Synteny view drawings can vary slightly between browser and scroll state

[cmdcolin]

The linear synteny view with all the polygons uses a render optimization where multiple drawing operations are batched into a single operation (multiple line drawing operations get a single canvas.stroke() and it draws a "polyline")

see

jbrowse-components/plugins/linear-comparative-view/src/LinearSyntenyDisplay/drawSynteny.ts

Line 90 in 9aaa5ba

// ctx.stroke once is much more efficient than calling stroke() many times

this does speed it up but it results in different alpha blending on chrome vs firefox sometimes with firefox appearing more "pale" due to the lack of alpha blending on the polyline not stacking up darker and darker alpha blends

options to address this could include

a) do nothing
b) gather user feedback to see how much it matters
c) remove the optimization, should "fix" it
d) fix it some other way that preserves polyline, or only remove polyline on firefox
e) don't use the alpha channel at all, and just always use flat colors, or use flat colors by default
f) see what the situation looks like after implementing other synteny coloring options

those are not all mutually exclusive...

[cmdcolin]

firefox initial page load

firefox after scrolling around a bit

chrome initial page load

[cmdcolin]

note: i am not exactly sure why scrolling around in firefox starts to enable the alpha blending

[cmdcolin]

note that after " f) see what the situation looks like after implementing other synteny coloring options" it may be harder to do polylines as all the elements of a polylines are a single color