[wxPython-users] number of objects drawn to dc

[Martin Landa]

Hi all,

trying to simplify my question..., 'stupid' example below

        import time
        start = time.clock()
        #nlines = self.__display.DrawMap(True) # force
        nlines = 1e4
        for line in range(nlines):
            self.mapWindow.pdcVector.SetId(line) # <--- HERE
            self.mapWindow.pdcVector.DrawLine(0,0,100,100)
        stop = time.clock()
        Debug.msg(3, "CDisplayDriver.DrawMap(): nlines=%d, sec=%f" % \
                      (nlines, stop-start))

On my machine it takes 3s (stop-start), if I comment out SetId() fn,
time is 0.04s. I am wondering why is pseudoDC.SetId() soooo
expensive...

Or I am just doing something wrong?

Thanks! Martin

2007/9/29, Martin Landa <landa.martin at gmail.com>:
> Hi Chris,
>
> thanks a lot for pointing me out to floatcanvas. I am quite newbie in
> wxPython as you can see;-)
>
> > Martin Landa wrote:
> > > I need to draw to DC huge number (> 1e6) of objects
> >
> > That's a LOT of objects -- can you really see them all at the same time?
> > You might want to do a bounding box check or something first. You might
> > also want to see if you can change what you draw depending on scale.
> >
> > Also, is all this stuff changing? you could perhaps buffer some of it.
> >
> > >(GIS application,
> > > tool for editing vector maps).
> >
> > Cool -- I"d love to see what you come up with. Also, be sure to check
> > out FloatCanvas (wx.lib.floatcanvas, or newer version at:
> >
> > http://morticia.cs.dal.ca/FloatCanvas/
> >
> > It takes care of a lot of this for you. I'm also hoping to add more
> > GISey stuff with it -- I'd love help!
> >
> > There is simplified OnPaint fn.
> > >         dc = wx.BufferedPaintDC(self, self._Buffer)
> > >         import time
> > >         start = time.clock()
> > >         nlines = 1000000
> > >         for i in range(nlines):
> > >             dc.DrawLine(0, 0, 100, 100)
> > >         stop = time.clock()
> > >         print >> sys.stderr, "time=%f" % (stop-start)
> >
> > Maybe this is just a test, but the point of a bufferedDC is that you can
> > just blit the buffer in the OnPaint -- you only want to draw when
> > something changes (again, see FloatCanvas)
>
> Well, this was not simplified OnPaint fn, anyway not good example...
>
> Currently I am using one pseudoDC for drawing background map,
> decorations, etc. The second pseudoDC for drawing vector map which is
> edited. This pseudoDC object is input for C++ driver (using Swig
> interface for Python). The C++ driver (library) is needed because
> vector objects of vector map need to be read using C API of the given
> GIS application.
>
> So OnPaint():
>
>        dc = wx.BufferedPaintDC(self, self._Buffer)
>
>         # we need to clear the dc BEFORE calling PrepareDC
>         bg = wx.Brush(self.GetBackgroundColour())
>         dc.SetBackground(bg)
>         dc.Clear()
>
>         # use PrepareDC to set position correctly
>         self.PrepareDC(dc)
>
>         # create a clipping rect from our position and size
>         # and update region
>         rgn = self.GetUpdateRegion().GetBox()
>         dc.SetClippingRect(rgn)
>         # draw to the dc using the calculated clipping rect
>         self.pdc.DrawToDCClipped(dc, rgn)
>
>         # draw vector map layer
>         if self.pdcVector:
>             self.pdcVector.DrawToDCClipped(dc, rgn)
>
> Vector objects are drawn to PseudoDC using C++ driver
> ...
> self.driver.DrawMap(self.pdcVector)
> ...
>
> There is DrawLine method, each rendered line need to have unique id.
>
> void DrawLine(line) {
> ...
>             dc->SetId(id++);
>             dc->DrawLines(pointsScreen->GetCount(), points);
> ...
> }
>
> There something very strange at least for me;-) If I comment out
> 'dc->SetId(startId);', speed of rendering is quite OK.
>
> E.g. for vector map with 1e4 lines/points (each line has two nodes
> which are also drawn), it takes 1.2s for drawing and 0.6s for each
> redrawing.
>
> If set up id by 'dc->SetId(startId++);' drawing takes 6s and more!!!
> The response is significantly worse. I am just wondering why is
> SetId() so expensive.
>
> Thanks again for any hits!
>
> Martin
>
> --
> Martin Landa <landa.martin at gmail.com> * http://gama.fsv.cvut.cz/~landa *
>


-- 
Martin Landa <landa.martin at gmail.com> * http://gama.fsv.cvut.cz/~landa *