OpenGLの描画内容を画像にする

-(UIImage *)createImage{

    int backingWidth = self.view.bounds.size.width;   // OpenGLのバッファの幅

    int backingHeight = self.view.bounds.size.height;   // OpenGLのバッファの高さ

    

    NSInteger myDataLength = backingWidth * backingHeight * 4;

    GLubyte *buffer = (GLubyte *) malloc(myDataLength);

    glReadPixels(0, 0, backingWidth, backingHeight, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

    

    // FIXME:上下をひっくり返す。この処理が勿体ない。

    GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);

    for(int y = 0; y <backingHeight; y++)

    {

        memcpy(&buffer2[((backingHeight-1) - y) * backingWidth * 4], &buffer[y * 4 * backingWidth], sizeof(GLubyte) * backingWidth * 4);

    }

    free(buffer);

    

    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, myDataLength, NULL);

    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();

    CGImageRef imageRef = CGImageCreate(backingWidth, backingHeight, 8, 32, 4 * backingWidth, colorSpaceRef, kCGBitmapByteOrderDefault, provider, NULL, NO, kCGRenderingIntentDefault);

    UIImage *image = [UIImage imageWithCGImage:imageRef];

    return image;

}