Lighting in OpenGL
An Introduction
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Prof. David Bernstein
James Madison University
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Computer Science Department
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bernstdh@jmu.edu
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Parts of the Process
- Specify normal vectors
- Specify material properties
- Create and position light sources
- Specify properties of the lighting model
- Enable lighting and light sources
Specifying Normal Vectors
- Function:
- Approaches:
- Face-by-face
- Vertex-by-vertex
Specifying Normal Vectors (cont.)
An Example
openglexamples/lighting/lighting.c
(Fragment: normals)
Specifying Material Properties
- The Function:
-
void glMaterial*(GLenum face, GLenum name, TYPE value)
- where
GLenum is GL_FRONT,
GL_BACK, or GL_FRONT_AND_BACK
- Specifying the Color of the Material (for Different Kinds of Reflection/Light):
- Name:
GL_AMBIENT, GL_DIFFUSE,
GL_AMBIENT_AND_DIFFUSE, or
GL_SPECULAR
- Value: RGBA color
- Specifying the Specular Exponent:
- Name:
GL_SHININESS
- Value: A
GLfloat
- Specifying the Emissive Color of the Material:
- Name:
GL_EMISSION
- Value: RGBA color
Specifying Material Properties (cont.)
An Example
openglexamples/lighting/lighting.c
(Fragment: material)
Some Materials
openglexamples/lighting/materials.h
Creating and Positioning Light Sources
- The Function:
-
void glLight*(GLenum light, GLenum name, TYPE value)
- where
light is GL_LIGHT0 ...
GL_LIGHT7
- Type of Reflection/Light:
- Name:
GL_AMBIENT, GL_DIFFUSE, or
GL_SPECULAR
- Value: RGBA color
- Position of the Light:
- Name:
GL_POSITION
- Value: A 3D or 4D point
- Attenuation:
- Name:
GL_CONSTANT_ATTENUATION,
GL_LINEAR_ATTENUATION, or
GL_QUADRATIC_ATTENUATION
- Value: A
GLfloat
Light Sources (cont.)
- Spotlights:
- You can instruct a light source to emit a cone of light
by setting additional parameters
- Size of the Arc:
- Name:
GL_SPOT_CUTOFF
- Value: An angle (180.0 is the default which corresponds to
no cutoff)
- Direction:
- Name:
GL_SPOT_DIRECTION
- Value: A 3D point
- Exponent:
- Name:
GL_SPOT_EXPONENT
- Value: A
GLfloat
Light Sources (cont.)
An Example
openglexamples/lighting/lighting.c
(Fragment: lightsource)
Specifying the Lighting Model
- The Function:
-
void glLightModel*(GLenum name, TYPE value)
- Ambient Light:
- Name:
GL_LIGHT_MODEL_AMBIENT
- Value: RGBA color
- Specular Angles:
- Name:
GL_LIGHT_MODEL_LOCAL_VIEWER
- Value:
GL_TRUE for a local viewer
GL_FALSE for a viewer at infinity
- Number of Sides:
- Name:
GL_LIGHT_MODEL_TWO_SIDE
- Value:
GL_TRUE to light both sides
or GL_FALSE to light the front
- Different Specular and Ambient/Diffuse Color:
- Name:
GL_LIGHT_MODEL_COLOR_CONTROL
- Value:
GL_SINGLE_COLOR or
GL_SEPARATE_SPECULAR_COLORS
Specifying the Lighting Model (cont.)
An Example
openglexamples/lighting/lighting.c
(Fragment: lightingmodel)
Enabling Lighting and Lights
- Enabling Lighting in General:
- Enabling Specific Lights:
-
void glEnable(GLenum light)
- where
light is GL_LIGHT0 ...
GL_LIGHT7
Enabling Lighting and Lights (cont.)
An Example
openglexamples/lighting/lighting.c
(Fragment: enable)
A Complete Example
Using a Sphere
openglexamples/lighting/sphere.c
Another Complete Example
Using a File Containing the Model
openglexamples/lighting/solidmodel.c
There's Always More to Learn