[winGRASS] Re: generic Windows GRASS driver

[Glynn Clements]

Mike Thomas wrote:

>     unsigned char red   = (pixel & 0x00FF0000) >> 16;
>     unsigned char green = (pixel & 0x0000FF00) >>  8;
>     unsigned char blue  = (pixel & 0x000000FF);

Ultimately this needs to use values derived from the
{red,green,blue}_mask fields from the Visual structure (the pixel
value is obtained from the RGB values using those fields), e.g.

    unsigned char red   = (pixel >> r_pos) << r_scale) & 0xFF;
    unsigned char green = (pixel >> g_pos) << g_scale) & 0xFF;
    unsigned char blue  = (pixel >> b_pos) << b_scale) & 0xFF;

That would allow the code to work on 15/16 bpp displays (X also
supports 8-bpp TrueColor visuals, but I suspect that Windows doesn't).

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