提取路径为的UIImage

Question

如何提取带有路径的UIImage？

我需要将路径中的内容获取到一个新的UIImage中。我需要的是一个旋转矩形的内容。这是我用来获取矩形边角的代码。（x，y=图像的中心。图像的宽度，高度）。

UIBezierPath* aPath = [UIBezierPath bezierPath];
//1
[aPath moveToPoint:CGPointMake(
                               x+(width/2)*cosf(A)-(height/2)*sinf(A),
                               y+(height/2)*cosf(A)+(width/2)*sinf(A))];
NSLog(@"%f, %f", x+(width/2)*cosf(A)-(height/2)*sinf(A),
      y+(height/2)*cosf(A)+(width/2)*sinf(A));

//2
[aPath moveToPoint:CGPointMake(
                               x-(width/2)*cosf(A)-(height/2)*sinf(A),
                               y+(height/2)*cosf(A)-(width/2)*sinf(A))];
NSLog(@"%f, %f", x-(width/2)*cosf(A)-(height/2)*sinf(A),
      y+(height/2)*cosf(A)-(width/2)*sinf(A));

//3
[aPath moveToPoint:CGPointMake(
                               x-(width/2)*cosf(A)+(height/2)*sinf(A),
                               y-(height/2)*cosf(A)-(width/2)*sinf(A))];
NSLog(@"%f, %f", x-(width/2)*cosf(A)+(height/2)*sinf(A),
      y-(height/2)*cosf(A)-(width/2)*sinf(A));

//4
[aPath moveToPoint:CGPointMake(
                               x+(width/2)*cosf(A)+(height/2)*sinf(A),
                               y-(height/2)*cosf(A)+(width/2)*sinf(A))];
NSLog(@"%f, %f", x+(width/2)*cosf(A)+(height/2)*sinf(A),
      y-(height/2)*cosf(A)+(width/2)*sinf(A));

//5
[aPath moveToPoint:CGPointMake(
                               x+(width/2)*cosf(A)-(height/2)*sinf(A),
                               y+(height/2)*cosf(A)+(width/2)*sinf(A))];
NSLog(@"%f, %f", x+(width/2)*cosf(A)-(height/2)*sinf(A),
      y+(height/2)*cosf(A)+(width/2)*sinf(A));
[aPath closePath];

我在想这样的事情：问题的图片。（这里的形状不同。）我希望黄色部分是一个新的UIImage。

Answer 1

使用UIBezierPath作为剪切路径。对此有addClip方法。

有关详细信息，请参阅Quartz2D编程指南，尤其是本部分。

这个想法是创建一个新的位图上下文，使用您的路径应用剪切，然后在这个位图上下文上绘制图像（因此会被剪切），最后从中生成UIImage

此外，与其自己计算旋转要用于剪切的CGRect，不如创建一个不进行任何旋转的CGRect，并使用CGAffineTransform来旋转它。这将避免使用cos/sin函数自己进行计算，并使代码更易于阅读

---

[EDIT]以下是的完整示例

• 生成Bezier路径并对其应用CGAffineTransform旋转
• 使用此贝塞尔路径来剪裁图像

我确实检查了一下，效果很好。

// Generate a UIBezierPath of a rounded rect rotated by angle radians
-(UIBezierPath*)computePathWithRect:(CGRect)rect
                       cornerRadius:(CGFloat)cornerRadius
                              angle:(CGFloat)radians;
{
  // Compute basic path
  UIBezierPath* path = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:cornerRadius];
  // Apply rotation.
  // Don't forget that rotations are around origin 0,0 so if you want to rotate around the rect's center,
  // you need to apply a translation so that the rect's center is at 0,0, then rotate, and translate it back at its original position.
  CGAffineTransform restoreCenterPosition = CGAffineTransformMakeTranslation(CGRectGetMidX(rect), CGRectGetMidY(rect));
  CGAffineTransform rotateFromOrigin = CGAffineTransformRotate(restoreCenterPosition,radians);
  CGAffineTransform rotateFromRectCenter = CGAffineTransformTranslate(rotateFromOrigin, -CGRectGetMidX(rect), -CGRectGetMidY(rect));
  [path applyTransform:rotateFromRectCenter];
  return path;
}
// Generate a new image from srcImage but clipped with the given path
-(UIImage*)clipImage:(UIImage*)srcImage withPath:(UIBezierPath*)path
{
  UIGraphicsBeginImageContextWithOptions(srcImage.size, NO, 0.0);
  // Add clipping path
  // Actually UIBezierPath has a method for that, that is equivalent to CGContextClip(currentContext, bezierPath.CGPath), so better use it
  [path addClip];
  // Flip coordinates before drawing image as UIKit and CoreGraphics have inverted coordinate system
  CGContextTranslateCTM(UIGraphicsGetCurrentContext(), 0, srcImage.size.height);
  CGContextScaleCTM(UIGraphicsGetCurrentContext(), 1, -1);
  // Draw image, that will thus be clipped, on the bitmap context
  CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, srcImage.size.width, srcImage.size.height), srcImage.CGImage);
  // Generate final (clipped) image
  UIImage* clippedImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return clippedImage;
}

// Usage example
- (void)doClipping
{
  UIImage* originalImage = ...
  UIBezierPath* path = [self computePathWithRect:CGRectMake(100,100,184,94)
                                    cornerRadius:10.f
                                           angle:30*M_PI/180.f];
  UIImage* clippedImage = [self clipImage:originalImage withPath:path];
  self.resultImageView.image = clippedImage;
}