ios - 用 Quartz 渐变填充 PNG

Question

如何用线性渐变填充 PNG UIImage 的非透明区域？我想为 MKAnnotationViews 重用 PNG 形状，但更改每个注释属性的渐变。

Answer 1

我最终将 Rob 的一些代码和我在http://coffeeshopped.com/2010/09/iphone-how-to-dynamically-color-a-uiimage找到的 UIImage 的扩展拼凑在一起

+ (UIImage *)imageNamed:(NSString *)name withGradient:(CGGradientRef)gradient
{
    // load the image
    UIImage *img = [UIImage imageNamed:name];

    // begin a new image context, to draw our colored image onto
    UIGraphicsBeginImageContextWithOptions(img.size, NO, [[UIScreen mainScreen] scale]);

    // get a reference to that context we created
    CGContextRef context = UIGraphicsGetCurrentContext();

    // translate/flip the graphics context (for transforming from CG* coords to UI* coords
    CGContextTranslateCTM(context, 0, img.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    // set the blend mode to overlay, and the original image
    CGContextSetBlendMode(context, kCGBlendModeOverlay);
    CGRect rect = CGRectMake(0, 0, img.size.width, img.size.height);

    // set a mask that matches the shape of the image, then draw (overlay) a colored rectangle
    CGContextClipToMask(context, rect, img.CGImage);
    CGContextAddRect(context, rect);

    //gradient
    CGPoint startPoint = CGPointMake(0.0, img.size.height);
    CGPoint endPoint   = CGPointMake(0.0, 0.0);
    CGContextDrawLinearGradient (context, gradient, startPoint, endPoint, 0);

    // generate a new UIImage from the graphics context we drew onto
    UIImage *coloredImg = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    CGGradientRelease(gradient);

    //return the color-burned image
    return coloredImg;

}

Answer 2

要将图像用作渐变的遮罩（即在图像的非透明像素形状中具有渐变），您可以：

• 创建一个带有渐变的简单视图（您可以创建一个简单的视图UIView并使用addGradientLayerToView下面显示的给它一个渐变，或者您可以提前创建渐变 PNG 并将其添加到您的包中）。

• 将您的 PNG 作为蒙版应用到该渐变视图：

  UIImage *mask = [UIImage imageNamed:@"mask.png"];
  CALayer *maskLayer = [CALayer layer];
  maskLayer.frame = CGRectMake(0, 0, mask.size.width, mask.size.height);
  maskLayer.contents = (id)[mask CGImage];
  gradientViewToMask.layer.mask = maskLayer;
  

---

要将渐变应用到透明像素，您可以：

1. 创建一个带有渐变的新图像：

   - (UIImage *)imageWithGradient:(UIImage *)image
   {
       UIGraphicsBeginImageContextWithOptions(image.size, NO, 1.0);
   
       CGContextRef context = UIGraphicsGetCurrentContext();
   
       size_t locationCount = 2;
       CGFloat locations[2] = { 0.0, 1.0 };
       CGFloat components[8] = { 0.0, 0.8, 0.8, 1.0,   // Start color
                                 0.9, 0.9, 0.9, 1.0 }; // End color
   
       CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
   
       CGGradientRef gradient = CGGradientCreateWithColorComponents (colorspace, components, locations, locationCount):
   
       CGPoint startPoint = CGPointMake(0.0, 0.0);
       CGPoint endPoint   = CGPointMake(0.0, image.size.height);
       CGContextDrawLinearGradient (context, gradient, startPoint, endPoint, 0);
   
       CGContextTranslateCTM(context, 0, image.size.height);
       CGContextScaleCTM(context, 1.0, -1.0);
   
       CGContextDrawImage(context, CGRectMake(0.0, 0.0, image.size.width, image.size.height), [image CGImage]);
   
       UIImage *gradientImage = UIGraphicsGetImageFromCurrentImageContext();
       UIGraphicsEndImageContext();
   
       CGGradientRelease(gradient);
       CGColorSpaceRelease(colorspace);
   
       return gradientImage;
   }
   

2. 您还可以将 a 添加CAGradientLayer到视图，然后将其添加为该UIImageView视图的子视图。

   - (void)addGradientLayerToView:(UIView *)view
   {
       CAGradientLayer *gradient = [CAGradientLayer layer];
       gradient.frame = view.bounds;
       gradient.colors = @[(id)[[UIColor colorWithRed:0.0 green:0.8 blue:0.8 alpha:1.0] CGColor],
                           (id)[[UIColor colorWithRed:0.9 green:0.9 blue:0.9 alpha:1.0] CGColor]];
       [view.layer insertSublayer:gradient atIndex:0];
   }
   

   请注意，您还必须#import <QuartzCore/QuartzCore.h>将 QuartzCore 框架添加到您的项目中。