如何在 iOS 中从 MTKView 制作屏幕截图图像？

我指的是金属套件必需品 https://developer.apple.com/metal/，并通过以下方式制作模型查看器应用程序MetalKit in iOS 9.1.

我想制作屏幕截图图像（RGBA 格式）MTKView。 但是，我只得到黑色图像。

我应该怎么办？

感谢您的阅读！

Code:

@implemtntation MetalViewController
{
    MTKView *metalView;
}

- (void)viewDidLoad
{
    [super viewDidload];
    [self setup];
}

- (void)setup
{
    metalDevice = MTLCreateSystemDefaultDevice();
    commandQueue = [metalDevice newCommandQueue];
    defaultLibrary = [metalDevice newDefaultLibrary];

    metalView = [[MTKView alloc] initWithFrame:self.view.frame];
    [self.view addSubview:metalView];

    metalView.delegate = self;
    metalView.device = metalDevice;
    metalView.sampleCount = 4;
    metalView.depthStencilPixelFormat = MTLPixelFormatDepth32Float_Stencil8;
    metalView.opaque = false;
    metalView.framebufferOnly = true;
    // and more set up for Metal ...
}

// if you make screen shot, call this method.
- (IBAction)onCapture:(id)sender
{
    CGRect screenRect = [[UIScreen mainScreen] bounds];
    UIGraphicsBeginImageContextWithOptions(screenRect.size, YES, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextFillRect(context, screenRect);

    // draw image to context
    [metalView.layer renderInContext:context];

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIImageWriteToSavedPhotosAlbum(image, self,
                                   @selector(completeSavedImage:didFinishSavingWithError:contextInfo:), nil);
}

- (void)completeSavedImage:(UIImage *)_image didFinishSavingWithError:(NSError *)_error contextInfo:(void *)_contextInfo
{
    if (!_error)
    {
        NSLog(@"ok");
    }
    else
    {
        NSLog(@"error");
    }
}

@end

自己解决了。

我发现了一个类似的topic https://stackoverflow.com/questions/33844130/take-a-snapshot-of-current-screen-with-metal-in-swift/33903182#33903182.

我为以下几点编写代码。

1：使用Objective-C

2：不使用扩展MTLTexture

- (IBAction)onCapture:(id)sender
{
    id<MTLTexture> lastDrawableDisplayed = [metalView.currentDrawable texture];

    int width = (int)[lastDrawableDisplayed width];
    int height = (int)[lastDrawableDisplayed height];
    int rowBytes = width * 4;
    int selfturesize = width * height * 4;

    void *p = malloc(selfturesize);

    [lastDrawableDisplayed getBytes:p bytesPerRow:rowBytes fromRegion:MTLRegionMake2D(0, 0, width, height) mipmapLevel:0];

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Little | kCGImageAlphaFirst;

    CGDataProviderRef provider = CGDataProviderCreateWithData(nil, p, selfturesize, nil);
    CGImageRef cgImageRef = CGImageCreate(width, height, 8, 32, rowBytes, colorSpace, bitmapInfo, provider, nil, true, (CGColorRenderingIntent)kCGRenderingIntentDefault);

    UIImage *getImage = [UIImage imageWithCGImage:cgImageRef];
    CFRelease(cgImageRef);
    free(p);

    NSData *pngData = UIImagePNGRepresentation(getImage);
    UIImage *pngImage = [UIImage imageWithData:pngData];
    UIImageWriteToSavedPhotosAlbum(pngImage, self,
        @selector(completeSavedImage:didFinishSavingWithError:contextInfo:), nil);
}

但是，我在 getBytes 方法中收到以下执行错误。

failed assertion `texture must not be a framebufferOnly texture.'

此错误已在以下修复中修复。 因此，我更改了 MTKView 的设置。

metalView.framebufferOnly = false;

Thanks.