SharpScene accumulation buffer, with sixteen bitsa vailable for each of the red,green,
blue, and alpha components. Two additional banks are available for storage of texture
maps, holding up to 64K additional texels. When not configured for accumulation
operations, the accumulation buffer planes are devoted to texture storage as well.
Due to the high degree of programmability of the PowerVision Image Engines, the
utilization of the bitplanes is extremely flexible. General arithmetic and logical
functions can be performed on 8-bit and 16-bit components of any pixel bank. This
enables advanced image operations, such as blending, transparency, compositing,
convolutions, and accumulation buffering to be performed in a highly parallel
manner. The texture planes can be used as a general purpose, 64K word linear storage
area for new applications in image processing.
An additional feature of the Raster Subsystem is the fast pixel read, write, and copy.
The achievable rate for any of these operations is 18 million pixels per second, due to
a bus structure that allows concurrent reading and writing.
3.1.7 Display Subsystem
The Display Subsystem receives pixel information from the frame buffer, routes it
through the appropriate display mode, and sends it to the Digital-to-Analog
Converters for display.
Multimode Graphics Processors
Five Multimode Graphics Processors (MGPS) read the contents of the Image and
Display WID Planes concurrently. Information from the Display WID Planes
deterimines the color mode format that should be used to interpret the data from the
image bit-ptanes. The PowerVision svstem displays multiple images simultaneously,
in an overlapping window environment, in single-buffered RGB, double-buffered
RGB, single-buffered color-index, and double-buffered color-index color modes.
The MGPs allow simultaneous display of up to 16 unique window styles. This allows
users to display both static and dynamic images at will, without having to consider
the underlying color representation scheme. The MGPs position and draw the user-
definable graphics cursor or a full-screen cross hair cursor and incorporate a 64 x 28
bit auxiliary color look-up table for overlays and underlays.
Linear RGB or mapped color indexed data is read from ten VRAMs in parallel onto
the Video Bus. Data is sent through the Video Output Formatter (VOF) to be
displayed. The VOF determines the video timing used to scan out the frame buffer.
The VOF is programmed in software, thus virtually any timing is possible. This
flexibility enables PowerVision to output anv resolution, from NTSC to PAL to HDTV.
High-speed Digital-to-Analog Converters (DACS) drive the red, green, and blue
electron guns of the color display. When the Graphics Subsystem operates in RGB
color mode, the DACs receive up to 24-bits of color information for each pixel. Eight
of these bits are assigned directly to each of the red, green, and blue DACS, to yield