iosスクリーンショット機能opengl実装

-(UIImage *) glToUIImage 
{
    int width = [self.view bounds].size.width;
    int height = [self.view bounds].size.height;
    
    NSInteger myDataLength = width * height * 4;
    
    // allocate array and read pixels into it.
    GLubyte *buffer = (GLubyte *) malloc(myDataLength);
    glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
    
    // gl renders "upside down" so swap top to bottom into new array.
    // there's gotta be a better way, but this works.
    GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);

    for(int y = 0; y <height; y++)
   {
        for(int x = 0; x <width * 4; x++)
       {
            buffer2[(height -1 - y) * width * 4 + x] = buffer[y * 4 * width + x];
        }
    }
    free(buffer);
    
    // make data provider with data.
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);
    
    // prep the ingredients
    int bitsPerComponent = 8;
    int bitsPerPixel = 32;
    int bytesPerRow = 4 * width;
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
    
    // make the cgimage
    CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
    
    // then make the uiimage from that
    UIImage *myImage =  [UIImage imageWithCGImage:imageRef];
    
   return myImage;