com.blockether.vis.ext.channel-tui.scrollbar — com.blockether/vis-channel-tui 0.1.2

Single source of truth for vertical scrollbars in the TUI.

One namespace owns geometry, drawing, hit-test, wheel handling and click/drag → scroll math. EVERY scrollbar — chat messages, slash menu, settings, file picker, provider/model cards, sessions, every other dialog — goes through here. No more bespoke thumb math per call site, no more drift between painter and hit-test layers.

Why one cell tall thumbs

Terminal.app renders stacked U+2588 FULL BLOCK cells as a ladder of separate boxes when the window is tall, which reads as multiple scroll positions instead of one current-position marker. So the visible thumb is intentionally one row high; the thumb's row index inside the track encodes the scroll fraction.

draw! clj

(draw! g
       {:keys [col top track-h total-h inner-h scroll track-fg track-bg thumb-fg
               thumb-bg]
        :or {track-fg t/dialog-border
             track-bg t/dialog-bg
             thumb-fg t/dialog-hint-key
             thumb-bg t/dialog-bg}})

Paint a vertical scrollbar.

Required opts: :col :top :track-h :total-h :inner-h :scroll. Optional opts: :track-fg :track-bg :thumb-fg :thumb-bg (default = dialog palette, used by every modal scrollbar).

Returns the geometry map (or nil when no overflow, in which case nothing is painted).

geometry clj

(geometry total-h inner-h scroll)

(geometry total-h inner-h track-h scroll)

Compute thumb geometry for a vertical scrollbar.

Arguments

• total-h total content size (rows OR item count — same math applies to row-pixels and item-windows).
• inner-h visible viewport size in the same unit as total-h.
• track-h optional track length in screen rows; defaults to inner-h. The track may extend past the viewport (e.g. into top/bottom breathing-room rows).
• scroll current scroll offset; nil ⇒ pinned to bottom (max-scroll). Out-of-range values are clamped.

Returns {:thumb-top-rel :thumb-h :max-scroll :track-h} when the content overflows the viewport, otherwise nil (no thumb should be drawn and every click hit-test below should return off-thumb).

on-thumb? clj

(on-thumb? mx
           my
           {:keys [col top x-band] :or {x-band 1}}
           {:keys [thumb-top-rel thumb-h]})

True when (mx,my) lands on the thumb. bar carries :col :top [:x-band]; geom is the result of geometry.

on-track? clj

(on-track? mx my {:keys [col top track-h x-band] :or {x-band 1}})

True when (mx,my) falls inside the scrollbar column at any track row.

bar is {:col :top :track-h [:x-band]}. :x-band widens the x-axis tolerance (default 1) — chat messages use 3 so users don't need pixel-perfect aim on the right gutter.

scroll-from-mouse-y clj

(scroll-from-mouse-y mouse-y top track-h total-h inner-h)

(scroll-from-mouse-y mouse-y top track-h total-h inner-h grip-offset)

Convert a mouse Y on the track into a clamped scroll value.

• mouse-y absolute row the cursor is at
• top track's first-row screen Y
• track-h track length
• total-h total content size
• inner-h viewport size
• grip-offset rows between thumb top and the user's grip-point; pass the offset saved at CLICK_DOWN so dragging preserves the grip (so the row under the finger stays glued to the same point on the thumb). Use 0 for click-to-position behaviour.

THUMB_H clj

wheel-delta clj

(wheel-delta event)

Return -1 for SCROLL_UP, +1 for SCROLL_DOWN, else nil. Accepts a Lanterna KeyStroke or MouseAction; non-mouse events return nil.

wheel-step clj

(wheel-step event)

Wheel delta multiplied by the coalesced event count carried in MouseAction#getButton. Lanterna stuffs the coalesced count into the button field when an upstream input loop drains a wheel flood, so one mouse tick can move multiple rows.