public final class AMDCompressed3DCTexture extends java.lang.ObjectNative bindings to the AMD_compressed_3DC_texture extension.
Two compression formats are introduced:
- A compression format for two component textures. When used to store normal vectors, the two components are commonly used with a fragment shader that derives the third component.
- A compression format for single component textures. The single component may be used as a luminance or an alpha value.
There are a large number of games that use luminance only and/or alpha only textures. For example, monochrome light maps used in a few popular games are 8-bit luminance textures. This extension describes a compression format that provides a 2:1 compression ratio for 8-bit single channel textures.
Normal maps are special textures that are used to add detail to 3D surfaces. They are an extension of earlier "bump map" textures, which contained per- pixel height values and were used to create the appearance of bumpiness on otherwise smooth surfaces. Normal maps contain more detailed surface information, allowing them to represent much more complex shapes.
Normal mapping is one of the key features that makes the current generation of games look so much better than earlier titles. A limitation to the effectiveness of this technique is the size of the textures required. In an ideal case where every surface has both a color texture map and a normal texture map, the texture memory and bandwidth requirements would double compared to using color maps alone.
In fact, the problem is much worse because existing block based compression methods such as DXTc, ETC, and S3TC are ineffective at compressing normal maps. They tend to have trouble capturing the small edges and subtle curvature that normal maps are designed to capture, and they also introduce unsightly block artifacts.
Because normal maps are used to capture light reflections and realistic surface highlights, these problems are amplified relative to their impact on color textures. The results are sufficiently poor that game artists and developers would rather not use normal map compression at all on most surfaces, and instead limit themselves to lower resolution maps on selected parts of the rendered scene.
3DC provides an ideal solution to the normal map compression problem. It provides up to 4:1 compression of normal maps, with image quality that is virtually indistinguishable from the uncompressed version. The technique is hardware accelerated, so the performance impact is minimal. Thus, developers are freed to use higher resolution, more detailed normal maps, and/or use them on all of the objects in a scene rather than just a select few.