VT8601 Via, VT8601 Datasheet - Page 139

• Manufacturer Part Number: VT8601
• Description: Slot-1 / Socket-370 PCI North Bridge
• Manufacturer: Via

GEbase + A4 – Texture Color .......................................... RW
GEbase + A8 – Texture Palette Data .............................. WO
An internal counter is used in loading the texture palette.
Writing to the Texture register (GEbase+A0) resets the
counter to 0. Writing to the Texture Palette Data register
writes the data to the place pointed to by the counter then
increments the counter by 1. Each write writes two entries into
the palette.
GEbase + AC – Texture Boundary .................................. RW
Revision 1.3 September 8, 1999
31-24 Alpha
31-16 Texel n+1
31-22 Maximum V
21-12 Minimum V
23-0 Texture Color Key
15-0 Texel n
11-8 Reserved
4-3
2-0
7
6
5
7HFKQRORJLHV ,QF
Constant alpha value when there is no alpha in the
texture format
Texture transparency color (888 RGB)
Reverse Texture Format
Texture Cache
Texture Map Shift
Compressed Texture Format
Dither Shift
:H &
:H &R R QQHFW
000 Disable LOD dithering
001 100% LOD dithering
010 80% LOD dithering
011 60% LOD dithering
100 40% LOD dithering
101 20% LOD dithering
11x -reserved-
00 No compression
01 DXT1 format
10 DXT2 format
11 -reserved-
0
1
0
1
0
1
QQHFW
Disable
Enable
Disable
Enable
Disable
Enable
........................................ always reads 0
-133
Texture Filtering
Texture data read back from the Memory Interface first goes
through palette translation if the texture is palettized. The
texture is then converted into common internal 8888 ARGB
format. If the texture doesn’t have alpha data, then a constant
alpha value is used. If the texture color key is enabled and the
texture color matches the key, set alpha to 0. Bi-linear or tri-
linear filtering is then performed on RGB and alpha. If the
color key is enabled and the result alpha is 0, the
corresponding pixel should be discarded. This is done by
attaching a validity bit with texture data passed from the
Texture Engine to the Data Path. It should be noted that
filtering depends on the LOD value.
different filter may be applied. In bi-linear filtering, if the
texel nearest to the texture coordinate is masked by the color
key, then the texel is considered as masked. Otherwise, the
texel is considered not masked.
VT8601 Apollo ProMedia
3D Graphics Engine Registers
When LOD < 0, a