added Tab Stops support (#175)

buffer/buffer.go

@@ -717,22 +717,11 @@ func (buffer *Buffer) CarriageReturn() {
 }
 
 func (buffer *Buffer) Tab() {
-	tabSize := 4
+	for buffer.terminalState.cursorX < buffer.terminalState.viewWidth-1 { // @todo rightMargin
-	max := tabSize
-
-	// @todo rightMargin
-	if buffer.terminalState.cursorX < buffer.terminalState.viewWidth {
-		max = int(buffer.terminalState.viewWidth - buffer.terminalState.cursorX - 1)
-	}
-
-	shift := tabSize - (int(buffer.terminalState.cursorX+1) % tabSize)
-
-	if shift > max {
-		shift = max
-	}
-
-	for i := 0; i < shift; i++ {
 		buffer.Write(' ')
+		if buffer.terminalState.IsTabSetAtCursor() {
+			break
+		}
 	}
 }
 

buffer/buffer_test.go

@@ -26,8 +26,8 @@ func TestTabbing(t *testing.T) {
 	b.CarriageReturn()
 	b.NewLine()
 	expected := `
-hello  x   goodbye
+hello   x   goodbye
-hell   xxx good
+hell    xxx good
 `
 
 	lines := b.GetVisibleLines()

buffer/terminal_state.go

@@ -15,6 +15,7 @@ type TerminalState struct {
 	LineFeedMode          bool
 	AutoWrap              bool
 	maxLines              uint64
+	tabStops              map[uint16]struct{}
 }
 
 // NewTerminalMode creates a new terminal state
@@ -31,6 +32,7 @@ func NewTerminalState(viewCols uint16, viewLines uint16, attr CellAttributes, ma
 		topMargin:    0,
 		bottomMargin: uint(viewLines - 1),
 	}
+	b.TabReset()
 	return b
 }
 
@@ -47,3 +49,48 @@ func (terminalState *TerminalState) ResetVerticalMargins() {
 func (terminalState *TerminalState) IsNewLineMode() bool {
 	return terminalState.LineFeedMode == false
 }
+
+func (terminalState *TerminalState) TabZonk() {
+	terminalState.tabStops = make(map[uint16]struct{})
+}
+
+func (terminalState *TerminalState) TabSet(index uint16) {
+	terminalState.tabStops[index] = struct{}{}
+}
+
+func (terminalState *TerminalState) TabClear(index uint16) {
+	delete(terminalState.tabStops, index)
+}
+
+func (terminalState *TerminalState) getTabIndexFromCursor() uint16 {
+	index := terminalState.cursorX
+	if index == terminalState.viewWidth {
+		index = 0
+	}
+	return index
+}
+
+func (terminalState *TerminalState) IsTabSetAtCursor() bool {
+	index := terminalState.getTabIndexFromCursor()
+	_, ok := terminalState.tabStops[index]
+	return ok
+}
+
+func (terminalState *TerminalState) TabClearAtCursor() {
+	terminalState.TabClear(terminalState.getTabIndexFromCursor())
+}
+
+func (terminalState *TerminalState) TabSetAtCursor() {
+	terminalState.TabSet(terminalState.getTabIndexFromCursor())
+}
+
+func (terminalState *TerminalState) TabReset() {
+	terminalState.TabZonk()
+	const MaxTabs uint16 = 1024
+	const TabStep = 4
+	var i uint16
+	for i < MaxTabs {
+		terminalState.TabSet(i)
+		i += TabStep
+	}
+}

terminal/ansi.go

@@ -12,6 +12,7 @@ var ansiSequenceMap = map[rune]escapeSequenceHandler{
 	'8': restoreCursorHandler,
 	'D': indexHandler,
 	'E': nextLineHandler, // NEL
+	'H': tabSetHandler,   // HTS
 	'M': reverseIndexHandler,
 	'P': sixelHandler,
 	'c': risHandler, //RIS
@@ -75,3 +76,8 @@ func nextLineHandler(pty chan rune, terminal *Terminal) error {
 	terminal.ActiveBuffer().NewLineEx(true)
 	return nil
 }
+
+func tabSetHandler(pty chan rune, terminal *Terminal) error {
+	terminal.terminalState.TabSetAtCursor()
+	return nil
+}

terminal/csi.go

@@ -24,6 +24,7 @@ var csiSequences = []csiMapping{
 	{id: 'c', handler: csiSendDeviceAttributesHandler, description: " Send Device Attributes (Primary/Secondary/Tertiary DA)"},
 	{id: 'd', handler: csiLinePositionAbsolute, expectedParams: &expectedParams{min: 0, max: 1}, description: "Line Position Absolute  [row] (default = [1,column]) (VPA)"},
 	{id: 'f', handler: csiCursorPositionHandler, description: "Horizontal and Vertical Position [row;column] (default = [1,1]) (HVP)"},
+	{id: 'g', handler: csiTabClearHandler, description: "Tab Clear (TBC)"},
 	{id: 'h', handler: csiSetModeHandler, expectedParams: &expectedParams{min: 1, max: 1}, description: "Set Mode (SM)"},
 	{id: 'l', handler: csiResetModeHandler, expectedParams: &expectedParams{min: 1, max: 1}, description: "Reset Mode (RM)"},
 	{id: 'm', handler: sgrSequenceHandler, description: "Character Attributes (SGR)"},
@@ -463,6 +464,24 @@ func csiDeleteHandler(params []string, terminal *Terminal) error {
 	return nil
 }
 
+func csiTabClearHandler(params []string, terminal *Terminal) error {
+	n := "0"
+	if len(params) > 0 {
+		n = params[0]
+	}
+	switch n {
+
+	case "0", "":
+		terminal.terminalState.TabClearAtCursor()
+	case "3":
+		terminal.terminalState.TabZonk()
+	default:
+		return fmt.Errorf("Ignored TBC: CSI %s g", n)
+	}
+
+	return nil
+}
+
 // CSI Ps J
 func csiEraseInDisplayHandler(params []string, terminal *Terminal) error {
 	n := "0"