VT8601 Apollo ProMedia
Revision 1.3 September 8, 1999
-123
3D Graphics Engine Registers
7HFKQRORJLHV ,QF
:H&
:H&RRQQHFW
QQHFW
Color Parameters
Color parameters are used for Gouraud shading. They consist
of starting values, incremental along the X and Y axis. In flat
color mode, this parameter only has the starting value.
DoubleWord 0 – Initial Values
31-24 Initial Alpha Value
Initial Alpha value on main edge (left edge of
trapezoid or long edge of triangle). Unsigned integer.
23-16 Initial Red Value
Initial Red value on main edge (left edge of trapezoid
or long edge of triangle). Unsigned integer.
15-8 Initial Green Value
Initial Green value on main edge (left edge of
trapezoid or long edge of triangle). Unsigned integer.
7-0
Initial Blue Value
Initial Blue value on main edge (left edge of
trapezoid or long edge of triangle). Unsigned integer.
DoubleWord 1 – X-Axis Blue Gradient
31-0 X-Axis Blue Gradient
Gradient of Blue along the X axis over the primitive
surface. Signed 20.12 number.
DoubleWord 2 – Y-Axis Blue Gradient
31-0 Y-Axis Blue Gradient
Gradient of Blue along the Y axis over the primitive
surface. Signed 20.12 number.
DoubleWord 3 – X-Axis Green Gradient
31-0 X-Axis Green Gradient
Gradient of Green along the X axis over the primitive
surface. Signed 20.12 number.
DoubleWord 4 – Y-Axis Green Gradient
31-0 Y-Axis Green Gradient
Gradient of Green along the Y axis over the primitive
surface. Signed 20.12 number.
DoubleWord 5 – X-Axis Red Gradient
31-0 X-Axis Red Gradient
Gradient of Red along the X axis over the primitive
surface. Signed 20.12 number.
DoubleWord 6 – Y-Axis Red Gradient
31-0 Y-Axis Red Gradient
Gradient of Red along the Y axis over the primitive
surface. Signed 20.12 number.
DoubleWord 7 – X-Axis Alpha Gradient
31-0 X-Axis Alpha Gradient
Gradient of Alpha along the X axis over the primitive
surface. Signed 20.12 number.
DoubleWord 8 – Y-Axis Alpha Gradient
31-0 Y-Axis Alpha Gradient
Gradient of Alpha along the Y axis over the primitive
surface. Signed 20.12 number.
Z Value Parameters
To the Rasterization Engine, the Z value is always a 25.8
signed integer internally regardless of Z buffer depth.
It
always passes a 24-bit unsigned integer to the Pixel Engine. It
is the Pixel Engine’s responsibility to scale Z to the depth of
the Z buffer.
Z parameters are used to calculate depth
information. Z values consist of starting values, incremental
along the X and Y axis.
DoubleWord 0 – Initial Z Value
31-0 Initial Z Value
Initial Z value on main edge (left edge of trapezoid or
long edge of triangle). Signed 25.7 integer.
DoubleWord 1 – X-Axis Z Gradient
31-0 X-Axis Z Gradient
Gradient of Z along the X axis over the primitive
surface. Signed 25.7 number.
DoubleWord 2 – Y-Axis Z Gradient
31-0 Y-Axis Z Gradient
Gradient of Z along the Y axis over the primitive
surface. Signed 25.7 number.
DoubleWord 3 – Minimum Z Threshold
31-24 Reserved
................................................... ignored
23-0 Minimum Z Threshold
Minimum of Z threshold. Unsigned 24-bit integer.
DoubleWord 4 – Maximum Z Threshold
31-24 Reserved
................................................... ignored
23-0 Maximum Z Threshold
Maximum of Z threshold. Unsigned 24-bit integer.
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