SDL transparency problem

unholy · 07-30-2004, 04:12 AM

I have 2 sprites in an sdl program. Sprite A has a large transparent center, sprite B is solid.

The transparency works fine for A as long as it is moving...however, if A stops on top of B (B is now visible through the transparency in A) - and B moves away, the image of B is still displayed as A's transparency, even though it is gone.

Sprite A has to be moved a distance for the correct transparency to be restored. Is this a common problem?

I can post code, but it's 300 lines long and I dont really know which sections are relevant.

Thanks in advance,

unholy

Cedrik · 07-30-2004, 04:45 AM

did you try a SDL_UpdateRect() right after your sprite stops ?

unholy · 07-31-2004, 07:52 AM

Thanks Cedrik,

The sprite is a SDL_Surface, but I will try your suggestion this evening.

Regards,

unholy

unholy · 08-03-2004, 09:59 AM

Cedrik,

I changed my sprite for a single image with a transparency, and there was no problem. I did also did not need to use updateRectangle(...).

But when I use a sprite, the problem does occur, and updateRectangle doesnt seem to help, the transparency doesnt get refresed unless the sprite is moved.

My sprite code came from this tutorial

http://cone3d.gamedev.net/cgi-bin/in...ls/gfxsdl/tut3

Cedrik · 08-03-2004, 11:34 AM

Code:

In the void CSprite::updateBG() function, I would try to add :
...
SDL_BlitSurface(mScreen, &srcrect, mBackreplacement, NULL);
SDL_UpdateRects(mScreen, 1, &srcrect);

and in the void DrawIMG(SDL_Surface *img, int x, int y) function  :
...
SDL_BlitSurface(img, NULL, screen, &dest);
SDL_UpdateRects(screen, 1, &dest);

unholy · 08-08-2004, 07:10 AM

Thanks Cedrik, I'll try that again.

Are there any other good resources for learning SDL? I have the documentation project stuff, and the tutorials from the website. I dont mind buying a book, but I'd prefer something on soft copy.

Cedrik · 08-08-2004, 09:13 AM

There is a nice book in PDF format here And you may want to browse the source directory to download source examples from the book.

unholy · 08-13-2004, 01:41 PM

Thanks a lot Cedrik, You've made my week!