SDL: FPS problems with simple bitmap

Question

I am currently working on a game in SDL which has destructible terrain. At the moment the terrain is one large (5000*500, for testing) bitmap which is randomly generated.

Each frame the main surface is cleared and the terrain bitmap is blitted into it. The current resolution is 1200 * 700, so when I was testing 1200 * 500 pixels were visible at most of the points.

Now the problem is: The FPS are already dropping! I thought one simple bitmap shouldn't show any effect - but I am already falling down to ~24 FPS with this!

• Why is blitting & drawing a bitmap of that size so slow?

• Am I taking a false approach at destructible terrain?

• How have games like Worms done this? The FPS seem really high although there's definitely a lot of pixels drawn in there

Answer 1

Whenever you initialize a surface, do it the following way:

SDL_Surface* mySurface;
SDL_Surface* tempSurface;
tempSurface = SDL_LoadIMG("./path/to/image/image.jpg_or_whatever"); 
/* SDL_LoadIMG() is correct name? Not sure now, I`m at work, so I can`t verify it. */
mySurface = SDL_DisplayFormat(tempSurface);
SDL_FreeSurface(tempSurface);

The SDL_DisplayFormat() method converts the pixel format of your surface to the format the video surface uses. If you don`t do it the way I described above, SDL does this each time the surface is blitted.

And always remember: just blit the necessary parts that really are visible to the player.

That`s my first guess, why you are having performance problems. Post your code or ask more specific questions, if you want more tipps. Good luck with your game.

Answer 2

If you redraw the whole screen at each frame your will always get a bad FPS. You have to redraw only part of the screen which have changed. You can also try to use SDL_HWSURFACE to use hardware but it won't work on every graphical card.

Answer 3

2d in SDL is pretty slow and there isn't much you can do to make it faster (on windows at least it uses GDI for drawing by default.) Your options are:

1. Go opengl and start using textured quads for sprites.
2. Try SFML. It provides a hardware accelerated 2d environment.
3. Use SDL 1.3 Get a source snapshot it is unstable and still under development but hardware accelerated 2d is supposed to be one of the main selling points.