Intel 815 Variable Length Vertex Formats for Rendering Instructions, Vertex Attribute Comments

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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13.1.6.Variable Length Vertex Formats for Rendering Instructions

The GC supports variable length vertex formats. These formats are determined, by enable bits contained in the variable length vertex format (VLVF) instructions. The following table specifies the attributes associated with each vertex. The order of the attributes must be strictly observed.

For any attribute that is defined as not present, the value of the corresponding attribute from the last triangle of last packet will be used for the triangles in this packet. However, in the case of strip and fan primitives, the vertex numbers rotate from one primitive to the next primitive (e.g., the third vertex of one triangle will become the first vertex of the next triangle). Therefore, the re-used attribute value from the last primitive will not be guaranteed to be on the same vertex of the next primitive. In this case, undesired results may occur. It is recommended to turn off features that have the corresponding attributes disabled (e.g., if no texture coordinate is send, then turn off texture mapping feature).

Vertex Attribute	Comments
X Position	Required for every vertex
Triangle Edge V2–V0 Enable	Required only on the first vertex of a triangle and on each new vertex,
	which defines a triangle when processing strips and fans.
Triangle Edge V1–V2 Enable	Required only on the first vertex of a triangle and on each new vertex,
	which defines a triangle when processing strips and fans.
Triangle Edge V0–V1 Enable	Required only on the first vertex of a triangle and on each new vertex,
	which defines a triangle when processing strips and fans.
Y Position	Required for every vertex
Z Position	Optional
Z Bias	Optional
Reciprocal of W	Optional
Diffuse Color (Alpha, Red, Green and	Optional
Blue)
Specular Color/Fog Factor	Optional
Texture Coordinate Set 0	Optional
Texture Coordinate Set 1	Optional

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