aboutsummaryrefslogtreecommitdiff
path: root/vendor/maunium.net/go/tview/textview.go
blob: 44aeb1ec6897b7ea6223015f29c596b6378756fd (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
package tview

import (
	"bytes"
	"fmt"
	"regexp"
	"sync"
	"unicode/utf8"

	"maunium.net/go/tcell"
	 "github.com/lucasb-eyer/go-colorful"
	runewidth "github.com/mattn/go-runewidth"
)

// TabSize is the number of spaces with which a tab character will be replaced.
var TabSize = 4

// textViewIndex contains information about each line displayed in the text
// view.
type textViewIndex struct {
	Line            int    // The index into the "buffer" variable.
	Pos             int    // The index into the "buffer" string (byte position).
	NextPos         int    // The (byte) index of the next character in this buffer line.
	Width           int    // The screen width of this line.
	ForegroundColor string // The starting foreground color ("" = don't change, "-" = reset).
	BackgroundColor string // The starting background color ("" = don't change, "-" = reset).
	Attributes      string // The starting attributes ("" = don't change, "-" = reset).
	Region          string // The starting region ID.
}

// TextView is a box which displays text. It implements the io.Writer interface
// so you can stream text to it. This does not trigger a redraw automatically
// but if a handler is installed via SetChangedFunc(), you can cause it to be
// redrawn.
//
// Navigation
//
// If the text view is scrollable (the default), text is kept in a buffer which
// may be larger than the screen and can be navigated similarly to Vim:
//
//   - h, left arrow: Move left.
//   - l, right arrow: Move right.
//   - j, down arrow: Move down.
//   - k, up arrow: Move up.
//   - g, home: Move to the top.
//   - G, end: Move to the bottom.
//   - Ctrl-F, page down: Move down by one page.
//   - Ctrl-B, page up: Move up by one page.
//
// If the text is not scrollable, any text above the top visible line is
// discarded.
//
// Use SetInputCapture() to override or modify keyboard input.
//
// Colors
//
// If dynamic colors are enabled via SetDynamicColors(), text color can be
// changed dynamically by embedding color strings in square brackets. This works
// the same way as anywhere else. Please see the package documentation for more
// information.
//
// Regions and Highlights
//
// If regions are enabled via SetRegions(), you can define text regions within
// the text and assign region IDs to them. Text regions start with region tags.
// Region tags are square brackets that contain a region ID in double quotes,
// for example:
//
//   We define a ["rg"]region[""] here.
//
// A text region ends with the next region tag. Tags with no region ID ([""])
// don't start new regions. They can therefore be used to mark the end of a
// region. Region IDs must satisfy the following regular expression:
//
//   [a-zA-Z0-9_,;: \-\.]+
//
// Regions can be highlighted by calling the Highlight() function with one or
// more region IDs. This can be used to display search results, for example.
//
// The ScrollToHighlight() function can be used to jump to the currently
// highlighted region once when the text view is drawn the next time.
//
// See https://github.com/rivo/tview/wiki/TextView for an example.
type TextView struct {
	sync.Mutex
	*Box

	// The text buffer.
	buffer []string

	// The last bytes that have been received but are not part of the buffer yet.
	recentBytes []byte

	// The processed line index. This is nil if the buffer has changed and needs
	// to be re-indexed.
	index []*textViewIndex

	// The text alignment, one of AlignLeft, AlignCenter, or AlignRight.
	align int

	// Indices into the "index" slice which correspond to the first line of the
	// first highlight and the last line of the last highlight. This is calculated
	// during re-indexing. Set to -1 if there is no current highlight.
	fromHighlight, toHighlight int

	// A set of region IDs that are currently highlighted.
	highlights map[string]struct{}

	// The last width for which the current table is drawn.
	lastWidth int

	// The screen width of the longest line in the index (not the buffer).
	longestLine int

	// The index of the first line shown in the text view.
	lineOffset int

	// If set to true, the text view will always remain at the end of the content.
	trackEnd bool

	// The number of characters to be skipped on each line (not in wrap mode).
	columnOffset int

	// The height of the content the last time the text view was drawn.
	pageSize int

	// If set to true, the text view will keep a buffer of text which can be
	// navigated when the text is longer than what fits into the box.
	scrollable bool

	// If set to true, lines that are longer than the available width are wrapped
	// onto the next line. If set to false, any characters beyond the available
	// width are discarded.
	wrap bool

	// If set to true and if wrap is also true, lines are split at spaces or
	// after punctuation characters.
	wordWrap bool

	// The (starting) color of the text.
	textColor tcell.Color

	// If set to true, the text color can be changed dynamically by piping color
	// strings in square brackets to the text view.
	dynamicColors bool

	// If set to true, region tags can be used to define regions.
	regions bool

	// A temporary flag which, when true, will automatically bring the current
	// highlight(s) into the visible screen.
	scrollToHighlights bool

	// An optional function which is called when the content of the text view has
	// changed.
	changed func()

	// An optional function which is called when the user presses one of the
	// following keys: Escape, Enter, Tab, Backtab.
	done func(tcell.Key)
}

// NewTextView returns a new text view.
func NewTextView() *TextView {
	return &TextView{
		Box:           NewBox(),
		highlights:    make(map[string]struct{}),
		lineOffset:    -1,
		scrollable:    true,
		align:         AlignLeft,
		wrap:          true,
		textColor:     Styles.PrimaryTextColor,
		dynamicColors: false,
	}
}

// SetScrollable sets the flag that decides whether or not the text view is
// scrollable. If true, text is kept in a buffer and can be navigated.
func (t *TextView) SetScrollable(scrollable bool) *TextView {
	t.scrollable = scrollable
	if !scrollable {
		t.trackEnd = true
	}
	return t
}

// SetWrap sets the flag that, if true, leads to lines that are longer than the
// available width being wrapped onto the next line. If false, any characters
// beyond the available width are not displayed.
func (t *TextView) SetWrap(wrap bool) *TextView {
	if t.wrap != wrap {
		t.index = nil
	}
	t.wrap = wrap
	return t
}

// SetWordWrap sets the flag that, if true and if the "wrap" flag is also true
// (see SetWrap()), wraps the line at spaces or after punctuation marks. Note
// that trailing spaces will not be printed.
//
// This flag is ignored if the "wrap" flag is false.
func (t *TextView) SetWordWrap(wrapOnWords bool) *TextView {
	if t.wordWrap != wrapOnWords {
		t.index = nil
	}
	t.wordWrap = wrapOnWords
	return t
}

// SetTextAlign sets the text alignment within the text view. This must be
// either AlignLeft, AlignCenter, or AlignRight.
func (t *TextView) SetTextAlign(align int) *TextView {
	if t.align != align {
		t.index = nil
	}
	t.align = align
	return t
}

// SetTextColor sets the initial color of the text (which can be changed
// dynamically by sending color strings in square brackets to the text view if
// dynamic colors are enabled).
func (t *TextView) SetTextColor(color tcell.Color) *TextView {
	t.textColor = color
	return t
}

// SetText sets the text of this text view to the provided string. Previously
// contained text will be removed.
func (t *TextView) SetText(text string) *TextView {
	t.Clear()
	fmt.Fprint(t, text)
	return t
}

// SetDynamicColors sets the flag that allows the text color to be changed
// dynamically. See class description for details.
func (t *TextView) SetDynamicColors(dynamic bool) *TextView {
	if t.dynamicColors != dynamic {
		t.index = nil
	}
	t.dynamicColors = dynamic
	return t
}

// SetRegions sets the flag that allows to define regions in the text. See class
// description for details.
func (t *TextView) SetRegions(regions bool) *TextView {
	if t.regions != regions {
		t.index = nil
	}
	t.regions = regions
	return t
}

// SetChangedFunc sets a handler function which is called when the text of the
// text view has changed. This is typically used to cause the application to
// redraw the screen.
func (t *TextView) SetChangedFunc(handler func()) *TextView {
	t.changed = handler
	return t
}

// SetDoneFunc sets a handler which is called when the user presses on the
// following keys: Escape, Enter, Tab, Backtab. The key is passed to the
// handler.
func (t *TextView) SetDoneFunc(handler func(key tcell.Key)) *TextView {
	t.done = handler
	return t
}

// ScrollToBeginning scrolls to the top left corner of the text if the text view
// is scrollable.
func (t *TextView) ScrollToBeginning() *TextView {
	if !t.scrollable {
		return t
	}
	t.trackEnd = false
	t.lineOffset = 0
	t.columnOffset = 0
	return t
}

// ScrollToEnd scrolls to the bottom left corner of the text if the text view
// is scrollable. Adding new rows to the end of the text view will cause it to
// scroll with the new data.
func (t *TextView) ScrollToEnd() *TextView {
	if !t.scrollable {
		return t
	}
	t.trackEnd = true
	t.columnOffset = 0
	return t
}

// Clear removes all text from the buffer.
func (t *TextView) Clear() *TextView {
	t.buffer = nil
	t.recentBytes = nil
	t.index = nil
	return t
}

// Highlight specifies which regions should be highlighted. See class
// description for details on regions. Empty region strings are ignored.
//
// Text in highlighted regions will be drawn inverted, i.e. with their
// background and foreground colors swapped.
//
// Calling this function will remove any previous highlights. To remove all
// highlights, call this function without any arguments.
func (t *TextView) Highlight(regionIDs ...string) *TextView {
	t.highlights = make(map[string]struct{})
	for _, id := range regionIDs {
		if id == "" {
			continue
		}
		t.highlights[id] = struct{}{}
	}
	t.index = nil
	return t
}

// GetHighlights returns the IDs of all currently highlighted regions.
func (t *TextView) GetHighlights() (regionIDs []string) {
	for id := range t.highlights {
		regionIDs = append(regionIDs, id)
	}
	return
}

// ScrollToHighlight will cause the visible area to be scrolled so that the
// highlighted regions appear in the visible area of the text view. This
// repositioning happens the next time the text view is drawn. It happens only
// once so you will need to call this function repeatedly to always keep
// highlighted regions in view.
//
// Nothing happens if there are no highlighted regions or if the text view is
// not scrollable.
func (t *TextView) ScrollToHighlight() *TextView {
	if len(t.highlights) == 0 || !t.scrollable || !t.regions {
		return t
	}
	t.index = nil
	t.scrollToHighlights = true
	t.trackEnd = false
	return t
}

// GetRegionText returns the text of the region with the given ID. If dynamic
// colors are enabled, color tags are stripped from the text. Newlines are
// always returned as '\n' runes.
//
// If the region does not exist or if regions are turned off, an empty string
// is returned.
func (t *TextView) GetRegionText(regionID string) string {
	if !t.regions || regionID == "" {
		return ""
	}

	var (
		buffer          bytes.Buffer
		currentRegionID string
	)

	for _, str := range t.buffer {
		// Find all color tags in this line.
		var colorTagIndices [][]int
		if t.dynamicColors {
			colorTagIndices = colorPattern.FindAllStringIndex(str, -1)
		}

		// Find all regions in this line.
		var (
			regionIndices [][]int
			regions       [][]string
		)
		if t.regions {
			regionIndices = regionPattern.FindAllStringIndex(str, -1)
			regions = regionPattern.FindAllStringSubmatch(str, -1)
		}

		// Analyze this line.
		var currentTag, currentRegion int
		for pos, ch := range str {
			// Skip any color tags.
			if currentTag < len(colorTagIndices) && pos >= colorTagIndices[currentTag][0] && pos < colorTagIndices[currentTag][1] {
				if pos == colorTagIndices[currentTag][1]-1 {
					currentTag++
				}
				continue
			}

			// Skip any regions.
			if currentRegion < len(regionIndices) && pos >= regionIndices[currentRegion][0] && pos < regionIndices[currentRegion][1] {
				if pos == regionIndices[currentRegion][1]-1 {
					if currentRegionID == regionID {
						// This is the end of the requested region. We're done.
						return buffer.String()
					}
					currentRegionID = regions[currentRegion][1]
					currentRegion++
				}
				continue
			}

			// Add this rune.
			if currentRegionID == regionID {
				buffer.WriteRune(ch)
			}
		}

		// Add newline.
		if currentRegionID == regionID {
			buffer.WriteRune('\n')
		}
	}

	return escapePattern.ReplaceAllString(buffer.String(), `[$1$2]`)
}

// Write lets us implement the io.Writer interface. Tab characters will be
// replaced with TabSize space characters. A "\n" or "\r\n" will be interpreted
// as a new line.
func (t *TextView) Write(p []byte) (n int, err error) {
	// Notify at the end.
	if t.changed != nil {
		defer t.changed()
	}

	t.Lock()
	defer t.Unlock()

	// Copy data over.
	newBytes := append(t.recentBytes, p...)
	t.recentBytes = nil

	// If we have a trailing invalid UTF-8 byte, we'll wait.
	if r, _ := utf8.DecodeLastRune(p); r == utf8.RuneError {
		t.recentBytes = newBytes
		return len(p), nil
	}

	// If we have a trailing open dynamic color, exclude it.
	if t.dynamicColors {
		openColor := regexp.MustCompile(`\[([a-zA-Z]*|#[0-9a-zA-Z]*)$`)
		location := openColor.FindIndex(newBytes)
		if location != nil {
			t.recentBytes = newBytes[location[0]:]
			newBytes = newBytes[:location[0]]
		}
	}

	// If we have a trailing open region, exclude it.
	if t.regions {
		openRegion := regexp.MustCompile(`\["[a-zA-Z0-9_,;: \-\.]*"?$`)
		location := openRegion.FindIndex(newBytes)
		if location != nil {
			t.recentBytes = newBytes[location[0]:]
			newBytes = newBytes[:location[0]]
		}
	}

	// Transform the new bytes into strings.
	newLine := regexp.MustCompile(`\r?\n`)
	newBytes = bytes.Replace(newBytes, []byte{'\t'}, bytes.Repeat([]byte{' '}, TabSize), -1)
	for index, line := range newLine.Split(string(newBytes), -1) {
		if index == 0 {
			if len(t.buffer) == 0 {
				t.buffer = []string{line}
			} else {
				t.buffer[len(t.buffer)-1] += line
			}
		} else {
			t.buffer = append(t.buffer, line)
		}
	}

	// Reset the index.
	t.index = nil

	return len(p), nil
}

// reindexBuffer re-indexes the buffer such that we can use it to easily draw
// the buffer onto the screen. Each line in the index will contain a pointer
// into the buffer from which on we will print text. It will also contain the
// color with which the line starts.
func (t *TextView) reindexBuffer(width int) {
	if t.index != nil {
		return // Nothing has changed. We can still use the current index.
	}
	t.index = nil
	t.fromHighlight, t.toHighlight = -1, -1

	// If there's no space, there's no index.
	if width < 1 {
		return
	}

	// Initial states.
	regionID := ""
	var highlighted bool

	// Go through each line in the buffer.
	for bufferIndex, str := range t.buffer {
		// Find all color tags in this line. Then remove them.
		var (
			colorTagIndices [][]int
			colorTags       [][]string
			escapeIndices   [][]int
		)
		if t.dynamicColors {
			colorTagIndices, colorTags, escapeIndices, str, _ = decomposeString(str)
		}

		// Find all regions in this line. Then remove them.
		var (
			regionIndices [][]int
			regions       [][]string
		)
		if t.regions {
			regionIndices = regionPattern.FindAllStringIndex(str, -1)
			regions = regionPattern.FindAllStringSubmatch(str, -1)
			str = regionPattern.ReplaceAllString(str, "")
			if !t.dynamicColors {
				// We haven't detected escape tags yet. Do it now.
				escapeIndices = escapePattern.FindAllStringIndex(str, -1)
				str = escapePattern.ReplaceAllString(str, "[$1$2]")
			}
		}

		// Split the line if required.
		var splitLines []string
		if t.wrap && len(str) > 0 {
			for len(str) > 0 {
				extract := runewidth.Truncate(str, width, "")
				if t.wordWrap && len(extract) < len(str) {
					// Add any spaces from the next line.
					if spaces := spacePattern.FindStringIndex(str[len(extract):]); spaces != nil && spaces[0] == 0 {
						extract = str[:len(extract)+spaces[1]]
					}

					// Can we split before the mandatory end?
					matches := boundaryPattern.FindAllStringIndex(extract, -1)
					if len(matches) > 0 {
						// Yes. Let's split there.
						extract = extract[:matches[len(matches)-1][1]]
					}
				}
				splitLines = append(splitLines, extract)
				str = str[len(extract):]
			}
		} else {
			// No need to split the line.
			splitLines = []string{str}
		}

		// Create index from split lines.
		var (
			originalPos, colorPos, regionPos, escapePos  int
			foregroundColor, backgroundColor, attributes string
		)
		for _, splitLine := range splitLines {
			line := &textViewIndex{
				Line:            bufferIndex,
				Pos:             originalPos,
				ForegroundColor: foregroundColor,
				BackgroundColor: backgroundColor,
				Attributes:      attributes,
				Region:          regionID,
			}

			// Shift original position with tags.
			lineLength := len(splitLine)
			for {
				if colorPos < len(colorTagIndices) && colorTagIndices[colorPos][0] <= originalPos+lineLength {
					// Process color tags.
					originalPos += colorTagIndices[colorPos][1] - colorTagIndices[colorPos][0]
					foregroundColor, backgroundColor, attributes = styleFromTag(foregroundColor, backgroundColor, attributes, colorTags[colorPos])
					colorPos++
				} else if regionPos < len(regionIndices) && regionIndices[regionPos][0] <= originalPos+lineLength {
					// Process region tags.
					originalPos += regionIndices[regionPos][1] - regionIndices[regionPos][0]
					regionID = regions[regionPos][1]
					_, highlighted = t.highlights[regionID]

					// Update highlight range.
					if highlighted {
						line := len(t.index)
						if t.fromHighlight < 0 {
							t.fromHighlight, t.toHighlight = line, line
						} else if line > t.toHighlight {
							t.toHighlight = line
						}
					}

					regionPos++
				} else if escapePos < len(escapeIndices) && escapeIndices[escapePos][0] <= originalPos+lineLength {
					// Process escape tags.
					originalPos++
					escapePos++
				} else {
					break
				}
			}

			// Advance to next line.
			originalPos += lineLength

			// Append this line.
			line.NextPos = originalPos
			line.Width = runewidth.StringWidth(splitLine)
			t.index = append(t.index, line)
		}

		// Word-wrapped lines may have trailing whitespace. Remove it.
		if t.wrap && t.wordWrap {
			for _, line := range t.index {
				str := t.buffer[line.Line][line.Pos:line.NextPos]
				spaces := spacePattern.FindAllStringIndex(str, -1)
				if spaces != nil && spaces[len(spaces)-1][1] == len(str) {
					oldNextPos := line.NextPos
					line.NextPos -= spaces[len(spaces)-1][1] - spaces[len(spaces)-1][0]
					line.Width -= runewidth.StringWidth(t.buffer[line.Line][line.NextPos:oldNextPos])
				}
			}
		}
	}

	// Calculate longest line.
	t.longestLine = 0
	for _, line := range t.index {
		if line.Width > t.longestLine {
			t.longestLine = line.Width
		}
	}
}

// Draw draws this primitive onto the screen.
func (t *TextView) Draw(screen tcell.Screen) {
	t.Lock()
	defer t.Unlock()
	t.Box.Draw(screen)

	// Get the available size.
	x, y, width, height := t.GetInnerRect()
	t.pageSize = height

	// If the width has changed, we need to reindex.
	if width != t.lastWidth {
		t.index = nil
	}
	t.lastWidth = width

	// Re-index.
	t.reindexBuffer(width)

	// If we don't have an index, there's nothing to draw.
	if t.index == nil {
		return
	}

	// Move to highlighted regions.
	if t.regions && t.scrollToHighlights && t.fromHighlight >= 0 {
		// Do we fit the entire height?
		if t.toHighlight-t.fromHighlight+1 < height {
			// Yes, let's center the highlights.
			t.lineOffset = (t.fromHighlight + t.toHighlight - height) / 2
		} else {
			// No, let's move to the start of the highlights.
			t.lineOffset = t.fromHighlight
		}
	}
	t.scrollToHighlights = false

	// Adjust line offset.
	if t.lineOffset+height > len(t.index) {
		t.trackEnd = true
	}
	if t.trackEnd {
		t.lineOffset = len(t.index) - height
	}
	if t.lineOffset < 0 {
		t.lineOffset = 0
	}

	// Adjust column offset.
	if t.align == AlignLeft {
		if t.columnOffset+width > t.longestLine {
			t.columnOffset = t.longestLine - width
		}
		if t.columnOffset < 0 {
			t.columnOffset = 0
		}
	} else if t.align == AlignRight {
		if t.columnOffset-width < -t.longestLine {
			t.columnOffset = width - t.longestLine
		}
		if t.columnOffset > 0 {
			t.columnOffset = 0
		}
	} else { // AlignCenter.
		half := (t.longestLine - width) / 2
		if half > 0 {
			if t.columnOffset > half {
				t.columnOffset = half
			}
			if t.columnOffset < -half {
				t.columnOffset = -half
			}
		} else {
			t.columnOffset = 0
		}
	}

	// Draw the buffer.
	defaultStyle := tcell.StyleDefault.Foreground(t.textColor)
	for line := t.lineOffset; line < len(t.index); line++ {
		// Are we done?
		if line-t.lineOffset >= height {
			break
		}

		// Get the text for this line.
		index := t.index[line]
		text := t.buffer[index.Line][index.Pos:index.NextPos]
		foregroundColor := index.ForegroundColor
		backgroundColor := index.BackgroundColor
		attributes := index.Attributes
		regionID := index.Region

		// Get color tags.
		var (
			colorTagIndices [][]int
			colorTags       [][]string
			escapeIndices   [][]int
		)
		if t.dynamicColors {
			colorTagIndices, colorTags, escapeIndices, _, _ = decomposeString(text)
		}

		// Get regions.
		var (
			regionIndices [][]int
			regions       [][]string
		)
		if t.regions {
			regionIndices = regionPattern.FindAllStringIndex(text, -1)
			regions = regionPattern.FindAllStringSubmatch(text, -1)
			if !t.dynamicColors {
				escapeIndices = escapePattern.FindAllStringIndex(text, -1)
			}
		}

		// Calculate the position of the line.
		var skip, posX int
		if t.align == AlignLeft {
			posX = -t.columnOffset
		} else if t.align == AlignRight {
			posX = width - index.Width - t.columnOffset
		} else { // AlignCenter.
			posX = (width-index.Width)/2 - t.columnOffset
		}
		if posX < 0 {
			skip = -posX
			posX = 0
		}

		// Print the line.
		var currentTag, currentRegion, currentEscapeTag, skipped, runeSeqWidth int
		runeSequence := make([]rune, 0, 10)
		flush := func() {
			if len(runeSequence) == 0 {
				return
			}

			// Mix the existing style with the new style.
			_, _, existingStyle, _ := screen.GetContent(x+posX, y+line-t.lineOffset)
			_, background, _ := existingStyle.Decompose()
			style := overlayStyle(background, defaultStyle, foregroundColor, backgroundColor, attributes)

			// Do we highlight this character?
			var highlighted bool
			if len(regionID) > 0 {
				if _, ok := t.highlights[regionID]; ok {
					highlighted = true
				}
			}
			if highlighted {
				fg, bg, _ := style.Decompose()
				if bg == tcell.ColorDefault {
					r, g, b := fg.RGB()
					c := colorful.Color{R: float64(r) / 255, G: float64(g) / 255, B: float64(b) / 255}
					_, _, li := c.Hcl()
					if li < .5 {
						bg = tcell.ColorWhite
					} else {
						bg = tcell.ColorBlack
					}
				}
				style = style.Background(fg).Foreground(bg)
			}

			// Draw the character.
			var comb []rune
			if len(runeSequence) > 1 {
				// Allocate space for the combining characters only when necessary.
				comb = make([]rune, len(runeSequence)-1)
				copy(comb, runeSequence[1:])
			}
			for offset := 0; offset < runeSeqWidth; offset++ {
				screen.SetContent(x+posX+offset, y+line-t.lineOffset, runeSequence[0], comb, style)
			}

			// Advance.
			posX += runeSeqWidth
			runeSequence = runeSequence[:0]
			runeSeqWidth = 0
		}
		for pos, ch := range text {
			// Get the color.
			if currentTag < len(colorTags) && pos >= colorTagIndices[currentTag][0] && pos < colorTagIndices[currentTag][1] {
				flush()
				if pos == colorTagIndices[currentTag][1]-1 {
					foregroundColor, backgroundColor, attributes = styleFromTag(foregroundColor, backgroundColor, attributes, colorTags[currentTag])
					currentTag++
				}
				continue
			}

			// Get the region.
			if currentRegion < len(regionIndices) && pos >= regionIndices[currentRegion][0] && pos < regionIndices[currentRegion][1] {
				flush()
				if pos == regionIndices[currentRegion][1]-1 {
					regionID = regions[currentRegion][1]
					currentRegion++
				}
				continue
			}

			// Skip the second-to-last character of an escape tag.
			if currentEscapeTag < len(escapeIndices) && pos >= escapeIndices[currentEscapeTag][0] && pos < escapeIndices[currentEscapeTag][1] {
				flush()
				if pos == escapeIndices[currentEscapeTag][1]-1 {
					currentEscapeTag++
				} else if pos == escapeIndices[currentEscapeTag][1]-2 {
					continue
				}
			}

			// Determine the width of this rune.
			chWidth := runewidth.RuneWidth(ch)
			if chWidth == 0 {
				// If this is not a modifier, we treat it as a space character.
				if len(runeSequence) == 0 {
					ch = ' '
					chWidth = 1
				} else {
					runeSequence = append(runeSequence, ch)
					continue
				}
			}

			// Skip to the right.
			if !t.wrap && skipped < skip {
				skipped += chWidth
				continue
			}

			// Stop at the right border.
			if posX+runeSeqWidth+chWidth > width {
				break
			}

			// Flush the rune sequence.
			flush()

			// Queue this rune.
			runeSequence = append(runeSequence, ch)
			runeSeqWidth += chWidth
		}
		if posX+runeSeqWidth <= width {
			flush()
		}
	}

	// If this view is not scrollable, we'll purge the buffer of lines that have
	// scrolled out of view.
	if !t.scrollable && t.lineOffset > 0 {
		t.buffer = t.buffer[t.index[t.lineOffset].Line:]
		t.index = nil
	}
}

// InputHandler returns the handler for this primitive.
func (t *TextView) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
	return t.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
		key := event.Key()

		if key == tcell.KeyEscape || key == tcell.KeyEnter || key == tcell.KeyTab || key == tcell.KeyBacktab {
			if t.done != nil {
				t.done(key)
			}
			return
		}

		if !t.scrollable {
			return
		}

		switch key {
		case tcell.KeyRune:
			switch event.Rune() {
			case 'g': // Home.
				t.trackEnd = false
				t.lineOffset = 0
				t.columnOffset = 0
			case 'G': // End.
				t.trackEnd = true
				t.columnOffset = 0
			case 'j': // Down.
				t.lineOffset++
			case 'k': // Up.
				t.trackEnd = false
				t.lineOffset--
			case 'h': // Left.
				t.columnOffset--
			case 'l': // Right.
				t.columnOffset++
			}
		case tcell.KeyHome:
			t.trackEnd = false
			t.lineOffset = 0
			t.columnOffset = 0
		case tcell.KeyEnd:
			t.trackEnd = true
			t.columnOffset = 0
		case tcell.KeyUp:
			t.trackEnd = false
			t.lineOffset--
		case tcell.KeyDown:
			t.lineOffset++
		case tcell.KeyLeft:
			t.columnOffset--
		case tcell.KeyRight:
			t.columnOffset++
		case tcell.KeyPgDn, tcell.KeyCtrlF:
			t.lineOffset += t.pageSize
		case tcell.KeyPgUp, tcell.KeyCtrlB:
			t.trackEnd = false
			t.lineOffset -= t.pageSize
		}
	})
}