Lecture 6

Lighting

Introduction• What is light?

• How do we percept colors?

• Lights in OpenGL

Different Types of Light• Ambient

• Diffuse

• Specular

Defining Lights in OpenGL

• Defining Light Source• Defining Material• Defining Light Model

Note: glColor will NOT work when using light in OpenGL

Light Source• Light sources are:

– Directional: • Source resides in infinity• Light rays are parallel• Example: Sun.

– Positional• Source resides in local scene• It radiates all directions by default unless

restricted by defining a spot light• Example: Desk lamp

Defining Light Source

Adding Light Source

void glLightv(GLenum light, GLenum pname, TYPE *param);

Example:GLfloat light_ambient[] = { 0.0, 0.0, 1.0, 1.0}; glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);

Enabling Light• glEnable(GL_LIGHTING)• glEnable(Light Source)

– Eight light source (0-7)

• Specifying shade model– glShadeModel(GL_SMOOTH)

Be Aware of Defaults• When lighting is enabled, all the default

values for all lights are loaded as shown in the table, unless you cancel them.

• Use lights other than light0 if you want them to be cancelled by default.

• Lights [1-7] have most of their default RGB values black.

Pitfall• When you use translate/rotate, it

applies to light direction and position as well.

• Solution: Use push/pop matrix if you don’t want your light sources to be affected.

Light Position/DirectionGLfloat light_position[] = { x, y, x, w };

W : Defines if the light source resides in infinity or in local scene.X, y, z: Location of light if light source resides in local view Or,

Direction of light if the light source resides in infinity.

Next Class• Review

• Discussion for Midterm

• Troubleshooting

Questions?