CALayer renderInContext: Position of Drawing

Question

I have a UIView with a custom shape drawn in drawRect:. The frame property is set to:

{5.f, 6.f, 50.f, 50.f}

Now, I render the view in an Image Context, but it is ignoring the frame property of the UIView, and always drawing the UIView in the top left.

[_shapeView.layer renderInContext:UIGraphicsGetCurrentContext()];

I tried to change the frame of the CALayer, but nothing changed. Modifying the bounds property made things worse. The only work around I found useful was:

CGRect frame = _shapeView.frame;
CGContextTranslateCTM(context, frame.origin.x, frame.origin.y);
[_shapeView.layer renderInContext:context];

But, this is impractical when I am dealing with many shapes, I want to just use the frame property.

Outreach

That is expected to happen. Think of what it would mean if the opposite was true. Anyhow, try changing the origin of the bounds instead. – Kovno

@DavidRönnqvist Thanks, changing the bounds would cause the upper 6 px and left 5 px of the drawing to be sliced :( , ie doesn't work. – Outreach

I discovered CGContextDrawLayer methods, which throw EXE_BAD_ACCESS when I try to use them.. I guess it's better to avoid those.. – Outreach

Answer 1

Using CGContextTranslateCTM is the proper way to go. As renderInContext: documentation states : "Renders in the coordinate space of the layer." This means the frame origin of your layer/view is ignored.

Regarding CGContextDrawLayer, it is not made to be used with CALayer, but with CGLayer. These are two very different things, and explains your crash.

Legibility

Great hint also for other modifications of the context before calling -renderInContext:! So the way is to prepare your context first and render to it afterwards. – Sophistication