Texas Instruments TVP4020 PERMEDIA 2, Справочное руководство

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TVP4020
Programmers Reference Manual
Graphics Programming
43
No parameters are corrupted by the calculations so parameter sharing
between primitives is simply achieved by not re-loading those
parameters. For example if the first triangle in a triangle strip is loaded
into V0, V1 and V2, then the next triangle will load V0, the next V1, etc..
This is shown below.
below:
T1
T2
T3
T4
0
1
2
0
1
2
Figure 5.2 Triangle Mesh.
The vertices are automatically sorted so any vertex can be associated
with any vertex store.
Similarly a triangle fan may be implemented initially loading V0, V1 and
V2 and then cycling through loading V1 and V2 as shown below (note
that T1 and T5 share a vertex which is loaded first in V1 and then in V2):
T1
T2
T3
T4
T5
0
1/2
2
1
2
1
Figure 5.3 Triangle Fan.
Individual triangles, strips, or fans may be backface culled such that
triangles that face away from the viewer are not drawn. Detection of
backfacing triangles is done by the sign of the area of the triangle, but
whether positive or negative areas should be rejected depends on the
definition of the triangle format (whether the vertices are considered to
go clockwise or counter-clockwise). It may also vary when meshed
primitives are drawn, such a strip where the sign of the area alternates
triangle by triangle. When backface culling is enabled in the Delta Unit,
the sign to reject may be set for each triangle as it is drawn.
Lines are handled slightly differently in that only V0 and V1 are used.
The direction of the line is defined as part of the command. Hence a line
may run either from V0 to V1 or from V1 to V0. A polyline may be drawn
by loading the first vertex into V0, the second vertex into V1, the third
vertex into V0, the fourth vertex into V1 etc..