ImagePlot panning issue at edge when zoomed in

[tangobravo]

After zooming in an image and panning so that image is almost outside the plot region, but only has 2 rows or columns visible, the image is drawn incorrectly, so the first row or column is duplicated across the entire plot region. Attached 2 screenshots to show when the problem appears - a Pan that makes 2.5 pixel columns visible is fine, but when the plot region contains >0 and <2 pixel columns the first column is stretched to fill the plot.

The plot in the screenshots was simply imshow('capitol.jpg') but seems to affect all ImagePlots.

I'm currently investigating. The problem appears to be in _calc_zoom_coords in image_plot.py as the gc_rect it returns does look spurious in these cases.

Working through the maths now and will submit a pull request when I get to the bottom of it.

[tangobravo]

This is an issue for my use as I'll be overlaying lots of small image patches on a larger base image and will want to zoom and pan around the whole plot.

[tangobravo]

I've added a pull request with the fix for this. The "really, really, subpixel cases" assumed the extremes of the computed subimage_coords were always outside the plot bounds, which is not the case when panning to an edge