Fix sidebar repaint and command restart navigation

internal/app/viewport_renderer.go

@@ -10,11 +10,13 @@ import (
 // viewportRenderer rewrites child PTY output so it lands inside the
 // main viewport instead of controlling patterm's full host terminal.
 type viewportRenderer struct {
-	mu      sync.Mutex
-	shifter *cursorShifter
-	layout  terminalLayout
-	row     int
-	col     int
+	mu           sync.Mutex
+	shifter      *cursorShifter
+	layout       terminalLayout
+	row          int
+	col          int
+	scrollTop    int
+	scrollBottom int
 
 	state   viewportState
 	buf     []byte
@@ -22,8 +24,9 @@ type viewportRenderer struct {
 
 	// 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.
+	// NEL / SU / SD / IL / DL, or LF / VT / FF at the bottom margin.
+	// 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
@@ -50,12 +53,14 @@ const (
 )
 
 func newViewportRenderer(l terminalLayout) *viewportRenderer {
-	return &viewportRenderer{
+	vr := &viewportRenderer{
 		shifter: newCursorShifter(int(l.mainTop)-1, int(l.childRows()), int(l.childCols())),
 		layout:  l,
 		row:     1,
 		col:     1,
 	}
+	vr.resetScrollRegion()
+	return vr
 }
 
 func (vr *viewportRenderer) SetLayout(l terminalLayout) {
@@ -63,6 +68,7 @@ func (vr *viewportRenderer) SetLayout(l terminalLayout) {
 	defer vr.mu.Unlock()
 	vr.layout = l
 	vr.shifter.SetGeometry(int(l.mainTop)-1, int(l.childRows()), int(l.childCols()))
+	vr.resetScrollRegion()
 }
 
 func (vr *viewportRenderer) Render(in []byte) []byte {
@@ -82,11 +88,10 @@ func (vr *viewportRenderer) ClearViewport() []byte {
 }
 
 // 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.
+// forwarded) a scroll action since the previous call. 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 vertically.
 func (vr *viewportRenderer) TookScrollAction() bool {
 	vr.mu.Lock()
 	defer vr.mu.Unlock()
@@ -326,6 +331,22 @@ func (vr *viewportRenderer) clearLine(n int) string {
 	}
 }
 
+func (vr *viewportRenderer) resetScrollRegion() {
+	vr.scrollTop = 1
+	vr.scrollBottom = int(vr.layout.childRows())
+	if vr.scrollBottom < 1 {
+		vr.scrollBottom = 1
+	}
+}
+
+func (vr *viewportRenderer) lineFeed() {
+	if vr.row >= vr.scrollTop && vr.row == vr.scrollBottom {
+		vr.scrolled = true
+		return
+	}
+	vr.row++
+}
+
 // feedPrintable handles one non-ESC byte in the vpNormal state. It both
 // advances vr's cursor model and decides whether the byte should be
 // forwarded to the host. Bytes that would land past the viewport's
@@ -342,8 +363,8 @@ func (vr *viewportRenderer) feedPrintable(b byte) {
 		switch b {
 		case '\r':
 			vr.col = 1
-		case '\n':
-			vr.row++
+		case '\n', '\v', '\f':
+			vr.lineFeed()
 		case '\b':
 			if vr.col > 1 {
 				vr.col--
@@ -437,10 +458,38 @@ func (vr *viewportRenderer) trackCSI(final byte, params []byte) {
 		if ok {
 			vr.col -= n
 		}
+	case 'r':
+		vr.trackScrollRegion(params)
 	}
 	vr.clampCursor()
 }
 
+func (vr *viewportRenderer) trackScrollRegion(params []byte) {
+	if len(params) == 0 {
+		vr.resetScrollRegion()
+		return
+	}
+	top, bottom, ok := parseTwoParams(params)
+	if !ok {
+		return
+	}
+	maxRows := int(vr.layout.childRows())
+	if maxRows < 1 {
+		maxRows = 1
+	}
+	if top < 1 {
+		top = 1
+	}
+	if bottom < 1 || bottom > maxRows {
+		bottom = maxRows
+	}
+	if top >= bottom {
+		return
+	}
+	vr.scrollTop = top
+	vr.scrollBottom = bottom
+}
+
 func (vr *viewportRenderer) clampCursor() {
 	if vr.row < 1 {
 		vr.row = 1