如何以编程方式创建渐变颜色,如下图所示。
当你说“将它作为渐变应用于图像”时,你的意思是作为一个面具(在顶部显示图像,让图像在底部淡化为透明)?如果是这种情况,您可以使用CAGradientLayer
将该渐变应用为蒙版:
CAGradientLayer *gradientMask = [CAGradientLayer layer];
gradientMask.frame = self.imageView.bounds;
gradientMask.colors = @[(id)[UIColor whiteColor].CGColor,
(id)[UIColor clearColor].CGColor];
self.imageView.layer.mask = gradientMask;
以上是一个简单的垂直渐变(因为默认是垂直,线性渐变)。但你问过startPoint
,endPoint
和locations
。例如,如果您希望水平应用蒙版,则可以执行以下操作:
gradientMask.startPoint = CGPointMake(0.0, 0.5); // start at left middle
gradientMask.endPoint = CGPointMake(1.0, 0.5); // end at right middle
如果你想要两个渐变,一个在前10%,另一个在最后10%,你会做:
gradientMask.colors = @[(id)[UIColor clearColor].CGColor,
(id)[UIColor whiteColor].CGColor,
(id)[UIColor whiteColor].CGColor,
(id)[UIColor clearColor].CGColor];
gradientMask.locations = @[@0.0, @0.10, @0.90, @1.0];
如果你想要一个简单的渐变(而不是一个蒙版),你需要创建一个view
然后添加渐变图层:
CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = view.bounds;
gradient.colors = @[(id)[UIColor whiteColor].CGColor,
(id)[UIColor blackColor].CGColor];
[view.layer addSublayer:gradient];
参见CAGradientLayer
class reference。
我刚刚为Swift 2.0编写了一个UIImage扩展。也许它有一些用处。您可以使用UIColor(任意数字)数组和应绘制渐变的框架来调用它。
extension UIImage {
class func convertGradientToImage(colors: [UIColor], frame: CGRect) -> UIImage {
// start with a CAGradientLayer
let gradientLayer = CAGradientLayer()
gradientLayer.frame = frame
// add colors as CGCologRef to a new array and calculate the distances
var colorsRef = [CGColor]()
var locations = [NSNumber]()
for i in 0 ... colors.count-1 {
colorsRef.append(colors[i].CGColor as CGColorRef)
locations.append(Float(i)/Float(colors.count-1))
}
gradientLayer.colors = colorsRef
gradientLayer.locations = locations
// now build a UIImage from the gradient
UIGraphicsBeginImageContext(gradientLayer.bounds.size)
gradientLayer.renderInContext(UIGraphicsGetCurrentContext()!)
let gradientImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
// return the gradient image
return gradientImage
}
}
像这样称呼它:
let colors = [
UIColor.blueColor(),
UIColor.greenColor()
// and many more if you wish
]
let gradientImage = UIImage.convertGradientToImage(colors, frame: navigationBar.bounds)
并申请:
.backgroundColor = UIColor(patternImage: gradientImage)
要么
.setBackgroundImage(gradientImage, forBarMetrics: .Default)
CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = self.view.bounds;
gradient.startPoint = CGPointMake(1.0, 1.0); //Dark From bottom
gradient.endPoint = CGPointMake(1.0, 0);
gradient.colors = [NSArray arrayWithObjects:
(id)[[UIColor blackColor] CGColor],
(id)[[UIColor clearColor] CGColor], nil];
[self.view.layer insertSublayer:gradient atIndex:0];
这是最好的方法,根据要求为我工作
CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = yourImageView.layer.bounds;
gradientLayer.colors = [NSArray arrayWithObjects:
(id)[UIColor colorWithWhite:1.0f alpha:1.0f].CGColor,
(id)[UIColor colorWithWhite:0.0f alpha:0.9f].CGColor,
nil];
gradientLayer.locations = [NSArray arrayWithObjects:
[NSNumber numberWithFloat:0.0f],
[NSNumber numberWithFloat:1.0f],
nil];
[yourImageView.layer addSublayer:gradientLayer];
-(void) drawGradientinBounds: (CGRect) currentBounds withColors:(NSArray*) colors andPercentages:(NSArray *)percentages andGradientDirectionIsVertical:(BOOL)isGradientDirectionVertical
{
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGGradientRef glossGradient;
CGColorSpaceRef rgbColorspace;
size_t num_locations = [percentages count];
CGFloat locations[num_locations];
for(int i=0;i<num_locations;i++)
locations[i] = [[percentages objectAtIndex:i] floatValue];
int comps = [colors count]*4;
CGFloat components[comps];
for(int i = [colors count]-1;i>=0;i--)
{
comps--;
UIColor *c = [colors objectAtIndex:i];
const CGFloat *cg = CGColorGetComponents([c CGColor]);
components[comps] = cg[3];
comps--;
components[comps] = cg[2];
comps--;
components[comps] = cg[1];
comps--;
components[comps] = cg[0];
}
rgbColorspace = CGColorSpaceCreateDeviceRGB();
glossGradient = CGGradientCreateWithColorComponents(rgbColorspace, components, locations, num_locations);
CGPoint topCenter;
CGPoint endCenter;
if(isGradientDirectionVertical)
{
topCenter = CGPointMake(CGRectGetMidX(currentBounds), currentBounds.origin.y);
endCenter = CGPointMake(CGRectGetMidX(currentBounds), CGRectGetHeight(currentBounds)+currentBounds.origin.y);
}
else
{
topCenter = CGPointMake( currentBounds.origin.x,CGRectGetMidY(currentBounds));
endCenter = CGPointMake(CGRectGetWidth(currentBounds)+currentBounds.origin.x,CGRectGetMidY(currentBounds));
}
CGContextDrawLinearGradient(currentContext, glossGradient, topCenter, endCenter, 0);
CGGradientRelease(glossGradient);
CGColorSpaceRelease(rgbColorspace);
}
并且此方法的输入是bounds,colorArray:
[NSArray arrayWithObjects:[UIColor blackColor], [UIColor whiteColor], nil]
percentageArray:
[NSArray arrayWithObjects:[NSNumber numberWithFloat:0.0], [NSNumber numberWithFloat:1.0], nil]