caps: implement explicit width support

Implement explicit width support based on the spec developed by kitty.
In the presence of both mode 2027 and explicit width, we opt for
explicit width

Reference: kovidgoyal/kitty#8226

README.md

@@ -80,6 +80,7 @@ most dank TUI library
 | Synchronized Output (DEC 2026) |  ✅   |  ❌   |    ❌     |    ✅     |
 | Unicode Core (DEC 2027)        |  ✅   |  ❌   |    ❌     |    ❌     |
 | Color Mode Updates (DEC 2031)  |  ✅   |  ❌   |    ❌     |    ❌     |
+| Explicit Width                 |  ✅   |  ❌   |    ❌     |    ❌     |
 | Images (full/space)            |  ✅   |  ❌   |    ❌     |    ✅     |
 | Images (half block)            |  ✅   |  ❌   |    ❌     |    ✅     |
 | Images (quadrant)              |  ❌   |  ❌   |    ❌     |    ✅     |

quirks.go

@@ -31,12 +31,14 @@ func (vx *Vaxis) applyQuirks() {
 	}
 	if os.Getenv("VAXIS_FORCE_WCWIDTH") != "" {
 		vx.caps.unicodeCore = false
+		vx.caps.explicitWidth = false
 	}
 	if os.Getenv("VAXIS_FORCE_UNICODE") != "" {
 		vx.caps.unicodeCore = true
 	}
 	if os.Getenv("VAXIS_FORCE_NOZWJ") != "" {
 		vx.caps.noZWJ = true
+		vx.caps.explicitWidth = false
 	}
 	if os.Getenv("VAXIS_DISABLE_NOZWJ") != "" {
 		vx.caps.noZWJ = false

sequences.go

@@ -25,18 +25,19 @@ const (
 	xtsmSixelGeom = "\x1b[?2;1;0S"
 
 	// Misc
-	clear        = "\x1b[H\x1b[2J"
-	cup          = "\x1B[%d;%dH"
-	osc8         = "\x1b]8;%s;%s\x1b\\"
-	osc11        = "\x1b]11;?\x07"
-	osc52put     = "\x1b]52;c;%s\x1b\\"
-	osc52pop     = "\x1b]52;c;?\x1b\\"
-	osc9notify   = "\x1b]9;%s\x1b\\"
-	osc777notify = "\x1b]777;notify;%s;%s\x1b\\"
-	setTitle     = "\x1b]2;%s\x1b\\"
-	getAppID     = "\x1b]176;?\x1b\\"
-	setAppID     = "\x1b]176;%s\x1b\\"
-	mouseShape   = "\x1b]22;%s\x1b\\"
+	clear         = "\x1b[H\x1b[2J"
+	cup           = "\x1B[%d;%dH"
+	osc8          = "\x1b]8;%s;%s\x1b\\"
+	osc11         = "\x1b]11;?\x07"
+	osc52put      = "\x1b]52;c;%s\x1b\\"
+	osc52pop      = "\x1b]52;c;?\x1b\\"
+	osc9notify    = "\x1b]9;%s\x1b\\"
+	osc777notify  = "\x1b]777;notify;%s;%s\x1b\\"
+	setTitle      = "\x1b]2;%s\x1b\\"
+	getAppID      = "\x1b]176;?\x1b\\"
+	setAppID      = "\x1b]176;%s\x1b\\"
+	mouseShape    = "\x1b]22;%s\x1b\\"
+	explicitWidth = "\x1b]66;w=%d;%s\x1b\\"
 
 	// SGR
 	sgrReset           = "\x1b[m"

styled_string.go

@@ -201,7 +201,7 @@ func (vx *Vaxis) NewStyledString(s string, defaultStyle Style) *StyledString {
 		default:
 			grapheme, s, width, _ = uniseg.FirstGraphemeClusterInString(s, -1)
 			switch {
-			case vx.caps.unicodeCore:
+			case vx.caps.unicodeCore || vx.caps.explicitWidth:
 				// we're done
 			case vx.caps.noZWJ:
 				width = gwidth(grapheme, noZWJ)

vaxis.go

@@ -35,6 +35,7 @@ type capabilities struct {
 	osc11              bool
 	osc176             bool
 	inBandResize       bool
+	explicitWidth      bool
 }
 
 type cursorState struct {
@@ -710,9 +711,11 @@ outerNew:
 				next.Width = vx.characterWidth(next.Grapheme)
 			}
 
-			switch next.Width {
-			case 0:
+			switch {
+			case next.Width == 0:
 				_, _ = vx.tw.WriteString(" ")
+			case next.Width > 1 && vx.caps.explicitWidth:
+				_, _ = fmt.Fprintf(vx.tw, explicitWidth, next.Width, next.Grapheme)
 			default:
 				_, _ = vx.tw.WriteString(next.Grapheme)
 			}
@@ -1090,6 +1093,17 @@ func (vx *Vaxis) sendQueries() {
 	// Can the terminal report it's own size?
 	_, _ = vx.tw.WriteString(textAreaSize)
 
+	// Explici width query
+	_, _ = vx.tw.WriteString("\x1b[H")
+	_, _ = fmt.Fprintf(vx.tw, explicitWidth, 1, " ")
+	_, col := vx.CursorPosition()
+	if col == 1 {
+		log.Debug("[capability] explicit width supported")
+		vx.mu.Lock()
+		vx.caps.explicitWidth = true
+		vx.mu.Unlock()
+	}
+
 	// Query some terminfo capabilities
 	// Just another way to see if we have RGB support
 	_, _ = vx.tw.WriteString(xtgettcap("RGB"))
@@ -1121,8 +1135,9 @@ func (vx *Vaxis) enableModes() {
 	if vx.caps.sixels {
 		_, _ = vx.tw.WriteString(decset(sixelScrolling))
 	}
-	// Mode 2027, unicode segmentation (for correct emoji/wc widths)
-	if vx.caps.unicodeCore {
+	// Mode 2027, unicode segmentation (for correct emoji/wc widths). We
+	// only enable if we don't also have explicitWidth
+	if vx.caps.unicodeCore && !vx.caps.explicitWidth {
 		_, _ = vx.tw.WriteString(decset(unicodeCore))
 	}
 
@@ -1171,7 +1186,7 @@ func (vx *Vaxis) disableModes() {
 	if vx.caps.sixels {
 		_, _ = vx.tw.WriteString(decrst(sixelScrolling))
 	}
-	if vx.caps.unicodeCore {
+	if vx.caps.unicodeCore && !vx.caps.explicitWidth {
 		_, _ = vx.tw.WriteString(decrst(unicodeCore))
 	}
 	if vx.caps.colorThemeUpdates {
@@ -1442,10 +1457,11 @@ func (vx *Vaxis) advance(cell Cell) int {
 // This call can be expensive, callers should consider caching the result for
 // strings or characters which will need to be measured frequently
 func (vx *Vaxis) RenderedWidth(s string) int {
-	if vx.caps.unicodeCore {
+	if vx.caps.unicodeCore || vx.caps.explicitWidth {
 		return gwidth(s, unicodeStd)
 	}
 	if vx.caps.noZWJ {
+		log.Debug("nozwj")
 		return gwidth(s, noZWJ)
 	}
 	return gwidth(s, wcwidth)
@@ -1502,6 +1518,10 @@ func (vx *Vaxis) CanUnicodeCore() bool {
 	return vx.caps.unicodeCore
 }
 
+func (vx *Vaxis) CanExplicitWidth() bool {
+	return vx.caps.explicitWidth
+}
+
 func (vx *Vaxis) nextGraphicID() uint64 {
 	vx.graphicsIDNext += 1
 	return vx.graphicsIDNext

window.go

@@ -166,7 +166,7 @@ func (win Window) Print(segs ...Segment) (col int, row int) {
 			if row > rows {
 				return col, row
 			}
-			if !win.Vx.caps.unicodeCore {
+			if !win.Vx.caps.unicodeCore || !win.Vx.caps.explicitWidth {
 				// characterWidth will cache the result
 				char.Width = win.Vx.characterWidth(char.Grapheme)
 			}
@@ -203,7 +203,7 @@ func (win Window) PrintTruncate(row int, segs ...Segment) {
 	}
 	for _, seg := range segs {
 		for _, char := range Characters(seg.Text) {
-			if !win.Vx.caps.unicodeCore {
+			if !win.Vx.caps.unicodeCore || !win.Vx.caps.explicitWidth {
 				// characterWidth will cache the result
 				char.Width = win.Vx.characterWidth(char.Grapheme)
 			}
@@ -237,18 +237,14 @@ func (win Window) Println(row int, segs ...Segment) {
 	col := 0
 	for _, seg := range segs {
 		for _, char := range Characters(seg.Text) {
-			if !win.Vx.caps.unicodeCore {
+			if !win.Vx.caps.unicodeCore || !win.Vx.caps.explicitWidth {
 				// characterWidth will cache the result
 				char.Width = win.Vx.characterWidth(char.Grapheme)
 			}
 			w := char.Width
 			if col+w > cols {
 				return
 			}
-			if !win.Vx.caps.unicodeCore {
-				// characterWidth will cache the result
-				win.Vx.characterWidth(char.Grapheme)
-			}
 			cell := Cell{
 				Character: char,
 				Style:     seg.Style,
@@ -277,7 +273,7 @@ func (win Window) Wrap(segs ...Segment) (col int, row int) {
 			chars := Characters(segment)
 			total := 0
 			for _, char := range chars {
-				if !win.Vx.caps.unicodeCore {
+				if !win.Vx.caps.unicodeCore || !win.Vx.caps.explicitWidth {
 					// characterWidth will cache the result
 					char.Width = win.Vx.characterWidth(char.Grapheme)
 				}