OpenGL Screencast 21: Skybox

021.c

#include "screencasts.h"

/*
 * initGlobals()
 * ------
 * Initializes the global variables.
 */
void initGlobals(void)
{
  /* WINDOW */
  windowHeight=DEF_WINDOW_HEIGHT;
  windowWidth=DEF_WINDOW_WIDTH;
  windowPosHeight=DEF_WINDOW_POS_H;
  windowPosWidth=DEF_WINDOW_POS_W;

  /* PROJECTION */
  dim=DEF_DIM;
  th=DEF_TH;
  ph=DEF_PH;
  fov=DEF_FOV;
  asp=DEF_ASP;
  ecX=DEF_ECX;
  ecY=DEF_ECY;
  ecZ=DEF_ECZ;
}

/*
 *  initSkybox
 *  ------
 *  initializes all of our textures for the skybox background
 */
void initSkybox(void)
{
  /*
    SKY_FRONT 0
    SKY_RIGHT 1
    SKY_LEFT 2
    SKY_BACK 3
    SKY_UP 4
    SKY_DOWN 5
   */
  skybox[SKY_FRONT] = loadTexBMP("txStormydays_front.bmp");
  skybox[SKY_RIGHT] = loadTexBMP("txStormydays_right.bmp");
  skybox[SKY_LEFT] = loadTexBMP("txStormydays_left.bmp");
  skybox[SKY_BACK] = loadTexBMP("txStormydays_back.bmp");
  skybox[SKY_UP] = loadTexBMP("txStormydays_up.bmp");
  skybox[SKY_DOWN] = loadTexBMP("txStormydays_down.bmp");
}


void windowKey(unsigned char key,int x,int y)
{
  /*  Exit on ESC */
  if (key == 27) exit(0);
  /*  Change field of view angle */
  else if (key == '-' && key>1) fov--;
  else if (key == '+' && key<179) fov++;

  redisplayAll();
}

void windowSpecial(int key,int x,int y)
{
  /*  Right/Left - rotate */
  if (key == GLUT_KEY_RIGHT) th += 5;
  else if (key == GLUT_KEY_LEFT) th -= 5;
  /*  Up/Down - elevation */
  else if (key == GLUT_KEY_UP) ph += 5;
  else if (key == GLUT_KEY_DOWN) ph -= 5;
  
  /*  Keep angles at +/- 360 degrees */
  th %= 360;
  ph %= 360;

  redisplayAll();
}

/*
 *  main()
 *  ----
 *  Start up GLUT and tell it what to do
 */
int main(int argc,char* argv[])
{
  initGlobals();

  /* screencast specific variables */
  windowName = "OpenGL screenscasts 21: Skybox";
  screencastID = 21;
  
  glutInit(&argc,argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
  glutInitWindowSize(windowWidth,windowHeight);
  glutInitWindowPosition(windowPosWidth,windowPosHeight);
  glutCreateWindow(windowName);

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

  initSkybox();

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

display.c

#include "screencasts.h"

/*
 *  displayInit()
 *  -------
 *  Initializes display
 */
void displayInit(void)
{
  glClearColor(1,0.0,0.0,0.0);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
  glEnable(GL_DEPTH_TEST);
  glLoadIdentity();
}

/*
 * displayEye()
 * ------
 * Set the eye position
 */
void displayEye(void)
{
  double Ex = -2*dim*Sin(th)*Cos(ph);
  double Ey = +2*dim        *Sin(ph);
  double Ez = +2*dim*Cos(th)*Cos(ph);
  /* camera/eye position, aim of camera lens, up-vector */
  gluLookAt(Ex+ecX,Ey,Ez+ecZ , ecX,ecY,ecZ , 0,Cos(ph),0);
}

/*
 *  displayReshape()
 *  ------
 *  GLUT calls this routine when the window is resized
 */
void displayReshape(int width,int height)
{
  asp = (height>0) ? (double)width/height : 1;
  glViewport(0,0, width,height);
  displayProject(fov,asp,dim);
}

/*
 * displayProject()
 * ------
 * Sets the projection
 */
void displayProject(double fov, double asp, double dim)
{
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluPerspective(fov,asp,dim/16,16*dim);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

/*
 *  display()
 *  ------
 *  Display the scene
 */
void display(void)
{
  /* setup functions */  
  displayInit();
  displayEye();

  /* Draw Scene */
  drawScene();

  /* Flush, SwapBuffers, and sanity check */
  glFlush();
  glutSwapBuffers();
  errCheck("display sanity check");
}

/*
 *  redisplayAll()
 *  ------
 *  This is called whenever we need to draw the display
 */
void redisplayAll(void)
{
  displayProject(fov,asp,dim);
  glutPostRedisplay();
}

/*
 *  drawScene()
 *  ------
 *  Draw the entire Scene
 */
void drawScene()
{
  drawSkybox(3.5*dim);
}

/*
 *  drawSkybox(double D)
 *  ------
 *  Draws the skybox around the entire screen
 */
void drawSkybox(double D)
{
  glColor3fv(white);
  glEnable(GL_TEXTURE_2D);

  /* Sides */
  glBindTexture(GL_TEXTURE_2D,skybox[SKY_RIGHT]);
  glBegin(GL_QUADS);
  glTexCoord2f(0,0); glVertex3f(-D,-D,-D);
  glTexCoord2f(1,0); glVertex3f(+D,-D,-D);
  glTexCoord2f(1,1); glVertex3f(+D,+D,-D);
  glTexCoord2f(0,1); glVertex3f(-D,+D,-D);
  glEnd();
  glBindTexture(GL_TEXTURE_2D,skybox[SKY_FRONT]);
  glBegin(GL_QUADS);
  glTexCoord2f(0,0); glVertex3f(+D,-D,-D);
  glTexCoord2f(1,0); glVertex3f(+D,-D,+D);
  glTexCoord2f(1,1); glVertex3f(+D,+D,+D);
  glTexCoord2f(0,1); glVertex3f(+D,+D,-D);
  glEnd();
  glBindTexture(GL_TEXTURE_2D,skybox[SKY_LEFT]);
  glBegin(GL_QUADS);
  glTexCoord2f(0,0); glVertex3f(+D,-D,+D);
  glTexCoord2f(1,0); glVertex3f(-D,-D,+D);
  glTexCoord2f(1,1); glVertex3f(-D,+D,+D);
  glTexCoord2f(0,1); glVertex3f(+D,+D,+D);
  glEnd();
  glBindTexture(GL_TEXTURE_2D,skybox[SKY_BACK]);
  glBegin(GL_QUADS);
  glTexCoord2f(0,0); glVertex3f(-D,-D,+D);
  glTexCoord2f(1,0); glVertex3f(-D,-D,-D);
  glTexCoord2f(1,1); glVertex3f(-D,+D,-D);
  glTexCoord2f(0,1); glVertex3f(-D,+D,+D);
  glEnd();

  /* Top and Bottom */
  glBindTexture(GL_TEXTURE_2D,skybox[SKY_UP]);
  glBegin(GL_QUADS);
  glTexCoord2f(0,0); glVertex3f(-D,+D,-D);
  glTexCoord2f(1,0); glVertex3f(+D,+D,-D);
  glTexCoord2f(1,1); glVertex3f(+D,+D,+D);
  glTexCoord2f(0,1); glVertex3f(-D,+D,+D);
  glEnd();
  glBindTexture(GL_TEXTURE_2D,skybox[SKY_DOWN]);
  glBegin(GL_QUADS);
  glTexCoord2f(1,1); glVertex3f(+D,-D,-D);
  glTexCoord2f(0,1); glVertex3f(-D,-D,-D);
  glTexCoord2f(0,0); glVertex3f(-D,-D,+D);
  glTexCoord2f(1,0); glVertex3f(+D,-D,+D);
  glEnd();

  glDisable(GL_TEXTURE_2D);
}