裁剪和缩放CGContext-iOS [英] Crop and Scale CGContext - iOS

问题描述

在上一个关于作物和规模CMSampleBufferRef 的问题之后，我发现一种修改CMSampleBufferRef内的CGContext的方法，我可以使用以下代码绘制CGContext的矩形，路径，圆形和空白矩形：

Following from my previous question about Crop and Scale CMSampleBufferRef, I found a way to modify the CGContext inside that CMSampleBufferRef and I am able to draw rectangle, path, circle and clear rect of the CGContext, using the following code:

- (void)modifyImage:(CMSampleBufferRef) sampleBuffer {
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
    
    // Lock the image buffer
    CVPixelBufferLockBaseAddress(imageBuffer,0); 
    
    // Get information about the image
    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer); 
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
    size_t width = CVPixelBufferGetWidth(imageBuffer); 
    size_t height = CVPixelBufferGetHeight(imageBuffer); 
    
    // Create a CGImageRef from the CVImageBufferRef
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
    
    CGContextSaveGState(context);

    CGContextSetFillColorWithColor(context, [[UIColor blackColor] CGColor]);
    CGContextFillRect(context, CGRectMake(0, 0, 400, 400));
    
    //restore the context and remove the clipping area.
    CGContextRestoreGState(context);
    
    
    // We unlock the image buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);
    
    // We release some components
    CGContextRelease(context); 
    CGColorSpaceRelease(colorSpace);
    return;
}

现在，我要做的是裁剪然后缩放此CGContext，我尝试使用 CGContextClipToRect（context，CGRectMake（0，0，360，640））; 和 CGContextScaleCTM（context，2，2）;

Now, what I want to do is to crop and then scale this CGContext, I tried with CGContextClipToRect(context, CGRectMake(0, 0, 360, 640)); and CGContextScaleCTM(context, 2, 2); but not successful.

有人可以在这里给我更多建议吗

Can anyone gives me some more advices here

推荐答案

您创建后无法更改CVImageBuffer的尺寸。如果需要更改尺寸，则必须创建一个新的缓冲区。

You cannot change the dimensions of a CVImageBuffer after creation. If you need to change the dimensions, you must create a new buffer.

如果要裁剪图像，然后将裁剪的部分放大到最大尺寸。原始图像，您需要在第二个缓冲区中执行缩放操作，然后从第二个缓冲区复制回第一个缓冲区。

If you want to crop the image, and then scale the cropped portion up to the size of the original image, you need to perform the scaling operation into a second buffer and then copy from the second buffer back to the first buffer.

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