INT32GP Graphics Programming: Tutorial #13: Lights

• To toggle between perspective and orthographic projection, press the p key.
• To toggle between a solid and a wireframe teapot, press the w key.
• To rotate the teapot around the y-axis, press the r key.
• Try resizing the window.

1. Initially, set up flat (not smooth) shading, enable lighting, and turn on GL_LIGHT0, which is associated with default RGB values for ambient light, Add the following code to the bottom of the function, initialisGL().

   glShadeModel(GL_FLAT);
   glEnable(GL_LIGHTING);
   glEnable(GL_LIGHT0);
   

2. Run the program and rotate the teapot. The appearance of the teapot is not very realistic because we also need to enable depth testing.
   • Replace glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB); void setUpGLUT(int argc,char ** argv) with the following code.
     glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);
   • Replace glClear(GL_COLOR_BUFFER_BIT); in void display() with the following code.
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   • Enable depth testing, by adding the following code to the bottom of initialiseGL().
     glEnable(GL_DEPTH_TEST);
3. Add the facility to toggle between GL_FLAT and GL_SMOOTH shading by pressing the s key.

1. Add keyboard facilities to enable and disable lighting and to turn light0 off and on.

   static int lighting=TRUE;
   static int light0=TRUE;
   
   
   case '0': light0=!light0;
             if(light0)glEnable(GL_LIGHT0);
                else glDisable(GL_LIGHT0);break;
   case 'l': lighting=!lighting;
             if(lighting)glEnable(GL_LIGHTING);
             else glDisable(GL_LIGHTING);break;
   

2. We will set up 3 lights. Add the following global definitions.

   /* manage lighting
   */
   enum {whiteLight,redLight,redLaserLight};
   GLfloat ambient[][4]={
      {0.5,0.5,0.5,1.0},{1.0,0.0,0.0,1.0},{0.05,0.0,0.0,1.0} };
   GLfloat diffuse[][4]={
      {1.0,1.0,1.0,1.0},{1.0,0.0,0.0,1.0},{0.10,0.0,0.0,1.0} };
   GLfloat specular[][4]=
      { {1.0,1.0,1.0,1.0},{1.0,0.0,0.0,1.0},{0.99,0.0,0.0,1.0} };
   GLfloat position[][4]={
      {0.0,10.0,0.0,0.0},{2.0,2.0,0.0,1.0},{2.0,2.0,0.0,1.0} };

3. Add the following function to set up the lights and call it from the top of display(), after the call to setCamera().

   void setLights(){
      int i, light=whiteLight;
      for(i=GL_LIGHT0;i<=GL_LIGHT2;i++){
         glLightfv(i,GL_POSITION,position[light]);
         glLightfv(i,GL_AMBIENT, ambient[light]);
         glLightfv(i,GL_DIFFUSE, diffuse[light]);
         glLightfv(i,GL_SPECULAR,specular[light++]);
      }
   }

4. Add keyboard facilities so that users can turn all three lights on and off.
5. Since we are using default material settings, we are not getting the full effect of the lights. We have to specify our own material.
• Add the following global definitions.

  /* manage materials
  */
  enum{whiteMaterial};
  GLfloat mAmbient[][4]={ {0.4,0.4,0.3,1} };
  GLfloat mDiffuse[][4]={ {0.5,0.5,0.5,1} };
  GLfloat mSpecular[][4]={ {0.6,0.6,0.5,1} };
  GLfloat mShine[]={ 25 };
  int current=whiteMaterial;

• Add a function to set the material.

  void setMaterial(){
     glMaterialfv(GL_FRONT,GL_AMBIENT,mAmbient[current]);
     glMaterialfv(GL_FRONT,GL_DIFFUSE,mDiffuse[current]);
     glMaterialfv(GL_FRONT,GL_SPECULAR,mSpecular[current]);
     glMaterialf(GL_FRONT,GL_SHININESS,mShine[current]);
  }
  

• Call the function from display() (after the call to set the lights).
6. What is the effect of the redLaserLight on its own? What is its effect when it is on with the white light?
7. Add a blue light, with the facility to turn it on and off.
8. What colour does the teapot appear when both the red and blue lights are on?
9. Add other materials (see Lecture #14 for some suggestions) with a keyboard facility to cycle through all the materials.