G400 Max: 24 bit vs 32 bit color?

What's the difference between these 2 modes? I can't tell much difference in
terms of pic quality and speed.

 

32-bit color is simply 24-bit color with an added 8-bit alpha
channel. This alpha channel is for transparency, and also used
for an 8-bit grayscale mask, which is for icon or cursor
shadows, animations etc.

Rick

 

The main purpose of 32-bit colour is really to pad out the pixels so they
take up one longword. This allows much faster indexing of a pixel, speeding
up graphics at the expense of RAM used.

As an example, to get the RGB values for a given pixel in m68k code in 24
and 32 bit modes (can be coded much more effectively, but it gives an idea
of the difference in complexity):

24-bit mode 32-bit mode
; a0 = Address of display buffer in a0
; d0 = Pixel number
; d1 = return value, in 00RRGGBB format
move.l d0,-(sp) move.l (a0,d0.l*4),d1
move.l d0,d1 andi.l #FFFFFF,d1
add.l d1,d0 rts
add.l d1,d0
moveq #0,d1
move.b (a0,d0.l),d1
lsl.w #8,d1
add.b 1(a0,d0.l),d1
lsl.w #8,d1
add.b 2(a0,d0.l),d1
move.l (sp)+,d0
rts


Regards,