[Qgis-developer] arrows on line strings?

[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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-- 
Tim Sutton
QGIS Project Steering Committee Member - Release  Manager
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