Re: Custom text via Core Text in a layer.

FROM : John Clayton
DATE : Mon Nov 19 23:29:22 2007

Well,

I'm definately not writing my own text system.  All I want to be able 
to do is stick some NSAttributedText into a bounded area, on a layer. 
Assuming CATextLayer isn't what I wanted, what would be the approach 
to adapting the code below to use the Cocoa based APi's to draw into 
that area? Is it actually easier?

<side track / background info / reality hiatus>
FYI: the original reason that I moved away from CATextLayer, was that 
I wanted to provide a 'duration' value for the layer - and doing that 
in conjunction with the way that I am rendering content (CARenderer) 
wasn't working.

So I decided that I needed more control.  I've since then moved 
entirely away from touching the beginTime/duration properties of 
layers at all, and have changed my custom rendering component to use 
two newly created properties (projectBeginTime and projectDuration) 
that define exactly the same thing, but are not influenced indirectly 
by the Core Animation rendering engine (i.e. CACurrentMediaTime + 
background modifications to the presentation layer).

Its actually more involved that that - but I thought I'd provide a wee 
bit of a sense of the tangle I'm getting myself in :-)

Incidentally, I can (and am) using a CATextLayer derived instance for 
textual rendering in my project, which now works OK [so long as I 
don't mess with duration] - my question is driven more out of 
curiosity and learning desire.
</side track / background info / reality hiatus>

E.g.  this is what I've got now (which draws not-quite-the-same as the 
standard CATextLayer).  The only reason I decided to use core-text was 
because there were about a handful of lines in there to get my text 
rendered into a CGContextRef.  If Cocoa has a better way of achieving 
the same thing (i.e. attributed strings, onto a CGContextRef, for use 
by a CALayer) - then I'm all ears.

// code begins...
- (void) drawInContext:(CGContextRef)context
{
   // core-text, here we come
   [NSGraphicsContext saveGraphicsState];
   [NSGraphicsContext setCurrentContext:[NSGraphicsContext 
graphicsContextWithGraphicsPort:context flipped:NO]];

   CGContextSetTextMatrix(context, CGAffineTransformIdentity);
   
   CGMutablePathRef path = CGPathCreateMutable();
   if(path)
   {
       CGPathAddRect(path, NULL, self.bounds);
       
       CTFramesetterRef framesetter = 
CTFramesetterCreateWithAttributedString(
           (CFAttributedStringRef)_string
       );
       
       // Create the frame and draw it into the graphics context
       CTFrameRef frame = CTFramesetterCreateFrame(framesetter,
                                                   CFRangeMake(0, 0), path, NULL);
       
       if(frame)
           CTFrameDraw(frame, context);
       
       if(framesetter)
           CFRelease(framesetter);
       
       if(frame)
           CFRelease(frame);
   }
   
   if(path)
       CFRelease(path);
   
   [NSGraphicsContext restoreGraphicsState];
}
// code ends...

thanks for making it this far..

On 19/11/2007, at 8:03 PM, Aki Inoue wrote:

>> Bad assumption??

> Yes 8-).
>
> CoreText is designed to be the base text layout engine for out 
> platform.
> And it's based on somewhat different graphics model from the Cocoa 
> Text System.
>
> CT is mostly relying on the CG graphics state for specifying 
> rendering attributes whereas the Text System is taking more markup 
> attribute kind of approach.
> So, even though some of the text attributes are toll-free bridged, 
> text attributes recognized by CF is subset of the Text System and 
> possibly stay that way.
>
> In other words, if you need to use all text attributes supported by 
> the Text System, you should stay with the Text System.
>
> You should have to go down to CT for very limited reasons (i.e. 
> writing your own text engine).
>
> Aki
>
> On 2007/11/19, at 10:46, John Clayton wrote:
>

>> I'm not - I just created a .rtf file in TextEdit, made some things 
>> bold, some thing yellow, gave the whole text a background shadow - 
>> and expected that this would then show up in core-text rendered 
>> graphics as well.
>>
>> Bad assumption??
>>
>>
>>
>> On 19/11/2007, at 6:46 PM, j o a r wrote:
>>

>>>
>>> On Nov 19, 2007, at 9:39 AM, John Clayton wrote:
>>>

>>>> I'm using the following code to draw an attributed string into a 
>>>> layer (my own CATextLayer), but the text *always* draws black - 
>>>> is there something simple that I'm doing wrong? I am of course 
>>>> assuming that the colour into in the attributed string would 
>>>> determine how that content is being drawn.

>>>
>>>
>>> Quick off-list question:
>>>
>>> How certain are you that your attributes are set up correctly? 
>>> Have you verified in some non-CT layer context that they do the 
>>> right thing?
>>>
>>> j o a r
>>>
>>>

>>
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