TVP4020
Programmers Reference Manual
Graphics Programming
109
See Appendix D for details of how to calculate delta values.
// Set DDA for Gouraud shaded mode
colorDDAMode.UnitEnable = PERMEDIA_ENABLE
colorDDAMode.Shade = PERMEDIA_GOURAUD_SHADE_MODE
ColorDDAMode(colorDDAMode)
// For lines we need only start values and dominant edge
// deltas
RStart()
// Set-up the red component start value
dRdyDom()
// Set-up the red component increment
GStart()
// Set-up the green component start value
dGdyDom()
// Set-up the green component increment
BStart()
// Set-up the blue component start value
dBdyDom () // Set-up the blue component increment
5.12
Texture/Fog/Blend
The Texture/Fog/Blend unit applies effects to the interpolated color. The
effects are applied in the order: texture then fog then blend.
5.12.1
Texture Application
There are two major types of texture application, one suitable for RGB
applications and one suitable for Ramp applications; Ramp applications
use RGB textures and framebuffer format but are limited to a white light
source. The enable bit in the TextureColorMode register and the
TextureEnable bit in the Render register must both be enabled before
texture will be applied.
RGB Texture Application
This is referred to elsewhere as the OpenGL type of texture application.
It can be done in one of three ways.
In copy mode, the texture color replaces the current fragment color.
In decal mode the texture color is blended with the fragment color using
the texture alpha value:
C
f
= C
t
A
t
+ C
f
(1-A
t
)
A
f
= A
f
where: C
f
is the fragment color, C
t
is the texture color , A
f
fragment
alpha and A
t
is the texture alpha. If the texture alpha value is one, decal
becomes the same as copy.
In modulate mode the color components are multiplied together:
Содержание TVP4020 PERMEDIA 2
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