Lighting

1
Lighting

• Jason Goffeney
• 4/5/2006

2
Lighting

• Lighting along with perspective viewing adds to
  the illusion of viewing 3D on a 2D screen

3
Lighting

• There are really 2 parts to any lighting system
• How the lights are defined
• How are the components of light set up?
• How many lights?
• Which type of lights?
• How objects in the scene are defined
• How are normals set up?
• What are the material properties?

4
Lighting

• By default with GL lighting turned off there is
  still white ambient light. But if GL lighting
  is enabled without a light set then there is no
  lighting at all.

5
Enabling Lighting

• To enable the lighting system
• glEnable(GL_LIGHTING)
• To turn on a single light
• glEnable(GL_LIGHT0)

6
Enabling Lighting

• The first default light has the following
  properties
• It has no ambient component
• It has white diffuse and specular components
• It is located at (0, 0, 1) on the coordinate
  system

7
Components of Light

• Ambient light is considered sourceless and
  effects everything in the scene equally.
• It does not add any depth to a scene.

8
Components of Light

• Diffuse light emanates from a source and has a
  direction.
• The part of an object hit directly will be more
  brightly lit than parts where the light glances
  off.

9
Components of Light

• Specular light is very directed light that
  reflects back to the viewer.
• It results in the highlight seen on shiny objects
  like metal or plastics.
• Specular light works with the material properties
  of an object. If the object is not shiny then
  specular does nothing.

10
Setting the Light Components

• The basic function for setting lighting
  components is
• glLightfv(gl light, gl light property, values)
  

Such as, light_position where light_position
0.0, 0.0, -200.0
GL_LIGHT0 GL_LIGHT1
GL_POSITION GL_AMBIENT GL_DIFFUSE
11
Setting the Light Components

• Setting the position of the light.
• Declare an array holding the x, y, z position of
  light
• GLfloat light_position 0.0, 0.0, -200.0
• Set the glLight function.
• glLightfv(GL_LIGHT0, GL_POSITION, light_position)

12
Setting the Light Components

• Setting the light color components.
• Declare the arrays holding the r, g, b, w color
  components.
• GLfloat light_ambient 0.1, 0.1, 0.1, 1.0
• GLfloat light_diffuse 1.0, 1.0, 0.0,
  1.0
• GLfloat light_specular 1.0, 1.0, 1.0, 1.0
• Set the glLight function.
• glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient)
• glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse)
• glLightfv(GL_LIGHT0, GL_SEPCULAR,
  light_specular)

13
Setting the Light Components

• Be sure to enable the lights when you are
  finished!
• Other controllable properties
• Light Attenuation
• Spotlight Properties
• Light Direction

14
Setting the Light Components

• A light is basically another object in the scene
  and can be affected by transformations.
• To keep a light in one place, set its position in
  glInitialize and forget about it.
• To move the light set its position after some
  transformation within glPaint.

15
Defining Materials

• Material properties are the other half of the
  model.
• The light components interact with the material
  properties for the final result.
• Light and material colors combine
• Material properties create dull or shiny objects

16
Defining Materials

• Materials can be defined once during
  initialization to affect all scene objects or
  before an object is drawn to affect it and
  anything after it until another call is made.

17
Defining Materials

• The function
• glMaterialfv( object face, material property,
  values)

Which side of the object faces should be included
in the model calculations GL_FRONT GL_BACK GL_FRO
NT_AND_BACK
GL_AMBIENT GL_DIFFUSE GL_AMBIENT_AND_DIFFUSE GL_SP
ECULAR GL_SHININESS GL_EMISSION
18
Material Properties

• Several of the properties complement their
  lighting counterparts. The others
• GL_SHININESS A single float value used with the
  specular component to determine how tight the
  highlight it. The higher the value the smaller
  the spot.
• GL_EMMISION Allows the material to appear as if
  it is internally lit (kind of).

19
Setting Material Properties

• Setting the values
• GLfloat mat_specular 1.0, 1.0, 1.0, 1.0
• GLfloat mat_diffuse 0.0, 0.3, 0.3, 1.0
• GLfloat mat_shininess 10.0
• GLfloat mat_emissive 0.5, 0.5, 0.0, 1.0
• Calling the functions
• glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse)
• glMaterialfv(GL_FRONT, GL_SPECULAR,
  mat_specular)
• glMaterialfv(GL_FRONT, GL_EMISSION,
  mat_emissive)
• glMaterialfv(GL_FRONT, GL_SHININESS,
  mat_shininess)

20
glColorMaterial

• Once you have set your materials you may wish to
  change one for your objects using glColor.
• Set the property to change for glColorMaterial
  within your initialization
• glColorMaterial(GL_FRONT, GL_DIFFUSE)
• glEnable(GL_COLOR_MATERIAL)
• Now every call to glColor will change the Diffuse
  property of the material of the next object