[Qgis-developer] arrows on line strings?

[Marco Hugentobler]

Hi Stefanie and Tim,

+1 for adding the patch to svn.
A comment on detail level: you could use M_PI from the standard library 
(#include <cmath>) instead of defining your own PI.

Regards,
Marco

Am Freitag 01 Februar 2008 19:31:57 schrieb Tim Sutton:
> Hi Stefanie
>
> I tried to apply your patch:
>
> [qgis] svn update -r 8092
> Na revisão 8092.
> [qgis] patch -p0 < ~/tmp/line_arrows.diff
> patching file src/core/qgsvectorlayer.cpp
> Hunk #1 FAILED at 425.
> Hunk #2 FAILED at 434.
> Hunk #3 FAILED at 452.
> 3 out of 3 hunks FAILED -- saving rejects to file
> src/core/qgsvectorlayer.cpp.rej
>
>
> I didnt have time to manually resolve the rejected but perhaps
> regenerating it off trunk might help. I can add a simple checkbox
> option to the vector props dialog and do the associated xml
> (de)serialisation. This would probably only happen in a month or so
> since we are in feature freeze for getting 0.9.2 final out (so I would
> target it for 0.9.3). I would suggest to go with your approach for now
> since we are trying to get 1.0 out and implementing the renderers
> approach described by Magnus will only happen post 1.0. On the other
> hand I have often been asked about the ability to show direction on
> lines so adding your basic implementation for now seems like a good
> way to go for 1.0 relase. If anyone vigorously disagrees let me know,
> otherwise I'll incorporate your patch in 0.9.3 with some additions
> from myself to enabled or disable line arrows via the layer props
> dialog, the vector api and the layer properties serialisation
> mechanism.
>
> Best regards
>
> Tim
>
> 2008/2/1, Stefanie Tellex <stefie10 at media.mit.edu>:
> > Hi,
> >
> > The attached patch against R8092 draws arrows on all linestrings
> > everywhere, no matter what, using code swiped from this GPL v2.0
> > licensed file:
> > http://doc.trolltech.com/4.3/graphicsview-diagramscene-arrow-cpp.html
> >
> > What's the best way to control arrow drawing so it only shows up on
> > particular layers? Seems like it should be written to the xml file also,
> > in which case it might be better to just wait until better rendering
> > happens, and live with patching QGIS myself until then...?
> >
> > There's also a bug on multi-line-strings where an arrow line gets drawn
> > to some random coordinate in the upper left hand corner which I'm not
> > motivated to fix since I only need arrows on line-strings...
> >
> > Stefanie
> >
> > Martin Dobias wrote:
> > > On Jan 31, 2008 5:49 PM, Stefanie Tellex <stefie10 at media.mit.edu> wrote:
> > >> Hi,
> > >>
> > >> I would like to draw arrows on line strings, since they represent
> > >> movement vectors and I want to show the direction of movement.  I
> > >> couldn't find any way to do that in the gui or any obvious way in the
> > >> programmatic API.  What's the best way to add this feature or is it
> > >> there already somewhere?
> > >
> > > Currently QGIS renderers work in a way that they just set some
> > > properties for painting and let the vector layer to draw the polyline,
> > > so it's not possible to create a renderer which would e.g. render
> > > arrows in the direction of the flow. We should allow renderers to do
> > > arbitrary drawing in future.
> > >
> > > Now it will be more complicated to acquire this effect: you can
> > > generate some points (e.g. in the middle of every line segment) and
> > > determine the angle of direction. Such generated vector layer with
> > > points you can load to map canvas and for rendering set a SVG symbol
> > > with an arrow and set rotation field appropriately to the field you've
> > > generated.
> > >
> > > Martin
> >
> > Index: src/core/qgsvectorlayer.cpp
> > ===================================================================
> > --- src/core/qgsvectorlayer.cpp (revision 8092)
> > +++ src/core/qgsvectorlayer.cpp (working copy)
> > @@ -425,6 +425,7 @@
> >    // 255 = opaque
> >    //
> >    QPen myTransparentPen = p->pen(); // store current pen
> > +  QBrush brush = p->brush(); //to be kept as original
> >    QColor myColor = myTransparentPen.color();
> >    //only set transparency from layer level if renderer does not provide
> >    //transparency on class level
> > @@ -433,7 +434,9 @@
> >        myColor.setAlpha(mTransparencyLevel);
> >      }
> >    myTransparentPen.setColor(myColor);
> > +
> >    p->setPen(myTransparentPen);
> > +
> >    p->drawPolyline(pa);
> >
> >    // draw vertex markers if in editing mode, but only to the main canvas
> > @@ -449,9 +452,43 @@
> >           drawVertexMarker((int)(*xIt), (int)(*yIt), *p);
> >         }
> >      }
> > +  // draw arrows
> > +#define PI 3.14159
> > +  p->setBrush(QBrush(myColor, Qt::SolidPattern));
> > +
> > +  for (int i = 0; i < pa.size(); ++i)
> > +    {
> > +      if (i > 0)
> > +       {
> > +         QPointF p1 = pa[i];
> > +         QPointF p2 = pa[i-1];
> >
> > +         QLineF line = QLineF(p1, p2);
> > +         double angle = ::acos(line.dx() / line.length());
> > +         if (line.dy() >= 0)
> > +           {
> > +           angle = (PI * 2) - angle;
> > +           }
> > +
> > +         float arrowSize = 10;
> > +         QPointF arrowP1 =
> > +           line.p1() + QPointF(sin(angle + PI / 3) * arrowSize,
> > +                               cos(angle + PI / 3) * arrowSize);
> > +         QPointF arrowP2 =
> > +           line.p1() + QPointF(sin(angle + PI - PI / 3) * arrowSize,
> > +                               cos(angle + PI - PI / 3) * arrowSize);
> > +         QPolygonF arrowHead;
> > +         arrowHead << line.p1() << arrowP1 << arrowP2;
> > +         p->drawPolygon(arrowHead);
> > +
> > +
> > +       }
> > +      QgsDebugMsgLevel("pa" + QString::number(pa.point(i).x()), 2);
> > +      QgsDebugMsgLevel("pa" + QString::number(pa.point(i).y()), 2);
> > +    }
> >    //restore the pen
> >    p->setPen(pen);
> > +  p->setBrush(brush);
> >
> >    return ptr;
> >  }
> >
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-- 
Dr. Marco Hugentobler
Institute of Cartography
ETH Zurich
Technical Advisor QGIS Project Steering Committee