The 3-D Color Graphics Processor is available in four configurations:
This adapter contains a 24-bit deep main frame buffer, 4 auxiliary planes dynamically configurable as overlay/underlay planes, and a 24-bit deep z-buffer. It contains a 4096-entry output color map (color lookup table) in onemap mode and sixteen 256-entry color maps in multimap mode.
In double buffer mode, the 24 main bitplanes are divided into a pair of buffers of 12 bits each. In RGB mode, these 12 bits are treated as 444 RGB, that is, as 4 bitplanes for storing red values, 4 bitplanes for storing green values, and 4 bitplanes for storing blue values. To maintain greater color fidelity and prevent color aliasing, dithering is automatically enabled, thus giving a greater perceived dynamic range (that is, more than 4 bits of accuracy for each band). The truncation of the nonleading bits and their convolution with the dithering matrix is performed automatically, and there is no modification of any of the drawing subroutines. The lrectwrite subroutine should be used for bit block transfers in RGB modes; it always assumes 888 RGB, and the appropriate bit-shifting to 444 is performed internally and automatically.
In double-buffered color map mode, all 12 bits of each buffer access the color map directly. Use the rectread and rectwrite subroutines for bit block transfers.
The 4 auxiliary bitplanes can be dynamically configured as 4 overlay planes, as 2 overlay and 2 underlay planes, or as 4 underlay planes.
Because this adapter does not have an alpha-blending buffer, the blendfunction subroutine returns without performing any action. Depth comparisons cannot be performed against the color buffer, therefore, the zsource subroutine returns without performing any action. The only valid value for the zsource subroutine is ZSRC_DEPTH.
This adapter contains a 24-bit deep main frame buffer and 4 auxiliary planes dynamically configurable as overlay/underlay planes. There is no z-buffer. It contains a 4096-entry output color map (color lookup table) in onemap mode and sixteen 256-entry color maps in multimap mode. The color maps are usable by the main frame buffer.
The main overlay/underlay and RGB/color map control functions operate identically as on the 24-bit processor with z-buffer option. The only difference between this adapter and the previously described adapter is that there is no z-buffer with this adapter. Therefore, none of the functions that control the z-buffer are operable; all return without performing any operation. These subroutines are as follows:
The action of the czclear subroutine is modified because this adapter does not have a z-buffer.
This adapter contains an 8-bit deep main frame buffer, 2 auxiliary planes dynamically configurable as overlay/underlay planes, and a 24-bit deep z-buffer. It contains a 256-entry output color map (color lookup table) in onemap mode and sixteen 16-entry color maps in multimap mode. The color maps are usable by the main frame buffer.
This adapter contains only 8 bits of main color buffer. It can be placed into RGB mode and into color map mode, and the operation of the subroutines that do this are unmodified.
In single-buffered RGB mode, pixels are written in 332 RGB: that is, with 3 bits of red, 3 bits of green, and 2 bits of blue. Dithering is always enabled. Because dithering uses the lesser significant bits to determine the color written into the frame buffer, the perceived accuracy of information stored in the frame buffer exceeds 8 bits and approaches 11 or 12 bits (as perceived by the human eye). (For more information on dithering, see "Working in Color Map and RGB Modes".)
In single-buffered color map mode, all 8 bits are used to address the color map. In onemap mode, the color map is accessed as a single map of 256 entries. In multimap mode, it is accessed as 16 maps of 16 entries each.
This adapter supports double buffering only in color map mode. In this case, the main color buffer is divided into a pair of buffers of 4 bits each. In onemap mode, only the lowest 16 entries in the color map are addressed. When double buffered, this adapter should be operated in multimap mode. Double buffering in RGB mode is not available.
This adapter has 2 auxiliary planes, which can be configured as 2 overlay planes or 2 underlay planes.
This adapter does not have gamma ramps. The gammaramp subroutine is not emulated and returns without performing any function.
Because the sizes of the color maps supported on this adapter differ from those on the 24-bit adapter, the actions of the onemap, multimap, and setmap subroutines are modified.
Because this adapter does not have an alpha blending buffer, the blendfunction subroutine returns without performing any action. Depth comparisons cannot be performed against the color buffer; therefore, the zsource subroutine returns without performing any action. The only valid value for the zsource subroutine is ZSRC_DEPTH.
This adapter contains an 8-bit deep main frame buffer, 2 auxiliary planes dynamically configurable as overlay/underlay planes. There is no z-buffer. It contains a 256-entry output color map (color lookup table) in onemap mode and sixteen 16-entry color maps in multimap mode. The color maps are usable by the main frame buffer.
The main, overlay/underlay, and RGB/color map control functions operate almost identically as those on the 8-bit with z-buffer option. The only difference between this adapter and the one previously described is that there is no z-buffer. Because there is no z-buffer, none of the functions that control the z-buffer are operable; all return without performing any action. The affected functions are as follows:
The action of the czclear subroutine is modified because this adapter does not have a z-buffer.
Because this adapter has no alpha blending buffer, the blendfunction subroutine returns without performing any action.