CMAP_FULL Translations

Some devices supported by the hpgcrx driver use a special color map organization internally to support hardware dithering. The modified color map is used on the GRX, CRX and Dual CRX. This hardware color map organization is known as modified 3:3:2 or modified 6|6|6 corresponding to the standard organizations described above. Under normal circumstances, this internal modified color map is transparent to the user.

The CRX-24, the CRX-24Z and the integrated graphics systems color configurations use the standard color maps.

On those devices that use the modified color maps in hardware, there are compatibility issues for some applications. These potential issues effect Starbase only in CMAP_FULL mode.

In most cases, Starbase hides the modified organization of the color map from the applications. However, there are some exceptions to this.

Starbase hides the color map organization by implementing a translation layer (SW_CMAP_FULL translation), where necessary, to convert from the standard 3:3:2 to modified 3:3:2, or from a standard 6|6|6 to the modified 6|6|6 on GRX/CRX. This translation layer is enabled or disabled with the GCRX_SW_CMAP_FULL gescape or when the raw parameter passed into block_write(3G) and block_read is set to TRUE. The default at the time of gopen is to enable translation.

The following sections describe the effects of this translation layer on the Starbase semantics.

Block Read and Block Write

The block_read and block_write calls hide the color map organization when enabling GCRX_SW_CMAP_FULL translation. The performance implications of GCRX_SW_CMAP_FULL translation mainly apply to these two routines. If performance is critical in this area, disable the translation with the GCRX_SW_CMAP_FULL graphics escape, and use the modified color map organization.

Index Color Attributes

Entry points which take a color attribute as a color map index value hide the color map organization if GCRX_SW_CMAP_FULL translation is enabled. This includes the define_color_table(3G) call as well as the following:

background_color_index
bf_fill_color_index
bf_perimeter_color_index
depth_cue_color_index
fill_color_index
highlight_color_index
inquire_color_table
line_color_index
marker_color_index
perimeter_color_index
text_color_index

Plane-oriented Operations

The standard 3:3:2 organization is plane-oriented, and as such, Starbase functions that operate on frame buffer planes are more predictable with the standard 3:3:2 organization than either the CRX modified 3:3:2 or any 6|6|6 color map organization. Examples of such Starbase functions are drawing_mode, write_enable, and display_enable Starbase echos which use XOR.

These display control functions (via display_enable, write_enable anddrawing_mode) do not hide the reorganized CRX color map organization. If you need display control functionality, turn off the translation with the GCRX_SW_CMAP_FULL gescape and work with the modified color map organization.

Cursors

The define_raster_echo(3G) call hides the modified CRX color map organization when SW_CMAP_FULL translation is enabled. Vector cursors do not hide the color map organization. (There is minimal impact to the resulting cursor display.)

Pattern Fills

The pattern_define call and the pattern-defining gescapes (R_DEF_FILL_PAT) hide the modified color map organization when the GCRX_SW_CMAP_FULL translation is in effect.

Background and Clear Control

When switching to or from CMAP_FULL using shade_mode(3G) with INIT, the CRX/GRX devices clear the entire display. The frame buffer is cleared to all zeros at gopen time when INIT is specified. After gopen, if the application changes the clear control to something less than the full display, and switches into CMAP_FULL with the modified 3:3:2 definition, the areas outside of the clear control will turn white since index 0 of the modified 3:3:2 color map is defined as red=green=blue=255.

When gopen is called with INIT, the default is to clear the display if shade_mode is called with INIT. When gopen is called without INIT, the default is to leave the frame buffer as is. Clearing the display when switching to and from CMAP_FULL with INIT is controlled with the GCRX_SW_CMAP_FULL gescape.