Colored underlines.

This supports UNIX and Windows.

_demos/style.go

@@ -171,6 +171,18 @@ func main() {
 	puts(s, style, 2, row, "Dashed Underline")
 	row++
 
+	style = plain.Underline(true).UnderlineColor(tcell.ColorBlue)
+	puts(s, style, 2, row, "Blue Underline")
+	row++
+
+	style = plain.Underline(true).UnderlineColor(tcell.ColorHoneydew)
+	puts(s, style, 2, row, "Honeydew Underline")
+	row++
+
+	style = plain.CurlyUnderline(true).UnderlineColor(tcell.NewRGBColor(0xc5, 0x8a, 0xf9))
+	puts(s, style, 2, row, "Pink Curly Underline")
+	row++
+
 	style = plain.Url("http://github.com/gdamore/tcell")
 	puts(s, style, 2, row, "HyperLink")
 	row++

console_win.go

@@ -168,6 +168,9 @@ const (
 	vtCurlyUnderline          = "\x1b[4:3m"
 	vtDottedUnderline         = "\x1b[4:4m"
 	vtDashedUnderline         = "\x1b[4:5m"
+	vtUnderColor              = "\x1b[58:5:%dm"
+	vtUnderColorRGB           = "\x1b[58:2::%d:%d:%dm"
+	vtUnderColorReset         = "\x1b[59m"
 )
 
 var vtCursorStyles = map[CursorStyle]string{
@@ -879,7 +882,7 @@ func mapColor2RGB(c Color) uint16 {
 
 // Map a tcell style to Windows attributes
 func (s *cScreen) mapStyle(style Style) uint16 {
-	f, b, a := style.Decompose()
+	f, b, a := style.fg, style.bg, style.attrs
 	fa := s.oscreen.attrs & 0xf
 	ba := (s.oscreen.attrs) >> 4 & 0xf
 	if f != ColorDefault && f != ColorReset {
@@ -916,7 +919,7 @@ func (s *cScreen) mapStyle(style Style) uint16 {
 func (s *cScreen) sendVtStyle(style Style) {
 	esc := &strings.Builder{}
 
-	fg, bg, attrs := style.Decompose()
+	fg, bg, uc, attrs := style.fg, style.bg, style.under, style.attrs
 
 	esc.WriteString(vtSgr0)
 
@@ -927,6 +930,17 @@ func (s *cScreen) sendVtStyle(style Style) {
 		esc.WriteString(vtBlink)
 	}
 	if attrs&(AttrUnderline|AttrDoubleUnderline|AttrCurlyUnderline|AttrDottedUnderline|AttrDashedUnderline) != 0 {
+		if uc.Valid() {
+			if uc == ColorReset {
+				esc.WriteString(vtUnderColorReset)
+			} else if uc.IsRGB() {
+				r, g, b := uc.RGB()
+				_, _ = fmt.Fprintf(esc, vtUnderColorRGB, int(r), int(g), int(b))
+			} else {
+				_, _ = fmt.Fprintf(esc, vtUnderColor, uc&0xff)
+			}
+		}
+
 		esc.WriteString(vtUnderline)
 		// legacy ConHost does not understand these but Terminal does
 		if (attrs & AttrDoubleUnderline) != 0 {

style.go

@@ -25,6 +25,7 @@ package tcell
 type Style struct {
 	fg    Color
 	bg    Color
+	under Color
 	attrs AttrMask
 	url   string
 	urlId string
@@ -40,50 +41,35 @@ var styleInvalid = Style{attrs: AttrInvalid}
 // Foreground returns a new style based on s, with the foreground color set
 // as requested.  ColorDefault can be used to select the global default.
 func (s Style) Foreground(c Color) Style {
-	return Style{
-		fg:    c,
-		bg:    s.bg,
-		attrs: s.attrs,
-		url:   s.url,
-		urlId: s.urlId,
-	}
+	s2 := s
+	s2.fg = c
+	return s2
 }
 
 // Background returns a new style based on s, with the background color set
 // as requested.  ColorDefault can be used to select the global default.
 func (s Style) Background(c Color) Style {
-	return Style{
-		fg:    s.fg,
-		bg:    c,
-		attrs: s.attrs,
-		url:   s.url,
-		urlId: s.urlId,
-	}
+	s2 := s
+	s2.bg = c
+	return s2
 }
 
 // Decompose breaks a style up, returning the foreground, background,
 // and other attributes.  The URL if set is not included.
+// Deprecated: Applications should not attempt to decompose style,
+// as this content is not sufficient to describe the actual style.
 func (s Style) Decompose() (fg Color, bg Color, attr AttrMask) {
 	return s.fg, s.bg, s.attrs
 }
 
 func (s Style) setAttrs(attrs AttrMask, on bool) Style {
+	s2 := s
 	if on {
-		return Style{
-			fg:    s.fg,
-			bg:    s.bg,
-			attrs: s.attrs | attrs,
-			url:   s.url,
-			urlId: s.urlId,
-		}
-	}
-	return Style{
-		fg:    s.fg,
-		bg:    s.bg,
-		attrs: s.attrs &^ attrs,
-		url:   s.url,
-		urlId: s.urlId,
+		s2.attrs |= attrs
+	} else {
+		s2.attrs &^= attrs
 	}
+	return s2
 }
 
 // Normal returns the style with all attributes disabled.
@@ -152,41 +138,35 @@ func (s Style) DashedUnderline(on bool) Style {
 	return s.setAttrs(AttrDashedUnderline, on)
 }
 
+func (s Style) UnderlineColor(c Color) Style {
+	s2 := s
+	s2.under = c
+	return s2
+}
+
 // Attributes returns a new style based on s, with its attributes set as
 // specified.
 func (s Style) Attributes(attrs AttrMask) Style {
-	return Style{
-		fg:    s.fg,
-		bg:    s.bg,
-		attrs: attrs,
-		url:   s.url,
-		urlId: s.urlId,
-	}
+	s2 := s
+	s2.attrs = attrs
+	return s2
 }
 
 // Url returns a style with the Url set.  If the provided Url is not empty,
 // and the terminal supports it, text will typically be marked up as a clickable
 // link to that Url.  If the Url is empty, then this mode is turned off.
 func (s Style) Url(url string) Style {
-	return Style{
-		fg:    s.fg,
-		bg:    s.bg,
-		attrs: s.attrs,
-		url:   url,
-		urlId: s.urlId,
-	}
+	s2 := s
+	s2.url = url
+	return s2
 }
 
 // UrlId returns a style with the UrlId set. If the provided UrlId is not empty,
 // any marked up Url with this style will be given the UrlId also. If the
 // terminal supports it, any text with the same UrlId will be grouped as if it
 // were one Url, even if it spans multiple lines.
 func (s Style) UrlId(id string) Style {
-	return Style{
-		fg:    s.fg,
-		bg:    s.bg,
-		attrs: s.attrs,
-		url:   s.url,
-		urlId: "id=" + id,
-	}
+	s2 := s
+	s2.urlId = "id=" + id
+	return s2
 }

style_test.go

@@ -1,4 +1,4 @@
-// Copyright 2018 The TCell Authors
+// Copyright 2024 The TCell Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use file except in compliance with the License.
@@ -23,7 +23,7 @@ func TestStyle(t *testing.T) {
 	defer s.Fini()
 
 	style := StyleDefault
-	fg, bg, attr := style.Decompose()
+	fg, bg, attr := style.fg, style.bg, style.attrs
 
 	if fg != ColorDefault || bg != ColorDefault || attr != AttrNone {
 		t.Errorf("Bad default style (%v, %v, %v)", fg, bg, attr)
@@ -34,7 +34,7 @@ func TestStyle(t *testing.T) {
 		Foreground(ColorBlue).
 		Blink(true)
 
-	fg, bg, attr = s2.Decompose()
+	fg, bg, attr = s2.fg, s2.bg, s2.attrs
 	if fg != ColorBlue || bg != ColorRed || attr != AttrBlink {
 		t.Errorf("Bad custom style (%v, %v, %v)", fg, bg, attr)
 	}

terminfo/terminfo.go

@@ -238,6 +238,9 @@ type Terminfo struct {
 	CurlyUnderline          string // Smulx with param 3
 	DottedUnderline         string // Smulx with param 4
 	DashedUnderline         string // Smulx with param 5
+	UnderlineColor          string // Setuc1
+	UnderlineColorRGB       string // Setulc
+	UnderlineColorReset     string // ol
 	XTermLike               bool   // (XT) has XTerm extensions
 }
 

tscreen.go

@@ -32,7 +32,6 @@ import (
 	"golang.org/x/text/transform"
 
 	"github.com/gdamore/tcell/v2/terminfo"
-
 )
 
 // NewTerminfoScreen returns a Screen that uses the stock TTY interface
@@ -156,6 +155,9 @@ type tScreen struct {
 	curlyUnder   string
 	dottedUnder  string
 	dashedUnder  string
+	underColor   string
+	underRGB     string
+	underFg      string
 	cursorStyles map[CursorStyle]string
 	cursorStyle  CursorStyle
 	saved        *term.State
@@ -356,20 +358,44 @@ func (t *tScreen) prepareUnderlines() {
 	}
 	if t.ti.CurlyUnderline != "" {
 		t.curlyUnder = t.ti.CurlyUnderline
-	} else {
+	} else if t.ti.XTermLike {
 		t.curlyUnder = "\x1b[4:3m"
 	}
 	if t.ti.DottedUnderline != "" {
 		t.dottedUnder = t.ti.DottedUnderline
-	} else {
+	} else if t.ti.XTermLike {
 		t.dottedUnder = "\x1b[4:4m"
 	}
 	if t.ti.DashedUnderline != "" {
 		t.dashedUnder = t.ti.DashedUnderline
-	} else {
+	} else if t.ti.XTermLike {
 		t.dashedUnder = "\x1b[4:5m"
 	}
-	// Still TODO: Underline Color
+
+	// Underline colors.  We're not going to rely upon terminfo for this
+	// Essentially all terminals that support the curly underlines are
+	// expected to also support coloring them too - which reflects actual
+	// practice since these were introduced at about the same time.
+	if t.ti.UnderlineColor != "" {
+		t.underColor = t.ti.UnderlineColor
+	} else if t.ti.CurlyUnderline != "" {
+		t.underColor = "\x1b[58:5:%p1%dm"
+	}
+	if t.ti.UnderlineColorRGB != "" {
+		// An interesting wart here is that in order to facilitate
+		// using just a single parameter, the Setulc parameter takes
+		// the 24-bit color as an integer rather than separate bytes.
+		// This matches the "new" style direct color approach that
+		// ncurses took, even though everyone else when another way.
+		t.underRGB = t.ti.UnderlineColorRGB
+	} else if t.ti.CurlyUnderline != "" {
+		t.underRGB = "\x1b[58:2::%p1%d:%p2%d:%p3%dm"
+	}
+	if t.ti.UnderlineColorReset != "" {
+		t.underFg = t.ti.UnderlineColorReset
+	} else if t.ti.CurlyUnderline != "" {
+		t.underFg = "\x1b[59m"
+	}
 }
 
 func (t *tScreen) prepareExtendedOSC() {
@@ -435,7 +461,6 @@ func (t *tScreen) prepareCursorStyles() {
 		}
 	}
 
-	// Still TODO: Cursor Color
 }
 
 func (t *tScreen) prepareKey(key Key, val string) {
@@ -771,7 +796,7 @@ func (t *tScreen) drawCell(x, y int) int {
 		style = t.style
 	}
 	if style != t.curstyle {
-		fg, bg, attrs := style.Decompose()
+		fg, bg, attrs, uc := style.fg, style.bg, style.attrs, style.under
 
 		t.TPuts(ti.AttrOff)
 
@@ -780,6 +805,27 @@ func (t *tScreen) drawCell(x, y int) int {
 			t.TPuts(ti.Bold)
 		}
 		if attrs&(AttrUnderline|AttrDoubleUnderline|AttrCurlyUnderline|AttrDottedUnderline|AttrDashedUnderline) != 0 {
+			if uc.Valid() && (t.underColor != "" || t.underRGB != "") {
+				if uc == ColorReset {
+					t.TPuts(t.underFg)
+				} else if uc.IsRGB() {
+					if t.underRGB != "" {
+						r, g, b := uc.RGB()
+						t.TPuts(ti.TParm(t.underRGB, int(r), int(g), int(b)))
+					} else {
+						if v, ok := t.colors[uc]; ok {
+							uc = v
+						} else {
+							v = FindColor(uc, t.palette)
+							t.colors[uc] = v
+							uc = v
+						}
+						t.TPuts(ti.TParm(t.underColor, int(uc&0xff)))
+					}
+				} else {
+					t.TPuts(ti.TParm(t.underColor, int(uc&0xff)))
+				}
+			}
 			t.TPuts(ti.Underline) // to ensure everyone gets at least a basic underline
 			if (attrs & AttrDoubleUnderline) != 0 {
 				t.TPuts(t.doubleUnder)
@@ -928,8 +974,7 @@ func (t *tScreen) Show() {
 func (t *tScreen) clearScreen() {
 	t.TPuts(t.ti.AttrOff)
 	t.TPuts(t.exitUrl)
-	fg, bg, _ := t.style.Decompose()
-	_ = t.sendFgBg(fg, bg, AttrNone)
+	_ = t.sendFgBg(t.style.fg, t.style.bg, AttrNone)
 	t.TPuts(t.ti.Clear)
 	t.clear = false
 }