Atlas Mapping

What is it? Why do it? and how hard can it be?

Atlas mapping can be put very simply as all (or most in some cases) of the textures used in a mesh on one big texture or map.

Morrowind's models all reference separate textures for each mesh part and thus has to render each one accordingly. This takes time to do in something called Draw Calls.

Each to a draw call is needed it renders the texture on the mesh which takes up valuable processor time. Processor time means a hit to the frame rate per second or FPS as no don't you have been calling it even before you knew what it meant.

Atlas mapping reduces the draw calls by completing a render in one (or very few) draw calls rather than multiple ones which improves the FPS.

The problem with Atlas mapping is the repeat or tiling of a texture. If the texture has no need to be seamless then atlas mapping is quite easy as I have done here;

This is not the models final texture but the map will stay the same.

On the other hand if it does need to be seamless then it brings up all sorts of problems when UV mapping. If you are making a new mesh you can cheat. Beams, columns, buttress's etc can be placed on seams to hide texture problems and this works very well indeed.

If it is a large continuous mesh that needs one texture that you can't divide by these cheating items, say, a roof for instance, then sometimes we have to take the hit on a draw call and use a separate texture.(Unless you have the patience and the ability to make that perfect texture - I do not).

There are ways to get around this mostly as in the texture above (the wood part). I know that to keep a nice looking texture on my finished model I'm going to need to repeat/ tile the texture horizontally at least. To cheat my way through and allow this to happen I've use a 2048x1024 seamless woo texture which allows me to go out of the natural boundaries of the texture on the horizontal.

Using my map above means that I can group all my walls and all the beams and wooden parts in one group together instead of several groups (TriShapes) thus reducing the draw calls each time me model is rendered on screen for your viewing pleasure.