feat(viewport)!: gutter column, soft wrap, search highlight (#697)

* horizontal scroll * rebase branch * add tests * add tests with 2 cells symbols * trimLeft, move to charmbracelete/x/ansi lib * up ansi package * Update viewport/viewport.go Co-authored-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> * fix: do not navigate out to the right * fix: cache line width on setcontent * fix tests * fix viewport tests * add test for preventing right overscroll * chore(viewport): increase horizontal step to 6 * chore(viewport): make horizontal scroll API better match vertical scroll API * fix: nolint * fix: use ansi.Cut * perf: do not cut anything if not needed * feat: expose HorizontalScrollPercent * fix: do not scroll if width is 0 Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> * fix: visible lines take frame into account * feat(viewport): column sign * feat: gutter, soft wrap * wip: search * wip: search * wip: search * fix: perf Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> * fix: rename * wip * wip * refactor: viewport highlight ranges * fix: ligloss update * doc: godoc * feat: fill height optional * fix: handle no content * fix: empty lines * wip * wip * Revert "wip" This reverts commit 933f181e88405c21d65a08b816a88030806ca03e. * Reapply "wip" This reverts commit 0e3e31b70f53d93250a1474547cc5157d50e9237. * fix: wide * fix: wide, find * still not quite there * fix: grapheme width * fix: cleanups * fix: refactors, improves highlight visibility * docs: godoc * chore: lipgloss update Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> * chore: x/ansi update Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> * fix: typos, godocs Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> * fix: rename Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> * fix: typo * fix: scroll when soft-wrapping * fix: soft wrap adjustments * fix: update Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> * fix: deps Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> --------- Signed-off-by: Carlos Alexandro Becker <caarlos0@users.noreply.github.com> Co-authored-by: Roman Suvorov <suvorov83@gmail.com> Co-authored-by: Roman Suvorov <tty2.rs@gmail.com> Co-authored-by: Christian Rocha <christian@rocha.is>
2026-08-05 04:36:07 +00:00 · 2025-02-04 13:15:40 -03:00
parent b2e3cc5371
commit edbb81c136
5 changed files with 646 additions and 56 deletions
@@ -0,0 +1,141 @@
+package viewport
+
+import (
+	"github.com/charmbracelet/lipgloss/v2"
+	"github.com/charmbracelet/x/ansi"
+	"github.com/rivo/uniseg"
+)
+
+// parseMatches converts the given matches into highlight ranges.
+//
+// Assumptions:
+// - matches are measured in bytes, e.g. what [regex.FindAllStringIndex] would return
+// - matches were made against the given content
+// - matches are in order
+// - matches do not overlap
+// - content is line terminated with \n only
+//
+// We'll then convert the ranges into [highlightInfo]s, which hold the starting
+// line and the grapheme positions.
+func parseMatches(
+	content string,
+	matches [][]int,
+) []highlightInfo {
+	if len(matches) == 0 {
+		return nil
+	}
+
+	line := 0
+	graphemePos := 0
+	previousLinesOffset := 0
+	bytePos := 0
+
+	highlights := make([]highlightInfo, 0, len(matches))
+	gr := uniseg.NewGraphemes(ansi.Strip(content))
+
+	for _, match := range matches {
+		byteStart, byteEnd := match[0], match[1]
+
+		// hilight for this match:
+		hi := highlightInfo{
+			lines: map[int][2]int{},
+		}
+
+		// find the beginning of this byte range, setup current line and
+		// grapheme position.
+		for byteStart > bytePos {
+			if !gr.Next() {
+				break
+			}
+			if content[bytePos] == '\n' {
+				previousLinesOffset = graphemePos + 1
+				line++
+			}
+			graphemePos += max(1, gr.Width())
+			bytePos += len(gr.Str())
+		}
+
+		hi.lineStart = line
+		hi.lineEnd = line
+
+		graphemeStart := graphemePos
+
+		// loop until we find the end
+		for byteEnd > bytePos {
+			if !gr.Next() {
+				break
+			}
+
+			// if it ends with a new line, add the range, increase line, and continue
+			if content[bytePos] == '\n' {
+				colstart := max(0, graphemeStart-previousLinesOffset)
+				colend := max(graphemePos-previousLinesOffset+1, colstart) // +1 its \n itself
+
+				if colend > colstart {
+					hi.lines[line] = [2]int{colstart, colend}
+					hi.lineEnd = line
+				}
+
+				previousLinesOffset = graphemePos + 1
+				line++
+			}
+
+			graphemePos += max(1, gr.Width())
+			bytePos += len(gr.Str())
+		}
+
+		// we found it!, add highlight and continue
+		if bytePos == byteEnd {
+			colstart := max(0, graphemeStart-previousLinesOffset)
+			colend := max(graphemePos-previousLinesOffset, colstart)
+
+			if colend > colstart {
+				hi.lines[line] = [2]int{colstart, colend}
+				hi.lineEnd = line
+			}
+		}
+
+		highlights = append(highlights, hi)
+	}
+
+	return highlights
+}
+
+type highlightInfo struct {
+	// in which line this highlight starts and ends
+	lineStart, lineEnd int
+
+	// the grapheme highlight ranges for each of these lines
+	lines map[int][2]int
+}
+
+// coords returns the line x column of this highlight.
+func (hi highlightInfo) coords() (int, int, int) {
+	for i := hi.lineStart; i <= hi.lineEnd; i++ {
+		hl, ok := hi.lines[i]
+		if !ok {
+			continue
+		}
+		return i, hl[0], hl[1]
+	}
+	return hi.lineStart, 0, 0
+}
+
+func makeHighlightRanges(
+	highlights []highlightInfo,
+	line int,
+	style lipgloss.Style,
+) []lipgloss.Range {
+	result := []lipgloss.Range{}
+	for _, hi := range highlights {
+		lihi, ok := hi.lines[line]
+		if !ok {
+			continue
+		}
+		if lihi == [2]int{} {
+			continue
+		}
+		result = append(result, lipgloss.NewRange(lihi[0], lihi[1], style))
+	}
+	return result
+}
@@ -1,6 +1,7 @@
 package viewport

 import (
+	"fmt"
 	"math"
 	"strings"

@@ -52,6 +53,13 @@ type Model struct {
 	height int
 	KeyMap KeyMap

+	// Whether or not to wrap text. If false, it'll allow horizontal scrolling
+	// instead.
+	SoftWrap bool
+
+	// Whether or not to fill to the height of the viewport with empty lines.
+	FillHeight bool
+
 	// Whether or not to respond to the mouse. The mouse must be enabled in
 	// Bubble Tea for this to work. For details, see the Bubble Tea docs.
 	MouseWheelEnabled bool
@@ -77,9 +85,54 @@ type Model struct {
 	// useful for setting borders, margins and padding.
 	Style lipgloss.Style

+	// LeftGutterFunc allows to define a [GutterFunc] that adds a column into
+	// the left of the viewport, which is kept when horizontal scrolling.
+	// This can be used for things like line numbers, selection indicators,
+	// show statuses, etc.
+	LeftGutterFunc GutterFunc
+
 	initialized      bool
 	lines            []string
 	longestLineWidth int
+
+	// HighlightStyle highlights the ranges set with [SetHighligths].
+	HighlightStyle lipgloss.Style
+
+	// SelectedHighlightStyle highlights the highlight range focused during
+	// navigation.
+	// Use [SetHighligths] to set the highlight ranges, and [HightlightNext]
+	// and [HihglightPrevious] to navigate.
+	SelectedHighlightStyle lipgloss.Style
+
+	highlights           []highlightInfo
+	hiIdx                int
+	memoizedMatchedLines []string
+}
+
+// GutterFunc can be implemented and set into [Model.LeftGutterFunc].
+type GutterFunc func(GutterContext) string
+
+// LineNumberGutter return a [GutterFunc] that shows line numbers.
+func LineNumberGutter(style lipgloss.Style) GutterFunc {
+	return func(info GutterContext) string {
+		if info.Soft {
+			return style.Render("     │ ")
+		}
+		if info.Index >= info.TotalLines {
+			return style.Render("   ~ │ ")
+		}
+		return style.Render(fmt.Sprintf("%4d │ ", info.Index+1))
+	}
+}
+
+// NoGutter is the default gutter used.
+var NoGutter = func(GutterContext) string { return "" }
+
+// GutterContext provides context to a [GutterFunc].
+type GutterContext struct {
+	Index      int
+	TotalLines int
+	Soft       bool
 }

 func (m *Model) setInitialValues() {
@@ -88,6 +141,7 @@ func (m *Model) setInitialValues() {
 	m.MouseWheelDelta = 3
 	m.initialized = true
 	m.horizontalStep = defaultHorizontalStep
+	m.LeftGutterFunc = NoGutter
 }

 // Init exists to satisfy the tea.Model interface for composability purposes.
@@ -134,12 +188,13 @@ func (m Model) PastBottom() bool {

 // ScrollPercent returns the amount scrolled as a float between 0 and 1.
 func (m Model) ScrollPercent() float64 {
-	if m.Height() >= len(m.lines) {
+	count := m.lineCount()
+	if m.Height() >= count {
 		return 1.0
 	}
 	y := float64(m.YOffset)
 	h := float64(m.Height())
-	t := float64(len(m.lines))
+	t := float64(count)
 	v := y / (t - h)
 	return math.Max(0.0, math.Min(1.0, v))
 }
@@ -158,43 +213,174 @@ func (m Model) HorizontalScrollPercent() float64 {
 }

 // SetContent set the pager's text content.
+// Line endings will be normalized to '\n'.
 func (m *Model) SetContent(s string) {
 	s = strings.ReplaceAll(s, "\r\n", "\n") // normalize line endings
 	m.lines = strings.Split(s, "\n")
-	m.longestLineWidth = findLongestLineWidth(m.lines)
+	// if there's no content, set content to actual nil instead of one empty
+	// line.
+	if len(m.lines) == 1 && ansi.StringWidth(m.lines[0]) == 0 {
+		m.lines = nil
+	}
+	m.longestLineWidth = maxLineWidth(m.lines)
+	m.ClearHighlights()

-	if m.YOffset > len(m.lines)-1 {
+	if m.YOffset > m.maxYOffset() {
 		m.GotoBottom()
 	}
 }

+// GetContent returns the entire content as a single string.
+// Line endings are normalized to '\n'.
+func (m Model) GetContent() string {
+	return strings.Join(m.lines, "\n")
+}
+
+// calculateLine taking soft wrapiing into account, returns the total viewable
+// lines and the real-line index for the given yoffset.
+func (m Model) calculateLine(yoffset int) (total, idx int) {
+	if !m.SoftWrap {
+		return len(m.lines), yoffset
+	}
+	maxWidth := m.maxWidth()
+	gutterSize := lipgloss.Width(m.LeftGutterFunc(GutterContext{}))
+	for i, line := range m.lines {
+		adjust := max(1, ansi.StringWidth(line)/(maxWidth-gutterSize))
+		if yoffset >= total && yoffset < total+adjust {
+			idx = i
+		}
+		total += adjust
+	}
+	return total, idx
+}
+
+// lineToIndex taking soft wrappign into account, return the real line index
+// for the given line.
+func (m Model) lineToIndex(y int) int {
+	_, idx := m.calculateLine(y)
+	return idx
+}
+
+// lineCount taking soft wrapping into account, return the total viewable line
+// count (real lines + soft wrapped line).
+func (m Model) lineCount() int {
+	total, _ := m.calculateLine(0)
+	return total
+}
+
 // maxYOffset returns the maximum possible value of the y-offset based on the
 // viewport's content and set height.
 func (m Model) maxYOffset() int {
-	return max(0, len(m.lines)-m.Height()+m.Style.GetVerticalFrameSize())
+	return max(0, m.lineCount()-m.Height()+m.Style.GetVerticalFrameSize())
+}
+
+// maxXOffset returns the maximum possible value of the x-offset based on the
+// viewport's content and set width.
+func (m Model) maxXOffset() int {
+	return max(0, m.longestLineWidth-m.Width())
+}
+
+func (m Model) maxWidth() int {
+	return m.Width() -
+		m.Style.GetHorizontalFrameSize() -
+		lipgloss.Width(m.LeftGutterFunc(GutterContext{}))
+}
+
+func (m Model) maxHeight() int {
+	return m.Height() - m.Style.GetVerticalFrameSize()
 }

 // visibleLines returns the lines that should currently be visible in the
 // viewport.
 func (m Model) visibleLines() (lines []string) {
-	h := m.Height() - m.Style.GetVerticalFrameSize()
-	w := m.Width() - m.Style.GetHorizontalFrameSize()
+	maxHeight := m.maxHeight()
+	maxWidth := m.maxWidth()

-	if len(m.lines) > 0 {
-		top := max(0, m.YOffset)
-		bottom := clamp(m.YOffset+h, top, len(m.lines))
-		lines = m.lines[top:bottom]
+	if m.lineCount() > 0 {
+		pos := m.lineToIndex(m.YOffset)
+		top := max(0, pos)
+		bottom := clamp(pos+maxHeight, top, len(m.lines))
+		lines = make([]string, bottom-top)
+		copy(lines, m.lines[top:bottom])
+		lines = m.highlightLines(lines, top)
 	}

-	if (m.xOffset == 0 && m.longestLineWidth <= w) || w == 0 {
+	for m.FillHeight && len(lines) < maxHeight {
+		lines = append(lines, "")
+	}
+
+	// if longest line fit within width, no need to do anything else.
+	if (m.xOffset == 0 && m.longestLineWidth <= maxWidth) || maxWidth == 0 {
+		return m.prependColumn(lines)
+	}
+
+	if m.SoftWrap {
+		return m.softWrap(lines, maxWidth)
+	}
+
+	for i := range lines {
+		lines[i] = ansi.Cut(lines[i], m.xOffset, m.xOffset+maxWidth)
+	}
+	return m.prependColumn(lines)
+}
+
+func (m Model) highlightLines(lines []string, offset int) []string {
+	if len(m.highlights) == 0 {
 		return lines
 	}
-
-	cutLines := make([]string, len(lines))
 	for i := range lines {
-		cutLines[i] = ansi.Cut(lines[i], m.xOffset, m.xOffset+w)
+		if memoized := m.memoizedMatchedLines[i+offset]; memoized != "" {
+			lines[i] = memoized
+		} else {
+			ranges := makeHighlightRanges(
+				m.highlights,
+				i+offset,
+				m.HighlightStyle,
+			)
+			lines[i] = lipgloss.StyleRanges(lines[i], ranges...)
+			m.memoizedMatchedLines[i+offset] = lines[i]
+		}
+		if m.hiIdx < 0 {
+			continue
+		}
+		sel := m.highlights[m.hiIdx]
+		if hi, ok := sel.lines[i+offset]; ok {
+			lines[i] = lipgloss.StyleRanges(lines[i], lipgloss.NewRange(
+				hi[0],
+				hi[1],
+				m.SelectedHighlightStyle,
+			))
+		}
 	}
-	return cutLines
+	return lines
+}
+
+func (m Model) softWrap(lines []string, maxWidth int) []string {
+	var wrappedLines []string
+	for i, line := range lines {
+		idx := 0
+		for ansi.StringWidth(line) >= idx {
+			truncatedLine := ansi.Cut(line, idx, maxWidth+idx)
+			wrappedLines = append(wrappedLines, m.LeftGutterFunc(GutterContext{
+				Index:      i + m.YOffset,
+				TotalLines: m.TotalLineCount(),
+				Soft:       idx > 0,
+			})+truncatedLine)
+			idx += maxWidth
+		}
+	}
+	return wrappedLines
+}
+
+func (m Model) prependColumn(lines []string) []string {
+	result := make([]string, len(lines))
+	for i, line := range lines {
+		result[i] = m.LeftGutterFunc(GutterContext{
+			Index:      i + m.YOffset,
+			TotalLines: m.TotalLineCount(),
+		}) + line
+	}
+	return result
 }

 // SetYOffset sets the Y offset.
@@ -202,6 +388,31 @@ func (m *Model) SetYOffset(n int) {
 	m.YOffset = clamp(n, 0, m.maxYOffset())
 }

+// SetXOffset sets the X offset.
+// No-op when soft wrap is enabled.
+func (m *Model) SetXOffset(n int) {
+	if m.SoftWrap {
+		return
+	}
+	m.xOffset = clamp(n, 0, m.maxXOffset())
+}
+
+// EnsureVisible ensures that the given line and column are in the viewport.
+func (m *Model) EnsureVisible(line, colstart, colend int) {
+	maxWidth := m.maxWidth()
+	if colend <= maxWidth {
+		m.SetXOffset(0)
+	} else {
+		m.SetXOffset(colstart - m.horizontalStep) // put one step to the left, feels more natural
+	}
+
+	if line < m.YOffset || line >= m.YOffset+m.maxHeight() {
+		m.SetYOffset(line)
+	}
+
+	m.visibleLines()
+}
+
 // ViewDown moves the view down by the number of lines in the viewport.
 // Basically, "page down".
 func (m *Model) ViewDown() {
@@ -249,6 +460,7 @@ func (m *Model) LineDown(n int) {
 	// greater than the number of lines we actually have left before we reach
 	// the bottom.
 	m.SetYOffset(m.YOffset + n)
+	m.hiIdx = m.findNearedtMatch()
 }

 // LineUp moves the view down by the given number of lines. Returns the new
@@ -261,11 +473,12 @@ func (m *Model) LineUp(n int) {
 	// Make sure the number of lines by which we're going to scroll isn't
 	// greater than the number of lines we are from the top.
 	m.SetYOffset(m.YOffset - n)
+	m.hiIdx = m.findNearedtMatch()
 }

 // TotalLineCount returns the total number of lines (both hidden and visible) within the viewport.
 func (m Model) TotalLineCount() int {
-	return len(m.lines)
+	return m.lineCount()
 }

 // VisibleLineCount returns the number of the visible lines within the viewport.
@@ -280,12 +493,14 @@ func (m *Model) GotoTop() (lines []string) {
 	}

 	m.SetYOffset(0)
+	m.hiIdx = m.findNearedtMatch()
 	return m.visibleLines()
 }

 // GotoBottom sets the viewport to the bottom position.
 func (m *Model) GotoBottom() (lines []string) {
 	m.SetYOffset(m.maxYOffset())
+	m.hiIdx = m.findNearedtMatch()
 	return m.visibleLines()
 }

@@ -311,7 +526,8 @@ func (m *Model) MoveLeft(cols int) {
 // MoveRight moves viewport to the right by the given number of columns.
 func (m *Model) MoveRight(cols int) {
 	// prevents over scrolling to the right
-	if m.xOffset >= m.longestLineWidth-m.Width() {
+	w := m.maxWidth()
+	if m.xOffset > m.longestLineWidth-w {
 		return
 	}
 	m.xOffset += cols
@@ -322,6 +538,68 @@ func (m *Model) ResetIndent() {
 	m.xOffset = 0
 }

+// SetHighlights sets ranges of characters to highlight.
+// For instance, `[]int{[]int{2, 10}, []int{20, 30}}` will highlight characters
+// 2 to 10 and 20 to 30.
+// Note that highlights are not expected to transpose each other, and are also
+// expected to be in order.
+// Use [Model.SetHighlights] to set the highlight ranges, and
+// [Model.HighlightNext] and [Model.HighlightPrevious] to navigate.
+// Use [Model.ClearHighlights] to remove all highlights.
+func (m *Model) SetHighlights(matches [][]int) {
+	if len(matches) == 0 || len(m.lines) == 0 {
+		return
+	}
+	m.memoizedMatchedLines = make([]string, len(m.lines))
+	m.highlights = parseMatches(m.GetContent(), matches)
+	m.hiIdx = m.findNearedtMatch()
+	m.showHighlight()
+}
+
+// ClearHighlights clears previously set highlights.
+func (m *Model) ClearHighlights() {
+	m.memoizedMatchedLines = nil
+	m.highlights = nil
+	m.hiIdx = -1
+}
+
+func (m *Model) showHighlight() {
+	if m.hiIdx == -1 {
+		return
+	}
+	line, colstart, colend := m.highlights[m.hiIdx].coords()
+	m.EnsureVisible(line, colstart, colend)
+}
+
+// HighlightNext highlights the next match.
+func (m *Model) HighlightNext() {
+	if m.highlights == nil {
+		return
+	}
+
+	m.hiIdx = (m.hiIdx + 1) % len(m.highlights)
+	m.showHighlight()
+}
+
+// HighlightPrevious highlights the previous match.
+func (m *Model) HighlightPrevious() {
+	if m.highlights == nil {
+		return
+	}
+
+	m.hiIdx = (m.hiIdx - 1 + len(m.highlights)) % len(m.highlights)
+	m.showHighlight()
+}
+
+func (m Model) findNearedtMatch() int {
+	for i, match := range m.highlights {
+		if match.lineStart >= m.YOffset {
+			return i
+		}
+	}
+	return -1
+}
+
 // Update handles standard message-based viewport updates.
 func (m Model) Update(msg tea.Msg) (Model, tea.Cmd) {
 	m = m.updateAsModel(msg)
@@ -423,12 +701,13 @@ func max(a, b int) int {
 	return b
 }

-func findLongestLineWidth(lines []string) int {
-	w := 0
-	for _, l := range lines {
-		if ww := ansi.StringWidth(l); ww > w {
-			w = ww
+func maxLineWidth(lines []string) int {
+	maxlen := 0
+	for _, line := range lines {
+		llen := ansi.StringWidth(line)
+		if llen > maxlen {
+			maxlen = llen
 		}
 	}
-	return w
+	return maxlen
 }
@@ -1,8 +1,12 @@
 package viewport

 import (
+	"reflect"
+	"regexp"
 	"strings"
 	"testing"
+
+	"github.com/charmbracelet/x/ansi"
 )

 func TestNew(t *testing.T) {
@@ -381,3 +385,180 @@ func TestRightOverscroll(t *testing.T) {
 		}
 	})
 }
+
+func TestMatchesToHighlights(t *testing.T) {
+	content := `hello
+world
+
+with empty rows
+
+wide chars: あいうえおafter
+
+爱开源 • Charm does open source
+
+Charm热爱开源 • Charm loves open source
+`
+
+	vt := New(WithWidth(100), WithHeight(100))
+	vt.SetContent(content)
+
+	t.Run("first", func(t *testing.T) {
+		testHighlights(t, content, regexp.MustCompile("hello"), []highlightInfo{
+			{
+				lineStart: 0,
+				lineEnd:   0,
+				lines: map[int][2]int{
+					0: {0, 5},
+				},
+			},
+		})
+	})
+
+	t.Run("multiple", func(t *testing.T) {
+		testHighlights(t, content, regexp.MustCompile("l"), []highlightInfo{
+			{
+				lineStart: 0,
+				lineEnd:   0,
+				lines: map[int][2]int{
+					0: {2, 3},
+				},
+			},
+			{
+				lineStart: 0,
+				lineEnd:   0,
+				lines: map[int][2]int{
+					0: {3, 4},
+				},
+			},
+			{
+				lineStart: 1,
+				lineEnd:   1,
+				lines: map[int][2]int{
+					1: {3, 4},
+				},
+			},
+			{
+				lineStart: 9,
+				lineEnd:   9,
+				lines: map[int][2]int{
+					9: {22, 23},
+				},
+			},
+		})
+	})
+
+	t.Run("span lines", func(t *testing.T) {
+		testHighlights(t, content, regexp.MustCompile("lo\nwo"), []highlightInfo{
+			{
+				lineStart: 0,
+				lineEnd:   1,
+				lines: map[int][2]int{
+					0: {3, 6},
+					1: {0, 2},
+				},
+			},
+		})
+	})
+
+	t.Run("ends with newline", func(t *testing.T) {
+		testHighlights(t, content, regexp.MustCompile("lo\n"), []highlightInfo{
+			{
+				lineStart: 0,
+				lineEnd:   0,
+				lines: map[int][2]int{
+					0: {3, 6},
+				},
+			},
+		})
+	})
+
+	t.Run("empty lines in the text", func(t *testing.T) {
+		testHighlights(t, content, regexp.MustCompile("ith"), []highlightInfo{
+			{
+				lineStart: 3,
+				lineEnd:   3,
+				lines: map[int][2]int{
+					3: {1, 4},
+				},
+			},
+		})
+	})
+
+	t.Run("empty lines in the text match start of new line", func(t *testing.T) {
+		testHighlights(t, content, regexp.MustCompile("with"), []highlightInfo{
+			{
+				lineStart: 3,
+				lineEnd:   3,
+				lines: map[int][2]int{
+					3: {0, 4},
+				},
+			},
+		})
+	})
+
+	t.Run("wide characteres", func(t *testing.T) {
+		testHighlights(t, content, regexp.MustCompile("after"), []highlightInfo{
+			{
+				lineStart: 5,
+				lineEnd:   5,
+				lines: map[int][2]int{
+					5: {22, 27},
+				},
+			},
+		})
+	})
+
+	t.Run("wide 2", func(t *testing.T) {
+		testHighlights(t, content, regexp.MustCompile("Charm"), []highlightInfo{
+			{
+				lineStart: 7,
+				lineEnd:   7,
+				lines: map[int][2]int{
+					7: {9, 14},
+				},
+			},
+			{
+				lineStart: 9,
+				lineEnd:   9,
+				lines: map[int][2]int{
+					9: {0, 5},
+				},
+			},
+			{
+				lineStart: 9,
+				lineEnd:   9,
+				lines: map[int][2]int{
+					9: {16, 21},
+				},
+			},
+		})
+	})
+}
+
+func testHighlights(tb testing.TB, content string, re *regexp.Regexp, expect []highlightInfo) {
+	tb.Helper()
+
+	vt := New(WithHeight(100), WithWidth(100))
+	vt.SetContent(content)
+
+	matches := re.FindAllStringIndex(vt.GetContent(), -1)
+	vt.SetHighlights(matches)
+
+	if !reflect.DeepEqual(expect, vt.highlights) {
+		tb.Errorf("\nexpect: %+v\n   got: %+v\n", expect, vt.highlights)
+	}
+
+	if strings.Contains(re.String(), "\n") {
+		tb.Log("cannot check text when regex has span lines")
+		return
+	}
+
+	for _, hi := range expect {
+		for line, hl := range hi.lines {
+			cut := ansi.Cut(vt.lines[line], hl[0], hl[1])
+			if !re.MatchString(cut) {
+				tb.Errorf("exptect to match '%s', got '%s': line: %d, cut: %+v", re.String(), cut, line, hl)
+			}
+		}
+	}
+}