Loading Texture2d on parallel thread

[axlsd]

Hello everybody,

my application has a NSTimer for rendering, I want to load my textures and other data in a parallel thread while timer renders a loading screen.

My problem is:
if I try to create a texture2d (using a code very similiar to crash landing example) starting an NSThread, glGenTextures call freezes my application and I can understand why..

Any help is appreciated, thanks.

[nuudles]

Originally Posted by axlsd

Hello everybody,

my application has a NSTimer for rendering, I want to load my textures and other data in a parallel thread while timer renders a loading screen.

My problem is:
if I try to create a texture2d (using a code very similiar to crash landing example) starting an NSThread, glGenTextures call freezes my application and I can understand why..

Any help is appreciated, thanks.

I actually got this working, but it's a big pain. What you're dealing with is the fact that your texture thread doesn't have an OpenGL context. You can create a new one for it, but then any texture you create in that context won't be shared between that context and your main thread's context. You have to use something called an EAGLSharegroup to link the contexts together so they can share resources. You can do this by changing your EAGLView code to initialize its context like this:

EAGLSharegroup *sharegroup = [[EAGLSharegroup alloc] init];
context = [[EAGLContext alloc] initWithAPI:EAGLRenderingAPIOpenGLES1 sharegroup:sharegroup];

Once this is done, go into your thread and create a context using the above call with the same sharegroup. You'll have to initialize the context with whatever OpenGL initializations you want, but you should be able to get it to work.

Note:
This code does not work in the Simulator. The EAGLContext initialization with a sharegroup crashes the Simulator. The code does, however, work on the device itself, so keep that in mind. I'd opened a bug report regarding this bug, 6367125, and currently it is in the Open state.

[axlsd]

Thanks for the answer..
you are right.. it seems a really big pain.

For now I skip the glGenTex error calling the initWithData function in the first draw call and not on parallel thread.. I think this is not the better solution.. but works pretty well.

glGenTex seems fast enough so I can posticipate it at first draw.

[jaguard]

Why don't you just swap buffers every once you load a new texture?
This will allow you to draw a smooth enough loading bar.

[joephish]

Originally Posted by jaguard

Why don't you just swap buffers every once you load a new texture?
This will allow you to draw a smooth enough loading bar.

Because having loading on a separate thread allows you to be loading in textures while the game itself is running, rather than a loading screen. Which means bypassing loading screens altogether, where possible.

Thanks everyone for this thread by the way, it's been extremely useful :-)

[csmartdalton]

I got around this issue by doing this before creating the textures:

[EAGLContext setCurrentContext:[my current context in EAGLView]];

It seems to work fine (in the Simulator as well as the device). Does anybody know if this could potentially cause problems?

[csmartdalton]

Originally Posted by csmartdalton

I got around this issue by doing this before creating the textures:

[EAGLContext setCurrentContext:[my current context in EAGLView]];

It seems to work fine (in the Simulator as well as the device). Does anybody know if this could potentially cause problems?

Never mind. Don't do this! It turns out to be a very bad idea. Your never know what state the other thread has the context in - is it drawing, updating the state, etc.? I ended up loading and decompressing the image file in the worker thread and just doing final calls to glGenTextures() and glTexImage2D() in the main thread.