更新到iOS 7.1后，OpenGL ES精灵不再渲染

Question

I am using a simple 2D sprite class based on this tutorial to render PNG bitmaps to the screen:

http://www.raywenderlich.com/9743/how-to-create-a-simple-2d-iphone-game-with-opengl-es-2-0-and-glkit-part-1

Everything worked fine on both my iPhone 4S running iOS 6.1 and my iPhone 5S running iOS 7. Since I updated to iOS 7.1, and on my MacBook Air updated to Mavericks and XCode 5.1, sprites no longer appear on the screen (I just get an empty white screen, which is the color I cleared the background to). When I build the app using XCode 5.1 and run on my iPhone 4S again, it still works.

Does anyone know what could be causing this? Has anyone run into this issue? I am having trouble getting to the source of the problem due to my lack of understanding of OpenGL ES among other things. :) My sprite class is exactly the same as the one in the tutorial.

Let me know if more details/code snippets are required.

Answer 1

I'm not even going to look at the sample code since it doesn't sound like it's the same as your current code. (You said 'based on'.) But I'll tell you how to find your problem.

First, clear to something other than white (like red) as a test.

If the screen turns red you at least know that your view and context and open gl in general is working. That knocks out a lot of possible culprits.

Second.. use the debug tools and chances are it will take you right to your problem. You have to run on a tethered device though and not the sim. Run your app...

Click on FPS in the debug navigator. Then click analyze and be patient. It will take a one frame snapshot of whats happening in open gl. It has to do a bunch of stuff to make that happen and it takes about 30 seconds. But then you'll have an interactive thing that shows you the frame and will let you step through processes and see what code is making that happen, and the frame as it draws each element. It's super cool actually. And probably it will show you an error message (in red).

My guess is that it's no longer loading your sprite images. Something probably changed between 6 and 7 or the versions of Xcode or of OSX. In that case the screen is blank because they're not loaded and therefore not being drawn.

EDIT: I think the analysis will help find your problem. But to offer more possibilities, in my experience when nothing is drawing it's often one of these things:

1. An overall OpenGL issue - set your clear color to red or blue to test.
2. Shader didn't compile - always output shader compile errors so you know.
3. Bad Shader math or logic - use gl_FragColor = vec4(0.0,0.0,1.0,1.0) or some contrasting color to test. Can you see your structures?
4. Program isn't getting an attribute. Did you remember glEnableVertexAttribArray
5. Program isn't getting a uniform. Use the Analyze feature above to check the uniform values to make sure they made it to the shader.

(i'll add more if I think of them)

When stuff does