圆形CAGradientLayer面具 - iOS

Question

我在我的图片上使用CAGradientLayer。我使用此代码执行此操作：

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];

但我想要的是径向渐变或圆形渐变效果。我只是在一边得到一个渐变。如何实现圆形渐变层？感谢。

Answer 1

如果需要圆形渐变图层，则必须子类化并覆盖- (void)drawInContext:(CGContextRef)ctx方法。因为代码非常简单，对于径向渐变应该看起来像这样：

        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);

请注意我现在无法测试代码，但应该没问题。如果您想要一个像这样的角度渐变而不是径向渐变：

你不幸，因为Objective c无法直接制作它。要做到这一点，你可以在你想要的颜色之间循环线性插值并直接绘制它们（不是很难实现但性能很差）或者使用图像作为掩模。

Answer 2

以下是产生所附图像所示输出的代码：

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;

[{] 1