How to use CTRunDelegate in iPad? - ipad

Question

I am a developing an iPad application in which i have to use CTRunDelegate. I have defined all the the callbacks that are required viz CTRunDelegateGetAscentCallback , CTRunDelegateGetDescentCallback , CTRunDelegateGetWidthCallback. I dont know how to use CTRunDelegateRef object that I am creating. Right now what is happening is that my callbacks are not getting called.
Any pointers in this regard will be highly appreciated.
Thanx in advance.

Answer 1

You should add your run delegate as an attribute for a range of characters in your attributed string. See Core Text String Attributes. When drawing, Core Text will call your callbacks to get the sizing of that characters.
Update
This is a sample code for a view drawing a simple text (Note that there's no memory management code here).
#implementation View
/* Callbacks */
void MyDeallocationCallback( void* refCon ){
}
CGFloat MyGetAscentCallback( void *refCon ){
return 10.0;
}
CGFloat MyGetDescentCallback( void *refCon ){
return 4.0;
}
CGFloat MyGetWidthCallback( void* refCon ){
return 125;
}
- (void)drawRect:(CGRect)rect {
// create an attributed string
NSMutableAttributedString * attrString = [[NSMutableAttributedString alloc] initWithString:#"This is my delegate space"];
// create the delegate
CTRunDelegateCallbacks callbacks;
callbacks.version = kCTRunDelegateVersion1;
callbacks.dealloc = MyDeallocationCallback;
callbacks.getAscent = MyGetAscentCallback;
callbacks.getDescent = MyGetDescentCallback;
callbacks.getWidth = MyGetWidthCallback;
CTRunDelegateRef delegate = CTRunDelegateCreate(&callbacks, NULL);
// set the delegate as an attribute
CFAttributedStringSetAttribute((CFMutableAttributedStringRef)attrString, CFRangeMake(19, 1), kCTRunDelegateAttributeName, delegate);
// create a frame and draw the text
CTFramesetterRef frameSetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attrString);
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, rect);
CTFrameRef frame = CTFramesetterCreateFrame(frameSetter, CFRangeMake(0, attrString.length), path, NULL);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetTextMatrix(context, CGAffineTransformIdentity);
CGContextSetTextPosition(context, 0.0, 0.0);
CTFrameDraw(frame, context);
}
#end
The size of the space character between "delegate" and "space" in the text are controlled by the run delegate.