The chart canvas only ever set its width/height attributes, so on a 2x
display the browser upscaled a half-resolution bitmap and every curve
came out soft. On top of that the CSS pinned the canvas to 100px while
the backing store was computed at 119px, squashing the plot vertically
by 0.84.
Let flex layout own the canvas's CSS size (it takes whatever the data
rows leave over) and size the backing store from the laid-out rect times
devicePixelRatio, with the context transform matching so drawCurves keeps
working in CSS pixels. A ResizeObserver re-syncs the backing store when
the rows first appear or the panel is resized.
The data rows are now flex: 0 0 auto so they can no longer be squeezed
out of view; the minimum panel height goes to 150 because 90 never had
room for them in the first place.
kk8bit
13609bcc02