Graphics Programming
TVP4020
Programmers Reference Manual
102
latter ignores this unit. Alternatively, the data can be loaded as some
other raw format into the FBSourceData register and have the
Texture/Fog/Blend unit convert it into the internal color format. The
Color Format unit can then convert it into the arrangement to be stored
in the framebuffer. Both techniques require setting up the Rasterizer
appropriately.
5.10.6
Fast Texture Download
Normal texture download is done as an image download. This involves
setting up the Rasterizer to draw a rectangle and changing the state of a
number of units. This is a good way to load the texture if any processing
needs to be done on it, such as color format conversion, color space
conversion or patching.
If the texture is held on the host in the raw framebuffer format, the fast
texture download approach can be used. The TextureDownloadOffset
register holds the base address of the framebuffer using 32 bit pixel
addressing. The TextureData register holds the texture data in raw
framebuffer format 32 bits at a time. The load of this register is ignored
by all other units in the pipeline so no state needs to be saved and
restored. Following the receipt of each TextureData value, the
TextureDownloadOffset value is incremented. If this register is read, it
returns the current count, not the original value.
If fast download is used, the texture map on the host must be in exactly
the format it will be stored in memory, including any color formatting,
byte swapping, or address patching. If a texture will be loaded several
times, it can be downloaded as an image the first time using all
formatting controls, and then uploaded again as a raw image for later
use.
Using this technique, framebuffer writes do not need to be enabled.
5.10.7
Hardware Writemasks
Hardware writemasks, if available, are controlled using the
FBHardwareWriteMask register. If the framebuffer memory devices
support hardware writemasks, and they are to be used, then software
writemasking should be disabled (by setting all the bits in the
FBSoftwareWriteMask register). This will result in fewer framebuffer
reads when no logical operations or alpha blending is needed.
If the framebuffer is used in 8 bit packed mode, then an 8 bit hardware
writemask must be repeated in all 4 bytes of the FBHardwareWriteMask
register. If the framebuffer is in 16 bit packed mode then the 16 bit
hardware writemask must be repeated in both halves of the
FBHardwareWriteMask register.
Summary of Contents for TVP4020 PERMEDIA 2
Page 1: ...Texas Instruments TVP4020 PERMEDIA 2 Programmer s Reference Manual Issue 4 ...
Page 284: ...TVP4020 Programmers Reference Manual A Gouraud Shaded Triangle 275 ...
Page 292: ...TVP4020 Programmers Reference Manual Register Tables 283 ...
Page 314: ...TVP4020 Programmers Reference Manual Index 305 ...
Page 315: ...Index TVP4020 Programmers Reference Manual 306 Index ...
Page 323: ...Index TVP4020 Programmers Reference Manual 314 ...