[Qgis-user] writing a new renderer in python

[Sebastien Vial]

Hello

I haven't read all your code
but IMHO you should have a look to
http://www.maths.lancs.ac.uk/~rowlings/Software/ratioRenderer/
which is a python renderer build as a qgis plugin !

Seb

2008/3/21, Anita Graser <anitagraser at gmx.at>:
>
> For my project I want to visualise speed on streets with a continuous
> color renderer. I'd like it to show slow in red then change to yellow then
> to green. Unfortunately QgsContinuousColorRenderer only allows to use two
> colors. So I'm trying to write a new renderer inheriting QgsContinuousColor
> Renderer.
>
> Is it possible to write a new renderer in python?
>
> I found some problems which I don't understand:
>
> 1.
> I tried to rewirte the renderFeature function:
> -------------------------------------------------------------
> def renderFeature(self, painter, feature, image, scalefactor, selected,
> widthScale=1):
>      attrs = feature.attributeMap()
>      fvalue = float(attrs[self.classificationField])
> -------------------------------------------------------------
> However, attributeMap() seems to always return a dictionary of length 1
> allthough there should be 12 attributes. So I can't get a value for fvalue.
>
> 2.
> If I catch the exception caused by problem 1 and set a default value the
> function will continue to it's end. But then, I get a typeError:
> TypeError: invalid result type from My3ColorRenderer.renderFeature()
> I'm confused because I thought that this function returns void ...
>
> Anyone got an idea what I'm doing wrong?
>
> Thank you!
>
> My Code:
>
> -----------------------------------------------------------------
>
> from PyQt4.QtCore import *
> from PyQt4.QtGui import *
> from qgis.core import *
> from qgis.gui import *
>
> class My3ColorRenderer(QgsContinuousColorRenderer):
>     def __init__(self,vectorType):
>         self.vectorType=vectorType
>         QgsContinuousColorRenderer.__init__(self,vectorType)
>
>     def setMiddleSymbol(self,symbol):
>         self.mMiddleSymbol=symbol
>     def middleSymbol(self):
>         return self.mMiddleSymbol
>
>     def name(self):
>         return "FleetVis3ColorRenderer"
>
>     def symbols(self):
>         list=[]
>         list.append(self.mMinimumSymbol)
>         list.append(self.mMiddleSymbol)
>         list.append(self.mMaximumSymbol)
>         return list
>
>     def setClassificationField(self,id):
>         self.classificationField=id
>
>     def renderFeature(self, painter, feature, image, scalefactor,
> selected, widthScale=1):
>         #first find out the value for the classification attribute
>         # ??? i dont know why it doesnt work ...
>         attrs = feature.attributeMap()
>         try:
>             fvalue = float(attrs[self.classificationField])
>         except:
>             fvalue=50.0
>
>         minvalue = float(self.minimumSymbol().lowerValue())
>         maxvalue = float(self.maximumSymbol().lowerValue())
>         middlevalue = minvalue + maxvalue
>         middlevalue=middlevalue/2
>
>         mincolor=QColor()
>         maxcolor=QColor()
>
>         if self.vectorType == QGis.Line or self.vectorType == QGis.Point:
>             mincolor = self.minimumSymbol().pen().color()
>             middlecolor=self.middleSymbol().pen().color()
>             maxcolor = self.maximumSymbol().pen().color()
>         else:#if polygon
>             painter.setPen(self.minimumSymbol().pen())
>             mincolor = self.minimumSymbol().fillColor()
>             middlecolor=self.middleSymbol().fillColor()
>             maxcolor = self.maximumSymbol().fillColor()
>
>         if (maxvalue - minvalue)!=0:
>             if(fvalue<middlevalue):
>                 red = int (middlecolor.red() * (fvalue - minvalue) /
> (middlevalue - minvalue) + mincolor.red() * (middlevalue - fvalue) /
> (middlevalue - minvalue))
>                 green = int (middlecolor.green() * (fvalue - minvalue) /
> (middlevalue - minvalue) + mincolor.green() * (middlevalue - fvalue) /
> (middlevalue - minvalue))
>                 blue =  int (middlecolor.blue() * (fvalue - minvalue) /
> (middlevalue - minvalue) + mincolor.blue() * (middlevalue - fvalue) /
> (middlevalue - minvalue))
>             elif(fvalue==middlevalue):
>                 red=int(middlecolor.red())
>                 green=int(middlecolor.green())
>                 blue=int(middlecolor.blue())
>             else:
>                 red = int (maxcolor.red() * (fvalue - middlevalue) /
> (maxvalue - middlevalue) + middlecolor.red() * (maxvalue - fvalue) /
> (maxvalue - middlevalue))
>                 green = int (maxcolor.green() * (fvalue - middlevalue) /
> (maxvalue - middlevalue) + middlecolor.green() * (maxvalue - fvalue) /
> (maxvalue - middlevalue))
>                 blue =  int (maxcolor.blue() * (fvalue - middlevalue) /
> (maxvalue - middlevalue) + middlecolor.blue() * (maxvalue - fvalue) /
> (maxvalue - middlevalue))
>         else:
>             red = int (mincolor.red())
>             green = int (mincolor.green())
>             blue = int (mincolor.blue())
>
>         if self.vectorType == QGis.Point:
>             pen = self.minimumSymbol().pen()
>             pen.setColor ( QColor(red, green, blue) )
>             pen.setWidthF ( widthScale * pen.width() )
>
>             brush = self.minimumSymbol().brush()
>
>             brush.setColor ( QColor(red, green, blue) )
>
>             brush.setStyle ( Qt.SolidPattern )
>
>             img = QgsMarkerCatalogue.instance().imageMarker (
> self.minimumSymbol().pointSymbolName(), self.minimumSymbol().pointSize(),pen,
> brush)
>
>             if scalefactor:
>                  scalefactor = 1
>
>         elif self.vectorType == QGis.Line:
>             painter.setPen( QPen(QColor(red, green, blue),int(widthScale*
> self.minimumSymbol().pen().width()) ))
>
>         else:
>             painter.setBrush(QColor(red, green, blue))
>             painter.setPen(Qt.NoPen)
>
>
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-- 
Sébastien VIAL
Prof d'Info - Resp. TIC/Comm - Formateur SIG
Lycée Agricole du Balcon des Ardennes
http://www.lebalcon.fr
tel : 03-24-57-66-71
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