将SceneKit场景渲染为视频输出

Question

作为一个主要的高级/ iOS开发者,我有兴趣将SceneKit用于动画项目.

几个月来我一直在玩SceneKit,尽管它显然是为"实时"互动设计的,但我觉得能够将SKScene"呈现"为视频非常有用.目前,我一直在使用Quicktime的屏幕录像机来捕获视频输出,但(当然)帧速率会下降.是否有一种替代方案可以按照自己的节奏渲染场景并输出为流畅的视频文件？

我明白这是不可能的......只是想我会问,以防我错过了一些低级别的东西!

Answer 1

您可以使用SCNRenderer渲染到屏幕外的CGImage,然后使用AVFoundation将CGImage添加到视频流中.

我写了这个Swift扩展来渲染成CGImage.

public extension SCNRenderer {

    public func renderToImageSize(size: CGSize, floatComponents: Bool, atTime time: NSTimeInterval) -> CGImage? {

        var thumbnailCGImage: CGImage?

        let width = GLsizei(size.width), height = GLsizei(size.height)
        let samplesPerPixel = 4

        #if os(iOS)
            let oldGLContext = EAGLContext.currentContext()
            let glContext = unsafeBitCast(context, EAGLContext.self)

            EAGLContext.setCurrentContext(glContext)
            objc_sync_enter(glContext)
        #elseif os(OSX)
            let oldGLContext = CGLGetCurrentContext()
            let glContext = unsafeBitCast(context, CGLContextObj.self)

            CGLSetCurrentContext(glContext)
            CGLLockContext(glContext)
        #endif

        // set up the OpenGL buffers
        var thumbnailFramebuffer: GLuint = 0
        glGenFramebuffers(1, &thumbnailFramebuffer)
        glBindFramebuffer(GLenum(GL_FRAMEBUFFER), thumbnailFramebuffer); checkGLErrors()

        var colorRenderbuffer: GLuint = 0
        glGenRenderbuffers(1, &colorRenderbuffer)
        glBindRenderbuffer(GLenum(GL_RENDERBUFFER), colorRenderbuffer)
        if floatComponents {
            glRenderbufferStorage(GLenum(GL_RENDERBUFFER), GLenum(GL_RGBA16F), width, height)
        } else {
            glRenderbufferStorage(GLenum(GL_RENDERBUFFER), GLenum(GL_RGBA8), width, height)
        }
        glFramebufferRenderbuffer(GLenum(GL_FRAMEBUFFER), GLenum(GL_COLOR_ATTACHMENT0), GLenum(GL_RENDERBUFFER), colorRenderbuffer); checkGLErrors()

        var depthRenderbuffer: GLuint = 0
        glGenRenderbuffers(1, &depthRenderbuffer)
        glBindRenderbuffer(GLenum(GL_RENDERBUFFER), depthRenderbuffer)
        glRenderbufferStorage(GLenum(GL_RENDERBUFFER), GLenum(GL_DEPTH_COMPONENT24), width, height)
        glFramebufferRenderbuffer(GLenum(GL_FRAMEBUFFER), GLenum(GL_DEPTH_ATTACHMENT), GLenum(GL_RENDERBUFFER), depthRenderbuffer); checkGLErrors()

        let framebufferStatus = Int32(glCheckFramebufferStatus(GLenum(GL_FRAMEBUFFER)))
        assert(framebufferStatus == GL_FRAMEBUFFER_COMPLETE)
        if framebufferStatus != GL_FRAMEBUFFER_COMPLETE {
            return nil
        }

        // clear buffer
        glViewport(0, 0, width, height)
        glClear(GLbitfield(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)); checkGLErrors()

        // render
        renderAtTime(time); checkGLErrors()

        // create the image
        if floatComponents { // float components (16-bits of actual precision)

            // slurp bytes out of OpenGL
            typealias ComponentType = Float

            var imageRawBuffer = [ComponentType](count: Int(width * height) * samplesPerPixel * sizeof(ComponentType), repeatedValue: 0)
            glReadPixels(GLint(0), GLint(0), width, height, GLenum(GL_RGBA), GLenum(GL_FLOAT), &imageRawBuffer)

            // flip image vertically — OpenGL has a different 'up' than CoreGraphics
            let rowLength = Int(width) * samplesPerPixel
            for rowIndex in 0..<(Int(height) / 2) {
                let baseIndex = rowIndex * rowLength
                let destinationIndex = (Int(height) - 1 - rowIndex) * rowLength

                swap(&imageRawBuffer[baseIndex..<(baseIndex + rowLength)], &imageRawBuffer[destinationIndex..<(destinationIndex + rowLength)])
            }

            // make the CGImage
            var imageBuffer = vImage_Buffer(
                data: UnsafeMutablePointer<Float>(imageRawBuffer),
                height: vImagePixelCount(height),
                width: vImagePixelCount(width),
                rowBytes: Int(width) * sizeof(ComponentType) * samplesPerPixel)

            var format = vImage_CGImageFormat(
                bitsPerComponent: UInt32(sizeof(ComponentType) * 8),
                bitsPerPixel: UInt32(sizeof(ComponentType) * samplesPerPixel * 8),
                colorSpace: nil, // defaults to sRGB
                bitmapInfo: CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue | CGBitmapInfo.ByteOrder32Little.rawValue | CGBitmapInfo.FloatComponents.rawValue),
                version: UInt32(0),
                decode: nil,
                renderingIntent: kCGRenderingIntentDefault)

            var error: vImage_Error = 0
            thumbnailCGImage = vImageCreateCGImageFromBuffer(&imageBuffer, &format, nil, nil, vImage_Flags(kvImagePrintDiagnosticsToConsole), &error)!.takeRetainedValue()

        } else { // byte components

            // slurp bytes out of OpenGL
            typealias ComponentType = UInt8

            var imageRawBuffer = [ComponentType](count: Int(width * height) * samplesPerPixel * sizeof(ComponentType), repeatedValue: 0)
            glReadPixels(GLint(0), GLint(0), width, height, GLenum(GL_RGBA), GLenum(GL_UNSIGNED_BYTE), &imageRawBuffer)

            // flip image vertically — OpenGL has a different 'up' than CoreGraphics
            let rowLength = Int(width) * samplesPerPixel
            for rowIndex in 0..<(Int(height) / 2) {
                let baseIndex = rowIndex * rowLength
                let destinationIndex = (Int(height) - 1 - rowIndex) * rowLength

                swap(&imageRawBuffer[baseIndex..<(baseIndex + rowLength)], &imageRawBuffer[destinationIndex..<(destinationIndex + rowLength)])
            }

            // make the CGImage
            var imageBuffer = vImage_Buffer(
                data: UnsafeMutablePointer<Float>(imageRawBuffer),
                height: vImagePixelCount(height),
                width: vImagePixelCount(width),
                rowBytes: Int(width) * sizeof(ComponentType) * samplesPerPixel)

            var format = vImage_CGImageFormat(
                bitsPerComponent: UInt32(sizeof(ComponentType) * 8),
                bitsPerPixel: UInt32(sizeof(ComponentType) * samplesPerPixel * 8),
                colorSpace: nil, // defaults to sRGB
                bitmapInfo: CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue | CGBitmapInfo.ByteOrder32Big.rawValue),
                version: UInt32(0),
                decode: nil,
                renderingIntent: kCGRenderingIntentDefault)

            var error: vImage_Error = 0
            thumbnailCGImage = vImageCreateCGImageFromBuffer(&imageBuffer, &format, nil, nil, vImage_Flags(kvImagePrintDiagnosticsToConsole), &error)!.takeRetainedValue()
        }

        #if os(iOS)
            objc_sync_exit(glContext)
            if oldGLContext != nil {
                EAGLContext.setCurrentContext(oldGLContext)
            }
        #elseif os(OSX)
            CGLUnlockContext(glContext)
            if oldGLContext != nil {
                CGLSetCurrentContext(oldGLContext)
            }
        #endif

        return thumbnailCGImage
    }
}


func checkGLErrors() {
    var glError: GLenum
    var hadError = false
    do {
        glError = glGetError()
        if glError != 0 {
            println(String(format: "OpenGL error %#x", glError))
            hadError = true
        }
    } while glError != 0
    assert(!hadError)
}

Answer 2

实际上这很容易！这是我如何做到这一点的伪代码（在 SCNView 上）：

int numberOfFrames = 300;
int currentFrame = 0;
int framesPerSecond = 30;

-(void) renderAFrame{
    [self renderAtTime:1/framesPerSecond];

    NSImage *frame = [self snapshot];

    // save the image with the frame number in the name such as f_001.png

    currentFrame++;

    if(currentFrame < numberOfFrames){
        [self renderAFrame];
    }

}

它将输出一系列图像，以每秒 30 帧的速度渲染，您可以将其导入任何编辑软件中并转换为视频。