1. Lighting and Shading
Lab 8:

2. Shading models
Shading refers to how the lighting equations are applied to a rasterized poly.
OpenGL supports two shading models:
GL_ SMOOTH.
GL_FLAT.

3. Smooth Model & Flat Model

4. Polygon shading
GL_SMOOTH: Lighting is evaluated at each vertex, and pixel coolers are linearly
interpolated across polys. This is more expensive, but it looks much better.
glShadeModel(GL_SMOOTH);

5. Smooth Model glBegin(GL_TRIANGLES); glEnd(); void display (void) {
glShadeModel(GL_SMOOTH);
glColor3f(1,0,0);
glVertex2f(5,5);
glColor3f(0,1,0);
glVertex2f(25,5);
glColor3f(0,0,1);
glVertex2f(5,25);
glEnd(); }

6. Gouraud shading
GL_FLAT: Lighting is evaluated once per poly, and the resulting colour value is
used for the whole thing.
glShadeModel(GL_FLAT);

7. Types of lighting implemented
1) Ambient:
No source point; affects all polys independent of position, orientation and viewing angle; used as a ‘fudge’ to approximate 2nd order and higher reflections.
GLfloat ambient0[] = {1, 0, 0, 1}; //red,green,blue,alpha
2) Diffuse:
Light scattered in all directions after it hits a poly; dependant upon incident angle. (GL_DIFFUSE is (1.0, 1.0, 1.0, 1.0) for GL_LIGHT0, ) The default value for any other light (GL_LIGHT1, ... , GL_LIGHT7) is (0.0, 0.0, 0.0, 0.0).
GLfloat diffuse0[] = {1, 0, 0, 1};
3) Specular:
‘Shininess’ ; dependant upon incident and viewing angles. GL_SPECULAR is (1.0, 1.0, 1.0, 1.0) for GL_LIGHT0 and (0.0, 0.0, 0.0, 0.0) for any other light.
GLfloat spedular0[] = {1, 1, 1, 1};
4) Emissive:
Makes a poly appear as though it is glowing; does not actually give off light.
GLfloat light0_pos[] = {1.0, 2.0, 3.0, 1.0};

8. Different types of light

9. the alpha value can be safely ignored.

10. Types of lighting implemented

11. Types of lighting implemented

12. Enable & Disable
opengl has two important functions called glEnable(GL_LIGHTING) and glDisable(GL_LIGHTING).
while these functions don't enable or disable anything in particular, they are reliant on the parameter passed to them. so in other words, you will be using these functions a lot when programming in opengl to turn a particular feature on or off.

13. Exercise
void init(){ glClearColor(1.0, 1.0, 1.0, 0.0); //glShadeModel(GL_SMOOTH); glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); } void display(){ // Create light components GLfloat ambientLight[] = { 1.0f, 0.0f, 0.0f, 1.0f }; GLfloat diffuseLight[] = { 0.8f, 0.8f, 0.8, 1.0f }; GLfloat specularLight[] = { 0.9f, 0.9f, 0.9f, 1.0f }; GLfloat position[] = { -8.5f, 5.0f, -10.0f, 1.0f }; // Assign created components to GL_LIGHT0 glLightfv(GL_LIGHT0, GL_AMBIENT, ambientLight); glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuseLight); glLightfv(GL_LIGHT0, GL_SPECULAR, specularLight); glLightfv(GL_LIGHT0, GL_POSITION, position); glClear(GL_COLOR_BUFFER_BIT); glColor3f(1.0, 1.0, 1.0); glLoadIdentity(); gluLookAt(0, 0, 5, 0, 0.0, 0.0, 0.0, 1.0, 0.0); glutSolidSphere(1.5,30,10); //glutSolidTeapot(1.5); glFlush();

14. Exercise void main(int argc, char** argv){ glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(800, 500);
glutInitWindowPosition(100, 100);
glutCreateWindow("");
init();
glutDisplayFunc(display);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-1, 1, -1, 1, 1.5, 20);
glMatrixMode(GL_MODELVIEW);
glutMainLoop(); }