VT8601 Via, VT8601 Datasheet - Page 137

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

GEbase + 7C – Alpha ........................................................ RW
GEbase + 84 – Bit Mask .................................................... RW
Revision 1.3 September 8, 1999
31-16 Reserved
15-8 Source Constant Alpha
31-0 Bit Mask
7-0
7HFKQRORJLHV ,QF
Destination Constant Alpha
One bits indicate that the corresponding color bit will
not be written to the frame buffer.
:H &
:H &R R QQHFW
QQHFW
........................................ always reads 0
-131
GEbase + 80 – Alpha Function ........................................ RW
31-24 Reserved
19-16 Alpha Test Function
15-8 Reference Alpha Value
7-4
3-0
23
22
21
20
Alpha Write
This bit should be set in 8-bit and 16-bit color modes.
Constant Source Alpha
Constant Destination Alpha
Result Alpha
Destination Blending Factor
Source Blending Factor
0000 Never accept the pixel
0001 Accept if alpha < reference alpha
0010 Accept if alpha == reference alpha
0011 Accept if alpha <= reference alpha
0100 Accept if alpha > reference alpha
0101 Accept if alpha != reference alpha
0110 Accept if alpha >= reference alpha
0111 Always accept the pixel
1xxx -reserved-
0000 (0,0,0,0)
0001 (1,1,1,1)
0010 (RS,GS,BS,AS)
0011 (1,1,1,1) - (RS,GS,BS,AS)
0100 (AS,AS,AS,AS)
0101 (1,1,1,1) – (AS,AS,AS,AS)
0110 (AD,AD,AD,AD)
0111 (1,1,1,1) – (AD,AD,AD,AD)
1xxx -reserved-
0000 (0,0,0,0)
0001 (1,1,1,1)
001x -reserved-
0100 (AS,AS,AS,AS)
0101 (1,1,1,1) – (AS,AS,AS,AS)
0110 (AD,AD,AD,AD)
0111 (1,1,1,1) – (AD,AD,AD,AD)
1000 (RD,GD,BD,AD)
1001 (1,1,1,1) - (RD,GD,BD,AD)
1010 (F,F,F,1); F = min (AS, 1-AD)
1011 -reserved-
11xx -reserved-
0
1
0
1
0
1
0
1
Disable................................................... default
Enable. Draw each pixel with a blended alpha
value if alpha blending is enabled. Otherwise
draw with source alpha (the upper byte of the
Foreground Color register if not available).
Disable .................................................. default
Enable
Disable .................................................. default
Enable
The result of blending ........................... default
Source alpha
........................................ always reads 0
VT8601 Apollo ProMedia
3D Graphics Engine Registers