The Future of Triangles Part 2: X-Plane 8

X-Plane 8 provides a useful baseline for rendering technology:

• It is finished and unchanging.
• Its use of shaders is very minimal, so even lower-end hardware can show the "X-plane 8 model" of lighting.
• X-Plane 8 rendering is completely supported in X-Plane 9.  (That is, turn off shaders, and OBJs should look the same in X-Plane 8 and 9.)

So what do we have, and is it any good?  Well, we have:

• Per-vertex lighting.  Lighting is calculated per vertex, and interpolated between vertices.
• Very limited materials.  Basically you can use attributes to set emissive lighting (so your day texture stays bright when back-lit, like taxiway signs) and shininess (to induce white specular hilites).  The shininess ratio isn't very flexible, but it does match what the built-in ACF shiny property does.
• Very fast vertex output within a batch.

I looked at some nice third party planes before writing this up, and one thing became clear: X-Plane can output a lot of vertices in an object if they are batched, and authors are using this aggressively.  The advantage of just using a lot of vertices is: curved surfaces look round, the errors that are induced by per-vertex lighting are less ugly, and the object looks the same everywhere (because this path isn't dependent on having pixel shaders).

The big weakness of the current situation is that you have to burn a lot of vertices to get close to per-pixel lighting, particularly for very shiny surfaces.  I saw at least one plane (I do not recall who authored it) that just had more triangles in the engine nacelles than you could imagine.  They look beautiful even in X-Plane 8 - great specular hilites.  But that eats into your vertex budget pretty severely - it's not a technique that you could use for every static airplane on a tarmac at LAX.