Question

On iOS I have always assume that it is not possible to do OpenGL texture creation – glTexImage2D – on a separate thread via an NSOperation subclass. Can someone please confirm/deny.

Since texture creation potentially hang the GUI – bad! – has anyone come up with a workaround that they are happy with?

Thanks,
Doug

Answer 1

Yes, take a look at CCTextureCache.m in cocos2d for iPhone.

cocos2d-iphone / cocos2d / CCTextureCache.m

NSAutoreleasePool *autoreleasepool = [[NSAutoreleasePool alloc] init];

// textures will be created on the main OpenGL context
// it seems that in SDK 2.2.x there can't be 2 threads creating textures at the same time
// the lock is used for this purpose: issue #472
[contextLock_ lock];
if( auxGLcontext == nil ) {
    auxGLcontext = [[EAGLContext alloc]
                           initWithAPI:kEAGLRenderingAPIOpenGLES1
                           sharegroup:[[[[CCDirector sharedDirector] openGLView] context] sharegroup]];

    if( ! auxGLcontext )
        CCLOG(@"cocos2d: TextureCache: Could not create EAGL context");
}

if( [EAGLContext setCurrentContext:auxGLcontext] ) {

    // load / create the texture
    CCTexture2D *tex = [self addImage:async.data];

    /* This method calls glTexImage2D. */


    // The callback will be executed on the main thread
    [async.target performSelectorOnMainThread:async.selector withObject:tex waitUntilDone:NO];        

    [EAGLContext setCurrentContext:nil];
} else {
    CCLOG(@"cocos2d: TetureCache: EAGLContext error");
}
[contextLock_ unlock];

[autoreleasepool release];