedisplay();}voidpassive(int x, int y){  eraserpos[X] = x;  eraserpos[Y] = winHeight - y;}voidmotion(int x, int y){  eraserpos[X] = x;  eraserpos[Y] = winHeight - y;  glutPostRedisplay();}/* ARGSUSED1 */void key(unsigned char key, int x, int y){  switch (key) {  case '\033':    exit(0);  }}void visible(int vis){  if (vis == GLUT_VISIBLE)    glutIdleFunc(idle);  else    glutIdleFunc(NULL);}const int TEXDIM = 256;GLfloat *tex = 0;main(int argc, char *argv[]){  static GLfloat sphere_mat[] =  {1.f, .5f, 0.f, 1.f};  static GLfloat cone_mat[] =  {0.f, .5f, 1.f, 1.f};  GLUquadricObj *sphere, *cone, *base;  glutInit(&argc, argv);  glutInitWindowSize(winWidth, winHeight);  glutInitDisplayMode(GLUT_DOUBLE | GLUT_STENCIL | GLUT_DEPTH);  (void) glutCreateWindow("dissolve");  glutDisplayFunc(redraw);  glutMouseFunc(mouse);  glutMotionFunc(motion);  glutPassiveMotionFunc(passive);  glutKeyboardFunc(key);  glutVisibilityFunc(visible);  glutReshapeFunc(reshape);  glutCreateMenu(menu);  glutAddMenuEntry("Clear Stencil", CLEAR);  glutAttachMenu(GLUT_RIGHT_BUTTON);  glNewList(SPHERE, GL_COMPILE);  /* make display lists for sphere and cone; for efficiency */  sphere = gluNewQuadric();  glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, sphere_mat);  gluSphere(sphere, 20.f, 20, 20);  gluDeleteQuadric(sphere);  glEndList();  glNewList(CONE, GL_COMPILE);  cone = gluNewQuadric();  base = gluNewQuadric();  glRotatef(-90.f, 1.f, 0.f, 0.f);  glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, cone_mat);  gluQuadricOrientation(base, GLU_INSIDE);  gluDisk(base, 0., 20., 20, 1);  gluCylinder(cone, 20., 0., 60., 20, 20);  gluDeleteQuadric(cone);  gluDeleteQuadric(base);  glEndList();  makeEraser();  /* load pattern for current 2d texture */  tex = make_texture(TEXDIM, TEXDIM);  glTexImage2D(GL_TEXTURE_2D, 0, 1, TEXDIM, TEXDIM, 0, GL_RED, GL_FLOAT, tex);  free(tex);  glClearStencil(2);  glEnable(GL_STENCIL_TEST);  /* used all the time */  glEnable(GL_CULL_FACE);  glCullFace(GL_BACK);  glutMainLoop();  return 0;             /* ANSI C requires main to return int. */}