feat: renderer: optimize cursor movements with backspace

This updates the renderer to use backspace to optimize cursor movements when the terminal supports it. This is similar to the hard tabs optimization, but for backspace to move the cursor left.
charmbracelet · Feb 7, 2025 · 076054d · 076054d
1 parent 70ab5cf
commit 076054d
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Showing 7 changed files with 15 additions and 9 deletions.
diff --git a/cursed_renderer.go b/cursed_renderer.go
@@ -23,15 +23,17 @@ type cursedRenderer struct {
 	altScreen     bool
 	cursorHidden  bool
 	hardTabs      bool // whether to use hard tabs to optimize cursor movements
+	backspace     bool // whether to use backspace to optimize cursor movements
 }
 
 var _ renderer = &cursedRenderer{}
 
-func newCursedRenderer(w io.Writer, term string, hardTabs bool) (s *cursedRenderer) {
+func newCursedRenderer(w io.Writer, term string, hardTabs, backspace bool) (s *cursedRenderer) {
 	s = new(cursedRenderer)
 	s.w = w
 	s.term = term
 	s.hardTabs = hardTabs
+	s.backspace = backspace
 	s.reset()
 	return
 }
@@ -118,6 +120,7 @@ func (s *cursedRenderer) reset() {
 		Width:          s.width,
 		Height:         s.height,
 		HardTabs:       s.hardTabs,
+		Backspace:      s.backspace,
 	})
 	s.mu.Unlock()
 }

diff --git a/examples/go.mod b/examples/go.mod
@@ -23,7 +23,7 @@ require (
 	github.com/aymanbagabas/go-udiff v0.2.0 // indirect
 	github.com/aymerick/douceur v0.2.0 // indirect
 	github.com/charmbracelet/lipgloss v1.0.0 // indirect
-	github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207213023-b9846c8eeefa // indirect
+	github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207223800-1f1a6c27426e // indirect
 	github.com/charmbracelet/x/exp/golden v0.0.0-20241212170349-ad4b7ae0f25f // indirect
 	github.com/charmbracelet/x/input v0.3.2 // indirect
 	github.com/charmbracelet/x/term v0.2.1 // indirect

diff --git a/examples/go.sum b/examples/go.sum
@@ -28,8 +28,8 @@ github.com/charmbracelet/lipgloss/v2 v2.0.0-alpha.2.0.20250127174346-dc93e7a83a4
 github.com/charmbracelet/lipgloss/v2 v2.0.0-alpha.2.0.20250127174346-dc93e7a83a4b/go.mod h1:wNdvvvSFeykFQxJ9rXcTA+IbZE9wgMEqhM4c8gV/faE=
 github.com/charmbracelet/x/ansi v0.8.0 h1:9GTq3xq9caJW8ZrBTe0LIe2fvfLR/bYXKTx2llXn7xE=
 github.com/charmbracelet/x/ansi v0.8.0/go.mod h1:wdYl/ONOLHLIVmQaxbIYEC/cRKOQyjTkowiI4blgS9Q=
-github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207213023-b9846c8eeefa h1:oKYvPGuwWdRdXun8kYXH6ib6G70XdWcmXwXuzRQb99k=
-github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207213023-b9846c8eeefa/go.mod h1:dKfNBxLovpvzzxAP6/GZfs5eb7vNxHlUDnwGhRmvIdY=
+github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207223800-1f1a6c27426e h1:hCO0Y612oQeo3mhM+TxywNLoZZvXMtGRc9EJtyZ83ag=
+github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207223800-1f1a6c27426e/go.mod h1:dKfNBxLovpvzzxAP6/GZfs5eb7vNxHlUDnwGhRmvIdY=
 github.com/charmbracelet/x/exp/golden v0.0.0-20241212170349-ad4b7ae0f25f h1:UytXHv0UxnsDFmL/7Z9Q5SBYPwSuRLXHbwx+6LycZ2w=
 github.com/charmbracelet/x/exp/golden v0.0.0-20241212170349-ad4b7ae0f25f/go.mod h1:wDlXFlCrmJ8J+swcL/MnGUuYnqgQdW9rhSD61oNMb6U=
 github.com/charmbracelet/x/exp/teatest/v2 v2.0.0-20241016014612-3b4d04043233 h1:2bTR/MtnJuq9RrCZSPwCOO34YSDByKL6nzXQMnsKK6U=

diff --git a/go.mod b/go.mod
@@ -5,7 +5,7 @@ go 1.18
 require (
 	github.com/charmbracelet/colorprofile v0.2.0
 	github.com/charmbracelet/x/ansi v0.8.0
-	github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207213023-b9846c8eeefa
+	github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207223800-1f1a6c27426e
 	github.com/charmbracelet/x/exp/golden v0.0.0-20241212170349-ad4b7ae0f25f
 	github.com/charmbracelet/x/input v0.3.2
 	github.com/charmbracelet/x/term v0.2.1

diff --git a/go.sum b/go.sum
@@ -4,8 +4,8 @@ github.com/charmbracelet/colorprofile v0.2.0 h1:iiIQlp3LSvoJPtR11KoDfIf9wqWm2mn/
 github.com/charmbracelet/colorprofile v0.2.0/go.mod h1:6wPrSSR4QtwYtOY3h0bLRw5YOUAIKWlZIJ02CTAsZsk=
 github.com/charmbracelet/x/ansi v0.8.0 h1:9GTq3xq9caJW8ZrBTe0LIe2fvfLR/bYXKTx2llXn7xE=
 github.com/charmbracelet/x/ansi v0.8.0/go.mod h1:wdYl/ONOLHLIVmQaxbIYEC/cRKOQyjTkowiI4blgS9Q=
-github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207213023-b9846c8eeefa h1:oKYvPGuwWdRdXun8kYXH6ib6G70XdWcmXwXuzRQb99k=
-github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207213023-b9846c8eeefa/go.mod h1:dKfNBxLovpvzzxAP6/GZfs5eb7vNxHlUDnwGhRmvIdY=
+github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207223800-1f1a6c27426e h1:hCO0Y612oQeo3mhM+TxywNLoZZvXMtGRc9EJtyZ83ag=
+github.com/charmbracelet/x/cellbuf v0.0.9-0.20250207223800-1f1a6c27426e/go.mod h1:dKfNBxLovpvzzxAP6/GZfs5eb7vNxHlUDnwGhRmvIdY=
 github.com/charmbracelet/x/exp/golden v0.0.0-20241212170349-ad4b7ae0f25f h1:UytXHv0UxnsDFmL/7Z9Q5SBYPwSuRLXHbwx+6LycZ2w=
 github.com/charmbracelet/x/exp/golden v0.0.0-20241212170349-ad4b7ae0f25f/go.mod h1:wDlXFlCrmJ8J+swcL/MnGUuYnqgQdW9rhSD61oNMb6U=
 github.com/charmbracelet/x/input v0.3.2 h1:6h/d/40Og6UP3a4VDjIbdoUhilEH4K+mxEuaSPIJwNQ=

diff --git a/tea.go b/tea.go
@@ -275,6 +275,8 @@ type Program struct {
 
 	// whether to use hard tabs to optimize cursor movements
 	useHardTabs bool
+	// whether to use backspace to optimize cursor movements
+	useBackspace bool
 }
 
 // Quit is a special command that tells the Bubble Tea program to exit.
@@ -822,7 +824,7 @@ func (p *Program) Run() (Model, error) {
 			p.renderer = newRenderer(p.output)
 		} else {
 			// If no renderer is set use the cursed one.
-			p.renderer = newCursedRenderer(p.output, p.getenv("TERM"), p.useHardTabs)
+			p.renderer = newCursedRenderer(p.output, p.getenv("TERM"), p.useHardTabs, p.useBackspace)
 		}
 	}
 

diff --git a/tty_unix.go b/tty_unix.go
@@ -24,7 +24,8 @@ func (p *Program) initInput() (err error) {
 
 		// OPTIM: We can use hard tabs to optimize cursor movements if the
 		// terminal doesn't have tab expansion enabled.
-		p.useHardTabs = p.previousTtyInputState.Oflag&unix.TABDLY == 0
+		p.useHardTabs = p.previousTtyInputState.Oflag&unix.TABDLY == unix.TAB0
+		p.useBackspace = p.previousTtyInputState.Lflag&unix.BSDLY == unix.BS0
 	}
 
 	if f, ok := p.output.Writer().(term.File); ok && term.IsTerminal(f.Fd()) {