CGBitmapContextCreateImage - vm_copy失败 - iPhone SDK [英] CGBitmapContextCreateImage - vm_copy failed - iPhone SDK

问题描述

我在iPhone应用程序中使用CGBitmapContextCreateImage时出现问题。

I am having an issue using CGBitmapContextCreateImage in my iPhone app.

我正在使用AV Foundation Framework使用此方法抓取相机帧：

I am using AV Foundation Framework to grab camera frames using this method:

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(imageBuffer,0);
    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGImageRef newImage = CGBitmapContextCreateImage(newContext);
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);
    CGContextRelease(newContext);
    CGColorSpaceRelease(colorSpace);

    UIImage *image= [UIImage imageWithCGImage:newImage scale:1.0 orientation:UIImageOrientationRight];
    self.imageView.image = image;

    CGImageRelease(newImage);

} 

但是，我在调试控制台中看到一个错误它的运行：

However, I am seeing an error in the debug console as its runs:

<Error>: CGDataProviderCreateWithCopyOfData: vm_copy failed: status 2.

有没有人见过这个？通过注释掉我已将问题界限缩小到：

Has anyone ever seen this? By commenting out lines I have narrowed the problem line out to:

CGImageRef newImage = CGBitmapContextCreateImage(newContext);

但我不知道如何摆脱它。从功能上讲，它很棒。很明显，CGImage正在创建，但我需要知道是什么导致错误，所以它不会影响其他部分。

but I am not sure how to get rid of it. Functionally, it works great. So clearly, the CGImage is being created, but I need to know what is causing the error so it doesn't affect other parts.

非常感谢。任何帮助/建议都会很棒！
Brett

Many thanks. Any help/advice would be great! Brett

推荐答案

免责声明：这是纯粹的猜测。 不再了。

Disclaimer: this is pure speculation. Not anymore.

vm_copy（）是将虚拟内存从一个地方复制到另一个地方的内核调用（< a href =http://www.fi.muni.cz/~xholer/macosx/xnu/vm_copy.html\"rel =noreferrer>联机帮助页）。

vm_copy() is a kernel call to copy virtual memory from one place to another (manpage).

您获得的返回值是KERN_PROTECTION_FAILURE，源区域受到保护以防止读取，或者目标区域受到保护以免写入。

The return value you get is KERN_PROTECTION_FAILURE, "The source region is protected against reading, or the destination region is protected against writing."

所以对于某些人来说原因CGDataProviderCreateWithCopyOfData调用它来复制一些内存，并失败。 也许它只是首先尝试将vm_copy作为快速方法，然后再回到较慢的方法（因为你说一切正常）。

So for some reason CGDataProviderCreateWithCopyOfData calls this to copy some memory, and fails. maybe it is just trying vm_copy as a fast method first, and then falls back to a slower method (since you say everything works).

如果您 malloc 一块内存，将内存从baseAddress记忆到您自己的内存，并使用它来创建图像，警告就会消失。所以：

If you malloc a chunk of memory, memcpy the memory from baseAddress to your own memory, and use that to create the image, the warning vanishes. So:

uint8_t *tmp = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
int bytes = ... // determine number of bytes from height * bytesperrow
uint8_t *baseAddress = malloc(bytes);
memcpy(baseAddress,tmp,bytes);

// unlock the memory, do other stuff, but don't forget:
free(baseAddress);

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