Release textures (GLKTextureInfo objects) allocated by GLKTextureLoader

Question

New to developing on iOS and in particular the new OpenGL related features on iOS 5, so I apologize if any of my questions are so basic.

The app I am working on is d

Answer 1

Not a direct answer, but something I noticed and it wont really fit in a comment.

If you're using GLKTextureLoader to load textures in the background to replace an existing texture, you have to delete the existing texture on the main thread. Deleting a texture in the completion handler will not work.

AFAIK this is because:

1. Every iOS thread requires its own EAGLContext, so the background queue has its own thread with its own context.
2. The completion handler is run on the queue you passed in, which is most likely not the main queue. (Else you wouldn't be doing the loading in the background...)

That is, this will leak memory.

NSDictionary *options = @{GLKTextureLoaderOriginBottomLeft:@YES};
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
[self.asyncTextureLoader textureWithContentsOfFile:@"my_texture_path.png"
                                           options:options
                                             queue:queue
                                 completionHandler:^(GLKTextureInfo *texture, NSError *e){
                                    GLuint name = self.myTexture.name;
                                    //
                                    // This delete textures call has no effect!!!
                                    //
                                    glDeleteTextures(1, &name);
                                    self.myTexture = texture;
                                  }];

To get around this issue you can either:

1. Delete the texture before the upload happens. Potentially sketchy depending on how your GL is architected.
2. Delete the texture on the main queue in the completion handler.

So, to fix the leak you need to do this:

//
// Method #1, delete before upload happens.
// Executed on the main thread so it works as expected.
// Potentially leaves some GL content untextured if you're still drawing it
// while the texture is being loaded in.
//

// Done on the main thread so it works as expected
GLuint name = self.myTexture.name;
glDeleteTextures(1, &name)

NSDictionary *options = @{GLKTextureLoaderOriginBottomLeft:@YES};
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
[self.asyncTextureLoader textureWithContentsOfFile:@"my_texture_path.png"
                                           options:options
                                             queue:queue
                                 completionHandler:^(GLKTextureInfo *texture, NSError *e){
                                    // no delete required, done previously.
                                    self.myTexture = texture;
                                  }];

or

//
// Method #2, delete in completion handler but do it on the main thread.
//
NSDictionary *options = @{GLKTextureLoaderOriginBottomLeft:@YES};
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
[self.asyncTextureLoader textureWithContentsOfFile:@"my_texture_path.png"
                                           options:options
                                             queue:queue
                                 completionHandler:^(GLKTextureInfo *texture, NSError *e){
                                    // you could potentially do non-gl related work here, still in the background
                                    // ...

                                    // Force the actual texture delete and re-assignment to happen on the main thread.
                                    dispatch_sync(dispatch_get_main_queue(), ^{
                                      GLuint name = self.myTexture.name;
                                      glDeleteTextures(1, &name);
                                      self.myTexture = texture;
                                    });
                                  }];