Computer Graphics

File Format for Defining a Material

The material properties for an object determines how the object reflects light, and therefore its perceived colour.

In this implementation an object as a whole can have a material property, and each individual face of the object may have a material. If a face does not have a material then it inherits the material of the object. If the object is not given a material, then it inherits a default material.

Note that setting the material for each face of an object considerably slows OpenGL rendering.

A material specification has the following components:

• whether it is being defined at all (0 or 1)

If the previous entry is 1, then it is followed by:

• model - whether a flat shading or smooth shading model is to be used (0=flat, 1=smooth)
• ambient reflection 0/1 r g b a, where 0=no ambient, rgb are red, green and blue intensities between 0.0 and 1.0, and a is the alpha channel for transparancy.
• diffuse reflection 0/1 r g b a, where 0=no diffuse component
• specular reflection 0/1 r g b a, where 0=no specular component
• shininess - if there is a specular component, then shininess is a positive number
• opacity = 0/1, 0 = opaque, 1 = transparant in the case of opacity = 1 then the alpha values above are used.

For example,

1
0 
1 0.2 0.2 0.2 1.0
1 0.9 0.1 0.1 1.0
0
0

means:

• there is a material being defined;
• there is no ambient reflection
• there is diffuse reflection, with the rgba values being 0.2 0.2 0.2 1.0
• there is specular reflection with the rgba values being 0.9 0.1 0.1 1.0
• The shininess is 0
• The object is opaque.