[Matplotlib-devel] Confusion about draw_artist

[Thomas Caswell]

The renderer is cached automatically the first time the figure is fully
rendered (typically delayed until it is shown on the screen).  If your
artist is not marked as animated, then just try..exect the call to
`draw_artist`, as the artist will be drawn as part of the normal draw
process when the figure is drawn.  If you have marked it as animated (which
you should if you are blitting) then you are going to need to have some
call backs in place for draw and resize events (as any 'animated' artists
will not be drawn if the figure is re-rendered from scratch by the GUI for
what ever reason and to re-grab the background if the window is resized) so
put the `draw_artist` in the callback (which comes out after the figure is
drawn so you will have a renderer at that point).

Tom

On Fri, Mar 24, 2017 at 10:27 AM Matthew Brett <matthew.brett at gmail.com>
wrote:

> On Fri, Mar 3, 2017 at 11:19 PM, Matthew Brett <matthew.brett at gmail.com>
> wrote:
> > Hi,
> >
> > On Thu, Jan 19, 2017 at 11:54 AM, Matthew Brett <matthew.brett at gmail.com>
> wrote:
> >> Hi,
> >>
> >> Sorry to keep displaying my confusion on this one but...
> >>
> >> On Wed, Jan 4, 2017 at 6:58 PM, Thomas Caswell <tcaswell at gmail.com>
> wrote:
> >>> Unless you have flagged the artist as `animated` (via `set_animated`
> or by
> >>> kwarg), it will be drawn as part of the next re-draw.
> >>
> >> Adding `set_animated` doesn't help in the example above;
> >>
> >> fig, ax = plt.subplots(1, 1)
> >> ax.set_animated(True)
> >> im = plt.imshow([[1, 2], [3, 4]])
> >> fig.canvas.draw()
> >> ax.draw_artist(im)
> >>
> >>> You are better off
> >>> just changing the `fig.canvas.draw()` to `fig.canvas.draw_idle()` and
> >>> letting the GUI decide when to re-draw things.
> >>
> >> Changing to `fig.canvas.draw_idle()` above doesn't prevent the error
> >> from `draw_artist`, but I guess I should not have expected it would.
> >> So I guess my question is - how do I use `draw_artist` in this case?
> >> Is there any way to make sure that the renderer is cached first?
> >>
> >>> If you want to get any performance gain from animated artists +
> draw_artist
> >>> you will need to use blitting (which will work with the OSX backend in
> 2.0).
> >>
> >> Yup, the real code does use blitting, but thanks for the reminder,
> >
> > Again - sorry to persist - but I'd be really grateful for any advice,
>
> Sorry - again again - but can I nose this one up towards the surface?
>
> Cheers,
>
> Matthew
>
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