Graphics Programming
TVP4020
Programmers Reference Manual
122
5.14.2
Software Writemasks
Software writemasking is normally only implemented when Hardware
writemasking is unavailable. It is controlled by the FBSoftwareWriteMask
register. The data field has one bit per framebuffer bit which when set,
allows the corresponding framebuffer bit to be updated. When reset, it
protects the bit from being written. Software writemasking is applied to
all fragments and is not controlled by an enable/disable bit. However it
may effectively be disabled by setting the mask to all 1's. If the mask is
not all 1’s, the ReadDestination bit must be enabled in the FBReadMode
register to correctly use software writemasks. See the Framebuffer
Read/Write section for details of how to enable/disable framebuffer
reads.
The software writemask MUST be set to all 1’s, except when software
writemasking is explicitly required.
5.14.3
Flat Shaded Rendering
A special P
ERMEDIA
rendering mode is available which allows rendering
of unshaded images.
Note: This method is no longer recommended on TVP4020. Other
methods of flat shading are as least as fast and are simpler to
set-up correctly. It has been included here for the benefit of
understanding legacy TVP4010 software.
•
Flat shaded primitive
•
No dithering required
•
No logical ops
•
No stencil or depth testing required
•
No alpha blending
The following are available:
•
Bit masking in the Rasterizer
•
Area and line stippling
•
User and Screen Scissor test
If all the conditions are met then rendering can be achieved by setting
the FBWriteData register to hold the framebuffer data (in raw framebuffer
format) and setting the UseConstantFBWriteData bit in the
LogicalOpMode register. All unused units should be disabled.
This mode is most useful for 2D applications or for clearing the
framebuffer when the memory does not support block writes. Note that
FBWriteData register should be considered volatile when context
switching.
Содержание TVP4020 PERMEDIA 2
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