Monotouch: Combine 4 images into 1 (UIImage)

Question

I have 4 UIImages (A,B,C,D), each the same 500x500

How can I combine them into a grid 1000x1000 like this:

AB
CD

So that the I have a single UIImage "E"

Answer 1

You have to create a new image context with the size of the final image:

UIGraphics.BeginImageContext(new SizeF(1000, 1000));

Then, draw each image in the appropriate rectangle:

image.Draw(new RectangleF(0,0,image.Size.Width,image.Size.Height));
//image2.Draw...

You then get the image:

UIImage finalImage = UIGraphics.GetImageFromCurrentImageContext();

And finally, you must end the image context:

UIGraphics.EndImageContext();

Answer 2

I don't specifically know how but I do know that Apple's PhotoScroller sample code might help? It's a pretty cool trick they have that might work for yours too. Let me know.

Answer 3

Remember that you can't use UIGrahpics.BeginImageContext() in a sub-thread, it has to be the main thread. If you want to do it in a sub-thread you have to use CGBitmapContext(), which is a little harder to deal with.