QCAD Bugtracker

  • Status Closed
  • Percent Complete
  • Task Type Bug Report
  • Category QCAD (main)
  • Assigned To
  • Operating System Windows 7
  • Severity Low
  • Priority Very Low
  • Reported Version 3.12.8
  • Due in Version Undecided
  • Due Date Undecided
  • Votes 1
  • Private
Attached to Project: QCAD Bugtracker
Opened by V. Oth - 20.02.2016
Last edited by Andrew - 20.02.2016

FS#1387 - Offset tool not working on rounded polylines

When “offset whole polyline” is selected and the mouse is moved over a rounded polyline, the preview is not working at least in Window 7/8.
This worked in older versions e.g. 3.6.3.

There is an example appended with an edged inner polyline and a rounded outer one. For the inner one, the offset preview is working as expected, for the rounded one it isn’t. Tested on two different PCs, one Win7 and the other one Win8.

Also see:

Closed by  Andrew
20.02.2016 22:09
Reason for closing:  Not a bug
Additional comments about closing:  

Limitation due to performance considerations

Husky commented on 20.02.2016 20:22

I can second that also with XP.

Andrew commented on 20.02.2016 22:08

Offsets to polylines with arc segments are deliberately not previewed for performance reasons (the clipper library used to produce offsets operates on line segments).

V. Oth commented on 20.02.2016 22:41

Errm, OK, but even letting aside that it worked in older versions: how is no preview at all supposed to be a proper solution?
This is extremely irritating and most certainly an anomaly. Letting away the rounded parts would be acceptable, but no preview at all is not.

Andrew commented on 21.02.2016 10:42
it worked in older versions

The old offset tool is still available under Misc > Draw > Polyline Offset (Alternative). You will quickly find that it has much more severe limitations.

how is no preview at all supposed to be a proper solution

Please understand that it is not possible performance wise to offer a preview for polylines with arcs using this algorithm. Leaving arcs away for the preview would (obviously) result in an entirely different offset curve giving a completely wrong preview which would in my opinion be much worse.
Anyway: thanks for your input.

V. Oth commented on 21.02.2016 15:30

I don't want to annoy you, it's just that having no preview for one single operations is really completely counter-intuitive. And the intuitive behavior was always what I liked most about QCad.
So just one last idea: since the preview works fine with the "alternative" offset tool and I understand the new offset tools gives better results, wouldn't it be a compromise to use the alternative tool for the preview and the new one for the actual operation?

Husky commented on 21.02.2016 22:17

Hi both of you! I understand both sides and like to ask a naive (that's me!) question:
Would it be possible/acceptable to let the user decide what works best for him? Better performance or preview for this task? I could imagine an option switch in "Application Preferences".

For me as a normal QCAD User I have the same "Understanding problem" like V. Oth. This tool is so nicely working with all other kinds of shapes and I'm just not expecting any problems with the "Round join" option.
Confusing for me is that it works flawless if you know how to handle it but till then you don't get any information that the "Round joint" option works different compared to "Bevel join" / "Miter join" / "Arcs with line segments". Maybe shame on me but believe me it took me a while until I figured out that I just have to click the mouse to get what I'm looking for. Yes, I was expecting something else and I just started to disbelieved in the quality of my own drawing ...

I would consider myself as a "little bit more" experienced user and I'm still confused with this behavior - how would a less or non experienced user judge this exceptional behavior at the same tool ...? Could it be a deal breaker?

What do you think?

Andrew commented on 22.02.2016 07:43
Would it be possible/acceptable to let the user decide what works best for him? Better performance or preview for this task?

Yes, of course this would almost immediately trigger a new bug report: "performance unacceptable when previewing offsets".

Note that the delay can be several seconds (every time the mouse is moved!), depending on the complexity of the polyline. Interrupting the process is not possible, since we're talking about an external library. Foreseeing the delay is not possible without doing the math first.

Could it be a deal breaker?

Yes, obviously everything can be a deal breaker, depending on the user.

Husky commented on 22.02.2016 08:09

Ok, this is inside knowledge what I can't have - it was just a thought to find a "between" solution. Thanks for your answer!


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