APR PR master v0p3p3

[alexpreynolds]

This PR for the HiGlass higlass-multivec track includes Pixi resource memory leak fixes, PNG/SVG export fixes, more graceful error handling for null Pixi objects, and feature enhancements for mouseover tooltips. This also includes a new track type called horizontal-stacked-delta-bar, which looks similar to the UCSC Genome Browser graph tracks where data series can be layered atop one another (see "Overlay" section here: https://genome.ucsc.edu/goldenpath/help/hgWiggleTrackHelp.html). This also integrates fixes that have been merged into the upstream (base) repository in the master branch (currently post v0.3.3).

[pkerpedjiev]

Any chance you could add a screenshot of the StackedDeltaBarChart?

[alexpreynolds]

Here is an example from visiting the Index DHS site at https://index.altius.org:

Mousing over bar elements shows their respective signal value. Bars are drawn from front to back, with smallest to largest signal, with some alpha transparency.

This is not used in the main desktop Index DHS app, once you get past the front portal page. But it is used for the mobile device version of the site, when the phone is in landscape mode and vertical space is at a premium. The StackedDeltaBarChart works better for situations when the screen is small and there are too many signals to be reasonably shown in a StackedBarChart track (such as on mobile devices).

I could edit the README to show this example, as well as examples of other uses of this track.