Re: [AD] Component ordering and mixing color depths

[Robert Jr Ohannessian <rohannessian@xxxxxxxxxx>]

Eric Botcazou wrote:
> > If you are using a 32-bpp overlay, then bmp_color_depth(screen) == 32, no?
>
>
> No, I can use 32-bpp overlays with bmp_color_depth(screen) == 15 on my ATI 
> card.

If you're not using the overlay as the screen bitmap, then what for?



> I thought you were pushing for an arbitrarily fixed RGBA layout... it's not 
> the case, is it ?

No! I was asking if we should do something like:

int set_gfx_mode() {
        call_driver_specific_code();

	if (depth == 16) {
		_r_shift_16 = /* whatever the driver gives us */
                _r_shift_32 = scale16_to_32[r_shift_16];
                /* repeat for all components */
         }
}

This way, the RGBA component ordering is the same in between 16 and 
32-bpp bitmaps, but the ordering itself (RGB vs BGR) can vary depending 
on the driver/platform/hardare.

Code is so much less ambiguous ^_^

In the end, I realized that users may have set a 32-bpp mode, loaded 
some bitmaps, then switched to a 16-bpp mode which may have a different 
component ordering from the 32-bpp mode. If set_gfx_mode would reset the 
32-bpp component shift values, then both color conversion and blending 
would come out wrong.

So I coded up two functions, one for blending RGB over RGB (or BGR over 
BGR - it's the same code), and one for RGB over BGR (or BGR over RGB).


--
- Robert Jr Ohannessian
http://bob.allegronetwork.com/
The peer will come and reset your connection. RUN WHILE YOU STILL CAN!