Add drop shadow to PNG using Cocoa

Question

I have some PNGs with transparent backgrounds that I would like to add shadows to programatically. I've seen examples of adding shadows to square objects, but haven't seen any with complex shapes.

So the two steps I think I'd have to do would be:

• Isolate the PNG shape
• Draw a shape behind the PNG that is blurred, faded, and offset.

I don't have much experience with drawing within Cocoa, so any insight on where to begin would be much appreciated!

Screenshot:

_{(source: iworkinprogress.com)}

Answer 1

Simplest way is to call CGContextSetShadow in your drawRect: before you draw the images.

- (void)drawRect:(CGRect)invalidRect
{
    CGContextRef c = UIGraphicsGetCurrentContext();
    CGContextSetShadow(c, CGSizeMake(5.0f, 5.0f), 5.0f);
    [myImage drawAtPoint:CGPointMake(50.0f, 50.0f)];
}

Answer 2

I found this category to be very useful: UIImage+Shadow.m

https://gist.github.com/kompozer/387210

Answer 3

I am not really a graphics person, but what about this: if you have a mask for these images, or if you can create one programatically, then you can probably use a blur function to add a shadow like effect.

Experiment in Photoshop/Acorn/Pixelmator?

Answer 4

Since you want shadows like they all have the same light source... it seems like you might actually be better off with an OpenGL view, that casts a light from above and the images would sit slightly above a flat plane to cast a shadow on. I'd look for 3D OpenGL frameworks that would let you add things pretty easily...