Review Request 127364: improving CircleCircleIntersection (towards what geogebra does)

[girish korgoankar]

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      From: Maurizio Paolini <paolini at dmf.unicatt.it>
 To: David Narváez <david.narvaez at computer.org>; Rex Dieter <rdieter at gmail.com> 
Cc: KDE Edu <kde-edu at kde.org>; Maurizio Paolini <paolini at dmf.unicatt.it>
 Sent: Sunday, 3 April 2016 5:24 PM
 Subject: Re: Review Request 127364: improving CircleCircleIntersection (towards what geogebra does)
   
  
|  This is an automatically generated e-mail. To reply, visit: https://git.reviewboard.kde.org/r/127364/  |

 

| Review request for KDE Edu, David Narváez and Rex Dieter.By Maurizio Paolini.Updated April 3, 2016, 11:54 a.m.
Changes

|  Do not add the new types CircleBTPoType and ArcBTPoType.  Instead replace CircleBTPType/ArcBTPType with the new version.
Also, compute correctly ArcLine intersection using the orientation and treat the case where the Arc degenerates into a Segment  |

 Repository: kig
Description 
 
|  I am addressing two related issues: intersection points that jump, circles degenerating to lines.When intersecting circles obtained as "circle by 3 points" it is possible that one or both degenerate into a straight line. At present when dinamically moving one of the three defining points of a circle across the line through the other two, the two intersection points exchange position, possibly causing the subsequent constructions to change abruptly.The other related issue is that at the moment the intersection point is not defined when oneof the two circles degenerate into a line.Motivation: this situations naturally arise, for example, when trying to construct the Disk Poincare' model of the hyperbolic plane, in which case it is essential to allow for circles to become lines.A sample kig file that exposes these issues is available as http://dmf.unicatt.it/~paolini/kig/bugs/test_circle_intersection_old.kigThe big black points can be moved across the other two defining one of the two circles, observe that the two intersection points exchange position. Moreover, if a black pointis precisely aligned with the other two (press the shift key to force the pointonto the grid), then the two intersection points disappear.  |


Testing 

|  Unfortunately, to address the "abrupt intersection points exchange" it seems necessary to add a (hidden) circle orientation for CircleImp(s). In the proposed patch this is achieved by allowing the "mradius" member to be negative (it is "private", so that we to not risk to expose this possibility; radius() method will now return the absolute value of mradius, and the new "orientation()" method returns the circle orientation).The additional 'orientation' information can then be used inside the CircleCircleIntersection::calc to avoid the abrupt jump of the intersection points.The new CircleBTPoType class constructs an "oriented" circle (note that the user will notbe able to directly access the orientation information), whereas the old CircleBTPType is left unchanges. CircleBTPoType substitutes CircleBTPType in builtin_stuff.cc.In this way we ensure backward compatibility for old saved kig files, whereas new constructions will take advantage of the orientation.Alternatively we can simply substitute the present CircleBTP with the new version.  |


Diffs (updated)
   
   - misc/common.cpp (2e1fac9)
   - objects/arc_type.h (a9a7296)
   - objects/arc_type.cc (26c05cc)
   - objects/circle_imp.h (dc63e06)
   - objects/circle_imp.cc (7450ef6)
   - objects/circle_type.h (37cf400)
   - objects/circle_type.cc (25ec233)
   - objects/intersection_types.cc (2fd07be)
   - objects/other_imp.h (31feda6)
   - objects/other_imp.cc (d773196)
View Diff
File Attachments 
    
   - old behaviour
   - new behaviour
   - constructing a locus: before
   - constructing a locus: after
  |

  
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