I'm developing a 2D game for the iPhone using OpenGL ES and I'd like to use a 320×480 bitmapped image as a persistent background.
My first thought was to create a 320×480 quad and then map a texture onto it that represents the background. So… I created a 512×512 texture with a 320×480 image on it. Then I mapped that to the 320×480 quad.
I draw this background every frame and then draw animated sprites on top of it. This works fine except that the drawing of all of these objects (background + sprites) is too slow.
I did some testing and discovered that my slowdown is in the pixel pipeline. Not surprisingly, the large background image is the main culprit. To prove this, I removed the background draw and everything else rendered very fast.
I am looking for advice on how to keep my background and also improve performance.
Here's some more info:
1) I am currently testing on the Simulator (still waiting on Apple for the license)
2) The background is a PVR texture squeezed down to 128k
3) I had hoped that there might be a way to cache this background into a color buffer but haven't had any luck with that. that may be due to my inexperience with OpenGL ES or it just might be a stupid idea that won't work 🙂
4) I realize that the entire background does not always have to refresh, just the parts that have been drawn over by the moving sprites. I started to look into techniques for refreshing (as necessary) parts of the the background either as separate textures or with a scissor box, however this seems less than elegant.
Any tips/advice would be greatly appreciated…
Thank you.
Best Answer
The differences to the real hardware are huge. In both directions.
Do not clear the framebuffer. The background will overdraw the whole thing anyway.
What about using a color gradient via vertex colors ?
E.g.: Lighting, Blending, Depth-Test, ...
If you could post some of your drawing code it would be a lot easier to help you.