New setting "barChartStretchToItem on" for bigBarCharts

[Brian Lee]

There is a new setting to expand the view of bar graphs in track hubs and custom tracks.  When using the bigBarChart format, https://genome.ucsc.edu/goldenPath/help/barChart.html, vertical rectangles allow designating a value for multiple sources in a region, often a gene, such as RNA-seq in multiple cell types. For instance, the bigBarChart format is featured heavily in a recent release of new Single Cell RNA-seq data on hg38: https://genome.ucsc.edu/goldenPath/newsarch.html#111721

To aid in customizing the display of the bigBarChart format a new setting "barChartStretchToItem on" extends the barCharts to cover the entire horizontal space available in the graph: https://genome.ucsc.edu/goldenPath/help/trackDb/trackDbHub.html#barChartStretchToItem

Here is an example of the new setting using a custom track shared on the help page for bigBarChart:

track type=bigBarChart barChartStretchToItem=on name="bigBarChart Example One" description="A bigBarChart file" barChartBars="adiposeSubcut breastMamTissue colonTransverse muscleSkeletal wholeBlood" visibility=pack bigDataUrl=http://genome.ucsc.edu/goldenPath/help/examples/barChart/hg38.gtexTranscripts.bb
browser position chr14:95,081,796-95,436,280

Here is an image difference, where the top track is using the new barChartStretchToItem=on setting, while the lower track is using the default display.