Re: Drawing strings on a line

[Andreas Höschler]

Hi David,

> > I am developing a mapping application where I need to draw labels in 
> > a view. Currently I am using (as a first approach)
> >
> >               [_name drawAtPoint:labelPoint withAttributes:nil];
> >
> > This works: However, it does not exactly has the desired effect, 
> > since the labels are always drawn horizontally. The labels are 
> > actually street names and the streets are drawn with NSBezierPath 
> > stroke. Ideally I would like the street label to be exactly drawn on 
> > the NSBezierPath which is a connected list of points, but at least to 
> > be drawn with the same angle as the NSBezierPath segment. There is 
> > this NSBezierPath
> >
> > - (void)appendBezierPathWithGlyphs:(NSGlyph *)glyphs count:(int)count 
> > inFont:(NSFont *)fontObj
>
> This is, without any doubts in my mind, the worst-named method in the 
> whole of AppKit.  It appends a set of gylphs, but they are drawn 
> horizontally at the current point, not along the path.  I've not 
> tested it on GNUstep, but the easiest way of doing this on OS X is to 
> do something like this:
>
> void drawAtPointWithAngle(NSAttributedString *str, NSPoint p, CGFloat 
> angle)
> {
>     NSAffineTransform * transform = [NSAffineTransform transform];
>     [transform translateXBy: -p.x yBy: -p.y];
>     [transform rotateByDegrees: angle];
>     [NSGraphicsContext saveGraphicsState];
>     [transform concat];
>     [str drawAtPoint: NSMakePoint(0,0)];
>     [NSGraphicsContext restoreGraphicsState];
> }
>
> Assuming I've not mixed up the transforms (it's late - I probably 
> have), this will set a coordinate transform for a translated, rotated, 
> system, draw the string horizontally at the origin in this space (i.e. 
> translated and rotated) and then reset the context.

Thanks for your responses. Since neither core foundation (MacOSX) nor 
cairo can be used I did stick to the above approach. The method that 
actually works for me is

- (void)drawString:(NSString *)str atPoint:(NSPoint)point 
angle:(float)angle offset:(BOOL)offset
{
   static NSDictionary *_attr = nil;
   if (!_attr) _attr = [[NSDictionary alloc] 
initWithObjectsAndKeys:LABELFONT, NSFontAttributeName, nil];
   NSSize size = [str sizeWithAttributes:_attr];
   NSAffineTransform * transform = [NSAffineTransform transform];
   [transform translateXBy: point.x yBy: point.y];
   [transform rotateByDegrees:angle];
   [transform translateXBy: (offset ? - size.width / 2 : 0.0) yBy: - 
size.height / 2]; // <--
   [NSGraphicsContext saveGraphicsState];
   [transform concat];
   [str drawAtPoint:NSMakePoint(0,0) withAttributes:_attr];
   [NSGraphicsContext restoreGraphicsState];
}

Thanks a lot,

  Andreas