1. Lighting – Material Properties
Lecture 13
Mon, Sep 24, 2007

2. Material Properties
The surface “interacts” with the light as determined by the material properties:
Reflection: ambient, diffuse, specular, shininess.
Color: red, green, blue.
Use the function glMaterial*() to specify the amount of red, green, and blue reflection of each type.

3. Example // A shiny red object
float mat_ambient[] = {1.0, 0.0, 0.0, 1.0};
float mat_diffuse[] = {1.0, 0.0, 0.0, 1.0};
float mat_specular[] = {1.0, 1.0, 1.0, 1.0};
float mat_shininess = 64.0;
glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
glMaterialf(GL_FRONT, GL_SHININESS, mat_shininess);

4. Material Properties Usually we use
The ambient and diffuse material properties to determine the color and brightness of the object.
The specular material properties to determine the shininess of the object.

5. glEnable(GL_COLOR_MATERIAL)
Material Properties
OpenGL allows the programmer to make an automatic connection between the glColor() function and the material color.
glEnable(GL_COLOR_MATERIAL)
The default sets the material ambient and diffuse reflections to the values given in glColor().

6. Material Properties
Use glColorMaterial() to specify which material property will track the current color.
GL_AMBIENT
GL_DIFFUSE
GL_SPECULAR
GL_AMBIENT_AND_DIFFUSE (default)
Only one mode is active at a time.

7. Material Properties
Typically, we want only ambient and diffuse properties to track the current color.
Specular material properties are usually set to (1.0, 1.0, 1.0) regardless of the surface color.

8. Material Properties
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9. Material Emissive Light
In a similar way, we can set the amount of emissive light emitted by an object.
The following code will make an object glow a bit reddish.
float mat_emissive[] = {0.5, 0.0, 0.0, 1.0};
glMaterialfv(GL_FRONT, GL_EMISSION, mat_emissive);

10. Material Emissive Red Light
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11. Viewer Location The viewer can be either local or at infinity.
The default is at infinity.
This setting can be changed by using glLightModel*().
glLightModeli(GL_LIGHT_MODEL_LOCAL_VIEWER, GL_TRUE);

12. Infinite Viewer
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13. Local Viewer
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14. A Metallic Effect
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15. Calculating the Lighting Effect
The light contributions for each color (red, green, and blue) are summed over
All light sources (LIGHT0, …, LIGHT8)
All types of light (ambient, diffuse, specular, emissive).
Each total is clamped to 1.0.
These color levels determine the shading of the vertex.

16. Lighting and Meshes
The lighting effects are calculated only at the vertices, then interpolated across the polygon.
Suppose the brightest point of reflection should be in the center of a square.
The center will have an interpolated shading derived from the corners; the center will be no brighter than the corners.

17. Lighting and Meshes
Rather than use one large rectangle, with only 4 vertices, it is better to use a mesh of smaller rectangles, with many vertices.
The lighting will be calculated at each vertex and interpolated across a small rectangle.

18. Lighting and Meshes
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