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TrackHeightMixin

Auto-generated @jbrowse/mobx-state-tree API for the current JBrowse release — see pluggable elements for concepts. Built into JBrowse core. View source.

#crossCuttingMixin Internal vertical scroll. scrollableHeight (default Infinity = doesn't scroll). Brings the clamped setScrollTop and the autorun that re-clamps when content shrinks

The display height is stored directly on the height config slot (drag-resize writes it via setSlot), so it survives a track being unticked and reticked — the config node outlives the ephemeral display instance. Displays with an auto-fit mode declare height as a maybeNumber slot (default undefined) and override the height getter to fall back to their computed content height when unset.

It also owns the internal vertical scroll every canvas display that scrolls its own content shares: the scrollTop volatile, a setScrollTop clamped against the overridable scrollableHeight hook, and the autorun that re-clamps when the content shrinks. Four displays (alignments, canvas, MAF, multi-sample variants) each carried their own copy of the last two, with four copies of the same "a virtual-scrolled canvas has no overflow container to self-correct" paragraph; a display now opts into all of it by overriding one getter.

Volatiles

MemberDescription
scrollTop
scrollTop: 0

Getters

MemberDescription
height
number
resizing
boolean		True for the duration of a height drag on this track, whichever handle is running it. A display whose row geometry is a function of the track height restretches every row per animation frame, and can use this to sit an expensive per-frame layer out of the drag (MAF's dense per-base letter overlay is a Canvas2D pass that scales with rows x columns).

The flag itself is the track's (BaseTrackModel), so the view brackets a drag without needing the active display to have opted into this mixin. Reading it here is what makes self.resizing available to a display that did.
scrollableHeight
number		Overridable hook: how far this display's content can scroll past its viewport, in px. Infinity (the default) means "this display doesn't scroll internally" — setScrollTop then never clamps and the re-clamp autorun below is inert, so a non-scrolling display pays nothing and, crucially, never evaluates a getter that would read view geometry.

A display that scrolls a canvas overrides this with max(0, contentHeight - viewportHeight), and gets the clamped setter plus the shrink autorun for free. It is the single "does it scroll, and by how much" answer: the wheel handler (useVirtualScrollWheel) and VerticalScrollbar read the same getter.

Actions

MemberDescription
setScrollTop
(scrollTop: number) => void		Clamped into [0, scrollableHeight], so no caller has to remember the bound. Unbounded for a display that leaves scrollableHeight at its Infinity default.
setHeight
(displayHeight: number) => number
resizeHeight
(distance: number) => number
expandToContentHeight
() => number		Grow the track by exactly the content it is currently hiding, so a display scrolled over a taller stack ends up showing all of it. The track's resize handle runs this on a double click.

scrollableHeight is the whole measurement — it is already every scrolling display's answer to "how much is off the bottom", so no display has to supply a second one. A display that doesn't scroll internally leaves it at Infinity and gets a no-op, as does one already showing everything (0).

Routed through resizeHeight rather than setHeight so grow mode's override still gets to leave grow first; going straight to the slot would let the reactive height re-derive grownHeight and the double click would appear to do nothing.