User's Manual

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0
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13.20. GFXRENDERSTATE_BOOLEAN_ENA_2
DWord Bit Description
0 31:29 Client : 03h – Render Processor
28:24 3DState24 : 04h
23:18 Reserved : 00h
17 Mapping Cache Enable Mask : 1 = Update; 0 = Do Not Update
16 Mapping Cache Enable : 1 = Enable, 0 = Disable (default)
Any change made to the Mapping Cache Enable state variable must be followed by a
GFXCMDPARSER_FLUSH instruction to cause the hardware to flush the 3D pipeline.
15 Alpha Dither Enable Mask : 1 = Update; 0 = Do Not Update
14 Alpha Dither Enable : 1 = Enable, 0 = Disable (default)
13 Fog Dither Enable Mask : 1 = Update; 0 = Do Not Update
12 Fog Dither Enable : 1 = Enable, 0 = Disable (default)
11 Specular Dither Enable Mask : 1 = Update; 0 = Do Not Update
10 Specular Dither Enable : 1 = Enable, 0 = Disable (default)
9 Color Dither Enable Mask : 1 = Update; 0 = Do Not Update
8 Color Dither Enable: 1 = Enable, 0 = Disable (default)
7:4 Reserved: 0h
3 Frame Buffer Write Enable Mask : 1 = Update; 0 = Do Not Update
2 Frame Buffer Write Enable : 1 = Enable, 0 = Disable (default)
1 Z Buffer Write Enable Mask : 1 = Update; 0 = Do Not Update
0 Z Buffer Write Enable : 1 = Enable, 0 = Disable (default)
The frame buffer write enable feature can be used to reliably render coplanar (layered) polygons. An
example of this type of layering would be to render a window on a wall. With a 16-bit z buffer, there is
not sufficient precision to render this type of scene with consistent priority. Some pixels of the window
will be intermixed with some pixels of the wall, due to precision inaccuracies.