For Example: vertex void computeNormal(uint vertexID [[vertex_id]], ... ) { ... } I can't debug such as this function, because it don't return any vertex output just a void function.

How to debug a void vertex function?

Hey, have you solved the problem yet?

Add more info here is the code of CVPixelBuffer    let attributes : [NSObject:AnyObject] = [    kCVPixelBufferCGImageCompatibilityKey : true as AnyObject,    kCVPixelBufferCGBitmapContextCompatibilityKey : true as AnyObject,    kCVPixelBufferIOSurfacePropertiesKey: [     "IOSurfaceOpenGLESFBOCompatibility": true,     "IOSurfaceOpenGLESTextureCompatibility": true,     "IOSurfaceCoreAnimationCompatibility": true     ] as AnyObject   ]       CVPixelBufferCreate(kCFAllocatorDefault,             Int(width), Int(height),             kCVPixelFormatType_420YpCbCr8BiPlanarFullRange,             attributes as CFDictionary,             &pixelBuffer)