Converting between color formats
In general, Allegro is designed to be used in only one color depth at a
time, so you will call set_color_depth() once and then store all your
bitmaps in the same format. If you want to mix several different pixel
formats, you can use create_bitmap_ex() in place of create_bitmap(), and
call bitmap_color_depth() to query the format of a specific image. Most of
the graphics routines require all their input parameters to be in the same
format (eg. you cannot stretch a 15-bit source bitmap onto a 24-bit
destination), but there are some exceptions:
blit() and the rotation routines can copy between bitmaps of any format,
converting the data as required.
draw_sprite() can draw 256-color source images onto destinations of any
draw_character_ex() _always_ uses a 256-color source bitmap, whatever the
format of the destination.
The draw_trans_sprite() and draw_trans_rle_sprite() functions are able to
draw 32-bit RGBA images onto any hicolor or truecolor destination, as long
as you call set_alpha_blender() first.
The draw_trans_sprite() function is able to draw an 8-bit alpha channel
image over the top of an existing 32-bit image, as long as you call
Expanding a 256-color source onto a truecolor destination is fairly fast
(obviously you must set the correct palette before doing this conversion!).
Converting between different truecolor formats is slightly slower, and
reducing truecolor images to a 256-color destination is very slow (it can be
sped up significantly if you set up the global rgb_map table before doing
- bestfit_color - Finds a palette color fitting the requested RGB values.
- rgb_map - Look up table to speed up reducing RGB values to palette colors.
- create_rgb_table - Generates an RGB mapping table with lookup data for a palette.
- rgb_to_hsv - Converts color values between the HSV and RGB colorspaces.