iOS: How to create and draw into (and save) an image larger than the screen?

Question

We're creating an iOS photo app. In doing this, we have to create dynamically sized images up to about 2500x1600px. Once this image has been created, we want to draw smaller images on top of the big one reasonably quickly.

The problem as we can see it is that it's impossible to get a context larger than the screen resolution. The call does not crash, but it returns a nil-context. How can such a seemingly simple task be achieved?

Secondly, once this context is created, what is the fastest way to draw a small image at a given position on top of the big one?

Edit:

We found the solution. CGBitmapContextCreate returns nil because the width and height parameters were set as floats, not ints. Sometimes the solution is right there in front of you, and you're too blind to see it. Hopefully this answer can help other people that somehow have the same problem.

Answer 1

Make sure you specify integer widths and heights as the arguments to CGBitmapContextCreate, otherwise it returns nil. Otherwise, the size of the context should not matter as long as you can malloc enough memory for it.