将离屏SCNScene渲染到UIImage中
我怎样才能渲染一个离屏的 SCNScene到UIImage ？
我知道SCNView提供了一个-snapshot方法，但不幸的是这对于离屏视图不起作用。 在其中一个答案build议使用glReadPixels从OpenGL读取位图数据之前，也曾经有过类似的问题 ，但是这种方法对于我来说不适用于离屏场景。
我试图使用SCNRenderer没有成功的渲染到GLKView的上下文中。
这是我写的一个小代码。 你可以用它做笔记。
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) }