horizontal scroll

viewport/keymap.go

@@ -15,6 +15,8 @@ type KeyMap struct {
 	HalfPageDown key.Binding
 	Down         key.Binding
 	Up           key.Binding
+	Left         key.Binding
+	Right        key.Binding
 }
 
 // DefaultKeyMap returns a set of pager-like default keybindings.
@@ -44,5 +46,13 @@ func DefaultKeyMap() KeyMap {
 			key.WithKeys("down", "j"),
 			key.WithHelp("↓/j", "down"),
 		),
+		Left: key.NewBinding(
+			key.WithKeys("left", "h"),
+			key.WithHelp("←/h", "move left"),
+		),
+		Right: key.NewBinding(
+			key.WithKeys("right", "l"),
+			key.WithHelp("→/l", "move right"),
+		),
 	}
 }

viewport/viewport.go

@@ -54,6 +54,10 @@ type Model struct {
 	// Deprecated: high performance rendering is now deprecated in Bubble Tea.
 	HighPerformanceRendering bool
 
+	// horizontal step represents the step of indent we add with one move left or right.
+	horizontalStep int
+
+	indent      int
 	initialized bool
 	lines       []string
 }
@@ -63,6 +67,7 @@ func (m *Model) setInitialValues() {
 	m.MouseWheelEnabled = true
 	m.MouseWheelDelta = 3
 	m.initialized = true
+	m.horizontalStep = 5
 }
 
 // Init exists to satisfy the tea.Model interface for composability purposes.
@@ -123,6 +128,16 @@ func (m Model) visibleLines() (lines []string) {
 		bottom := clamp(m.YOffset+m.Height, top, len(m.lines))
 		lines = m.lines[top:bottom]
 	}
+
+	if m.indent > 0 {
+		cutLines := make([]string, len(lines))
+		for i := range lines {
+			cutLines[i] = getStringWithIndent(lines[i], m.indent)
+		}
+
+		return cutLines
+	}
+
 	return lines
 }
 
@@ -290,6 +305,36 @@ func ViewUp(m Model, lines []string) tea.Cmd {
 	return tea.ScrollUp(lines, top, bottom)
 }
 
+// SetHorizontalStep is a setter for `horizontalStep`.
+// Must be set before `MoveLeft` or `MoveRight` is used.
+// If 0 or negative, left/right movement doesn't work.
+func (m *Model) SetHorizontalStep(n int) {
+	if n < 1 {
+		n = 0
+	}
+
+	m.horizontalStep = n
+}
+
+// MoveLeft moves all lines to set runes left.
+// If current indent is 0, it doesn't work.
+func (m *Model) MoveLeft() {
+	m.indent -= m.horizontalStep
+	if m.indent < 0 {
+		m.indent = 0
+	}
+}
+
+// MoveRight moves all lines to set runes right.
+func (m *Model) MoveRight() {
+	m.indent += m.horizontalStep
+}
+
+// Resets lines indent to zero.
+func (m *Model) ResetIndent() {
+	m.indent = 0
+}
+
 // Update handles standard message-based viewport updates.
 func (m Model) Update(msg tea.Msg) (Model, tea.Cmd) {
 	var cmd tea.Cmd
@@ -344,6 +389,12 @@ func (m Model) updateAsModel(msg tea.Msg) (Model, tea.Cmd) {
 			if m.HighPerformanceRendering {
 				cmd = ViewUp(m, lines)
 			}
+
+		case key.Matches(msg, m.KeyMap.Left):
+			m.MoveLeft()
+
+		case key.Matches(msg, m.KeyMap.Right):
+			m.MoveRight()
 		}
 
 	case tea.MouseMsg:
@@ -418,3 +469,16 @@ func max(a, b int) int {
 	}
 	return b
 }
+
+func getStringWithIndent(s string, indent int) string {
+	if indent == 0 {
+		return s
+	}
+
+	r := []rune(s)
+	if indent > len(r) {
+		return ""
+	}
+
+	return string(r[indent:])
+}