OpenGL 2D performance question...

[Johanovski]

Hi there!

I'm working in a 2D OpenGL project and I'm wondering if it's better to use various images for an animation or use a single imageSet containing all the sprites and then drawing a sub-image each time...
So for example let's say I have 3 kinds of characters with 4 sprites each one (and each sprite is 64 x 64). Which is the better option (for OpenGL performance)?

Option1:

// Three arrays of four images each one:
for(int i=0; i<4; i++)
{
     spritesChar1[i] = [[Image alloc] initWithImage:[...]];
     spritesChar2[i] = [[Image alloc] initWithImage:[...]];
     spritesChar3[i] = [[Image alloc] initWithImage:[...]];
}
// So I have 12 (64 x 64) images allocated, but each time I have to render one I do it for the entire image:

(...)

[spritesChar1[sprite] renderAtPoint:p];

Option2:

// Three images containing each one the four sprites:

spritesChar1 = [[Image alloc] initWithImage:[...]];
spritesChar2 = [[Image alloc] initWithImage:[...]];
spritesChar3 = [[Image alloc] initWithImage:[...]];

// So I have 3 (256 x 64) images allocated, but each time I have to render one I have to get a sub-image to draw only the sprite:

(...)

[spritesChar1 renderSubImageAtPoint:p WithOffset:offset AndSpriteSize:size];

Option3:

// A single image containing the three characters and each character's sprites:

spritesChars = [[Image alloc] initWithImage:[...]];

// So I have 3 (256 x 196) images allocated, but each time I have to render one I have to get a sub-image to draw only the sprite:

(...)

[spritesChar1 renderSubImageAtPoint:p WithOffset:offset AndSpriteSize:size];

Which is the best way for performance?

Thanks for your time!

[smasher]

Whichever method has the fewest number of calls to glDrawArrays or glDrawElements should have the better performance, and whichever method has the fewest calls to glBindTexture.

I don't know what renderSubImageAtPoint looks like, but I assume it calls both glBindTexture and glDrawArrays; in that case you probably won't see much difference between these three methods.

In the long term, a single image with all of the textures has the biggest chance of speedup in the future. With a single texture it's possible to batch all of your sprites together to draw all or most of them with a single call to glDrawArrays. That would give you a tremendous speedup. You'd probably have to rewrite your drawing class, though.