使用renderInContext：为由cgpaths创建的蒙版

Question

我最近发现，renderinContext:方法会忽略任何图层蒙版。我正在试图捕捉我的应用程序屏幕的视频，在其中我对蒙版CALayer的路径进行动画处理。

为了录制屏幕，我使用了在网上找到的ScreenCaptureView类。该视图每x秒钟拍摄一次其子视图的“截图”，并将它们编译成一个视频。

在drawRect方法中，我调用

[[self.layer presentationLayer] renderInContext:context];

在网上查找后，我找到了一个人的解决方案； 但是，它适用于图像掩码（我的掩码是CGPath）。

-(UIImage*) imageFromView:(UIView*)originalView
{
    //Creating a fakeView which is initialized as our original view.
    //Actually i render images on a fakeView and take screenshot of this fakeView.
    UIView *fakeView = [[UIView alloc] initWithFrame:originalView.frame];

   [fakeView.layer setMasksToBounds:originalView.layer.masksToBounds];

            //Getting subviews of originalView.
            for (UIView *view in originalView.subviews)
            {
                //Getting screenshot of layer of view.
                UIGraphicsBeginImageContext(view.bounds.size);
                [view.layer renderInContext:UIGraphicsGetCurrentContext()];
                UIImage *imageLayer = UIGraphicsGetImageFromCurrentImageContext();
                UIGraphicsEndImageContext();

                //If it is masked view, then get masked image.
                if (view.layer.mask)
                {
                    //getting screenshot of masked layer.
                    UIGraphicsBeginImageContext(view.bounds.size);
                    [view.layer.mask renderInContext:UIGraphicsGetCurrentContext()];

                    //PNG Representation is most important. otherwise this masked image will not work.
                    UIImage *maskedLayerImage=[UIImage imageWithData:UIImagePNGRepresentation(UIGraphicsGetImageFromCurrentImageContext())];
                    UIGraphicsEndImageContext();

                    //getting image by masking original image.
                    imageLayer = [self maskImage:imageLayer withMask:maskedLayerImage];
                }

                //If imageLayer is pointing to a valid object, then setting this image to UIImageView, our UIImageView frame having exactly as view.frame.
                if (imageLayer)
                {
                    UIImageView *imageView = [[UIImageView alloc] initWithFrame:view.frame];
                    [imageView setImage:imageLayer];
                    [fakeView addSubview:imageView];
                }
            }

            //At the end, taking screenshot of fakeView. This will get your Original Image.
            UIGraphicsBeginImageContext(fakeView.bounds.size);
            [fakeView.layer renderInContext:UIGraphicsGetCurrentContext()];
            UIImage *previewCapturedImage = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
            return previewCapturedImage;
        }
}

//Method is used to get masked image.
- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage
{
    CGImageRef maskRef = maskImage.CGImage; 
    CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
                                        CGImageGetHeight(maskRef),
                                        CGImageGetBitsPerComponent(maskRef),
                                        CGImageGetBitsPerPixel(maskRef),
                                        CGImageGetBytesPerRow(maskRef),
                                        CGImageGetDataProvider(maskRef), NULL, false);

    CGImageRef masked = CGImageCreateWithMask([image CGImage], mask);

    return [UIImage imageWithCGImage:masked];
}

我可以为cgpaths的蒙版做类似的事情吗？

- Mahir

Answer 1

在编写 renderInContext: 代码时，你可以使用 CGContextClip() 方法来将其剪切矩形路径：

- (void)renderInContext:(CGContextRef)context {

    // Assign maskPath to whatever path you want to mask to (Here, it's assumed that your layer's mask is a CAShapeLayer)
    CGPathPathRef maskPath = [(CAShapeLayer *)self.mask path];
    CGContextAddPath(context, maskPath);
    CGContextClip(context);

    // Do drawing code here
}

- Austin