ios - 在 Metal 中渲染后翻转图片
问题描述
我正在尝试在 MTKView 中渲染动画并遇到一个奇怪的问题。在模拟器中,我看到翻转的图片,但在设备上一切都很好。我还使用相同的方法渲染视频,并且图片在设备和模拟器上具有相同的方向。
这是重现我的问题的最简化示例:
class TestVC: UIViewController {
var output: MTKView!
let device: MTLDevice
let context: CIContext
let colorSpace = CGColorSpaceCreateDeviceRGB()
let queue: MTLCommandQueue?
let image: CIImage
init() {
let defaultDevice = MTLCreateSystemDefaultDevice()!
self.device = defaultDevice
self.context = CIContext(mtlDevice: defaultDevice)
self.queue = defaultDevice.makeCommandQueue()
self.image = CIImage(image: UIImage(named: "lena.png")!)!
super.init(nibName: nil, bundle: nil)
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .red
makeOutputView()
}
func makeOutputView() {
let side = min(view.frame.size.width, view.frame.size.height) * 0.9
let viewFrame = CGRect(x: 0, y: 0, width: side, height: side)
output = MTKView(frame: viewFrame, device: device)
view.addSubview(output)
output.center = view.center
output.framebufferOnly = false
output.delegate = self
}
}
extension TestVC: MTKViewDelegate {
func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {}
func draw(in view: MTKView) {
let buffer = queue?.makeCommandBuffer()
guard let drawable = view.currentDrawable else { return }
let dpi = UIScreen.main.nativeScale
let width = view.bounds.width * dpi
let height = view.bounds.height * dpi
let rect = CGRect(x: 0, y: 0, width: width, height: height)
let extent = image.extent
let xScale = extent.width > 0 ? width / extent.width : 1
let yScale = extent.height > 0 ? height / extent.height : 1
let scale = max(xScale, yScale)
let tx = (width - extent.width * scale) / 2
let ty = (height - extent.height * scale) / 2
let transform = CGAffineTransform(a: scale, b: 0, c: 0, d: scale, tx: tx, ty: ty)
let filter = CIFilter(name: "CIAffineTransform",
parameters: ["inputImage": image, "inputTransform": transform])!
let scaledImage = filter.outputImage!
context.render(scaledImage,
to: drawable.texture,
commandBuffer: buffer,
bounds: rect,
colorSpace: colorSpace)
buffer?.present(drawable)
buffer?.commit()
}
}
解决方案
此问题与使用 Mac 上使用不同坐标系的 GPU 的模拟器有关。一个快速的解决方法是在模拟器中运行图像时翻转图像。
var scaledImage = filter.outputImage!
#if targetEnvironment(simulator)
scaledImage = scaledImage.transformed(by: CGAffineTransform(scaleX: 1, y: -1))
.transformed(by: CGAffineTransform(translationX: 0, y: scaledImage.extent.height))
#endif
context.render(scaledImage,
to: drawable.texture,
commandBuffer: buffer,
bounds: rect,
colorSpace: colorSpace)
buffer?.present(drawable)
buffer?.commit()
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