VT8601 Datasheet, PDF (114/144 Pages) List of Unclassifed Manufacturers – Single-Chip Slot-1 / Socket-370 PCI North Bridge With Integrated AGP 2D / 3D Graphics Accelerator and Advanced Memory Controller

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Geometry Primitives
The ProMedia supports the following geometry primitives:
line, and polygon. Each geometry primitive can be further
modified for 3D, shading, and texture mapping. A different
mechanism, called sequential loading, performs the geometry
primitive set up operation.
Loading Mechanism
There are two ways to set up a geometry primitive, random
loading and sequential loading. Like the random access, the
order is not important in random loading, but the address is.
Writing to a certain address in the register space causes a
certain pre-determined action. On the other hand, like
sequential access, the order decides the data semantics in
sequential loading. The ProMedia uses sequential loading in
the Rasterization Engine and the Setup Engine.
In the ProMedia, parameters don’t have to be the fixed
addresses. ProMedia parameters are treated as a data stream
and interpreted based on the type of primitive. Parameters
must be set in a stream as follows:
6WUHDP %\WHV


3
3

3Q
'DWD _{6WUHDP +HDG 3DUDPHWHU  3DUDPHWHU  3DUDPHWHU }  _{3DUDPHWHU Q}
P1 is the number of bytes for parameter 1, P2-P1 for
parameter 2, etc.
For the Rasterization Engine, there are 9 kinds of parameters:
Bresenham Edge, DDA Edge, Z, Texture, Perspective, Color,
Specular/fog Start, Specular, and Fog. Parameters must
appear in the following order:
Edge(Major), Texture, Perspective, Color, Specular/fog Start,
Specular, Fog, Z, Edge(Minor)
There are two kinds of edges and only one kind can appear in
a parameter stream. Bresenham Edge can only appear in 2D
primitives (without values for iterators).
For the Setup Engine, there is only one kind of parameter:
vertex. However, each primitive could have one or three
vertices. The size of each vertex is variable depending on
triangle attribute.
Only polygon and line primitives can use this sequential
loading feature. In the following sections, each primitive is
addressed in detail.
VT8601 Apollo ProMedia
Revision 1.3 September 8, 1999
-108
3D Graphics Engine Registers