Re: NSGraphicsContext restore crashes my xtension
Re: NSGraphicsContext restore crashes my xtension
- Subject: Re: NSGraphicsContext restore crashes my xtension
- From: glenn andreas <email@hidden>
- Date: Sun, 27 Jul 2008 13:53:07 -0500
On Jul 27, 2008, at 1:33 PM, email@hidden wrote:
-------------- Original message ----------------------
From: glenn andreas <email@hidden>
restoreGraphicsState restores the state of the current context - it
does not restore the context to the previous context. You need to
explicitly save the current context before you do setCurrentContext:
NSGraphicsContext *oldContext = [NSGraphicsContext currentContext];
[NSGraphicsContext setCurrentContext: nsContext];
... do drawing in the nsContext (save/restoreGraphics state impacts
internal variables of nsContext)
[NSGraphicsContext setCurrentContext: oldContext];
I think part of the difficulty I'm having is that I'm using
CGGraphicsContext for the bulk of the drawing but found the CGxxx
styled text drawing too tedious so switch to NSGraphic context
methods just to draw the text and then attempt to switch back to
CGGraphicsContext
You'll note that I'm passing in a CGContextRef to
drawImageTextInCGContext and creating a temporary context just for
the text drawing with this line:
NSGraphicsContext *nsContext = [NSGraphicsContext
graphicsContextWithGraphicsPort: inContextRef flipped: NO];
Doesn't matter. When you do [NSGraphicsContext setCurrent: nsContext]
you're changing global states associated with the current thread. You
need to set it back to what it was before when you're done, or, at
best, you'll get weird, inconsistent drawing (and more likely, crashes
like you're seeing).
By my (perhaps flawed) understanding, I'm really just using the
passed in context with an NSGraphics context wrapper, no? Do I
restore the passed in context? And if so, how?
CG is "stateless", in that there is no "current context" (all drawing
to a CGContext requires passing the CGContextRef). NSGraphicsContext,
on the other hand, involves an implicit "current context". If you
change that, you need to change it back - that's what currentContext/
setCurrentContext does. Just because NSGraphicsContext is built on
top of CGContextRef doesn't mean that they have the same semantics
(nor is NSGraphicsContext "just a wrapper" - it does a few more things).
Glenn Andreas email@hidden
<http://www.gandreas.com/> wicked fun!
JSKit | the easy way to unite JavaScript and Objective C
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