Texturing Opengl Terrain?

Question

What is the best way to texture terrain made from quads in OpenGL? I have around 30 different textures I want to have for my terrains (1 texture per terrain type, so 30 terrain types) and would like to have smooth transitions between any two of the terrains.

I have been doing some browsing on the web and found that there are many different methods, including 3d texturing, Alpha channels, blending, and using shaders. However, which of these is the most efficient and can handle the amount of textures I am looking to use? For example: This popular answer describes how to use some techniques, but since the mixmap only has 4 properties (RGBA) and so can only support 4 textures.

I should also note that I know nothing about shaders, so non-shader required techniques would be preferable.

Answer 1

Since you linked to an answer that describes texture splatting , and its question mentions the game Oblivion, I can provide some additional insight into that.

Basic texture splatting with an RGBA mixmap only supports four textures per terrain quad, but you can use different sets of textures for different quads. Oblivion divides its terrain into squares (called "cells") of 32 grid points (192 feet) per side, and each cell defines its own set of four terrain textures. So you can't have lots of texture diversity within a small area, but you can easily vary your textures over larger regions. If you prefer, you can define texture sets for smaller regions, even individual quads, at the expense of using more memory.

If you really need more than four textures in a quad, you can use multiple mixmaps. For each additional one, you just do another texture lookup to get four more blending factors, and blend in four more textures on top of the results from the previous mixmap. You can scale up to as many textures as you want, again at the expense of memory.

Texture splatting can be tricky to combine with with LOD techniques on the height map, because when a single low-detail terrain quad represents a group of high-detail quads, you have to sample several different mixmaps for different regions of the big quad. Oblivion sidesteps that problem by using texture splatting only for full-detail terrain; distant cells, rendered at lower resolution, use precomputed textures produced by the editor, which does the splatting and downscaling in advance.

Answer 2

One alternative to texture splatting is to use a clipmap to render a " megatexture ". With this approach, you have a single large texture that represents your entire terrain, and you avoid filling up your RAM by loading different parts of it with only as much detail as is actually needed to render it based on the viewer's current position. (Distant parts of the terrain can't be seen at full detail, so there's no need to load them at full detail.)

The advantage of this approach is its artistic freedom: you can place fine details anywhere you want in the texture, without regard to the vertex grid. The disadvantage is that it's rather complex to implement, and the entire clipmap has to be stored somewhere , probably in a big file on disk, so that you can load parts of it into RAM as needed.