feat: add alt-gutter color option (#4602)

* Add alt-gutter color option

* Simplify the code

---------

Co-authored-by: Junegunn Choi <junegunn.c@gmail.com>

man/man1/fzf.1

@@ -272,6 +272,7 @@ color mappings. Each entry is separated by a comma and/or whitespaces.
       \fBgutter              \fRGutter on the left
     \fBcurrent\-hl (hl+)      \fRHighlighted substrings (current line)
     \fBalt\-bg                \fRAlternate background color to create striped lines
+    \fBalt\-gutter            \fRAlternate gutter color to create the striped pattern
     \fBquery (input\-fg)      \fRQuery string
       \fBghost               \fRGhost text (\fB\-\-ghost\fR, \fBdim\fR applied by default)
       \fBdisabled            \fRQuery string when search is disabled (\fB\-\-disabled\fR)

src/options.go

@@ -1476,6 +1476,8 @@ func parseTheme(defaultTheme *tui.ColorTheme, str string) (*tui.ColorTheme, *tui
 				mergeAttr(&theme.Nomatch)
 			case "gutter":
 				mergeAttr(&theme.Gutter)
+			case "alt-gutter":
+				mergeAttr(&theme.AltGutter)
 			case "hl":
 				mergeAttr(&theme.Match)
 			case "current-hl", "hl+":

src/terminal.go

@@ -3202,15 +3202,23 @@ func (t *Terminal) renderEmptyLine(line int, barRange [2]int) {
 	t.renderBar(line, barRange)
 }
 
-func (t *Terminal) gutter(current bool) {
+func (t *Terminal) gutter(current bool, alt bool) {
 	var color tui.ColorPair
 	if current {
 		color = tui.ColCurrentCursorEmpty
 	} else if !t.raw && t.gutterReverse || t.raw && t.gutterRawReverse {
+		if alt {
+			color = tui.ColAltCursorEmpty
+		} else {
 			color = tui.ColCursorEmpty
+		}
+	} else {
+		if alt {
+			color = tui.ColAltCursorEmptyChar
 		} else {
 			color = tui.ColCursorEmptyChar
 		}
+	}
 	gutter := t.pointerEmpty
 	if t.raw {
 		gutter = t.pointerEmptyRaw
@@ -3220,7 +3228,7 @@ func (t *Terminal) gutter(current bool) {
 
 func (t *Terminal) renderGapLine(line int, barRange [2]int, drawLine bool) {
 	t.move(line, 0, false)
-	t.gutter(false)
+	t.gutter(false, false)
 	t.window.Print(t.markerEmpty)
 	x := t.pointerLen + t.markerLen
 
@@ -3394,7 +3402,7 @@ func (t *Terminal) printItem(result Result, line int, maxLine int, index int, cu
 				return indentSize
 			}
 			if len(label) == 0 {
-				t.gutter(true)
+				t.gutter(true, false)
 			} else {
 				t.window.CPrint(tui.ColCurrentCursor, label)
 			}
@@ -3416,7 +3424,7 @@ func (t *Terminal) printItem(result Result, line int, maxLine int, index int, cu
 				return indentSize
 			}
 			if len(label) == 0 {
-				t.gutter(false)
+				t.gutter(false, index%2 == 1)
 			} else {
 				t.window.CPrint(tui.ColCursor, label)
 			}

src/tui/tui.go

@@ -456,6 +456,7 @@ type ColorTheme struct {
 	PreviewBg        ColorAttr
 	DarkBg           ColorAttr
 	Gutter           ColorAttr
+	AltGutter        ColorAttr
 	Prompt           ColorAttr
 	InputBg          ColorAttr
 	InputBorder      ColorAttr
@@ -826,6 +827,8 @@ var (
 	ColCursor               ColorPair
 	ColCursorEmpty          ColorPair
 	ColCursorEmptyChar      ColorPair
+	ColAltCursorEmpty       ColorPair
+	ColAltCursorEmptyChar   ColorPair
 	ColMarker               ColorPair
 	ColSelected             ColorPair
 	ColSelectedMatch        ColorPair
@@ -891,6 +894,7 @@ func init() {
 		PreviewFg:        defaultColor,
 		PreviewBg:        defaultColor,
 		Gutter:           undefined,
+		AltGutter:        undefined,
 		PreviewBorder:    defaultColor,
 		PreviewScrollbar: defaultColor,
 		PreviewLabel:     defaultColor,
@@ -943,6 +947,7 @@ func init() {
 		PreviewFg:        undefined,
 		PreviewBg:        undefined,
 		Gutter:           undefined,
+		AltGutter:        undefined,
 		PreviewBorder:    undefined,
 		PreviewScrollbar: undefined,
 		PreviewLabel:     undefined,
@@ -991,6 +996,7 @@ func init() {
 		PreviewFg:        undefined,
 		PreviewBg:        undefined,
 		Gutter:           undefined,
+		AltGutter:        undefined,
 		PreviewBorder:    undefined,
 		PreviewScrollbar: undefined,
 		PreviewLabel:     undefined,
@@ -1041,6 +1047,7 @@ func init() {
 		PreviewFg:        undefined,
 		PreviewBg:        undefined,
 		Gutter:           undefined,
+		AltGutter:        undefined,
 		PreviewBorder:    undefined,
 		PreviewScrollbar: undefined,
 		PreviewLabel:     undefined,
@@ -1091,6 +1098,7 @@ func init() {
 		PreviewFg:        undefined,
 		PreviewBg:        undefined,
 		Gutter:           undefined,
+		AltGutter:        undefined,
 		PreviewBorder:    undefined,
 		PreviewScrollbar: undefined,
 		PreviewLabel:     undefined,
@@ -1208,6 +1216,7 @@ func InitTheme(theme *ColorTheme, baseTheme *ColorTheme, boldify bool, forceBlac
 		gutter.Attr = Dim
 	}
 	theme.Gutter = o(theme.DarkBg, gutter)
+	theme.AltGutter = o(theme.Gutter, theme.AltGutter)
 	theme.PreviewFg = o(theme.Fg, theme.PreviewFg)
 	theme.PreviewBg = o(theme.Bg, theme.PreviewBg)
 	theme.PreviewLabel = o(theme.BorderLabel, theme.PreviewLabel)
@@ -1277,6 +1286,8 @@ func initPalette(theme *ColorTheme) {
 	ColCursor = pair(theme.Cursor, theme.Gutter)
 	ColCursorEmpty = pair(blank, theme.Gutter)
 	ColCursorEmptyChar = pair(theme.Gutter, theme.ListBg)
+	ColAltCursorEmpty = pair(blank, theme.AltGutter)
+	ColAltCursorEmptyChar = pair(theme.AltGutter, theme.ListBg)
 	if theme.SelectedBg.Color != theme.ListBg.Color {
 		ColMarker = pair(theme.Marker, theme.SelectedBg)
 	} else {