Re: [matplotlib-devel] banded pcolor

[Jeremy O'D. <je...@o-...>]

John Hunter said:
>
> The GTK and wx backends have the same problem with pixel rounding on
> pcolor.  I just cured it with GTK and I bet you can do the same for
> wx.  The trick is to floor the positions and ceil the scales.  This
> will make it much more likely that the left edge of one rectangle will
> align with the right edge of another.  Eg, for the GTK backend
>
[code snipped]

I'm sure you're right. I'll try it tomorrow.

> Secondly, I am considering making a minor backend change for drawing
> 2D solids (arcs, rectangles, polygons) in the Renderer.  Rather than
> calling the functions twice, once for edge and once for face, I would
> like to define them like
>
>    def draw_rectangle(self, gcEdge, x, y, width, height, gcFace=3DNone)=
:
>
> that is, the gcFace takes the place of fill.  If None, don't fill,
> otherwise fill with the gc in gcFace.
>
> This will avoid 2 function calls per patch (once on the patch.py end
> and once in the backend forwarding it to the underlying renderer, and
> will enable backends, eg, postscript, to take advantage of a native
> fill commands.  For PS, this will at least halve the size of pcolor
> output files, which are currently obscenely large.

This seems very sensible. The changes required in backend_wx will be
minimal, and wx has a native fill (well, a brush...), so I can take
advantage of this. Halving the size of PS output is very worthwhile, and
it'll probably double the speed of pcolor on wx.

Regards

Jeremy