Decreased memory size/bandwidth requirements = increased performance &
better image quality
The obvious benefit that texture compression provides is that a given amount
of texture data can be stored using significantly less memory. This is most
critical when texturing out of the local frame buffer. Equally important is the
fact that the memory and bus bandwidth required to read textures is greatly
reduced, translating too much improved performance over AGP.
System memory and AGP bus bandwidths are finite resources. With compression, the
accelerator can take better advantage of these resources. As more compressed
textures can be stored in local graphics memory, the use of local texturing is
maximized. Reduced bandwidth also enables performance boost when texturing over
AGP or from local frame buffer. The peak transfer rate for AGP-2x is 512MB/s.
With 4x to 8x compression, you have the equivalent of 2.0GB/s to 4.0GB/s.
Larger and more numerous textures
Texture compression can allow for larger textures. While smaller, less
detailed texture maps typically result in surfaces that look blurry or blocky,
larger textures let the application provide more surface detail. Texture
compression can also allow for a greater variety of textures to be used at any
given time, permitting more varied scenes.
When texturing out of local frame buffer memory, compression may free up enough
memory to increase the display resolution or to perform triple buffering. A
higher resolution display provides a smoother, more detailed look, while triple
buffering can improve performance by allowing the rendering engine to start on a
new scene without waiting for the display's vertical sync. The use of triple
buffering can result in a significant increase in frame rate (typically 30%).
Mip-mapping
The extra memory available with compressed textures allows for the use of Mip-maps
even with the added memory storage required (30%) over the base texture map
level. Mip-maps help to reduce aliasing artifacts visible on textured surfaces
that span significant distances. Without Mip-maps, a pixels on an object far
away may be associated with several texels from the original texture map. Low-pass
filtering is used to retain the information, while not introducing unwanted
artifacts (shimmering, crawling pixels). Real time filtering is expensive,
so staged Mip-map levels can be used that are pre-computed filtered images,
dramatically lowering the filtering complexity.
