TVP4020
Programmers Reference Manual
Graphics Programming
101
via the FastFillEnable bit in the Render command register. The block
color is 64 bits wide; normally the same values are used in the upper
and lower halves of the register so they are both set with one register,
FBBlockColor. If different data is required in both halves of the register,
use the FBBlockColorUpper and FBBlockColorLower registers. The
data put in the color registers should be of the raw framebuffer format.
When using the framebuffer in 8 bit packed mode, the data should be
repeated in each byte. When using the framebuffer in packed 16 bit
mode, the data should be repeated in the top 16 bits.
Note that due to restrictions in the way that the memory devices
implement block fills, a packed 24 bit RGB framestore may only use
block fills for colors that have all bytes in the pixel set to the same value.
When uploading images the UpLoadData bit can be set to allow color
formatting. See sections §5.12.6 for more details.
5.10.3
Patching
Data in the framebuffer can use patched addressing to improve
performance under certain circumstances. However, only non-visible
data is normally patched. Patch mode organizes data for efficient
drawing of scanline primitives; it also helps line drawing. This form is
typically used in the localbuffer, see §5.5.4, for patching the depth buffer.
The SubPatch mode re-organizes data for efficient texture operations;
see section §5.8.5. SubPatchPack mode is used when 4 bit textures are
loaded as 8 bits i.e. the subpatch packing takes into account the 2 texels
per byte.
5.10.4
Packed Copies
Packed copies move 32 bits at a time even though the real pixel size
may be 8, 16, or 24 bits. The PackedDataLimits register holds the left
and right X coordinates for the destination area of the screen in the
native pixel format. Any pixels outside this area are not plotted. The
relative offset field in the FBReadMode register specifies the number of
pixels that the source data has to be adjusted to align with the
destination data. The relative offset field is also available in the
PackedDataLimits register, the value from the last register loaded takes
effect.
5.10.5
Image Downloads
An image download can be performed in one of four ways. It can be
achieved by loading the data in standard color format into the Color
register and using the Color Format unit to organize it into the
framestore format. Or it can be achieved by loading the data in raw
framebuffer format either into the Color register or the FBData register.
The former requires that the Color Format unit is disabled whilst the
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