如何在 iOS 中从 MTKView 制作屏幕截图？

Question

我参考MetalKitEssentials，并通过MetalKit在iOS 9.1中制作模型查看器应用程序。

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

我该怎么办？

感谢您的阅读！

代码：

@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

Answer 1

自行解决。

我找到了一个类似的topic。

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 exec 错误。

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

此错误已在以下修复中得到修复。 所以，我改变了 MTKView 的设置。

metalView.framebufferOnly = false;

谢谢。

Answer 2

参考：https://stackoverflow.com/a/33903182/767280.

对于 swift 4.0，

let lastDrawableDisplayed = metalView?.currentDrawable?.texture

if let imageRef = lastDrawableDisplayed?.toImage() {
    let uiImage:UIImage = UIImage.init(cgImage: imageRef)
}

extension MTLTexture {

    func bytes() -> UnsafeMutableRawPointer {
        let width = self.width
        let height   = self.height
        let rowBytes = self.width * 4
        let p = malloc(width * height * 4)

        self.getBytes(p!, bytesPerRow: rowBytes, from: MTLRegionMake2D(0, 0, width, height), mipmapLevel: 0)

        return p!
    }

    func toImage() -> CGImage? {
        let p = bytes()

        let pColorSpace = CGColorSpaceCreateDeviceRGB()

        let rawBitmapInfo = CGImageAlphaInfo.noneSkipFirst.rawValue | CGBitmapInfo.byteOrder32Little.rawValue
        let bitmapInfo:CGBitmapInfo = CGBitmapInfo(rawValue: rawBitmapInfo)

        let selftureSize = self.width * self.height * 4
        let rowBytes = self.width * 4
        let releaseMaskImagePixelData: CGDataProviderReleaseDataCallback = { (info: UnsafeMutableRawPointer?, data: UnsafeRawPointer, size: Int) -> () in
            return
        }
        let provider = CGDataProvider(dataInfo: nil, data: p, size: selftureSize, releaseData: releaseMaskImagePixelData)
        let cgImageRef = CGImage(width: self.width, height: self.height, bitsPerComponent: 8, bitsPerPixel: 32, bytesPerRow: rowBytes, space: pColorSpace, bitmapInfo: bitmapInfo, provider: provider!, decode: nil, shouldInterpolate: true, intent: CGColorRenderingIntent.defaultIntent)!

        return cgImageRef
    }
}

Answer 3

self.mtkView.framebufferOnly = 否；

- (UIImage *)imageWithCurrentTexture:(MTKView *)mtkView {
     CIContext * context = [CIContext contextWithMTLDevice:mtkView.device];
     CIImage *outputImage = [[CIImage alloc] initWithMTLTexture:mtkView.currentDrawable.texture options:@{kCIImageColorSpace:(__bridge_transfer id)CGColorSpaceCreateDeviceRGB()}];
     CGImageRef cgImg = [context createCGImage:outputImage fromRect:CGRectMake(0, 0, [UIScreen mainScreen].nativeBounds.size.width, [UIScreen mainScreen].nativeBounds.size.height)];
     UIImage *resultImg = [UIImage imageWithCGImage:cgImg scale:1.0 orientation:UIImageOrientationDownMirrored];
     CGImageRelease(cgImg);
     return resultImg;
}