VT8601 Apollo ProMedia
Revision 1.3 September 8, 1999
-109
3D Graphics Engine Registers
7HFKQRORJLHV ,QF
:H&
:H&RRQQHFW
QQHFW
Polygon
General polygons can only be drawn by directly using the
Rasterization Engine. In the ProMedia, all polygons must be
Y-monolithic, meaning, when walking from the vertex with
minimal Y to the vertex with maximum Y, the Y coordinates
of the vertices are monolithically increased.
A polygon is
drawn by drawing a series of segments:
Sequence Content
0
Drawing Command (Polygon)
1
Full Polygon Segment
2
Polygon Segment (Full or Partial)
3
Polygon Segment (Full or Partial)
….
….
n
Polygon Segment (Full or Partial) or a Null Primitive
A partial segment consists of only one primitive type and one
minor edge parameter.
A full segment consists of one
primitive
type,
edge
parameter(s),
and
interpolation
parameters (Z, color, texture, etc.). The rule is whenever a
new major edge is in the segment a full segment must be used,
otherwise a partial segment has to be used.
Most bit fields in primitive type define the data to be loaded to
Rasterization Engine. If the “Re-load” bit is set, they also
define the data set to be passed to Pixel Engine. The primitive
type of the first and only the first segment must have the “Re-
load” bit set to signal Rasterization Engine the data set to be
passed to Pixel Engine. The primitive type of the last and
only the last segment must have the “Last” bit set to signal the
end of the sequence. The last of the primitive can be a Null
primitive (others must be polygon).
Null primitive has no
parameter.
This mechanism can be used to draw a single polygon, as well
as multiple polygons with the same attributes (e.g. 3D texture
mapped).
All that is required is that somewhere in the
sequence we pass a full segment with starting edges of a new
polygon.
The following example shows how to draw two shaded
polygons.
Sequence Content
0
Drawing Command
1
Full Segment including
Primitive Type: Re-loading, Major & minor edge, color
Major edge L1
Color Parameter for L1
Minor edge L2
2
Partial Segment including
Primitive Type: minor edge
Minor Edge L3
3
Full Segment including
Primitive Type: Major edge, color
Major Edge L4
Color for L4
4
Partial Segment including
Primitive Type: Minor edge
Minor Edge L5
5
Full Segment including:
Primitive Type: Major & minor edge, color, negative scan
direction
Major edge L6
Color Parameter for L6
Minor edge L7
6
Partial Segment including:
Primitive Type: Minor edge, “Last”
Minor Edge L8
/
/
/
/
/
/
/
/
The following sections are about complete segments (a full
segment with both major and minor edges) with different
attributes. A normal full segment may not have the minor
edge parameter. A partial segment has no other parameters
except the minor edge.
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