Do not split preview header through an image

--preview-window ~N draws the header in its own pass, resuming the body
in the middle of an image: an image arrives as one line but takes up many
rows. ~N is typically global and meant for text, while the same preview
command also renders images.

src/terminal.go

@@ -57,6 +57,7 @@ var offsetComponentRegex *regexp.Regexp
 var offsetTrimCharsRegex *regexp.Regexp
 var passThroughBeginRegex *regexp.Regexp
 var passThroughEndTmuxRegex *regexp.Regexp
+var sixelBeginRegex *regexp.Regexp
 var ttyin *os.File
 
 var inTmux = len(os.Getenv("TMUX")) > 0
@@ -94,6 +95,7 @@ func init() {
 	*/
 	passThroughBeginRegex = regexp.MustCompile(`\x1bPtmux;\x1b\x1b|\x1b(_G|P[0-9;]*q)|\x1b]1337;`)
 	passThroughEndTmuxRegex = regexp.MustCompile(`[^\x1b]\x1b\\`)
+	sixelBeginRegex = regexp.MustCompile(`^\x1bP[0-9;]*q`)
 }
 
 type jumpMode int
@@ -4677,15 +4679,23 @@ func (t *Terminal) renderPreviewArea(unchanged bool) {
 	height := t.pwindow.Height()
 	body := t.previewer.lines
 	headerLines := t.activePreviewOpts.headerLines
+	lineNo := -t.previewer.offset + headerLines
+	// Scrollbar is sized from the body alone, split off or not
+	scrollLines := len(body)
 	// Do not enable preview header lines if it's value is too large
 	if headerLines > 0 && headerLines < min(len(body), height) {
+		scrollLines -= headerLines
 		header := t.previewer.lines[0:headerLines]
-		body = t.previewer.lines[headerLines:]
-		// Always redraw header
-		t.renderPreviewText(height, header, 0, false)
-		t.pwindow.MoveAndClear(t.pwindow.Y(), 0)
+		// A separate header pass would resume the body inside an image, which
+		// takes up more rows than the line it arrives on
+		if !containsImage(header) {
+			// Always redraw header
+			t.renderPreviewText(height, header, 0, false)
+			t.pwindow.MoveAndClear(t.pwindow.Y(), 0)
+			body = t.previewer.lines[headerLines:]
+		}
 	}
-	t.renderPreviewText(height, body, -t.previewer.offset+headerLines, unchanged)
+	t.renderPreviewText(height, body, lineNo, unchanged)
 
 	if !unchanged {
 		t.pwindow.FinishFill()
@@ -4696,7 +4706,7 @@ func (t *Terminal) renderPreviewArea(unchanged bool) {
 	}
 
 	effectiveHeight := height - headerLines
-	barLength, barStart := getScrollbar(1, len(body), effectiveHeight, min(len(body)-effectiveHeight, t.previewer.offset-headerLines))
+	barLength, barStart := getScrollbar(1, scrollLines, effectiveHeight, min(scrollLines-effectiveHeight, t.previewer.offset-headerLines))
 	t.renderPreviewScrollbar(headerLines, barLength, barStart)
 }
 
@@ -4776,6 +4786,50 @@ func wrapPassThrough(passThrough string, tmux bool) string {
 	return "\x1bPtmux;" + strings.ReplaceAll(passThrough, "\x1b", "\x1b\x1b") + "\x1b\\" + suffix
 }
 
+// Whether the sequence draws an image. Kitty commands that only transmit or
+// delete do not
+func isImagePassThrough(passThrough string) bool {
+	// Unwrap the tmux passthrough sequence, in which every ESC is doubled
+	if after, ok := strings.CutPrefix(passThrough, "\x1bPtmux;"); ok {
+		passThrough = strings.ReplaceAll(after, "\x1b\x1b", "\x1b")
+	}
+	if after, ok := strings.CutPrefix(passThrough, "\x1b_G"); ok {
+		// Control data ends at the payload delimiter or at the terminator
+		keys := after
+		if index := strings.IndexAny(keys, ";\x1b"); index >= 0 {
+			keys = keys[:index]
+		}
+		for _, key := range strings.Split(keys, ",") {
+			// Transmit and display, or put an image already transmitted
+			if key == "a=T" || key == "a=p" {
+				return true
+			}
+		}
+		return false
+	}
+	if after, ok := strings.CutPrefix(passThrough, "\x1b]1337;"); ok {
+		return strings.HasPrefix(after, "File=") || strings.HasPrefix(after, "MultipartFile=")
+	}
+	return sixelBeginRegex.MatchString(passThrough)
+}
+
+// Whether any line carries an image
+func containsImage(lines []string) bool {
+	for _, line := range lines {
+		for {
+			loc := findPassThrough(line)
+			if loc == nil {
+				break
+			}
+			if isImagePassThrough(line[loc[0]:loc[1]]) {
+				return true
+			}
+			line = line[loc[1]:]
+		}
+	}
+	return false
+}
+
 func extractPassThroughs(line string) ([]string, string) {
 	passThroughs := []string{}
 	transformed := ""

src/terminal_test.go

@@ -578,6 +578,60 @@ func TestWrapPassThrough(t *testing.T) {
 	}
 }
 
+func TestIsImagePassThrough(t *testing.T) {
+	for _, tc := range []struct {
+		given string
+		image bool
+	}{
+		// Kitty
+		{"\x1b_Ga=T,f=32,s=1258,v=1295,c=74,r=35,m=1\x1b\\", true},
+		{"\x1b_Ga=p,i=1\x1b\\", true},
+		// The action key is not always first, and a put carries no payload
+		{"\x1b_Gi=1,a=p\x1b\\", true},
+		{"\x1b_Ga=p\x1b\\", true},
+		{"\x1b_Ga=T,f=100\x1b\\\r", true},
+		{"\x1b_Gi=1,a=d\x1b\\", false},
+		{"\x1b_Ga=d,d=A\x1b\\", false},          // 'kitten icat --clear'
+		{"\x1b_Ga=q,i=1\x1b\\", false},          // query
+		{"\x1b_Gi=1,f=100\x1b\\", false},        // transmit only, the default action
+		{"\x1b_Gm=1;AAAA\x1b\\", false},         // continuation chunk
+		{"\x1b_Ga=f,i=1;AAAA\x1b\\", false},     // animation frame
+		{"\x1b_Ga=T,U=1,f=32;AAAA\x1b\\", true}, // unicode placeholder
+		// Wrapped in the tmux passthrough sequence
+		{"\x1bPtmux;\x1b\x1b_Ga=T,f=100\x1b\x1b\\\x1b\\", true},
+		{"\x1bPtmux;\x1b\x1b_Ga=d,d=A\x1b\x1b\\\x1b\\", false},
+		{"\x1bPtmux;\x1b\x1b_Gi=1,a=p\x1b\x1b\\\x1b\\", true},
+		// iTerm2
+		{"\x1b]1337;File=inline=1:AAAA\a", true},
+		{"\x1b]1337;MultipartFile=inline=1\a", true},
+		{"\x1b]1337;SetUserVar=foo=YmFy\a", false},
+		{"\x1b]1337;CurrentDir=/tmp\a", false},
+		// Sixel
+		{"\x1bP0;1;0q#0;2;0;0;0#0~~@@vv@@~~@\x1b\\", true},
+		{"\x1bPq#0~~\x1b\\", true},
+		{"\x1bPtmux;\x1b\x1bP0;1;0q#0~~\x1b\x1b\\\x1b\\", true},
+		{"", false},
+	} {
+		if actual := isImagePassThrough(tc.given); actual != tc.image {
+			t.Errorf("expected %v for %q, got %v", tc.image, tc.given, actual)
+		}
+	}
+
+	if containsImage([]string{"foo", "bar"}) {
+		t.Error("plain text carries no image")
+	}
+	if !containsImage([]string{"foo", "bar\x1b_Ga=T,f=100\x1b\\baz"}) {
+		t.Error("failed to find an image in a line")
+	}
+	if containsImage([]string{"foo\x1b_Ga=d,d=A\x1b\\"}) {
+		t.Error("a delete command is not an image")
+	}
+	// The image is not the first passthrough on the line
+	if !containsImage([]string{"\x1b_Ga=d,d=A\x1b\\text\x1b_Ga=T,f=100;AAAA\x1b\\"}) {
+		t.Error("failed to look past an earlier passthrough")
+	}
+}
+
 /* utilities section */
 
 // Item represents one line in fzf UI. Usually it is relative path to files and folders.