[Qt-interest] Detecting intersections in a QPainterPath

[benswerts at telenet.be]

Thanks to everyone who replied.

I don't think I can use the QPainterPath::intersects function as it closes any open paths. I also cannot specify any bounds as the points are in floating point format.

I decided to go for a fully customized solution and wrote functions that can detect whether a line intersects with an arc or whether two arcs intersect. The one constraint I have is the fact that the arcs are circular so I could base them on line/circle and circle/circle intersection algorithms. The final algorithm is O(N^2), just like the original version that only worked on linear segments.

Greets,


  Ben

----- Originele e-mail  -----
Van: "Atlant Schmidt" <aschmidt at dekaresearch.com>
Aan: "Ben Swerts" <benswerts at telenet.be>, qt-interest at trolltech.com
Verzonden: Dinsdag 10 augustus 2010 16:51:00 GMT +01:00 Amsterdam / Berlijn / Bern / Rome / Stockholm / Wenen
Onderwerp: RE: [Qt-interest] Detecting intersections in a QPainterPath

Ben:

  To simplify things, are there any bounds we can place
  upon the "problem space"?

  For example, is there a maximum XY rect that will
  encompass all possible paths?

  Asking the question from the opposite direction,
  are the vertices of the paths points specified as
  integer [X,Y] pairs or are they arbitrarily fine-
  pitched floating point pairs?

  If both limits can be applied (so you have a
  bounded space of integer points), we might take
  a different approach than if the space can be either
  arbitrarily large or arbitrarily "fine-grained".

                      Atlant


-----Original Message-----
From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Ben Swerts
Sent: Monday, August 09, 2010 17:07 PM
To: qt-interest at trolltech.com
Subject: [Qt-interest] Detecting intersections in a QPainterPath

Hello all,

I have a QPainterPath created from a number of line and arc segments. This
path is allowed to be concave but it is not allowed to be self-intersecting.

If the path consists of only line segments this self-intersection test is
easy: check for a bounding intersection (with QLineF::intersect) between all
non-adjacent segments.

If the path also contains arced segments I have no idea how I should check
for intersections. I was kind of hoping the existing QPainterPath API
already has something to solve this.

Many thanks in advance!
Greets,


        Ben

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