[GRASS5] Cell driver

[Glynn Clements]

Reinhard Brunzema wrote:

> I still have color problems with the CELL driver. Displaying floating
> point maps with the CELL driver produces maps with less colors than
> displaying it with the XDRiVER.

1. The CELL and PNG drivers are both limited to 8 bits per pixel (256
colours), but XDRIVER uses the actual depth of the display.

2. displaylib handles colours differently for integer and FP maps.

For FP maps, the net result is that D_set_colors always uses a palette
which evenly samples the RGB colour space. This will result in much
lower colour resolution than a palette which is limited to the map's
colour table.

NB: on a 24-bpp display, D_set_colors only provides 15-bpp resolution
(before this "feature" was added, D_set_colors would attempt to create
a palette containing 16 million colors).

The bottom line is that the problem is inherent in the way that
displaylib handles colours for FP maps. Currently, the only workaround
is to convert maps to integer for display.

-- 
Glynn Clements <glynn.clements at virgin.net>