[AD] load_bitmap() and 24->8 conversion

[bnd25@xxxxxxxxxx]

Hi,

This problem has existed for a long time, and I guess no one reported it 
because work-arounds are possible and, at least in my case, it never really 
affected me. However, maybe it should be fixed...

Consider the following code:

BITMAP *bmp;
PALETTE pal;
allegro_init();
set_color_depth(8);
set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0);
create_my_uber1337_palette(pal);
bmp = load_bitmap("my_uber1337_true_colour_bitmap.bmp", pal);

The user obviously wants the bitmap converted to 8-bit using the palette 
passed. However, this is not what load_bitmap() does. The palette is 
initialised with a 332 palette, and then colour 0 is set to Magic Pink. 
IMHO this is a completely useless palette...

My first thought was to have load_bitmap() read in a palette for you if the 
bitmap on disk was paletted, or return a palette to you if the bitmap on 
disk was true colour. However, this is a little ugly because the meaning of 
the parameter changes depending on the file.

An alternative would be to provide some complementary functions which use 
your palette:

BITMAP *load_bitmap_conv(AL_CONST char *filename, AL_CONST PALETTE pal);
BITMAP *load_bmp_conv(AL_CONST char *filename, AL_CONST PALETTE pal);
etc.

These functions load the bitmap and convert it to 8-bit. If it's already 
8-bit, these functions 'transcolorise' it (they convert the bitmap so it 
uses the palette passed, bypassing the conversion if the palettes are 
identical).

Note that these functions would always convert to 8-bit. People use 8-bit 
sprites in true-colour modes, don't they? :) That also makes palette 
remapping possible, allowing for fast tinting and so on.

Opinions?

I should add that I don't really have the resources to work on this myself.

- entheh