Layer backed NSView with Retina support

VWLayerBackedBaseView.mm

@interface VWLayerBackedBaseView : NSView

@end

@interface VWLayerBackedBaseView ()
- (void)_updateContentScale;
@end

@implementation VWLayerBackedBaseView

#pragma mark Retina Display Support

- (void)_updateContentScale
{
    if (![self window]) return;
    
    CALayer *layer = self.layer;
    if ([layer respondsToSelector:@selector(contentsScale)]) {
        CGFloat scale = [(id)[self window] backingScaleFactor];
        [(id)self.layer setContentsScale:scale];
        // If this instance holds any other CALayers, set their contents scale here
        // ...
    }
}

- (void)scaleDidChange:(NSNotification *)n
{
    [self _updateContentScale];
}

- (void)viewDidMoveToWindow
{
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(scaleDidChange:)
                                                 name:@"NSWindowDidChangeBackingPropertiesNotification"
                                               object:[self window]];
    
    // immediately update scale after the view has been added to a window
    [self _updateContentScale];
}

- (void)removeFromSuperview
{
    [super removeFromSuperview];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:@"NSWindowDidChangeBackingPropertiesNotification" object:[self window]];
}

@end