Re: NSBezierPath containsPoint?
Re: NSBezierPath containsPoint?
- Subject: Re: NSBezierPath containsPoint?
- From: Scott Thompson <email@hidden>
- Date: Fri, 21 Oct 2005 08:52:08 -0500
On Oct 20, 2005, at 9:47 PM, Brian O'Brien wrote:
On 20-Oct-05, at 8:23 PM, Robert Clair wrote:
There HAS to be a better way!
I'm curious. What evidence, exactly, do you have for this
statement ?
Of course I could write the algorithm. I could have written the
polygon interior test myself as well,
BUT it would be irresponsible to do the work if it had already been
done (AND tested).
I guess I just find it hard to believe that the NS classes have no
contingency for wanting to test
if you have touched an object within a degree of tolerance.
NSBezierPath is a drawing class, not a class for working with
arbitrary Bezier curves. In other words it is a drawing tool, not a
data modeling tool.
Adding routines like the one you describe would be wholly
inappropriate. That's why it has not been done.
Some things are intrinsically non-trivial - the best you can to do
is hope to pass the problem on to someone else by finding code
that they have already written.
Why should I believe that it has not already been done?
There is no reason you should not believe it has already been done.
Quite the opposite, I would assume that it has been done and that the
information is available with a Google search (which it is). You can
then use that information to tailor the algorithm to your particular
data model.
It is equally possible that someone has written a general purpose 3rd
party library for handling Bezier paths and their geometry.
you have merely passed this work on to someone else who has coded
the above algorithm, or its moral equivalent.
The mark of a great development environment is exactly that!
Leverage. Leverage. Leverage.
This is true, to an extent. It is also the mark of a good software
engineer to understand which responsibilities fall to the framework,
and which are the province of the application. The Cocoa framework
designers realize that adding arbitrary geometric functionality to a
drawing class is not the best idea. They also recognize that trying
to provide a class to handle arbitrary bezier path operations is
likely to be of limited use to the broader range of applications that
might be written with Cocoa.
Believe it or not that was what I decided to do on my own...
basically its a rectangle with height 3 and a variable width.
There is no outline but it is solid filled. Still I believe that
the NSBezier class should do this for me... Rather then a million
programmers writing this over and over and over.
(and a million mailing list readers answering this question over
and over and over)
Your belief is misplaced. NSBezierPath is a drawing tool, not a data
model tool. It's not a question of millions of programmers wanting
to do this. Most developers would be content with "Point IN Rect"
hit testing. Those that are trying to create drawing applications
are likely to need more sophistication in their data model, and their
hit testing, than NSBezierPath could ever provide.
A concern I have is that this may be easy for horizontal and
vertical lines but it may fail for different orientations...
This is true. In such cases you could create a parallelogram by
using four points that are perpendicular to the line and 1/2 a stroke
width's distance away and then hit test that parallellogram.
For more hints, you might look at:
<http://developer.apple.com/documentation/Carbon/Conceptual/
QuickDrawToQuartz2D/tq_hit_test/chapter_9_section_1.html#//apple_ref/
doc/uid/TP40001098-CH229-TPXREF101>
Which, while directed at QuickDraw developers, may also be of use to
you.
Finally, Tiger includes the routines
CGContextReplacePathWithStrokedPath and CGContextPathContainsPoint.
If you have the luxury of being Tiger only, these routines might also
help you hit test your stroked paths.
Others have already mentioned Sketch, you might also look at
CarbonSketch for sample hit testing routines.
Scott
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