Re: fast scatter plots - advice sought

[David Bateman]

Jaroslav Hajek wrote:
> On Mon, Jan 11, 2010 at 8:17 AM, David Bateman <address@hidden> wrote:
>   
> > Jaroslav Hajek wrote:
> >     
> > > hi,
> > >
> > > I recently started some work where I'm going to use scatter plots
> > > heavily with a few thousand points.
> > > I found out, however, that scatter plots were unusably slow with so
> > > many points. This has also been reported before:
> > >
> > > http://old.nabble.com/scatter3-is-really-slow-to24312164.htm
> > >
> > > by this changeset
> > > http://hg.savannah.gnu.org/hgweb/octave/rev/2f435ed48143
> > >
> > > I tried to optimize the plotting strategy to get more reasonable
> > > times, especially in the simplest cases. The old strategy of creating
> > > one object per point is only used for small numbers of points (<= 20).
> > > Otherwise, the points are split into subsets with common color and
> > > size, and these subsets are plotted using a single primitive. This
> > > seems similar to what Matlab does.
> > >
> > >       
> > If this is done in the baackend ok, but I deliberately didn't make this
> > change in the frontend as it breaks matlab compatibility
> >
> >     
>
> What breaks Matlab compatibility? Please explain. Note that it is
> *not* true that Matlab always creates one object per point (as you
> seemed to imply in the above linked mail), at least in 2007a. It does
> so only when there is a small number of points:
>   
I wrote scatter with individual patch objects because that was the way 
matlab worked when I tested it, though I mght have missed the 100 point 
transition to a single patch object... It should however keep using 
patch objects for compatibility and to allow the use of colormaps with 
scatter plots like

n=100; x=randn(1,100);y=randn(1,100);c=sqrt(x.^2+y.^2); 
scatter(x,y,2,c); colormap hot

I don't see how you can support that with line objects, and if it you 
did it wouldn't keep the same children hierarchy for compatibility

D.