Add scrollbar

Close #3096

7 files changed, 116 insertions, 9 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e6126451..d2838d50 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,14 @@ CHANGELOG
   # Send actions to the server
   curl -XPOST localhost:6266 -d 'reload(seq 100)+change-prompt(hundred> )'
   ```
+- Added scrollbar on the main search window
+  ```sh
+  # Hide scrollbar
+  fzf --no-scrollbar
+
+  # Customize scrollbar
+  fzf --scrollbar ┆ --color scrollbar:blue
+  ```
 - New event
     - Added `load` event that is triggered when the input stream is complete
       and the initial processing of the list is complete.
diff --git a/man/man1/fzf.1 b/man/man1/fzf.1
index e981a13c..9ac213cd 100644
--- a/man/man1/fzf.1
+++ b/man/man1/fzf.1
@@ -357,6 +357,15 @@ Do not display horizontal separator on the info line. A synonym for
 \fB--separator=''\fB
 
 .TP
+.BI "--scrollbar=" "CHAR"
+Use the given character to render scrollbar. (default: '▏' or ':' depending on
+\fB--no-unicode\fR).
+
+.TP
+.B "--no-scrollbar"
+Do not display scrollbar. A synonym for \fB--scrollbar=''\fB
+
+.TP
 .BI "--prompt=" "STR"
 Input prompt (default: '> ')
 .TP
diff --git a/src/options.go b/src/options.go
index 0ee7db33..e4a6aa39 100644
--- a/src/options.go
+++ b/src/options.go
@@ -73,6 +73,8 @@ const usage = `usage: fzf [options]
     --info=STYLE           Finder info style [default|inline|hidden]
     --separator=STR        String to form horizontal separator on info line
     --no-separator         Hide info line separator
+    --scrollbar[=CHAR]     Scrollbar character
+    --no-scrollbar         Hide scrollbar
     --prompt=STR           Input prompt (default: '> ')
     --pointer=STR          Pointer to the current line (default: '>')
     --marker=STR           Multi-select marker (default: '>')
@@ -290,6 +292,7 @@ type Options struct {
 	HeaderLines  int
 	HeaderFirst  bool
 	Ellipsis     string
+	Scrollbar    *string
 	Margin       [4]sizeSpec
 	Padding      [4]sizeSpec
 	BorderShape  tui.BorderShape
@@ -359,6 +362,7 @@ func defaultOptions() *Options {
 		HeaderLines:  0,
 		HeaderFirst:  false,
 		Ellipsis:     "..",
+		Scrollbar:    nil,
 		Margin:       defaultMargin(),
 		Padding:      defaultMargin(),
 		Unicode:      true,
@@ -847,6 +851,8 @@ func parseTheme(defaultTheme *tui.ColorTheme, str string) *tui.ColorTheme {
 				mergeAttr(&theme.Border)
 			case "separator":
 				mergeAttr(&theme.Separator)
+			case "scrollbar":
+				mergeAttr(&theme.Scrollbar)
 			case "label":
 				mergeAttr(&theme.BorderLabel)
 			case "preview-label":
@@ -1570,6 +1576,16 @@ func parseOptions(opts *Options, allArgs []string) {
 		case "--no-separator":
 			nosep := ""
 			opts.Separator = &nosep
+		case "--scrollbar":
+			given, bar := optionalNextString(allArgs, &i)
+			if given {
+				opts.Scrollbar = &bar
+			} else {
+				opts.Scrollbar = nil
+			}
+		case "--no-scrollbar":
+			noBar := ""
+			opts.Scrollbar = &noBar
 		case "--jump-labels":
 			opts.JumpLabels = nextString(allArgs, &i, "label characters required")
 			validateJumpLabels = true
@@ -1739,6 +1755,8 @@ func parseOptions(opts *Options, allArgs []string) {
 				opts.InfoStyle = parseInfoStyle(value)
 			} else if match, value := optString(arg, "--separator="); match {
 				opts.Separator = &value
+			} else if match, value := optString(arg, "--scrollbar="); match {
+				opts.Scrollbar = &value
 			} else if match, value := optString(arg, "--toggle-sort="); match {
 				parseToggleSort(opts.Keymap, value)
 			} else if match, value := optString(arg, "--expect="); match {
@@ -1845,6 +1863,11 @@ func postProcessOptions(opts *Options) {
 	if !opts.Version && !tui.IsLightRendererSupported() && opts.Height.size > 0 {
 		errorExit("--height option is currently not supported on this platform")
 	}
+
+	if opts.Scrollbar != nil && runewidth.StringWidth(*opts.Scrollbar) > 1 {
+		errorExit("scrollbar display width should be 1")
+	}
+
 	// Default actions for CTRL-N / CTRL-P when --history is set
 	if opts.History != nil {
 		if _, prs := opts.Keymap[tui.CtrlP.AsEvent()]; !prs {
diff --git a/src/terminal.go b/src/terminal.go
index a89b6ac8..ed585e9d 100644
--- a/src/terminal.go
+++ b/src/terminal.go
@@ -97,6 +97,7 @@ type itemLine struct {
 	label    string
 	queryLen int
 	width    int
+	bar      bool
 	result   Result
 }
 
@@ -161,6 +162,7 @@ type Terminal struct {
 	header             []string
 	header0            []string
 	ellipsis           string
+	scrollbar          string
 	ansi               bool
 	tabstop            int
 	margin             [4]sizeSpec
@@ -632,6 +634,15 @@ func NewTerminal(opts *Options, eventBox *util.EventBox) *Terminal {
 		}
 		t.separator, t.separatorLen = t.ansiLabelPrinter(bar, &tui.ColSeparator, true)
 	}
+	if opts.Scrollbar == nil {
+		if t.unicode {
+			t.scrollbar = "▏" // Left one eighth block
+		} else {
+			t.scrollbar = "|"
+		}
+	} else {
+		t.scrollbar = *opts.Scrollbar
+	}
 
 	_, t.hasLoadActions = t.keymap[tui.Load.AsEvent()]
 
@@ -763,6 +774,27 @@ func (t *Terminal) noInfoLine() bool {
 	return t.infoStyle != infoDefault
 }
 
+func (t *Terminal) getScrollbar() (int, int) {
+	total := t.merger.Length()
+	if total == 0 {
+		return 0, 0
+	}
+
+	maxItems := t.maxItems()
+	barLength := util.Max(1, maxItems*maxItems/total)
+	if total <= maxItems {
+		return 0, 0
+	}
+
+	var barStart int
+	if total == maxItems {
+		barStart = 0
+	} else {
+		barStart = (maxItems - barLength) * t.offset / (total - maxItems)
+	}
+	return barLength, barStart
+}
+
 // Input returns current query string
 func (t *Terminal) Input() (bool, []rune) {
 	t.mutex.Lock()
@@ -1349,6 +1381,7 @@ func (t *Terminal) printHeader() {
 
 func (t *Terminal) printList() {
 	t.constrain()
+	barLength, barStart := t.getScrollbar()
 
 	maxy := t.maxItems()
 	count := t.merger.Length() - t.offset
@@ -1362,7 +1395,7 @@ func (t *Terminal) printList() {
 			line--
 		}
 		if i < count {
-			t.printItem(t.merger.Get(i+t.offset), line, i, i == t.cy-t.offset)
+			t.printItem(t.merger.Get(i+t.offset), line, i, i == t.cy-t.offset, i >= barStart && i < barStart+barLength)
 		} else if t.prevLines[i] != emptyLine {
 			t.prevLines[i] = emptyLine
 			t.move(line, 0, true)
@@ -1370,7 +1403,7 @@ func (t *Terminal) printList() {
 	}
 }
 
-func (t *Terminal) printItem(result Result, line int, i int, current bool) {
+func (t *Terminal) printItem(result Result, line int, i int, current bool, bar bool) {
 	item := result.item
 	_, selected := t.selected[item.Index()]
 	label := ""
@@ -1386,7 +1419,7 @@ func (t *Terminal) printItem(result Result, line int, i int, current bool) {
 
 	// Avoid unnecessary redraw
 	newLine := itemLine{current: current, selected: selected, label: label,
-		result: result, queryLen: len(t.input), width: 0}
+		result: result, queryLen: len(t.input), width: 0, bar: bar}
 	prevLine := t.prevLines[i]
 	if prevLine.current == newLine.current &&
 		prevLine.selected == newLine.selected &&
@@ -1426,6 +1459,12 @@ func (t *Terminal) printItem(result Result, line int, i int, current bool) {
 	if fillSpaces > 0 {
 		t.window.Print(strings.Repeat(" ", fillSpaces))
 	}
+	if len(t.scrollbar) > 0 && bar != prevLine.bar {
+		t.move(line, t.window.Width()-1, true)
+		if bar {
+			t.window.CPrint(tui.ColScrollbar, t.scrollbar)
+		}
+	}
 	t.prevLines[i] = newLine
 }
 
@@ -2999,8 +3038,9 @@ func (t *Terminal) Loop() {
 					}
 				} else if t.window.Enclose(my, mx) {
 					mx -= t.window.Left()
-					my -= t.window.Top()
+					bar := mx == t.window.Width()-1
 					mx = util.Constrain(mx-t.promptLen, 0, len(t.input))
+					my -= t.window.Top()
 					min := 2 + len(t.header)
 					if t.noInfoLine() {
 						min--
@@ -3016,7 +3056,20 @@ func (t *Terminal) Loop() {
 							my = h - my - 1
 						}
 					}
-					if me.Double {
+					if bar && my >= min {
+						barLength, barStart := t.getScrollbar()
+						if barLength > 0 {
+							maxItems := t.maxItems()
+							if newBarStart := util.Constrain(my-min-barLength/2, 0, maxItems-barLength); newBarStart != barStart {
+								total := t.merger.Length()
+								prevOffset := t.offset
+								// barStart = (maxItems - barLength) * t.offset / (total - maxItems)
+								t.offset = int(math.Ceil(float64(newBarStart) * float64(total-maxItems) / float64(maxItems-barLength)))
+								t.cy = t.offset + t.cy - prevOffset
+								req(reqList)
+							}
+						}
+					} else if me.Double {
 						// Double-click
 						if my >= min {
 							if t.vset(t.offset+my-min) && t.cy < t.merger.Length() {
diff --git a/src/tui/light.go b/src/tui/light.go
index 4225fc52..83020a71 100644
--- a/src/tui/light.go
+++ b/src/tui/light.go
@@ -176,6 +176,7 @@ func (r *LightRenderer) Init() {
 
 	if r.mouse {
 		r.csi("?1000h")
+		r.csi("?1002h")
 		r.csi("?1006h")
 	}
 	r.csi(fmt.Sprintf("%dA", r.MaxY()-1))
@@ -569,12 +570,14 @@ func (r *LightRenderer) mouseSequence(sz *int) Event {
 	// ctrl := t & 0b1000
 	mod := t&0b1100 > 0
 
+	drag := t&0b100000 > 0
+
 	if scroll != 0 {
 		return Event{Mouse, 0, &MouseEvent{y, x, scroll, false, false, false, mod}}
 	}
 
 	double := false
-	if down {
+	if down && !drag {
 		now := time.Now()
 		if !left { // Right double click is not allowed
 			r.clickY = []int{}
diff --git a/src/tui/tui.go b/src/tui/tui.go
index d1bb571a..e0fc6330 100644
--- a/src/tui/tui.go
+++ b/src/tui/tui.go
@@ -269,6 +269,7 @@ type ColorTheme struct {
 	Selected     ColorAttr
 	Header       ColorAttr
 	Separator    ColorAttr
+	Scrollbar    ColorAttr
 	Border       ColorAttr
 	BorderLabel  ColorAttr
 	PreviewLabel ColorAttr
@@ -466,6 +467,7 @@ var (
 	ColInfo                 ColorPair
 	ColHeader               ColorPair
 	ColSeparator            ColorPair
+	ColScrollbar            ColorPair
 	ColBorder               ColorPair
 	ColPreview              ColorPair
 	ColPreviewBorder        ColorPair
@@ -490,6 +492,7 @@ func EmptyTheme() *ColorTheme {
 		Selected:     ColorAttr{colUndefined, AttrUndefined},
 		Header:       ColorAttr{colUndefined, AttrUndefined},
 		Separator:    ColorAttr{colUndefined, AttrUndefined},
+		Scrollbar:    ColorAttr{colUndefined, AttrUndefined},
 		Border:       ColorAttr{colUndefined, AttrUndefined},
 		BorderLabel:  ColorAttr{colUndefined, AttrUndefined},
 		Disabled:     ColorAttr{colUndefined, AttrUndefined},
@@ -517,6 +520,7 @@ func NoColorTheme() *ColorTheme {
 		Selected:     ColorAttr{colDefault, AttrRegular},
 		Header:       ColorAttr{colDefault, AttrRegular},
 		Separator:    ColorAttr{colDefault, AttrRegular},
+		Scrollbar:    ColorAttr{colDefault, AttrRegular},
 		Border:       ColorAttr{colDefault, AttrRegular},
 		BorderLabel:  ColorAttr{colDefault, AttrRegular},
 		Disabled:     ColorAttr{colDefault, AttrRegular},
@@ -549,6 +553,7 @@ func init() {
 		Selected:     ColorAttr{colMagenta, AttrUndefined},
 		Header:       ColorAttr{colCyan, AttrUndefined},
 		Separator:    ColorAttr{colBlack, AttrUndefined},
+		Scrollbar:    ColorAttr{colBlack, AttrUndefined},
 		Border:       ColorAttr{colBlack, AttrUndefined},
 		BorderLabel:  ColorAttr{colWhite, AttrUndefined},
 		Disabled:     ColorAttr{colUndefined, AttrUndefined},
@@ -573,6 +578,7 @@ func init() {
 		Selected:     ColorAttr{168, AttrUndefined},
 		Header:       ColorAttr{109, AttrUndefined},
 		Separator:    ColorAttr{59, AttrUndefined},
+		Scrollbar:    ColorAttr{59, AttrUndefined},
 		Border:       ColorAttr{59, AttrUndefined},
 		BorderLabel:  ColorAttr{145, AttrUndefined},
 		Disabled:     ColorAttr{colUndefined, AttrUndefined},
@@ -597,6 +603,7 @@ func init() {
 		Selected:     ColorAttr{168, AttrUndefined},
 		Header:       ColorAttr{31, AttrUndefined},
 		Separator:    ColorAttr{145, AttrUndefined},
+		Scrollbar:    ColorAttr{145, AttrUndefined},
 		Border:       ColorAttr{145, AttrUndefined},
 		BorderLabel:  ColorAttr{59, AttrUndefined},
 		Disabled:     ColorAttr{colUndefined, AttrUndefined},
@@ -645,6 +652,7 @@ func initTheme(theme *ColorTheme, baseTheme *ColorTheme, forceBlack bool) {
 	theme.PreviewFg = o(theme.Fg, theme.PreviewFg)
 	theme.PreviewBg = o(theme.Bg, theme.PreviewBg)
 	theme.PreviewLabel = o(theme.BorderLabel, theme.PreviewLabel)
+	theme.Scrollbar = o(theme.Separator, theme.Scrollbar)
 
 	initPalette(theme)
 }
@@ -677,6 +685,7 @@ func initPalette(theme *ColorTheme) {
 	ColInfo = pair(theme.Info, theme.Bg)
 	ColHeader = pair(theme.Header, theme.Bg)
 	ColSeparator = pair(theme.Separator, theme.Bg)
+	ColScrollbar = pair(theme.Scrollbar, theme.Bg)
 	ColBorder = pair(theme.Border, theme.Bg)
 	ColBorderLabel = pair(theme.BorderLabel, theme.Bg)
 	ColPreviewLabel = pair(theme.PreviewLabel, theme.PreviewBg)
diff --git a/test/test_go.rb b/test/test_go.rb
index 45c661a7..68caa352 100755
--- a/test/test_go.rb
+++ b/test/test_go.rb
@@ -23,7 +23,7 @@ DEFAULT_TIMEOUT = 10
 FILE = File.expand_path(__FILE__)
 BASE = File.expand_path('..', __dir__)
 Dir.chdir(BASE)
-FZF = "FZF_DEFAULT_OPTS= FZF_DEFAULT_COMMAND= #{BASE}/bin/fzf"
+FZF = "FZF_DEFAULT_OPTS=--no-scrollbar FZF_DEFAULT_COMMAND= #{BASE}/bin/fzf"
 
 def wait
   since = Time.now
@@ -65,7 +65,7 @@ class Shell
     end
 
     def fish
-      UNSETS.map { |v| v + '= ' }.join + 'fish'
+      UNSETS.map { |v| v + '= ' }.join + ' FZF_DEFAULT_OPTS=--no-scrollbar fish'
     end
   end
 end
@@ -2908,7 +2908,7 @@ class TestFish < TestBase
   end
 
   def new_shell
-    tmux.send_keys 'env FZF_TMUX=1 fish', :Enter
+    tmux.send_keys 'env FZF_TMUX=1 FZF_DEFAULT_OPTS=--no-scrollbar fish', :Enter
     tmux.send_keys 'function fish_prompt; end; clear', :Enter
     tmux.until { |lines| assert_empty lines }
   end
@@ -2927,6 +2927,8 @@ unset <%= UNSETS.join(' ') %>
 unset $(env | sed -n /^_fzf_orig/s/=.*//p)
 unset $(declare -F | sed -n "/_fzf/s/.*-f //p")
 
+export FZF_DEFAULT_OPTS=--no-scrollbar
+
 # Setup fzf
 # ---------
 if [[ ! "$PATH" == *<%= BASE %>/bin* ]]; then