iOS实现高效裁剪图片圆角算法教程

//CGContext裁剪
+ (UIImage *)CGContextClip:(UIImage *)img cornerRadius:(CGFloat)c;

// CGContext 裁剪
+ (UIImage *)CGContextClip:(UIImage *)img cornerRadius:(CGFloat)c{
 int w = img.size.width * img.scale;
 int h = img.size.height * img.scale;
 UIGraphicsBeginImageContextWithOptions(CGSizeMake(w, h), false, 1.0);
 CGContextRef context = UIGraphicsGetCurrentContext();
 CGContextMoveToPoint(context, 0, c);
 CGContextAddArcToPoint(context, 0, 0, c, 0, c);
 CGContextAddLineToPoint(context, w-c, 0);
 CGContextAddArcToPoint(context, w, 0, w, c, c);
 CGContextAddLineToPoint(context, w, h-c);
 CGContextAddArcToPoint(context, w, h, w-c, h, c);
 CGContextAddLineToPoint(context, c, h);
 CGContextAddArcToPoint(context, 0, h, 0, h-c, c);
 CGContextAddLineToPoint(context, 0, c);
 CGContextClosePath(context);
 
 // 先裁剪 context，再画图，就会在裁剪后的 path 中画
 CGContextClip(context);
 [img drawInRect:CGRectMake(0, 0, w, h)]; // 画图
 CGContextDrawPath(context, kCGPathFill);
 UIImage *ret = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();
 
 return ret;
}

[Util CGContextClip:image cornerRadius:radius];

//UIBezierPath 裁剪
+ (UIImage *)UIBezierPathClip:(UIImage *)img cornerRadius:(CGFloat)c;

//UIBezierPath 裁剪
+ (UIImage *)UIBezierPathClip:(UIImage *)img cornerRadius:(CGFloat)c{
 int w = img.size.width * img.scale;
 int h = img.size.height * img.scale;
 CGRect rect = CGRectMake(0, 0, w, h);
 UIGraphicsBeginImageContextWithOptions(CGSizeMake(w, h), false, 1.0);
 [[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:c] addClip];
 [img drawInRect:rect];
 
 UIImage *ret = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();
 return ret;
}

+ (UIImage *)dealImage:(UIImage *)img cornerRadius:(CGFloat)c

+ (UIImage *)dealImage:(UIImage *)img cornerRadius:(CGFloat)c {
 // 1.CGDataProviderRef 把 CGImage 转 二进制流
 CGDataProviderRef provider = CGImageGetDataProvider(img.CGImage);
 void *imgData = (void *)CFDataGetBytePtr(CGDataProviderCopyData(provider));
 int width = img.size.width * img.scale;
 int height = img.size.height * img.scale;
 
 // 2.处理 imgData
// dealImage(imgData, width, height);
 cornerImage(imgData, width, height, c);
 
 // 3.CGDataProviderRef 把 二进制流 转 CGImage
 CGDataProviderRef pv = CGDataProviderCreateWithData(NULL, imgData, width * height * 4, releaseData);
 CGImageRef content = CGImageCreate(width , height, 8, 32, 4 * width, CGColorSpaceCreateDeviceRGB(), kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast, pv, NULL, true, kCGRenderingIntentDefault);
 UIImage *result = [UIImage imageWithCGImage:content];
 CGDataProviderRelease(pv); // 释放空间
 CGImageRelease(content);
 
 return result;
}

void releaseData(void *info, const void *data, size_t size) {
 free((void *)data);
}

// 在 img 上处理图片, 测试用
void dealImage(UInt32 *img, int w, int h) {
 int num = w * h;
 UInt32 *cur = img;
 for (int i=0; i<num; i++, cur++) {
 UInt8 *p = (UInt8 *)cur;
 // RGBA 排列
 // f(x) = 255 - g(x) 求负片
 p[0] = 255 - p[0];
 p[1] = 255 - p[1];
 p[2] = 255 - p[2];
 p[3] = 255;
 }
}

// 裁剪圆角
void cornerImage(UInt32 *const img, int w, int h, CGFloat cornerRadius) {
 CGFloat c = cornerRadius;
 CGFloat min = w > h ? h : w;
 
 if (c < 0) { c = 0; }
 if (c > min * 0.5) { c = min * 0.5; }
 
 // 左上 y:[0, c), x:[x, c-y)
 for (int y=0; y<c; y++) {
 for (int x=0; x<c-y; x++) {
  UInt32 *p = img + y * w + x; // p 32位指针，RGBA排列，各8位
  if (isCircle(c, c, c, x, y) == false) {
  *p = 0;
  }
 }
 }
 // 右上 y:[0, c), x:[w-c+y, w)
 int tmp = w-c;
 for (int y=0; y<c; y++) {
 for (int x=tmp+y; x<w; x++) {
  UInt32 *p = img + y * w + x;
  if (isCircle(w-c, c, c, x, y) == false) {
  *p = 0;
  }
 }
 }
 // 左下 y:[h-c, h), x:[0, y-h+c)
 tmp = h-c;
 for (int y=h-c; y<h; y++) {
 for (int x=0; x<y-tmp; x++) {
  UInt32 *p = img + y * w + x;
  if (isCircle(c, h-c, c, x, y) == false) {
  *p = 0;
  }
 }
 }
 // 右下 y~[h-c, h), x~[w-c+h-y, w)
 tmp = w-c+h;
 for (int y=h-c; y<h; y++) {
 for (int x=tmp-y; x<w; x++) {
  UInt32 *p = img + y * w + x;
  if (isCircle(w-c, h-c, c, x, y) == false) {
  *p = 0;
  }
 }
 }
}

// 判断点 (px, py) 在不在圆心 (cx, cy) 半径 r 的圆内
static inline bool isCircle(float cx, float cy, float r, float px, float py) {
 if ((px-cx) * (px-cx) + (py-cy) * (py-cy) > r * r) {
 return false;
 }
 return true;
}

// 其他图像效果可以自己写函数，然后在 dealImage: 中调用 otherImage 即可
void otherImage(UInt32 *const img, int w, int h) {
 // 自定义处理
}