Question

I have some UIViews that have different centers and transforms applied to them.
I want to reconstruct these views on to a bitmap context. (Basically I want to take what the user has created on screen and render it on to a movie file)

I am able to get the view rendered in the context to look almost correct however there seems to be an offset. I am thinking the problem is that the UIImageView’s .center property is not reflected in the transforms that I am doing. However I am unsure how to do it.
Note that the UIViews are originally positioned/transformed relative to a 1024×768 ipad screen where as the video buffer is 352 x 288 pixels

If I just add a CGContextTranslateCTM(newContext,img.center.x,img.center.y) then everything looks completely off. Any ideas how to properly transform the view to the correct center?

CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
CGContextRotateCTM(newContext, M_PI_2);
CGContextScaleCTM(newContext, 1, -1);

for(int i=0; i<[self.renderObjects count]; i++){
    UIImageView * img = [self.renderObjects objectAtIndex:i];
    [img setNeedsDisplay];
    [img setBackgroundColor:[UIColor colorWithRed:1 green:1 blue:1 alpha:0.2]];
    CGContextSaveGState(newContext);
    CGContextScaleCTM(newContext, 0.375, 0.34);
    CGContextConcatCTM(newContext, img.transform);
    [img.layer renderInContext:newContext];
    CGContextRestoreGState(newContext);

}

Answer 1

Here is the code that made it work for me: note that the 1024, 768 is because the UIImageViews were positioned in the iPad coordinate system. The rotations are inverted though so if someone can find a general solution for that it would be great.

     UIImageView * curr =  your image
     [curr setNeedsDisplay];
     CGContextSaveGState(newContext);
     CGContextScaleCTM(newContext,height/768.0,width/1024.0);
     CGContextTranslateCTM(newContext, 768-curr.center.x, curr.center.y);
     CGContextConcatCTM(newContext, curr.transform);
     CGContextTranslateCTM(newContext, -curr.bounds.size.width/2, -curr.bounds.size.height/2);
     [curr.layer renderInContext:newContext];
     CGContextRestoreGState(newContext);