VT8601 Via, VT8601 Datasheet - Page 117

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

Triangle
Triangles can be drawn using the Polygon Mechanism
described above. Additionally, triangles can also be drawn by
using the Setup Engine if they meet certain criteria. Triangles
and polygons can also be freely mixed in a drawing sequence.
The ProMedia supports stand-alone triangles as well as a
triangle list in a sequence as follows:
Each primitive consists of a triangle attribute and one or three
vertices. The order of the data in each primitive is: Triangle
Attribute, Vertex 0, Vertex 1 (optional), Vertex 2 (optional).
Whether vertices 1 and 2 are to be loaded depends on the
Triangle Attribute. Writing to BA+192 triggers a loading
sequence in the Setup Engine. The order of the data in a
vertex is: Z, RGBA, UV, W, XY. Not every one has to appear
in every vertex. Whether a particular item is present in a
vertex is decided by the Triangle Attribute. For example, the
Data in a stream for a texture mapped triangle strip may look
like: Triangle Attribute, U0V0, X0Y0.
Due to the limited precision of the setup engine, only triangles
smaller than a certain size will be passed. Software will only
pass triangles smaller than 64x128 or 128x64 to the hardware.
Also, delta values of RGBAUVZ across a triangle will be less
than 128. There is no limitation on the delta of W since it is
impossible to exceed 1.
Line
Parameters for line primitives are very similar to their polygon
counter-parts. The differences are as follows:
There are only major edge parameters.
All the dXm values (dRm, dUm, etc.) are ignored.
The following example shows these differences for a texture
mapped primitive:
Using the same mechanism for multiple polygons, multiple
lines can also be drawn by issuing one drawing command.
Revision 1.3 September 8, 1999
Sequence Content
Sequence
…
0
1
2
3
1
0
1
2
3
4
7HFKQRORJLHV ,QF
:H &
:H &R R QQHFW
Drawing Command (Polygon)
Triangle primitive
Triangle primitive
Triangle primitive
…
Triangle primitive
Polygon Content
Drawing Command
Primitive Type
Major Edge
Texture Parameter
Minor Edge
QQHFW
Line Content
Drawing Command
Primitive Type
Major Edge
Texture Parameter
-111
Synchronization
Reset and status operations can be performed in any order and
at any time including in the middle of another operation.
However, be aware of the consequence (reset) and what to
expect (status).
Generally, Drawing Environment and Frame Buffer Control
operations should be performed before the drawing operation
to take effect.
The primitive operation is considered atomic; i.e., no other
operation (except for status and reset) can be performed inside
a Geometry Primitive operation.
Functional Blocks
The ProMedia hardware is divided into 6 major functional
blocks. They are:
Each functional block conceptually works independently of
other blocks. The term "Graphics Engine (GE)” indicates the
combination of the Setup Engine, the Rasterization Engine,
and the Pixel Engine.
Bus Interface
The bus interface block connects the AGP bus on one side and
the GE and VGA on the other side.
Bus Interface (BI)
VGA core (VGA)
Setup Engine (SE)
Rasterization Engine (RE)
Pixel Engine (PE)
Memory Interface (MI)
VT8601 Apollo ProMedia
3D Graphics Engine Registers