Here is the system for creating, categorizing, and naming the terrain blend preset images. It's designed to give a useful and uniform core set of presets, allow for expandability without creating disorganized chaos.
The terrain system is expanded to include alpha blending between two textures. The includes the ability to control the alpha blend in real time in Radiant. First you need to build special two stage alpha blend shaders like the one displayed below.
The surfaceparam nolightmap statement tells q3map not to calculate a light map for the terrain brush. The qer_editorimage statement with two texture names tells Radiant to display the both textures as a single shader in the texture window. This second texture name is an optional parameter.
The first texture in the qer_editorimage statement appears on the left in the Radiant texture window and the second texture appears on the right in the Radiant texture window. In addition, the first texture in the qer_editorimage statment must be the first stage texture and the second texture in the qer_editorimage statment must be the second stage texture.
The first stage of the shader renders the first texture with verterx lighting and the second stage renders the second texture on top of the first using the alpha blend data created in Radiant. The second stage also applies vertex lighting to the second texture.
Once a two stage alpha blend shader has been created, the alpha blend on a terrain brush is editable in real time.
Preset blends may also be applied to terrain brushes.
Blend Preset Image Specifications
The shader name for blend presets must be blends/presetimagefilename (the shader name following "blends/" must be identical to the Targa image's filename so Radiant can find the image from the shader's name.
Here are the basic blend types and methods:
Blend Preset shaders are completely separate from the Terrain shaders. Every blend preset is a shader that blends between with 2 base images referenced in a separate terrain shader entry. The first is the "A" texture and the second is the "B" texture. The blend is from "A" to "B" when in normal mode, and from "B" to "A" when Inverse Blend is activated.
The actual blend texture must be a 9x9 24-bit targa file. Even though depicted as a hue neutral (grayscale) image, the blend must be in the red, green, and blue channels. Each blend preset shader must also have a QEReditorimage that represents the blend. While terrain blend preset images are 9x9 pixels, corresponding with the verts of a terrain tile, this is too small to see in the editor and so QEReditorimages for blend preset shaders need to be 64x64 so it is viewable in Radiant without changing any settings.
The procedure to make a QEReditorimage for blend presets in PhotoShop is: