TVP4020
Programmers Reference Manual
Graphics Programming
49
triangle will be excluded. This excluded edge will get drawn as part of
the lower half of the triangle.
To minimize delta calculations, triangles may be scan converted from left
to right or from right to left. The direction depends on the dominant edge
that is the edge which has the maximum range of Y values. Rendering
always proceeds from the dominant edge towards the relevant
subordinate edge. In the example above, the dominant edge is 1-3 so
rendering will be from right to left.
Subordinate Edge 1-2
Dominant Edge 1-
dXDom
Top
Trapezoid
Bottom
Trapezoid
(X1,Y1)
Subordinate Edge 2-3
dXSub 1-2
dXSub 2-3
(X2,Y2)
(X3,Y3)
Knee
Figure 5.4
Rasterizing a triangle.
The sequence of actions required to render a triangle (with a 'knee') are:
•
Load the edge parameters and derivatives for the dominant edge and
the first subordinate edges in the first triangle.
•
Send the Render command. This starts the scan conversion of the first
triangle, working from the dominant edge. This means that for triangles
where the knee is on the left we are scanning right to left, and vice
versa for triangles where the knee is on the right.
•
Load the edge parameters and derivatives for the remaining
subordinate edge in the second triangle.
•
Send the ContinueNewSub command. This starts the scan conversion
of the second triangle.
Содержание TVP4020 PERMEDIA 2
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