Circular CAGradientLayer Mask - iOS

Question

I'm using CAGradientLayer on my image. I use this code to do this:

UIImage *image = [UIImage imageNamed:@"perfect.jpg"];

[testImage setImage:image];

CAGradientLayer *myLayer = [CAGradientLayer layer];

myLayer.anchorPoint = CGPointZero;

//starts in bottom left
myLayer.startPoint = CGPointMake(1.0f,1.0f);

//ends in top right
myLayer.endPoint = CGPointMake(1.0f, 0.0f);

UIColor *outerColor = [UIColor colorWithWhite:1.0 alpha:0.0];
UIColor *innerColor = [UIColor colorWithWhite:1.0 alpha:1.0];

//an array of colors that dictatates the gradient(s)
myLayer.colors = @[(id)outerColor.CGColor, (id)outerColor.CGColor, (id)innerColor.CGColor, (id)innerColor.CGColor];

//these are percentage points along the line defined by our startPoint and endPoint and correspond to our colors array. The gradient will shift between the colors between these percentage points.
myLayer.locations = @[@0.0, @0.15, @0.5, @1.0f];

myLayer.bounds = CGRectMake(0, 0, CGRectGetWidth(testImage.bounds), CGRectGetHeight(testImage.bounds));

testImage.layer.mask = myLayer;

[self.view addSubview:testImage];

But what I want is a Radial gradient or circle gradient effect. I'm only getting a gradient on one side. How can I achieve a circular gradient layer? Thanks.

try this...it will help you. http://stackoverflow.com/questions/8125623/how-do-i-add-a-radial-gradient-to-a-uiview — , May 06 '14 at 07:39

score 0 · Answer 1 · answered May 06 '14 at 07:11

If you want a circular gradient layer you will have to subclass and override the - (void)drawInContext:(CGContextRef)ctx method. In that the code is pretty straight forward and should looks like to something like this for a radial gradient:

        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
        NSArray* colors = @[(id)[UIColor whiteColor].CGColor, (id)[UIColor blackColor].CGColor];
        CGFloat locations[] = {.25, .75};
        CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (CFArrayRef)colors, locations);
        CGPoint center = (CGPoint){self.bounds.size.width / 2, self.bounds.size.height  / 2};
        CGContextDrawRadialGradient(ctx, gradient, center, 20, center, 40, kCGGradientDrawsAfterEndLocation);

        CGGradientRelease(gradient);
        CGColorSpaceRelease(colorSpace);

Mind that I cannot test the code right now, but it should be fine. If instead of a radial gradient you want an angle gradient like this one:

enter image description here

You are unlucky since Objective c has no way to make it directly. To make it you can either loop through a linear interpolation between the colors you want and directly draw them (not so hard to implement but has poor performance) or use an image as a mask.

Did you subclass a CLayer or a gradient layer? Im not able to performe the gradient you have in your image. — João Nunes, Mar 30 '15 at 11:45
Please read better: **If instead of a radial gradient you want an angle gradient like this one: [image_here] you are unlucky since Objective c has no way to make it directly. To make it you can either loop through a linear interpolation between the colors you want and directly draw them (not so hard to implement but has poor performance) or use an image as a mask.** — Antonio E., Mar 30 '15 at 12:07
What i did was: I created 2 gradient Boxs that simulate that effect (one one the left and one on the right). It is not perfect but works. Maybe i should try the image mask as you say :) — João Nunes, Mar 30 '15 at 12:15

score -1 · Answer 2 · answered Oct 03 '18 at 17:42

Here's the code that produces the output shown by the attached image:

CAGradientLayer *gradientLayer = [CAGradientLayer layer];
                        gradientLayer.frame = self.clockView.bounds;
                        [self.clockView.layer addSublayer:gradientLayer];
                        // TO-DO:
                        // add durations
                        gradientLayer.colors = @[(__bridge id)[UIColor colorWithRed:1.0/255.0 green:025.0/255.0 blue:147.0/255.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:0.0 green:118.0/255.0 blue:186.0/255.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:153.0/255.0 green:25.0/255.0 blue:94.0/255.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:181.0/255.0 green:23.0/255.0 blue:0.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:255.0/255.0 green:147.0/255.0 blue:0.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:250.0/255.0 green:226.0/255.0 blue:50.0/255.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:255.0/255.0 green:255.0/255.0 blue:255.0/255.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:255.0/255.0 green:255.0/255.0 blue:255.0/255.0 alpha:1.0].CGColor,

                                                 (__bridge id)[UIColor colorWithRed:250.0/255.0 green:226.0/255.0 blue:50.0/255.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:255.0/255.0 green:147.0/255.0 blue:0.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:181.0/255.0 green:23.0/255.0 blue:0.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:153.0/255.0 green:25.0/255.0 blue:94.0/255.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:0.0 green:118.0/255.0 blue:186.0/255.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:1.0/255.0 green:025.0/255.0 blue:147.0/255.0 alpha:1.0].CGColor,
                        (__bridge id)[UIColor colorWithRed:1.0/255.0 green:025.0/255.0 blue:147.0/255.0 alpha:1.0].CGColor,
                                                 (__bridge id)[UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:1.0].CGColor] ;

                        gradientLayer.type = kCAGradientLayerConic;
                        gradientLayer.startPoint = CGPointMake(0.5, 0.5);
                        gradientLayer.endPoint = CGPointMake(1, 1.0);

                        // Circular mask layer
                        CAShapeLayer *maskLayer = [CAShapeLayer layer];
                        maskLayer.frame = gradientLayer.bounds;

                        CGMutablePathRef circlePath = CGPathCreateMutable();
                        CGPathAddEllipseInRect(circlePath, NULL, CGRectInset(self.clockView.layer.bounds, 10.0 , 10.0));

                        maskLayer.path = circlePath;
                        CGPathRelease(circlePath);

                        gradientLayer.mask = maskLayer;

                        // second, smaller circle
                        CALayer *gradientLayer2 = [CALayer layer];
                        gradientLayer2.frame = gradientLayer.bounds;// CGRectMake(0.0, 0.0, self.clockView.bounds.size.width / 2.0, self.clockView.bounds.size.height / 2.0);
                        [gradientLayer2 setBackgroundColor:[UIColor darkGrayColor].CGColor];
                        [self.clockView.layer insertSublayer:gradientLayer2 atIndex:1];

                        // Circular mask layer
                        CAShapeLayer *maskLayer2 = [CAShapeLayer layer];
                        maskLayer2.frame = gradientLayer2.bounds;

                        CGMutablePathRef circlePath2 = CGPathCreateMutable();
                        CGPathAddEllipseInRect(circlePath2, NULL, CGRectInset(self.clockView.layer.bounds, 20.0 , 20.0));

                        maskLayer2.path = circlePath2;
                        CGPathRelease(circlePath2);

                        gradientLayer2.mask = maskLayer2;

[ enter image description here ]1

Circular CAGradientLayer Mask - iOS

2 Answers2

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