Re: [Lib2geom-devel] Bug in nearest-point?

[Nathan H. <nj...@nj...>]

Hi Diederik, I spent some time last night isolating the bug.  I
haven't succeeded, but I did find some interesting breakage:

It is definitely wrong.  I've looked at the example svgd using
toys/point-curve-nearest-point (you can pass an svgd file as a
parameter and using the 6 option.)

What I've noticed is that if the path is < 0 in the y axis then the
misbehaviour you've noticed happens, if it lies wholely above y = 0
then it behaves correctly.  The X position seems unconnected.

>     Let me explain: I'm using nearestPoint() to find the closest
>     point
>     on a path segment, and snap to it. Now for some segments this
>     only
>     returns the desired time t for about half of the path, whereas
>     for
>     the other part it simply returns t = 0. <br>

I'm seeing it skip whole curves, it is coincidence that the nearest
curve point is at the start point.  I have a strong suspicion that the
problem is in the Path::nearestPoint, rather than the curve
nearestPoint code.  I can't reproduce this behaviour in single
curves^H^H^H^  Actually, I can....

njh


On Fri, Sep 23, 2011 at 08:49:46PM +0200, Diederik van Lierop wrote:
> Hi all,
> 
> This is more illustrative:
> http://www.diedenrezi.nl/SingleSegmentPath.webm. Watch the green
> diamond, which indicates what 2geom believes to be the closest
> point.
> 
> Now the problem is demonstrated using a path with only a single
> segment. I've also updated my patch to eliminate the trailing tail
> of the snap indicator, and have attached this very basic SVG file.
> 
> Thanks,
> 
> Diederik


> === modified file 'src/2geom/bezier-curve.cpp'
> --- src/2geom/bezier-curve.cpp	2011-07-25 01:06:47 +0000
> +++ src/2geom/bezier-curve.cpp	2011-09-21 21:10:45 +0000
> @@ -166,6 +166,7 @@
>  template<>
>  Coord BezierCurveN<1>::nearestPoint(Point const& p, Coord from, Coord to) const
>  {
> +    std::cout << "(entering nearestPoint in bezier-curve.cpp, line 169)" << std::endl;
>      if ( from > to ) std::swap(from, to);
>      Point ip = pointAt(from);
>      Point fp = pointAt(to);
> @@ -173,9 +174,18 @@
>      Coord l2v = L2sq(v);
>      if (l2v == 0) return 0;
>      Coord t = dot( p - ip, v ) / l2v;
> -    if ( t <= 0 )  		return from;
> -    else if ( t >= 1 )  return to;
> -    else return from + t*(to-from);
> +    if ( t <= 0 ) {
> +        std::cout << "  zero nr. 0 | t -> " << from << std::endl;
> +        return from;
> +        }
> +    else if ( t >= 1 ) {
> +        std::cout << "  zero nr. 0 | t -> " << to << std::endl;
> +        return to;
> +    }
> +    else {
> +        std::cout << "  zero nr. 0 | t -> " << from + t*(to-from) << std::endl;
> +        return from + t*(to-from);
> +    }
>  }
>  
>  
> 
> === modified file 'src/2geom/nearest-point.cpp'
> --- src/2geom/nearest-point.cpp	2008-11-21 05:24:08 +0000
> +++ src/2geom/nearest-point.cpp	2011-09-21 19:42:11 +0000
> @@ -54,6 +54,7 @@
>                        D2<SBasis> const& dc,
>                        double from, double to )
>  {
> +    std::cout << "(entering nearest_point in nearest-point.cpp, line 57)" << std::endl;
>      if ( from > to ) std::swap(from, to);
>      if ( from < 0 || to > 1 )
>      {
> @@ -66,6 +67,9 @@
>      double closest = from;
>      double min_dist_sq = L2sq(c(from) - p);
>      double distsq;
> +    if (zeros.size() == 0) {
> +        std::cout << "  No zeroes found; how can there possibly be NO nearest points for any segment?" << std::endl;
> +    }
>      for ( unsigned int i = 0; i < zeros.size(); ++i )
>      {
>          distsq = L2sq(c(zeros[i]) - p);
> @@ -74,9 +78,12 @@
>              closest = zeros[i];
>              min_dist_sq = distsq;
>          }
> +        std::cout << "  zero nr. " << i << " | t -> " << zeros[i] << std::endl;
>      }
>      if ( min_dist_sq > L2sq( c(to) - p ) )
>          closest = to;
> +
> +    std::cout << "All zeros have been examined; closest t = " << closest;
>      return closest;
>  
>  }
> 
> === modified file 'src/2geom/nearest-point.h'
> --- src/2geom/nearest-point.h	2008-10-28 04:45:31 +0000
> +++ src/2geom/nearest-point.h	2011-09-21 19:42:11 +0000
> @@ -77,7 +77,7 @@
>  		              D2<SBasis> const& c,
>  		              double from = 0, double to = 1 )
>  {
> -	return nearest_point(p, c, Geom::derivative(c), from, to);
> +    return nearest_point(p, c, Geom::derivative(c), from, to);
>  }
>  
>  /*
> @@ -110,7 +110,7 @@
>  inline
>  double nearest_point( Point const& p, Piecewise< D2<SBasis> > const& c )
>  {
> -	return nearest_point(p, c, c.cuts[0], c.cuts[c.size()]);
> +    return nearest_point(p, c, c.cuts[0], c.cuts[c.size()]);
>  }
>  
>  
> 
> === modified file 'src/2geom/path.cpp'
> --- src/2geom/path.cpp	2011-02-02 21:24:36 +0000
> +++ src/2geom/path.cpp	2011-09-21 18:30:05 +0000
> @@ -205,11 +205,18 @@
>  {
>  	//return a single nearest point for each curve in this path
>  	std::vector<double> np;
> +	int count = 0;
> +	std::cout << "Mouse pointer is at " << _point << std::endl;
>  	for (const_iterator it = begin() ; it != end_default() ; ++it)
>  	//for (std::vector<Path>::const_iterator it = _path.begin(); it != _path.end(), ++it){
>  	{
> -	    np.push_back(it->nearestPoint(_point));
> +	    std::cout << "***** Start examining segment nr." << count << " *****" << std::endl;
> +	    double dummy = it->nearestPoint(_point);
> +	    std::cout << " | point = " << it->pointAt(dummy) << std::endl;
> +	    np.push_back(dummy);
> +	    count++;
>      }
> +	std::cout << "************** Done with this path*****************" << std::endl;
>  	return np;
>  }  
>  
> 
> === modified file 'src/2geom/path.h'
> --- src/2geom/path.h	2011-06-23 16:38:51 +0000
> +++ src/2geom/path.h	2011-09-21 19:42:11 +0000
> @@ -681,7 +681,7 @@
>  inline
>  Coord nearest_point(Point const& p, Path const& c)
>  {
> -	return c.nearestPoint(p);
> +    return c.nearestPoint(p);
>  }
>  
>  }  // end namespace Geom
> 
> === modified file 'src/display/snap-indicator.cpp'
> --- src/display/snap-indicator.cpp	2011-09-18 17:09:29 +0000
> +++ src/display/snap-indicator.cpp	2011-09-23 18:32:57 +0000
> @@ -302,7 +302,7 @@
>  void
>  SnapIndicator::set_new_snapsource(Inkscape::SnapCandidatePoint const &p)
>  {
> -    remove_snapsource();
> +    //remove_snapsource();
>  
>      g_assert(_desktop != NULL);
>  
> @@ -326,6 +326,25 @@
>  }
>  
>  void
> +SnapIndicator::set_new_debugging_point(Geom::Point const &p)
> +{
> +    g_assert(_desktop != NULL);
> +    SPCanvasItem * canvasitem = sp_canvas_item_new( sp_desktop_tempgroup (_desktop),
> +                                                    SP_TYPE_CTRL,
> +                                                    "anchor", GTK_ANCHOR_CENTER,
> +                                                    "size", 10.0,
> +                                                    "fill_color", 0x00ff00ff,
> +                                                    "stroked", FALSE,
> +                                                    "mode", SP_KNOT_MODE_XOR,
> +                                                    "shape", SP_KNOT_SHAPE_DIAMOND,
> +                                                    NULL );
> +
> +    SP_CTRL(canvasitem)->moveto(p);
> +    _debugging_points.push_back(_desktop->add_temporary_canvasitem(canvasitem, 5000));
> +
> +}
> +
> +void
>  SnapIndicator::remove_snapsource()
>  {
>      if (_snapsource) {
> @@ -334,6 +353,16 @@
>      }
>  }
>  
> +void
> +SnapIndicator::remove_debugging_points()
> +{
> +    for (std::list<TemporaryItem *>::const_iterator i = _debugging_points.begin(); i != _debugging_points.end(); i++) {
> +        _desktop->remove_temporary_canvasitem(*i);
> +    }
> +    _debugging_points.clear();
> +}
> +
> +
>  } //namespace Display
>  } /* namespace Inkscape */
>  
> 
> === modified file 'src/display/snap-indicator.h'
> --- src/display/snap-indicator.h	2010-12-23 08:10:28 +0000
> +++ src/display/snap-indicator.h	2011-09-23 18:15:57 +0000
> @@ -33,11 +33,15 @@
>      void set_new_snapsource(Inkscape::SnapCandidatePoint const &p);
>      void remove_snapsource();
>  
> +    void set_new_debugging_point(Geom::Point const &p);
> +    void remove_debugging_points();
> +
>  protected:
>      TemporaryItem *_snaptarget;
>      TemporaryItem *_snaptarget_tooltip;
>      TemporaryItem *_snaptarget_bbox;
>      TemporaryItem *_snapsource;
> +    std::list<TemporaryItem *> _debugging_points;
>      bool _snaptarget_is_presnap;
>      SPDesktop *_desktop;
>  
> 
> === modified file 'src/object-snapper.cpp'
> --- src/object-snapper.cpp	2011-09-17 12:08:49 +0000
> +++ src/object-snapper.cpp	2011-09-23 18:23:54 +0000
> @@ -506,6 +506,7 @@
>  
>      bool strict_snapping = _snapmanager->snapprefs.getStrictSnapping();
>  
> +    _snapmanager->getDesktop()->snapindicator->remove_debugging_points();
>      for (std::vector<SnapCandidatePath >::const_iterator it_p = _paths_to_snap_to->begin(); it_p != _paths_to_snap_to->end(); it_p++) {
>          if (_allowSourceToSnapToTarget(p.getSourceType(), (*it_p).target_type, strict_snapping)) {
>              bool const being_edited = node_tool_active && (*it_p).currently_being_edited;
> @@ -516,12 +517,14 @@
>                  // n curves will return n time values with 0 <= t <= 1
>                  std::vector<double> anp = (*it_pv).nearestPointPerCurve(p_doc);
>  
> +                std::cout << "#nearest points = " << anp.size() << " | p = " << p.getPoint() << std::endl;
>                  std::vector<double>::const_iterator np = anp.begin();
>                  unsigned int index = 0;
>                  for (; np != anp.end(); np++, index++) {
>                      Geom::Curve const *curve = &((*it_pv).at_index(index));
>                      Geom::Point const sp_doc = curve->pointAt(*np);
> -
> +                    //_snapmanager->getDesktop()->snapindicator->set_new_snapsource(Inkscape::SnapCandidatePoint(sp_doc*_snapmanager->getDesktop()->doc2dt(), SNAPSOURCE_UNDEFINED));
> +                    _snapmanager->getDesktop()->snapindicator->set_new_debugging_point(sp_doc*_snapmanager->getDesktop()->doc2dt());
>                      bool c1 = true;
>                      bool c2 = true;
>                      if (being_edited) {
> @@ -547,6 +550,7 @@
>                      Geom::Point const sp_dt = _snapmanager->getDesktop()->doc2dt(sp_doc);
>                      if (!being_edited || (c1 && c2)) {
>                          Geom::Coord const dist = Geom::distance(sp_doc, p_doc);
> +                        std::cout << "  dist -> " << dist << std::endl;
>                          if (dist < getSnapperTolerance()) {
>                              isr.curves.push_back(SnappedCurve(sp_dt, num_path, index, dist, getSnapperTolerance(), getSnapperAlwaysSnap(), false, curve, p.getSourceType(), p.getSourceNum(), it_p->target_type, it_p->target_bbox));
>                          }
> 

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