I think I am still missing some things. For example, the tick marks still don't match those using the agg backend.

Here's what the interactive macosx backend output looked like before the change:

And after the change:

These plots were done with @efiring's test script:

import numpy as np
import matplotlib
matplotlib.use("macosx")
matplotlib.rcParams['figure.dpi'] = 240
import matplotlib.pyplot as plt

fig, ax = plt.subplots(1, figsize=(3,2)) # 2 inches high
ax.plot([1,2,3], lw=72) # line 1 inch wide
fig.savefig("testdpi.png", dpi=240)
plt.show()

Are there any other properties that are missing? Maybe linestyles and such? @pmarshwx, this PR might be of interest to you with the problem you discovered during SciPy 2012.

Things like markeredgewidth are covered by this change.

Edit: Though, it is possible I may have missed something. Perhaps I should add some sort of test for this?

I don't think we have any way of testing this sort of thing automatically.
I think the macosx author, Michiel de Hoon, will be able to review this pull request this weekend.

There are probably other ways to do what I have done, perhaps better ways, so his feedback would certainly be appreciated. Thanks.

Marking this for 1.2.x, as it's really a follow-on to #786.

It's nice to fix this for linewidth, but I wonder if we couldn't also fix this at a deeper level and also resolve #113? (I say this having not looked at the code at all...)

@mdboom, if Michiel can look at it this weekend and either approve @dmcdougall's PR or come up with a better one, why shouldn't this go into 1.2? I think this PR does address all of the aspects that have been clearly identified, and the changes it makes are simple.

@efiring: I think we're in agreement. I think this should go into 1.2.

@dmcdougall: This looks good to go. Is there anything else from your end?

@mdboom In short, no. I consider this ready to merge.

The long answer is: I'd like to also solve the dpi issue in the osx backend, but I think I will do that in a different PR. I feel passing in the dpi like this sets up the necessary groundwork for extending a to a solution for that problem.