Question

I want to draw map overlay with blend mode. But this code just draw white overlay without any blend mode. What I’m doing wrong?

- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context
{
    UIGraphicsPushContext(context);

    CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
    CGContextSetBlendMode(context, kCGBlendModeSaturation);
    CGContextFillRect(context, [self rectForMapRect:mapRect]);

    UIGraphicsPopContext();
}

Here is result that I want. I make it in Photoshop with three layers:

1. original google map.
2. black layer with saturation blend mode.
3. white layer with exclusion blend mode.
   

Answer 1

I guess you cannot acces the real mapview context directly. So probably you have to take a “screenshot” of the map and draw it again in your context. After that you can apply your effects of course.