OpenGL Screencast 18: Overlays

018.c

#include "screencasts.h"

/*
 *  main()
 *  ----
 *  Start up GLUT and tell it what to do
 */
int main(int argc,char* argv[])
{
  initializeGlobals();
  /* screencast specific variables */
  windowName = "OpenGL screenscasts 18: Overlays";
  screencastID = 18;
  toggleAxes = 0;
  toggleAnimation = 0;

  glutInit(&argc,argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
  glutInitWindowSize(windowWidth,windowHeight);
  glutInitWindowPosition(450,350);
  glutCreateWindow(windowName);

  glutDisplayFunc(display);
  glutReshapeFunc(displayReshape);
  glutKeyboardFunc(windowKey);
  glutSpecialFunc(windowSpecial);

  initializeTextures();
  initializeObjs();
  timer(toggleAnimation);

  redisplayAll();
  glutMainLoop();
  return 0;
}

draw.c

/*
 * drawOverlay()
 * ------
 * Our overlay is just a 2D picture placed over the 3D scene
 */
void drawOverlay(void)
{
  if (toggleOverlay) {
  glDisable(GL_LIGHTING);
  // Save transform attributes (Matrix Mode and Enabled Modes)
  glPushAttrib(GL_TRANSFORM_BIT|GL_ENABLE_BIT);
  // Save projection matrix and set unit transform
  glMatrixMode(GL_PROJECTION);
  glPushMatrix();
  glLoadIdentity();
  glOrtho(-asp,+asp,-1,1,-1,1);
  // Save model view matrix and set to identity
  glMatrixMode(GL_MODELVIEW);
  glPushMatrix();
  glLoadIdentity();
  // Draw bottom with texture
  glColor3f(1,1,1);
  glEnable(GL_TEXTURE_2D);
  glBindTexture(GL_TEXTURE_2D,currentTexture);
  glBegin(GL_QUADS);
  glTexCoord2d(0,0);glVertex2f(-2,-1);
  glTexCoord2d(1,0);glVertex2f(+2,-1);
  glTexCoord2d(1,1);glVertex2f(+2, 0);
  glTexCoord2d(0,1);glVertex2f(-2, 0);
  glEnd();
  glDisable(GL_TEXTURE_2D);
  // Draw the inside in grey
  glColor3f(0.6,0.6,0.6);
  glBegin(GL_QUADS);
  // Left
  glVertex2f(-2,-1);
  glVertex2f(-2,+1);
  glVertex2f(-8,+1);
  glVertex2f(-8,-1);
  // Right
  glVertex2f(+2,-1);
  glVertex2f(+2,+1);
  glVertex2f(+8,+1);
  glVertex2f(+8,-1);
  // Left overhead
  glVertex2f(-2.00,+0.8);
  glVertex2f(-2.00,+1);
  glVertex2f(-0.02,+1);
  glVertex2f(-0.02,+0.9);
  // Right overhead
  glVertex2f(+2.00,+0.8);
  glVertex2f(+2.00,+1);
  glVertex2f(+0.02,+1);
  glVertex2f(+0.02,+0.9);
  // Middle divider
  glVertex2f(-0.02,+1);
  glVertex2f(+0.02,+1);
  glVertex2f(+0.02,+0);
  glVertex2f(-0.02,+0);
  glEnd();
  //  Reset model view matrix
  glPopMatrix();
  //  Reset projection matrix
  glMatrixMode(GL_PROJECTION);
  glPopMatrix();
  //  Pop transform attributes (Matrix Mode and Enabled Modes)
  glPopAttrib();
  if (toggleLight) glEnable(GL_LIGHTING);
  }
}



/*
 * drawScene()
 * ------
 * Draws the scene with everything we need in it
 */
void drawScene(void)
{
  int i;
  drawAxes();
  drawParameters();
  currentTexture = textures[TEX_DEFAULT];
  drawLight();
  currentTexture = textures[TEX_CRATE];
  for (i = 0; i < Length(cubes); i++)
    drawCube(cubes[i]);
  /* This must be drawn last */
  currentTexture = textures[TEX_VENUS];
  drawOverlay();
  currentTexture = textures[TEX_DEFAULT];
}