iOS 不规则图形切图

效果如下：

Untitled.gif

研究背景

最近在做一个和人脸识别有关的

把人脸的眉毛、眼睛、鼻子等切出来 （后来改成只切一张人脸）

解决方法

第三方人脸识别的SDK会返回一些点给我们，如下图所示

然后用这些坐标绘制一个不规则的图像

最后用这个不规则的图像做遮罩层，把图片切出来

如果有需要 保存不规则图片的大小就好，把空白的去掉，那就要再写多一步，原理相同

image.png

多边形切图代码

- (UIImage *) cropImageWithImageV:(UIImageView *)imageV pointArr:(NSMutableArray *)pointArr {

CGRect rect = CGRectZero;

rect.size = imageV.image.size;

UIGraphicsBeginImageContextWithOptions(rect.size, YES, 0.0);

[[UIColor blackColor] setFill];

UIRectFill(rect);

[[UIColor whiteColor] setFill];

UIBezierPath *aPath = [UIBezierPath bezierPath];

//起点

NSValue * v = pointArr[0];

CGPoint p = [v CGPointValue];

CGPoint m_p = [self convertCGPoint:p fromRect1:imageV.frame.size toRect2:imageV.frame.size];

[aPath moveToPoint:m_p];

//其他点

for (int i = 1; i

NSValue * v1 = pointArr[i];

CGPoint p1 = [v1 CGPointValue];

CGPoint m_p = [self convertCGPoint:p1 fromRect1:imageV.frame.size toRect2:imageV.frame.size];

[aPath addLineToPoint:m_p];

}

[aPath closePath];

[aPath fill];

//遮罩层

UIImage *mask = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0.0);

CGContextClipToMask(UIGraphicsGetCurrentContext(), rect, mask.CGImage);

[imageV.image drawAtPoint:CGPointZero];

UIImage *maskedImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return maskedImage;

}

- (CGPoint)convertCGPoint:(CGPoint)point1 fromRect1:(CGSize)rect1 toRect2:(CGSize)rect2 {

point1.y = rect1.height - point1.y;

CGPoint result = CGPointMake((point1.x*rect2.width)/rect1.width, (point1.y*rect2.height)/rect1.height);

return result;

}

而如果你需要把空白的去掉 只保留有内容的图片大小就好，则要求 包含所有点的最小矩形 或直接求多边形 直接求多边形的算法我还没去研究 现在我只需要一个矩形就可以了

最小矩形算法

//算出包含数组里所有点的最小矩形

- (CGRect)returnMinRectangleWith:(NSMutableArray *)arr {

if (arr.count

NSValue * tempValue = arr[0];

CGPoint tempP = [tempValue CGPointValue];

CGFloat xMin = tempP.x;

CGFloat xMax = tempP.x;

CGFloat yMin = tempP.y;

CGFloat yMax = tempP.y;

for (int i = 1; i

NSValue * value = arr[I];

CGPoint p = [value CGPointValue];

if (p.x > xMax) xMax = p.x;

if (p.x

if (p.y > yMax) yMax = p.y;

if (p.y

}

return CGRectMake(xMin, yMin, xMax-xMin, yMax-yMin);

}

切割图片

//缩小图片

- (UIImage *)screenshotWithRect:(CGRect)rect imageView:(UIImageView *)imageV {

UIGraphicsBeginImageContextWithOptions(rect.size, NO, [UIScreen mainScreen].scale);

CGContextRef context = UIGraphicsGetCurrentContext();

if (context == NULL) return nil;

CGContextSaveGState(context);

CGContextTranslateCTM(context, -rect.origin.x, -rect.origin.y);

if( [self respondsToSelector:@selector(drawViewHierarchyInRect:afterScreenUpdates:)])

{

[imageV drawViewHierarchyInRect:imageV.bounds afterScreenUpdates:NO];

}

else

{

[imageV.layer renderInContext:context];

}

CGContextRestoreGState(context);

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return image;

}

作者：李境沛

链接：https://www.jianshu.com/p/4c47ac91c85f