[Examples] contour_plot demo has issues

[rahulporuri]

specifically, examples/demo/basic/contour_plot.py.
Running the script works fine but the plot generated is what has a few issues.

1. There is a white box in the contour plot, which I assume is a legend. See below.

2. I don't know if this is the expected behavior but Zooming in and out using the scroll wheel doesn't change the plot, unless I pan/move the plot.

Reproduced on both Py2.7.13 and Py3.6.0 env. OSX.

[corranwebster]

1. The white box is demonstrating the (new) capability to mask regions of the plot (see Fix contour plot grids #326)

2. Did the plot have focus when you first used the scroll wheel? Ie. I would expect that you may not get scroll wheel zoom until you have at least clicked on the plot or the window containing it.

[rahulporuri]

The white box is demonstrating the (new) capability to mask regions of the plot (see #326)

Ahh. My bad. Now I see (https://github.com/enthought/chaco/blob/master/examples/demo/basic/contour_plot.py#L40-L42). I'll add the same info and update the plot on the docs.

Did the plot have focus when you first used the scroll wheel? Ie. I would expect that you may not get scroll wheel zoom until you have at least clicked on the plot or the window containing it.

You're right. I wasn't able to get the scroll wheel zoom to work until I clicked on the plot. I don't quite understand what's going here so i'm sorry if im missing something trivial/straight-forward.

[corranwebster]

If you haven't run into the concept of "focus" in UIs before, it's just the notion of a widget being the target of events which aren't specifically tied to a point on the screen - most notably being which widget should get keystrokes when the user types, but the scroll wheel potentially being another (possibly depending on the OS you are running on, as well). And if you have run into the concept I apologise for explaining it 😉

So I think what is happening is that when you click on the plot, it (or at least the QWidget it is embedded in) gets focus and starts being able to get scroll wheel events. This may be unexpected in a modern UI, because browser based UIs tend to be a bit more lax about the idea of focus.

Still, it might be worth looking into the Enable event code to check that we're not doing something dumb with the scroll events.

[jvkersch]

@rahulporuri @corranwebster Is there something to do here, or can this issue be closed?

[jvkersch]

@rahulporuri I'll close this issue since there's nothing actionable anymore, but feel free to reopen if I've overlooked anything.