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Graphics Programming
TVP4020
Programmers Reference Manual
64
RasterizerMod
e
See below
Defines the long term mode of operation of the
Rasterizer.
StartXDom
Signed fixed point 12.15
format
Initial X value for the dominant edge in trapezoid filling,
or initial X value in line drawing.
dXDom
Signed fixed point 12.15
format
Value added when moving from one scanline to the
next for the dominant edge in trapezoid filling.
Also holds the change in X when plotting lines so for Y
major lines this will be some fraction (dx/dy), otherwise
it is normally ± 1.0, depending on the required
scanning direction.
StartXSub
Signed fixed point 12.15
format
Initial X value for the subordinate edge.
dXSub
Signed fixed point 12.15
format
Value added when moving from one scanline to the
next for the subordinate edge in trapezoid filling.
StartY
Signed fixed point 12.15
format
Initial scanline in trapezoid filling, or initial Y position for
line drawing.
dY
Signed fixed point 12.15
format
Value added to Y to move from one scanline to the
next. For X major lines this will be some fraction
(dy/dx), otherwise it is normally ± 1.0, depending on
the required scanning direction.
Count
12 bit integer
Number of pixels in a line. Number of scanlines in a
trapezoid.
Xlimits
Xmax: 2’s complement 12
bit value in the upper
word.
Xmin: 2’s complement 12
bit value in the lower word.
Defines the X extents that the Rasterizer should fill
between. A span is rasterized if its X value satisfies:
Xmin £ X < Xmax
Ylimits
Ymax: 2’s complement 12
bit value in the upper
word.
Ymin: 2’s complement 12
bit value in the lower word.
Defines the Y extents that the Rasterizer should fill
between. A scanline is filled if its Y value satisfies:
Ymin £ Y < Ymax
RectangleOrigi
n
Y: 2’s complement 12 bit
value in the upper word.
X: 2’s complement 12 bit
value in the lower word.
Defines the origin of a rectangle primitive. The corner
of the rectangle this refers to is controlled by the
rectangle fill direction fields in the Render command.
RectangleSize
Height: 2’s complement 12
bit value in the upper
word.
Width: 2’s complement 12
bit value in the lower word.
Table 5.5
Rasterizer Control Registers
Summary of Contents for TVP4020 PERMEDIA 2
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Page 284: ...TVP4020 Programmers Reference Manual A Gouraud Shaded Triangle 275 ...
Page 292: ...TVP4020 Programmers Reference Manual Register Tables 283 ...
Page 314: ...TVP4020 Programmers Reference Manual Index 305 ...
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