Object Materials - Some Rough Thoughts

First, we're not going to get an OBJ materials model in 930.  930 is crammed full of stuff, and I don't want to add anything more!  I am not sure when we'll get OBJ materials, or even if this is how it will go down.  But this is what I am thinking:

• Materials will be controlled on the "batch" level, that is, by using ATTRibutes.  You'll be able to change materials mid-object.
• Materials will be grouped into "material classes" - the material class will be mutually exclusive.  So if we have a metal material class and a "plastic" material class, you won't be able to combine them.
• There will be some kind of material class that corresponds to the current behavior, and all of the existing attributes will keep working; probably there will be a newer, cleaner way to state in an OBJ what you can already do now.
• You will set all material class parameters at once.  This simplifies the syntax and assures that we don't have any strange mix & match combinations.

To this last point, consider that OBJ currently has a number of strange cases where you can set attributes that don't have any effect.  For example, you can set the shininess while drawing the cockpit texture (which is unlit).  Code like this has historically been buggy, partly because it's not necessarily obvious to a human reader what the object should do.

I do not yet know how normal and gloss maps fit in.  Normal maps may be useful to multiple material classes; gloss maps are somewhat material class specific (in that if a material class has no concept of gloss, the gloss map is moot).  It is definitely advantageous to pack a normal map and gloss map into a single texture (a la blender).

The main point of material classes is to create the infrastructure for complex extensions to the material system in a clean way.  Adding additional attributes creates an NxN problem - for each new attribute I add, I have to consider how it interacts with every other attribute.  By comparison, a new material class by definition shuts all other material classes off.