Added native dpi option for print_figure

[patchen]

As per #305, Added the option to set dpi='native' in canvas.print_figure(). Doing so will set the "canvas print_figure" dpi equal to the figure dpi.

[mdboom]

Interesting idea, but I'm not sure the term native is terribly obvious. Maybe same or screen?

[patchen]

How about "preserve" or "figure" ?

[tacaswell]

How does this interact with Figure.savefig? This change should probably be made at that level, rather than at this level. At a minimum it should be documented there as I think that is the API route that most users go through.

[patchen]

I moved the dpi='figure' option to the Figure.savefig() level as suggested and left the default implementations untouched.

It seems like a common gotcha with users where the Figure dpi (screen) and Figure.savefig() dpi (output) differ.

[efiring]

I like it.

[tacaswell]

👍 from me too.

@patchen Can you add an entry to https://github.com/matplotlib/matplotlib/tree/master/doc/users/whats_new ?

The validation the the dpi kwarg should also be updated to allow 'figure' as a valid value.

[patchen]

The validation the the dpi kwarg should also be updated to allow 'figure' as a valid value.

@tacaswell
Can you clarify this bit for me? Thanks.

[tacaswell]

If you try to do matplotlib.rcParams['savefig.dpi'] = 'figure' it will raise an exception (as 'figure' is not a valid DPI). The validation code should be updated to special case allowing 'figure'. Have a look at rcsetup.py.