[SDL] 32 bit Surface: Colorkey won't work

Engines and Middleware Programming

Started by Modred October 17, 2011 05:31 PM

2 comments, last by rip-off 12 years, 6 months ago

Modred

100

Author

October 17, 2011 05:31 PM

Short and simple: I create a 32 bit surface with alpha - channel (R8G8B8A8), and colorkeys stop working.



#include <SDL/SDL.h>

#include <iostream>

using namespace std;

int main(int argc, char **argv)

{

  SDL_Init(SDL_INIT_EVERYTHING);

  SDL_SetVideoMode(800, 480, 16, SDL_SWSURFACE);



  //SDL_Surface *src = SDL_CreateRGBSurface(0, 400, 400, 32, 0xff<<16, 0xff<<8, 0xff, 0);

  SDL_Surface *src = SDL_CreateRGBSurface(0, 400, 400, 32, 0xff<<24, 0xff<<16, 0xff<<8, 0xff<<0);





  SDL_SetColorKey(src, SDL_SRCCOLORKEY, SDL_MapRGB(src->format, 255, 0, 128));

  SDL_FillRect(src, NULL, SDL_MapRGB(src->format, 255, 0, 128));



  SDL_BlitSurface(src, NULL, SDL_GetVideoSurface(), NULL);

  SDL_Flip(SDL_GetVideoSurface());

  SDL_Delay(2000);

}

...would I use the first, commented line to create the surface, everything works.

rip-off

11,000

October 17, 2011 08:44 PM

SDL_BlitSurface does not support simultaneous alpha channel and colour keying. One solution is to modify the colour keyed pixels to have a transparent alpha value.

blog | twitter

Modred

100

Author

October 18, 2011 08:34 AM

Oha... Reffering to this:

if (source surface has SDL_SRCALPHA set) {

	if (source surface has alpha channel (that is, format->Amask != 0))

    	blit using per-pixel alpha, ignoring any colour key

	else {

    	if (source surface has SDL_SRCCOLORKEY set)

        	blit using the colour key AND the per-surface alpha value

    	else

        	blit using the per-surface alpha value

	}

} else {

	if (source surface has SDL_SRCCOLORKEY set)

    	blit using the colour key

	else

    	ordinary opaque rectangular blit

}

I haven't set SDL_SRCALPHA(or is it set automaticly?), so following that code I should end with "blit using the colour key", shouldn't I?

rip-off

11,000

October 18, 2011 09:48 AM

You can check if SDL is setting it automatically by inspecting the value of (src->flags & SDL_SRCALPHA). This is the case on my system.

blog | twitter

[SDL] 32 bit Surface: Colorkey won't work

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

[SDL] 32 bit Surface: Colorkey won't work

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines