Re: [matplotlib-devel] dpi-related positioning errors in Agg savefig

[Eric F. <ef...@ha...>]

John Hunter wrote:
> On Sun, Apr 27, 2008 at 12:56 PM, Eric Firing <ef...@ha...> wrote:
> 
>>  The plot thickens.  The postscript backend is completely confused by the
>> quiver plot.  Try the attached example.
> 
> 
> Argg, that was a subtle one -- there was a bug in backend ps which was
> exposed only if you are using a path collection with offsets,
> transoffset and clippath and cliprect both None.  In that scenario,
> the translate in the bind def function was not getting wrapped in a
> gsave/grestore pair, which was causing the axes to be drawn in the
> wrong place because the translate from the offset remained in effect.
> I tried following the draw_markers logic and putting the
> gsave/grestore in the ps_cmd, eg in draw_markers Michael writes ijn a
> comment:
> 
>         ps_cmd = ['/o {', 'gsave', 'newpath', 'translate'] # dont want
> the translate to be global
> 
> so clearly he was bumping up against the same problem with markers.
> For some reason, trying the same thing in the path_collection was not
> working for me, so I resorted to the somewhat hackish approach of
> forcing _draw_ps to wrap a gsave/grestore if it wasn't getting one
> from the cliprect or clippath:
> 
>         needwrap = not (clippath or cliprect)
>         if needwrap:
>             # we need to make sure that there is at least 1
>             # save/grestore around each ps write so we'll force it if
>             # we're not getting one from the cliprecot or clippath.
>             # hackish, yes
>             write('gsave\n')
> 
> and then
> 
>         if needwrap:
>             write('grestore\n')
> 
> I think there will be cleaner way, but it will need some fresh
> eyeballs tomorrow and this will provide a temporary fix.

I went ahead and committed an alternative fix that I think is cleaner, 
and greatly reduces the number of needless gsave/grestore pairs.  Your 
version of the method is still there, with a mangled name, for easy 
reference and testing until we are sure which way to go.

Sorry for whatever duplicated effort there has been.  I did not intend 
to spend a fair chunk of the day working on this, but I let myself get 
sucked in.  It was a challenge.

As mentioned in a message a few minutes ago that I don't think went to 
the list, my gs interpreter is choking on the apostrophe (single quote) 
character, as in title or label strings.  I can't find any reason why 
this should cause trouble--maybe it is a particular version or 
configuration of gs.

Eric