[Drawkit] Hit testing at high scale factor

[Brad Larson]

I've been experiencing a glitch with hit testing that I can't seem to  
track down and thought I'd check to see if there was an obvious  
solution to it.  What I'm experiencing is that when I click to the up  
and left of an object, I select it, even though I'm a ways away from  
the object.  This happens in a square starting a the object and going  
up and to the left.  It does not occur below or to the right of the  
object.  From logging positions, it looks like the hit testing is  
marking a hit in a region up to 1.0 points to the left and up of the  
object.  That is, any click within that region is a hit on the  
object.  At the high scale factors (~500) we use for our micron units,  
this can be a significant distance and really complicate object  
selection.

Oddly, this is not a problem for control points, only the selection  
and movement of the bulk paths.  I've traveled down the hit test  
chain, and it looks like the appropriate transformed view coordinates  
are being used all the way down.  The object bounds are giving me some  
weird results, in that they are showing a bounds of 6.0 points for the  
small paths and objects we're working with, when the bounds should be  
around 0.12 points or lower.  There are some 6.0 point constants in  
DKKnob, but I checked that and it appears to be scaling properly to  
the small sizes.  In any case, the bounds should just be the start of  
the hit test, with the actual testing done by lower-level items.

This weirdness happens with both custom DKDrawablePath subclasses as  
well as DKDrawablePath itself.  I haven't tried DKDrawableShape to see  
how it responds.

Also, the point DKDrawablePath subclass seems to have a weird  
selection behavior that may be related to this.  When you move the  
selection box over the point, it will be selected, but as you grow the  
box to a certain size, the point will become deselected.  If you  
shrink the box, it will become selected again.  This is less  
noticeable on the DKDrawablePaths, but I still see some inaccuracies  
in when the paths are selected by the box and when they are not.

Where else would you suggest I look: DKStyle, NSBezierPath?  This is a  
problem most people wouldn't encounter at their size scale, and I can  
hunt it down myself if I know the general area that might be  
responsible.

______________________
Brad Larson
SonoPlot, Inc.
3030 Laura Lane, Suite 120
Middleton, WI 53562