Take snapshot from CAEAGLLayer

CAEAGLLayer+Snapshot.swift

import QuartzCore
import OpenGLES

extension CAEAGLLayer {
    func takeSnapshot(from renderBuffer: GLuint? = nil) -> UIImage {
        var bufferWidth: GLint = 0
        var bufferHeight: GLint = 0
        
        if let buffer = renderBuffer {
            glBindRenderbufferOES(GLenum(GL_RENDERBUFFER_OES), buffer)
        }
        glGetRenderbufferParameterivOES(GLenum(GL_RENDERBUFFER_OES), GLenum(GL_RENDERBUFFER_WIDTH_OES), &bufferWidth)
        glGetRenderbufferParameterivOES(GLenum(GL_RENDERBUFFER_OES), GLenum(GL_RENDERBUFFER_HEIGHT_OES), &bufferHeight)
        
        let width = Int(bufferWidth)
        let height = Int(bufferHeight)
        let length = Int(width * height * 4)
        let data = malloc(length * sizeof(GLubyte))
        
        glPixelStorei(GLenum(GL_PACK_ALIGNMENT), 4)
        glReadPixels(0, 0, bufferWidth, bufferHeight, GLenum(GL_RGBA), GLenum(GL_UNSIGNED_BYTE), data)
        
        let dataProvider = CGDataProviderCreateWithData(nil, data, length, nil)
        let colorspace = CGColorSpaceCreateDeviceRGB()
        let image = CGImageCreate(width, height, 8, 32, width * 4, colorspace, .ByteOrderDefault, dataProvider, nil, true, .RenderingIntentDefault)!
        
        UIGraphicsBeginImageContextWithOptions(CGSize(width: width, height: height), false, contentsScale)
        let context = UIGraphicsGetCurrentContext()
        CGContextSetBlendMode(context, .Copy)
        CGContextDrawImage(context, CGRect(x: 0, y: 0, width: width, height: height), image)
        let renderedImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        free(data)
        
        return renderedImage
    }
}