Merge 6a2d2bb into 3cfeb8a

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- The `Text` widget has a new option `MaxTextCells` which can be used to limit
+  the maximum number of cells the widget keeps in memory.
+
 ### Changed
 
 - Bump github.com/mattn/go-runewidth from 0.0.10 to 0.0.12.

private/runewidth/runewidth_test.go

@@ -34,7 +34,7 @@ func TestRuneWidth(t *testing.T) {
 		},
 		{
 			desc:  "non-printable characters from mattn/runewidth/runewidth_test",
-			runes: []rune{'\x00', '\x01', '\u0300', '\u2028', '\u2029'},
+			runes: []rune{'\x00', '\x01', '\u0300', '\u2028', '\u2029', '\n'},
 			want:  0,
 		},
 		{

widgets/text/options.go

@@ -36,6 +36,7 @@ type options struct {
 	scrollDown       rune
 	wrapMode         wrap.Mode
 	rollContent      bool
+	maxTextCells     int
 	disableScrolling bool
 	mouseUpButton    mouse.Button
 	mouseDownButton  mouse.Button
@@ -56,6 +57,7 @@ func newOptions(opts ...Option) *options {
 		keyDown:         DefaultScrollKeyDown,
 		keyPgUp:         DefaultScrollKeyPageUp,
 		keyPgDown:       DefaultScrollKeyPageDown,
+		maxTextCells:    DefaultMaxTextCells,
 	}
 	for _, o := range opts {
 		o.set(opt)
@@ -77,6 +79,9 @@ func (o *options) validate() error {
 	if o.mouseUpButton == o.mouseDownButton {
 		return fmt.Errorf("invalid ScrollMouseButtons(up:%v, down:%v), the buttons must be unique", o.mouseUpButton, o.mouseDownButton)
 	}
+	if o.maxTextCells < 0 {
+		return fmt.Errorf("invalid MaxTextCells(%d), must be zero or a positive integer", o.maxTextCells)
+	}
 	return nil
 }
 
@@ -174,3 +179,23 @@ func ScrollKeys(up, down, pageUp, pageDown keyboard.Key) Option {
 		opts.keyPgDown = pageDown
 	})
 }
+
+// The default value for the MaxTextCells option.
+// Use zero as no limit, for logs you may wish to try 10,000 or higher.
+const (
+	DefaultMaxTextCells = 0
+)
+
+// MaxTextCells limits the text content to this number of terminal cells.
+// This is useful when sending large amounts of text to the Text widget, e.g.
+// when tailing logs as it will limit the memory usage.
+// When the newly added content goes over this number of cells, the Text widget
+// behaves as a circular buffer and drops earlier content to accommodate the
+// new one.
+// Note the count is in cells, not runes, some wide runes can take multiple
+// terminal cells.
+func MaxTextCells(max int) Option {
+	return option(func(opts *options) {
+		opts.maxTextCells = max
+	})
+}

widgets/text/text.go

@@ -18,10 +18,12 @@ package text
 import (
 	"fmt"
 	"image"
+	"strings"
 	"sync"
 
 	"github.com/mum4k/termdash/private/canvas"
 	"github.com/mum4k/termdash/private/canvas/buffer"
+	"github.com/mum4k/termdash/private/runewidth"
 	"github.com/mum4k/termdash/private/wrap"
 	"github.com/mum4k/termdash/terminal/terminalapi"
 	"github.com/mum4k/termdash/widgetapi"
@@ -90,6 +92,16 @@ func (t *Text) reset() {
 	t.contentChanged = true
 }
 
+// contentCells calculates the number of cells the content takes to display on
+// terminal.
+func (t *Text) contentCells() int {
+	cells := 0
+	for _, c := range t.content {
+		cells += runeWidth(c.Rune)
+	}
+	return cells
+}
+
 // Write writes text for the widget to display. Multiple calls append
 // additional text. The text contain cannot control characters
 // (unicode.IsControl) or space character (unicode.IsSpace) other than:
@@ -108,7 +120,17 @@ func (t *Text) Write(text string, wOpts ...WriteOption) error {
 	if opts.replace {
 		t.reset()
 	}
-	for _, r := range text {
+
+	truncated := truncateToCells(text, t.opts.maxTextCells)
+	textCells := stringWidth(truncated)
+	contentCells := t.contentCells()
+	// If MaxTextCells has been set, limit the content if needed.
+	if t.opts.maxTextCells > 0 && contentCells+textCells > t.opts.maxTextCells {
+		diff := contentCells + textCells - t.opts.maxTextCells
+		t.content = t.content[diff:]
+	}
+
+	for _, r := range truncated {
 		t.content = append(t.content, buffer.NewCell(r, opts.cellOpts))
 	}
 	t.contentChanged = true
@@ -284,3 +306,47 @@ func (t *Text) Options() widgetapi.Options {
 		WantKeyboard: ks,
 	}
 }
+
+// runeWidth is line runewidth.RuneWidth, but assumes newline characters take 1
+// cell.
+func runeWidth(r rune) int {
+	if r == '\n' {
+		return 1
+	}
+	return runewidth.RuneWidth(r)
+}
+
+// stringWidth is like runewidth.StringWidth, but assumes newline characters
+// take 1 cell.
+func stringWidth(s string) int {
+	var width int
+	for _, r := range []rune(s) {
+		width += runeWidth(r)
+	}
+	return width
+}
+
+// truncateToCells truncates the beginning of text, so that it can be displayed
+// in at most maxCells. Setting maxCells to zero disables truncating.
+func truncateToCells(text string, maxCells int) string {
+	textCells := stringWidth(text)
+	if maxCells == 0 || textCells <= maxCells {
+		return text
+	}
+
+	haveCells := 0
+	textRunes := []rune(text)
+	i := len(textRunes) - 1
+	for ; i >= 0; i-- {
+		haveCells += runeWidth(textRunes[i])
+		if haveCells > maxCells {
+			break
+		}
+	}
+
+	var b strings.Builder
+	for j := i + 1; j < len(textRunes); j++ {
+		b.WriteRune(textRunes[j])
+	}
+	return b.String()
+}