working with large sprite sheets on iphone

Question

Hi All,

I am trying to use sprite sheet animation in my application. The first POC with a small sprite sheet worked fine but as i change the sprite sheet to a bigger one, i get "check_safe_call: could not restore current frame" warning and the application quits.

A quick search revealed that this problem meant my app is taking too much memory or the image is too huge in dimension.

My image is 4.9 Mb and dimensions are 6720 * 10080 (oops!!). i read that iphone allows maximum 3 Mb image with dimensions up to 1024 * 1024. Also that the sprite sheet image dimensions should be a power of two.

So please let me know how i can use a sprite sheet this big.

One approach could be to cut the sprite sheet into many smaller sprite sheets and use them one at a time.

Please suggest if you know any other/better approach to accommodate bigger sprite sheets and whether the problem with my sprite sheet is size (4.9 Mb) OR dimensions (6720 * 10080).

(Just FYI, i am not trying to play a movie so using MP4 file instead is not an option for me. i need to animate the sprite sheet based on accelerometer input and i have been able to achieve that in my POC with smaller sprite sheet.)

Thanks, Swapnil

Answer 1

You should cut up the sprite sheet into multiple textures as you describe. The iPhone's memory and graphics chip simply can't hold an image/texture of that size in memory at once. By splitting up the sprite sheet it will deal with loading/unloading the appropriate textures into memory when you use them.

You might also consider optimizing the image format. Using the PVRTC format can save a huge amount of memory, but it is only well-suited to certain kinds of images. See this Apple page for more information.

Answer 2

definitely keep it within powers of 2. also, keep the sprites within the spritesheet in containers that are powers of 2 (say, you have a 17x31 sprite... put it in a 32x32 container). the problem with your sprite sheet is both the 4.9mb and the dimensions. i would consider using adobe fireworks or pngcrusher to bring the size of your sprite sheet down considerably.

mike weller's right about splitting the sprite sheet up (you simply cannot max 1024). i think the best bet would be to reorganize what you're doing with your sprite sheet into elements (though it's tough to say without knowing particulars). only things that move should have multiple frames. overlay those over a background (from the same spritesheet) by calling there location on the spritesheet and tossing them into play.