ios - SceneKit - 在不使用单独的 SCNRenderer 的情况下从 SCNView 获取渲染场景作为 MTLTexture

Question

我的 SCNView 使用 Metal 作为渲染 API，我想知道是否有一种方法可以将渲染场景抓取为 MTLTexture 而无需使用单独的SCN渲染器？当我尝试通过 SCNView 显示场景并通过 SCNRenderer 将屏幕外的场景重新渲染到 MTLTexture 时，性能下降(我试图抓取每一帧的输出)。

SCNView 让我可以访问它使用的 MTLDevice、MTLRenderCommandEncoder 和 MTLCommandQueue，但不能为了获得MTLTexture(通过renderPassDescriptor.colorAttachments[0].texture)我需要底层的MTLRenderPassDescriptor

我尝试的一些替代方法是尝试使用 SCNView.snapshot() 获取 UIImage 并转换它，但性能更差。

Answer 1

针对 Swift 4 更新:

Swift 4 不支持 dispatch_once()，并且在替换函数中添加了@objc。这是更新的 swizzle 设置。这已经过测试，对我来说效果很好。

extension CAMetalLayer {

    // Interface so user can grab this drawable at any time
    private struct nextDrawableExtPropertyData {
        static var _currentSceneDrawable : CAMetalDrawable? = nil
    }
    var currentSceneDrawable : CAMetalDrawable? {
        get {
            return nextDrawableExtPropertyData._currentSceneDrawable
        }
    }

    // The rest of this is just swizzling
    private static let doJustOnce : Any? = {
        print ("***** Doing the doJustOnce *****")
        CAMetalLayer.setupSwizzling()

        return nil
    }()

    public static func enableNextDrawableSwizzle() {
        _ = CAMetalLayer.doJustOnce
    }

    public static func setupSwizzling() {
        print ("***** Doing the setupSwizzling *****")

        let copiedOriginalSelector = #selector(CAMetalLayer.originalNextDrawable)
        let originalSelector = #selector(CAMetalLayer.nextDrawable)
        let swizzledSelector = #selector(CAMetalLayer.newNextDrawable)

        let copiedOriginalMethod = class_getInstanceMethod(self, copiedOriginalSelector)
        let originalMethod = class_getInstanceMethod(self, originalSelector)
        let swizzledMethod = class_getInstanceMethod(self, swizzledSelector)

        let oldImp = method_getImplementation(originalMethod!)
        method_setImplementation(copiedOriginalMethod!, oldImp)

        let newImp = method_getImplementation(swizzledMethod!)
        method_setImplementation(originalMethod!, newImp)

    }


    @objc func newNextDrawable() -> CAMetalDrawable? {
        // After swizzling, originalNextDrawable() actually calls the real nextDrawable()
        let drawable = originalNextDrawable()

        // Save the drawable
        nextDrawableExtPropertyData._currentSceneDrawable = drawable

        return drawable
    }

    @objc func originalNextDrawable() -> CAMetalDrawable? {
        // This is just a placeholder. Implementation will be replaced with nextDrawable.
        // ***** This will never be called *****
        return nil
    }
}

在你的 AppDelegate 中:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.

    // Swizzle
    CAMetalLayer.enableNextDrawableSwizzle()

    return true
}

已更新以将 currentSceneDrawable 属性添加到 CAMetalLayer，因此您只需使用 layer.currentSceneDrawable 即可访问它，而不是让扩展程序将其存储在外部。