Applying a Gradient to CAShapeLayer

Question

Does anyone have any experience in applying a Gradient to a CAShapeLayer? CAShapeLayer is a fantastic layer class, but it appears to only support solid fill coloring, whereas I'd like it to have a gradient fill (actually an animatable gradient at that).

Everything else to do with CAShapeLayer (shadows, shapes, stroke color, animatable shape path) is fantastic.

I've tried placing a CAGradientLayer inside a CAShapeLayer, or indeed setting the CAShapeLayer as the mask of the GradientLayer and adding both to a container layer, but these don't have the right outcome.

Should I subclass CAShapeLayer, or is there a better way forward?

Thanks.

Answer 1

You could use the path of your shape to create a masking layer and apply that on the gradient layer, like this:

UIView *v = [[UIView alloc] initWithFrame:self.window.frame];

CAShapeLayer *gradientMask = [CAShapeLayer layer];   
gradientMask.fillColor = [[UIColor clearColor] CGColor];
gradientMask.strokeColor = [[UIColor blackColor] CGColor];
gradientMask.lineWidth = 4;
gradientMask.frame = CGRectMake(0, 0, v.bounds.size.width, v.bounds.size.height);

CGMutablePathRef t = CGPathCreateMutable();    
CGPathMoveToPoint(t, NULL, 0, 0);
CGPathAddLineToPoint(t, NULL, v.bounds.size.width, v.bounds.size.height);

gradientMask.path = t;


CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.startPoint = CGPointMake(0.5,1.0);
gradientLayer.endPoint = CGPointMake(0.5,0.0);
gradientLayer.frame = CGRectMake(0, 0, v.bounds.size.width, v.bounds.size.height);
NSMutableArray *colors = [NSMutableArray array];
for (int i = 0; i < 10; i++) {
    [colors addObject:(id)[[UIColor colorWithHue:(0.1 * i) saturation:1 brightness:.8 alpha:1] CGColor]];
}
gradientLayer.colors = colors;

[gradientLayer setMask:gradientMask];
[v.layer addSublayer:gradientLayer];

If you want to also use the shadows, you would have to place a "duplicate" of the shape layer under the gradient layer, recycling the same path reference.