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Editorial Team
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Asked: 2026-06-12T09:44:40+00:00

I’m working on a educational app involving complex scripts in which I paint parts

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I’m working on a educational app involving complex scripts in which I paint parts of different ‘letters’ different colours. UILabel is out of the question, so I’ve drilled down into Core Text and am having a surprisingly successful go of painting glyphs in CALayers.

What I haven’t managed to do is animate the size of my custom drawn text. Basically I have text on ’tiles’ (CALayers) that move around the screen. The moving around is okay, but now I want to zoom in on the ones that users press.

My idea is to try to cache a ‘full resolution’ tile and then draw it to scale during an animation of an image bounds. So far I’ve tried to draw and cache and then redraw such a tile in the following way:

UIGraphicsBeginImageContext(CGSizeMake(50, 50));
CGContextRef context = UIGraphicsGetCurrentContext();

//do some drawing...

myTextImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

Then in [CALayer drawInContext:(CGContextRef)context],
I call [myTextImage drawAtPoint:CGPointZero].

When I run the app, the console shows <Error>: CGContextDrawImage: invalid context 0x0. Meanwhile I can perfectly while just continue to draw text in context in the same method even after that error is logged.

So I have two questions: (1) Why isn’t this working? Should I be using CGBitmap instead?
And more important: (2) Is there a smarter way of solving the overall problem? Maybe storing my text as paths and then somehow getting CAAnimation to draw it at different scales as the bounds of the enclosing CALayer change?

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1 Answer

  1. Editorial Team

    Okay, this is much easier than I thought. Simply draw the text in the drawInContext: of a CALayer inside of a UIView. Then animate the view using the transform property, and the text will shrink or expand as you like.

    Just pay attention to scaling so that the text doesn’t get blocky. The easiest way to do that is to make sure the transform scale factors do not go above 1. In other words, make the ‘default’ 1:1 size of your UIView the largest size you ever want to display it.

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