[SDL] Re: Displaying transparent images

[NBarnes]

--- Thomas Harte <T.Harte at btinternet.com> wrote:

> > I had a lot of problems loading(and displaying) a gif image that
> > contains some transparent areas..

> Presumably whatever method you are using to load GIFs is telling you 
> which colour is the transparent one, or else you are just assuming
> it is colour 0 or something?
> 
> What you want to do is to use SDL_SetColorKey to establish the 
> transparent colour for the surface with the sprite in it, use 
> SDL_SetAlpha to enable SDL_SRCALPHA but leave the alpha flag at 128.
> 
> Following this, blit should work with transparent pixels removed.

 I'm curious.  To set transparency for the chosen transparency color
in my work, I have just the following line of code....

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

with no call to SDL_SetAlpha().

 It appears to work fine in my application.  Why do you feel the call
to SDL_SetAlpha() is important?  What are the consequences of not
having it?

 I'm not using .GIFs to load my images, I'm using .BMPs.

                                                            NBarnes

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