Material System Details

Design and implementation ideas for our material system.

Initial Features

• Add simple tests that verify the material by rendering a polygon. Currently, we don't have tests for most materials.
• Explore materials implemented using procedural textures, i.e., brick, marble, granite, wood, asphalt, etc. Later, we'll procedurally shade a city with these building blocks.
• Add an opacity/alpha map material.
• Decouple diffuse and specular components.
  • Split agi_getMaterialColor into two separate GLSL functions: agi_getMaterialDiffuseComponent and agi_getMaterialSpecularComponent.
  • Add gloss/specular map material.
  • This will slightly impact the lighting code.
• Allow the material to modify the surface normal.
  • Add a third GLSL function that materials can optionally implement called agi_getMaterialNormal that takes and returns a normal.
  • Implement a bump map material using this. Implement a normal map material too.
• Add the world-space eye direction, i.e. the vector from the camera to the fragment in world coordinates, to agi_getMaterial* (or do we only need it for agi_getMaterialDiffuseComponent initially?). Use this to implement:
  • A diffuse reflective material that uses an environment map for reflection, and a 2D texture for the diffuse component. Blend these with a reflectivity parameter.
  • A diffuse refractive material that also uses an environment map. Expose the two indices of refraction.
  • A Fresnel material - approximate, of course.
  • Include optional reflection and refractive maps for the above reflective and refractive materials, maybe Fresnel.

Full Features

• How does this fit with the effects framework for models? They should work well together.
• How do we combine multiple materials, e.g.,
  • Blend two diffuse maps based on a parameter or third map.
  • A bump and specular map.
  • A bumpy diffuse reflective surface that combines the bump map and diffuse reflection materials.
  • Crumbling bricks that combine brick and bump map materials.
• Add materials to polylines. Polylines will need to be able to compute at least 1D texture coordinates. I could see some potential for 2D and 3D coordinates as well.

Other Material Systems

• Effects frameworks like CgFX and COLLADA FX have materials as does every graphics engine under the sun, such as:
  • Three.js
  • Unity
  • C4 Engine
  • Id tech 4