I just noticed (i.e. got bitten by 
a quirk in the way that SDL deals
with 15 and 16 bit display modes.
The BitsPerPixel field in the SDL_PixelFormat struct is 16 for both 15
(eg rgb555) and 16 (eg rgb565) bit modes. You can still distinguish
between modes using the colour bitmasks.
SDL_SetVideoMode() seems to take a bitsperpixel of 15 or 16 - and no
bit masks - to distinguish between 15 and 16 bit modes.
Is this a bug or a quirk that should be documented?
Should BitsPerPixel in SDL_PixelFormat should be 15 for 15 bit modes?
Ben.–
Ben Campbell (ben.campbell at creaturelabs.com)
Programmer, Creature Labs.
http://www.creaturelabs.com
I just noticed (i.e. got bitten by a quirk in the way that SDL deals
with 15 and 16 bit display modes.
The BitsPerPixel field in the SDL_PixelFormat struct is 16 for both 15
(eg rgb555) and 16 (eg rgb565) bit modes. You can still distinguish
between modes using the colour bitmasks.
BitsPerPixel is not the depth (=the number of significant bits per pixel),
but the number of bits of storage that each pixel occupies.
SDL_SetVideoMode() seems to take a bitsperpixel of 15 or 16 - and no
bit masks - to distinguish between 15 and 16 bit modes.
The terminology is admittedly a bit vague and mixed up here. I propose
we use the X11 terms: depth = bits actually used, and bpp = bits per
pixel = bits the pixel occupies in memory. So a 32bpp mode has depth=24 bits.
SDL_SetVideoMode should take a depth parameter, not bpp (or the 15 vs 16
makes no sense).
Is this a bug or a quirk that should be documented?
Yes it should probably be clarified. Martin!
Should BitsPerPixel in SDL_PixelFormat should be 15 for 15 bit modes?
No, I think not. It isn’t really important, is it? They only differ
in the masks anyway