User's Manual

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0
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13.13. GFXRENDERSTATE_MAP_ALPHA_BLEND_STAGES
The Rendering Engine supports three map color blend stages for the alpha channel. Any of these stages
may perform an operation utilizing the alpha channel from up to two texels from the Mapping Engine,
the iterated alpha and/or a constant color.
Figure 40. State Variable Relationships
Coordinate Sets Map Information
Blending Stages
Texels
The following equations are supported by each blending stage.
Blend Equation Description
Alpha
out
= Arg1 Select Arg1
Alpha
out
= Arg2 Select Arg2
Alpha
out
= Arg1 * Arg2 Modulate
Alpha
out
= Arg1 * Arg2 * 2 Modulate and Multiply by 2
Alpha
out
= Arg1 * Arg2 * 4 Modulate and Multiply by 4
Alpha
out
= Arg1 + Arg2 Add
Alpha
out
= Arg1 + Arg2 - 0.5 Add Signed (Excess 128)
Alpha
out
= α
Iterated
* Arg1 + (1 - α
Iterated
) * Arg2 Linearly Blend using Iterated Alpha
Alpha
out
= α
Factor
* Arg1 + (1 - α
Factor
) * Arg2 Linearly Blend using Alpha Factor
Alpha
out
= α
Texel0
* Arg1 + (1 - α
Texel0
) * Arg2 Linearly Blend using Texel0’s Alpha
Alpha
out
= α
Texel1
* Arg1 + (1 - α
Texel1
) * Arg2 Linearly Blend using Texel1’s Alpha