To facilitate high quality textured imagery, SkyWriter utilizes a technique called Mip
Mapping. Mip Map is from Latin, meaning "many maps". This process involves the generation
of pre-filtered lower resolution versions of each texture to enable the application of textures
which are very close in size to the polygon to which they are being applied.
220.127.116.11 Texture Memory
Since the texture mapping functions for SkyWriter are performed by the parallel image engines
in the Raster Subsystem, each image engine must have its own, unique copy of every texture
currently active such that there are no memory contention problems when applying the same
texture simultaneously to multiple pixels in different areas of the screen.
Each pipeline of the SkyWriter system is independent, having its own texture memory and
processors. In each Raster Subsystem, there are 40 image engines operating upon the full
frame buffer resolution of 1280x1024. Upon each individual raster board, there are 20 image
engines divided across that same resolution and arranged in a matrix 5 across and 4 down.
Dividing the horizontal and vertical resolutions of the frame buffer (1280x1024) by the image
engine matrix width and height (5x4), we get a maximum texture resolution of 256x256 texels
with a maximum depth of 32 bits (RGBA). This is the largest resolution of an individual
texture whether or not the Mip Mapping capability is used. All textures must be defined as
equal width and height with texel dimensions limited to powers of two.
A SkyWriter system can hold up to seven 128x128 texel textures simultaneously in each
pipeline. These textures may be paged in dynamically from main memory by the texture
manager in the operating system, but there is some overhead associated with this operation due
to the data transfer time, so it is not recommended that applications exceed the maximum on-
line texture count for real-time performance.