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Repaint sidebar after child scrolls the host scroll region

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Codex (Ratatui) emits an 8x RI burst on startup right after setting
DECSTBM. RI at the top of the scroll region scrolls the region down,
and DECSTBM only constrains rows -- so the scroll spans every column
and drags the right-rail session-tree entries down with the main pane.
The chrome cache then hid the clobber because the computed sidebar
frame was unchanged.

The viewport renderer now flags any chunk containing RI / IND / NEL /
SU / SD / IL / DL and OnPTYOut drops the sidebar cache when the flag
is set, so the next drawSidebar repaints over the drift.

Adds unit tests for the new flag and a harness regression scenario
(sidebar_survives_ri_scroll) that fails without the fix.
This commit is contained in:
Harry Bayliss
2026-05-14 20:01:14 +01:00
parent 3622c41fd0
commit 58dbb56937
5 changed files with 151 additions and 0 deletions
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43
internal/app/viewport_renderer.go
View File

@@ -19,6 +19,14 @@ type viewportRenderer struct {
state viewportState
buf []byte
pending strings.Builder
// scrolled is set when the chunk contained an escape that shifts
// content row-wise within the host's scroll region — RI / IND /
// NEL / SU / SD / IL / DL. DECSTBM constrains rows but not columns,
// so these scrolls drag the right-hand sidebar content with them.
// OnPTYOut consumes the flag and invalidates the sidebar chrome
// cache so the next drawSidebar repaints over the clobber.
scrolled bool
}
type viewportState int
@@ -67,6 +75,20 @@ func (vr *viewportRenderer) ClearViewport() []byte {
return []byte(vr.clearViewport())
}
// TookScrollAction reports whether the most recent Render emitted (or
// forwarded) a scroll-triggering escape — RI / IND / NEL / SU / SD /
// IL / DL — since the previous call. The flag is reset on read.
// Callers use it to invalidate sidebar-cache state, because the host's
// scroll region spans the full row width and any scroll there drags
// the sidebar content downward.
func (vr *viewportRenderer) TookScrollAction() bool {
vr.mu.Lock()
defer vr.mu.Unlock()
out := vr.scrolled
vr.scrolled = false
return out
}
func (vr *viewportRenderer) feed(b byte) {
switch vr.state {
case vpNormal:
@@ -89,6 +111,18 @@ func (vr *viewportRenderer) feed(b byte) {
vr.state = vpDCS
case 'X', '^', '_':
vr.state = vpSOSPMAPC
case 'M', 'D', 'E':
// RI (ESC M), IND (ESC D), NEL (ESC E). All three can scroll
// the host's scroll region when the cursor is at the top
// (RI) or bottom (IND/NEL) edge. The region spans the full
// row width, so the scroll drags the sidebar columns along
// with the main pane. Forward as-is and flag for sidebar
// cache invalidation. Codex emits 8× RI on startup, which
// is what motivated this branch.
vr.pending.Write(vr.buf)
vr.scrolled = true
vr.state = vpNormal
vr.buf = vr.buf[:0]
default:
vr.pending.Write(vr.buf)
vr.state = vpNormal
@@ -177,6 +211,15 @@ func (vr *viewportRenderer) emitCSI() {
return
}
vr.pending.WriteString(vr.clearLine(n))
case 'S', 'T', 'L', 'M':
// SU (S) / SD (T) / IL (L) / DL (M) all shift content within
// the host's scroll region row-wise across every column. The
// sidebar lives at the right of the host, inside the scroll
// region's row range, so any of these drag its cells along
// with the main pane. Forward verbatim and flag the chunk so
// the sidebar is repainted afterwards.
vr.pending.Write(vr.shifter.Shift(vr.buf))
vr.scrolled = true
default:
vr.pending.Write(vr.shifter.Shift(vr.buf))
}