iOS 不规则（多边形）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< pointArr.count; 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 <NSValue *> *)arr {
    
    if (arr.count<=0) return CGRectZero;
    
    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< arr.count; i++) {
        
        NSValue * value = arr[I];
        
        CGPoint p = [value CGPointValue];
        
        if (p.x > xMax) xMax = p.x;

        if (p.x < xMin) xMin = p.x;

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

        if (p.y < yMin) yMin = 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;
}

最后编辑于：2018.03.23 16:17:07