Выдержка из оригинальной справки. (NDL Gamebryo 1.1)
Detail Maps are RGB maps that define high-frequency detail to be overlaid on a base texture. An example of the need for detail maps is often seen in so-called "First-person shooter" games, when the player walks up very close to a wall while facing it. With just a base texture, most applications cannot afford infinite detail in the map (since that would require huge textures), so the filtering produces a blurred, soft image. This is jarring to players who had been drawn into believing in the otherwise detailed game world. Detail Maps can alleviate this by using an important observation: when the camera is close enough to a surface that it looks blurry, they can only see a small part of the Base Map at a time.
Enter the Detail Map.
Generally applied at a much higher wrapping frequency than the Base Map (often 16x to 64x), the Detail Map only becomes visible when the camera moves close enough that the base texture would be blurry. However, by the time the camera is that close, the Detail Map is at a level such that the pixel-to-texel ratio is almost one, avoiding any blurriness. In some ways, it is similar to the effect of a Dark Map, using two small textures to create the appearance of one very large texture. In fact, these techniques can be used together (easily affordable on reasonably powerful hardware), to create textures that appear to be enormous. For example, a 64x64 Detail Map repeated 32 times over a Base Map that is itself repeated 16 times over a Dark Map gives an overall texturing effect that appears to be 64 times 32 times 16 — effectively, what appears to be a 32,768 x 32,768 pixel texture.
Note that Detail Mapping, unlike the other forms of multitexturing mentioned thus far, is an optional effect — a given renderer on a given piece of 3D hardware may not be able to support the effect. As a result, applications must be prepared to handle the fact that on low-end hardware, the Detail Map will be omitted. The best way to prepare for this is to understand how a Detail Map works.
Detail Maps are applied using a so-called "multiply 2X" mode. The color of the Base Map and the color of the Detail Map are multiplied together. The result is multiplied by two. The Detail Map may thus darken or brighten the Base Map. If the Detail Map is ½ brightness, the brightness of the Base Map will be unchanged. If the Detail Map is fully white, the color of the Base Map will be doubled. The best way to ensure that the effect will look as similar as possible with and without Detail Map support is to create a Detail Map whose colors are centered about ½ brightness. In this way, when the object is viewed at a distance, it will appear the same with or without the Detail Map. A common way to create such a texture is to create a noise texture with a range from 0 to ¼ brightness, and then add a constant 3/8 brightness to each texel. The resulting texture will have a mean of ½ and amplitude of ¼.
