The idea of glass objects is to let you make translucency that works from any view angle. To make multiple layers of glass, the trick is to use pairs of one-sided triangles. The glass (visible from the inside only) goes first, then the glass (visible only from the outside) goes second. All of this goes into the object with the "glass" property in Plane-Maker.
One side benefit of the two-triangle approach is that the inside and outside of the windows can be tinted differently.
Having glass objects does three things for us architecturally:
- It takes pressure off the interior cockpit object. The interior cockpit is the only object that can have manipulators, so texture space in the interior cockpit object is quite valuable. By allowing translucency in an attached object, you can put your window textures somewhere else and save texture space for the cockpit object.
- It gets around the current weirdness where the interior cockpit object is drawn last but the exterior cockpit object is drawn first. The glass object is always drawn last. Period.
- It sets us up someday for some kind of shadowing scheme in the cockpit. This is a bit pie in the sky, but most pixel-based shadowing algorithms go a bit bonkers on translucent geometry; by flagging the whole object as "glass" we can simply omit it from shadow calculations.
Now that there are attached objects, people are modeling a lot more of the airplane, the usual approach is to have all 3-d present all the time, so that a roaming camera won't reveal missing parts of the airplane.