GLKView set drawable properties

Question

I\'m trying to port Apples GLPaint example to use GLKit. Using a UIView, its possible to return the CAEAGLLayer of the view and set the drawableProperties to include kEAGLDrawab

Answer 1

Simeon's answer works but changes the behavior for all EAGL-based views in an application. I have some views which need the backing forced and others which don't, so I came up with a slightly different solution by creating subclasses of GLKView and CEAGLLayer, like this:

@interface RetainedEAGLLayer : CAEAGLLayer
@end

@implementation RetainedEAGLLayer
- (void)setDrawableProperties:(NSDictionary *)drawableProperties {
    // Copy the dictionary and add/modify the retained property
    NSMutableDictionary *mutableDictionary = [[NSMutableDictionary alloc] initWithCapacity:drawableProperties.count + 1];
    [drawableProperties enumerateKeysAndObjectsUsingBlock:^(id key, id object, BOOL *stop) {
        // Copy all keys except the retained backing
        if (![key isKindOfClass:[NSString class]]
        || ![(NSString *)key isEqualToString:kEAGLDrawablePropertyRetainedBacking])
            [mutableDictionary setObject:object forKey:key];
    }];
    // Add the retained backing setting
    [mutableDictionary setObject:@(YES) forKey:kEAGLDrawablePropertyRetainedBacking];
    // Continue
    [super setDrawableProperties:mutableDictionary];
    [mutableDictionary release];
}
@end

and this

@interface RetainedGLKView : GLKView
@end

@implementation RetainedGLKView
+ (Class)layerClass {
    return [RetainedEAGLLayer class];
}
@end

Now I can just use RetainedGLKView instead of GLKView for those views where I want to force a retained backing.