1 /*
2 * Copyright 1998-2001 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 /*
27 * (C) Copyright Taligent, Inc. 1996 - 1997, All Rights Reserved
28 * (C) Copyright IBM Corp. 1996 - 1998, All Rights Reserved
29 *
30 * The original version of this source code and documentation is
31 * copyrighted and owned by Taligent, Inc., a wholly-owned subsidiary
32 * of IBM. These materials are provided under terms of a License
33 * Agreement between Taligent and Sun. This technology is protected
34 * by multiple US and International patents.
35 *
36 * This notice and attribution to Taligent may not be removed.
37 * Taligent is a registered trademark of Taligent, Inc.
38 *
39 */
40
41 package java.awt.font;
42
43 import java.text.BreakIterator;
44 import java.text.CharacterIterator;
45 import java.text.AttributedCharacterIterator;
46 import java.awt.font.FontRenderContext;
47
48 /**
49 * The <code>LineBreakMeasurer</code> class allows styled text to be
50 * broken into lines (or segments) that fit within a particular visual
51 * advance. This is useful for clients who wish to display a paragraph of
52 * text that fits within a specific width, called the <b>wrapping
53 * width</b>.
54 * <p>
55 * <code>LineBreakMeasurer</code> is constructed with an iterator over
56 * styled text. The iterator's range should be a single paragraph in the
57 * text.
58 * <code>LineBreakMeasurer</code> maintains a position in the text for the
59 * start of the next text segment. Initially, this position is the
60 * start of text. Paragraphs are assigned an overall direction (either
61 * left-to-right or right-to-left) according to the bidirectional
62 * formatting rules. All segments obtained from a paragraph have the
63 * same direction as the paragraph.
64 * <p>
65 * Segments of text are obtained by calling the method
66 * <code>nextLayout</code>, which returns a {@link TextLayout}
67 * representing the text that fits within the wrapping width.
68 * The <code>nextLayout</code> method moves the current position
69 * to the end of the layout returned from <code>nextLayout</code>.
70 * <p>
71 * <code>LineBreakMeasurer</code> implements the most commonly used
72 * line-breaking policy: Every word that fits within the wrapping
73 * width is placed on the line. If the first word does not fit, then all
74 * of the characters that fit within the wrapping width are placed on the
75 * line. At least one character is placed on each line.
76 * <p>
77 * The <code>TextLayout</code> instances returned by
78 * <code>LineBreakMeasurer</code> treat tabs like 0-width spaces. Clients
79 * who wish to obtain tab-delimited segments for positioning should use
80 * the overload of <code>nextLayout</code> which takes a limiting offset
81 * in the text.
82 * The limiting offset should be the first character after the tab.
83 * The <code>TextLayout</code> objects returned from this method end
84 * at the limit provided (or before, if the text between the current
85 * position and the limit won't fit entirely within the wrapping
86 * width).
87 * <p>
88 * Clients who are laying out tab-delimited text need a slightly
89 * different line-breaking policy after the first segment has been
90 * placed on a line. Instead of fitting partial words in the
91 * remaining space, they should place words which don't fit in the
92 * remaining space entirely on the next line. This change of policy
93 * can be requested in the overload of <code>nextLayout</code> which
94 * takes a <code>boolean</code> parameter. If this parameter is
95 * <code>true</code>, <code>nextLayout</code> returns
96 * <code>null</code> if the first word won't fit in
97 * the given space. See the tab sample below.
98 * <p>
99 * In general, if the text used to construct the
100 * <code>LineBreakMeasurer</code> changes, a new
101 * <code>LineBreakMeasurer</code> must be constructed to reflect
102 * the change. (The old <code>LineBreakMeasurer</code> continues to
103 * function properly, but it won't be aware of the text change.)
104 * Nevertheless, if the text change is the insertion or deletion of a
105 * single character, an existing <code>LineBreakMeasurer</code> can be
106 * 'updated' by calling <code>insertChar</code> or
107 * <code>deleteChar</code>. Updating an existing
108 * <code>LineBreakMeasurer</code> is much faster than creating a new one.
109 * Clients who modify text based on user typing should take advantage
110 * of these methods.
111 * <p>
112 * <strong>Examples</strong>:<p>
113 * Rendering a paragraph in a component
114 * <blockquote>
115 * <pre>
116 * public void paint(Graphics graphics) {
117 *
118 * Point2D pen = new Point2D(10, 20);
119 * Graphics2D g2d = (Graphics2D)graphics;
120 * FontRenderContext frc = g2d.getFontRenderContext();
121 *
122 * // let styledText be an AttributedCharacterIterator containing at least
123 * // one character
124 *
125 * LineBreakMeasurer measurer = new LineBreakMeasurer(styledText, frc);
126 * float wrappingWidth = getSize().width - 15;
127 *
128 * while (measurer.getPosition() < fStyledText.length()) {
129 *
130 * TextLayout layout = measurer.nextLayout(wrappingWidth);
131 *
132 * pen.y += (layout.getAscent());
133 * float dx = layout.isLeftToRight() ?
134 * 0 : (wrappingWidth - layout.getAdvance());
135 *
136 * layout.draw(graphics, pen.x + dx, pen.y);
137 * pen.y += layout.getDescent() + layout.getLeading();
138 * }
139 * }
140 * </pre>
141 * </blockquote>
142 * <p>
143 * Rendering text with tabs. For simplicity, the overall text
144 * direction is assumed to be left-to-right
145 * <blockquote>
146 * <pre>
147 * public void paint(Graphics graphics) {
148 *
149 * float leftMargin = 10, rightMargin = 310;
150 * float[] tabStops = { 100, 250 };
151 *
152 * // assume styledText is an AttributedCharacterIterator, and the number
153 * // of tabs in styledText is tabCount
154 *
155 * int[] tabLocations = new int[tabCount+1];
156 *
157 * int i = 0;
158 * for (char c = styledText.first(); c != styledText.DONE; c = styledText.next()) {
159 * if (c == '\t') {
160 * tabLocations[i++] = styledText.getIndex();
161 * }
162 * }
163 * tabLocations[tabCount] = styledText.getEndIndex() - 1;
164 *
165 * // Now tabLocations has an entry for every tab's offset in
166 * // the text. For convenience, the last entry is tabLocations
167 * // is the offset of the last character in the text.
168 *
169 * LineBreakMeasurer measurer = new LineBreakMeasurer(styledText);
170 * int currentTab = 0;
171 * float verticalPos = 20;
172 *
173 * while (measurer.getPosition() < styledText.getEndIndex()) {
174 *
175 * // Lay out and draw each line. All segments on a line
176 * // must be computed before any drawing can occur, since
177 * // we must know the largest ascent on the line.
178 * // TextLayouts are computed and stored in a Vector;
179 * // their horizontal positions are stored in a parallel
180 * // Vector.
181 *
182 * // lineContainsText is true after first segment is drawn
183 * boolean lineContainsText = false;
184 * boolean lineComplete = false;
185 * float maxAscent = 0, maxDescent = 0;
186 * float horizontalPos = leftMargin;
187 * Vector layouts = new Vector(1);
188 * Vector penPositions = new Vector(1);
189 *
190 * while (!lineComplete) {
191 * float wrappingWidth = rightMargin - horizontalPos;
192 * TextLayout layout =
193 * measurer.nextLayout(wrappingWidth,
194 * tabLocations[currentTab]+1,
195 * lineContainsText);
196 *
197 * // layout can be null if lineContainsText is true
198 * if (layout != null) {
199 * layouts.addElement(layout);
200 * penPositions.addElement(new Float(horizontalPos));
201 * horizontalPos += layout.getAdvance();
202 * maxAscent = Math.max(maxAscent, layout.getAscent());
203 * maxDescent = Math.max(maxDescent,
204 * layout.getDescent() + layout.getLeading());
205 * } else {
206 * lineComplete = true;
207 * }
208 *
209 * lineContainsText = true;
210 *
211 * if (measurer.getPosition() == tabLocations[currentTab]+1) {
212 * currentTab++;
213 * }
214 *
215 * if (measurer.getPosition() == styledText.getEndIndex())
216 * lineComplete = true;
217 * else if (horizontalPos >= tabStops[tabStops.length-1])
218 * lineComplete = true;
219 *
220 * if (!lineComplete) {
221 * // move to next tab stop
222 * int j;
223 * for (j=0; horizontalPos >= tabStops[j]; j++) {}
224 * horizontalPos = tabStops[j];
225 * }
226 * }
227 *
228 * verticalPos += maxAscent;
229 *
230 * Enumeration layoutEnum = layouts.elements();
231 * Enumeration positionEnum = penPositions.elements();
232 *
233 * // now iterate through layouts and draw them
234 * while (layoutEnum.hasMoreElements()) {
235 * TextLayout nextLayout = (TextLayout) layoutEnum.nextElement();
236 * Float nextPosition = (Float) positionEnum.nextElement();
237 * nextLayout.draw(graphics, nextPosition.floatValue(), verticalPos);
238 * }
239 *
240 * verticalPos += maxDescent;
241 * }
242 * }
243 * </pre>
244 * </blockquote>
245 * @see TextLayout
246 */
247
248 public final class LineBreakMeasurer {
249
250 private BreakIterator breakIter;
251 private int start;
252 private int pos;
253 private int limit;
254 private TextMeasurer measurer;
255 private CharArrayIterator charIter;
256
257 /**
258 * Constructs a <code>LineBreakMeasurer</code> for the specified text.
259 *
260 * @param text the text for which this <code>LineBreakMeasurer</code>
261 * produces <code>TextLayout</code> objects; the text must contain
262 * at least one character; if the text available through
263 * <code>iter</code> changes, further calls to this
264 * <code>LineBreakMeasurer</code> instance are undefined (except,
265 * in some cases, when <code>insertChar</code> or
266 * <code>deleteChar</code> are invoked afterward - see below)
267 * @param frc contains information about a graphics device which is
268 * needed to measure the text correctly;
269 * text measurements can vary slightly depending on the
270 * device resolution, and attributes such as antialiasing; this
271 * parameter does not specify a translation between the
272 * <code>LineBreakMeasurer</code> and user space
273 * @see LineBreakMeasurer#insertChar
274 * @see LineBreakMeasurer#deleteChar
275 */
276 public LineBreakMeasurer(AttributedCharacterIterator text, FontRenderContext frc) {
277 this(text, BreakIterator.getLineInstance(), frc);
278 }
279
280 /**
281 * Constructs a <code>LineBreakMeasurer</code> for the specified text.
282 *
283 * @param text the text for which this <code>LineBreakMeasurer</code>
284 * produces <code>TextLayout</code> objects; the text must contain
285 * at least one character; if the text available through
286 * <code>iter</code> changes, further calls to this
287 * <code>LineBreakMeasurer</code> instance are undefined (except,
288 * in some cases, when <code>insertChar</code> or
289 * <code>deleteChar</code> are invoked afterward - see below)
290 * @param breakIter the {@link BreakIterator} which defines line
291 * breaks
292 * @param frc contains information about a graphics device which is
293 * needed to measure the text correctly;
294 * text measurements can vary slightly depending on the
295 * device resolution, and attributes such as antialiasing; this
296 * parameter does not specify a translation between the
297 * <code>LineBreakMeasurer</code> and user space
298 * @throws IllegalArgumentException if the text has less than one character
299 * @see LineBreakMeasurer#insertChar
300 * @see LineBreakMeasurer#deleteChar
301 */
302 public LineBreakMeasurer(AttributedCharacterIterator text,
303 BreakIterator breakIter,
304 FontRenderContext frc) {
305 if (text.getEndIndex() - text.getBeginIndex() < 1) {
306 throw new IllegalArgumentException("Text must contain at least one character.");
307 }
308
309 this.breakIter = breakIter;
310 this.measurer = new TextMeasurer(text, frc);
311 this.limit = text.getEndIndex();
312 this.pos = this.start = text.getBeginIndex();
313
314 charIter = new CharArrayIterator(measurer.getChars(), this.start);
315 this.breakIter.setText(charIter);
316 }
317
318 /**
319 * Returns the position at the end of the next layout. Does NOT
320 * update the current position of this <code>LineBreakMeasurer</code>.
321 *
322 * @param wrappingWidth the maximum visible advance permitted for
323 * the text in the next layout
324 * @return an offset in the text representing the limit of the
325 * next <code>TextLayout</code>.
326 */
327 public int nextOffset(float wrappingWidth) {
328 return nextOffset(wrappingWidth, limit, false);
329 }
330
331 /**
332 * Returns the position at the end of the next layout. Does NOT
333 * update the current position of this <code>LineBreakMeasurer</code>.
334 *
335 * @param wrappingWidth the maximum visible advance permitted for
336 * the text in the next layout
337 * @param offsetLimit the first character that can not be included
338 * in the next layout, even if the text after the limit would fit
339 * within the wrapping width; <code>offsetLimit</code> must be
340 * greater than the current position
341 * @param requireNextWord if <code>true</code>, the current position
342 * that is returned if the entire next word does not fit within
343 * <code>wrappingWidth</code>; if <code>false</code>, the offset
344 * returned is at least one greater than the current position
345 * @return an offset in the text representing the limit of the
346 * next <code>TextLayout</code>
347 */
348 public int nextOffset(float wrappingWidth, int offsetLimit,
349 boolean requireNextWord) {
350
351 int nextOffset = pos;
352
353 if (pos < limit) {
354 if (offsetLimit <= pos) {
355 throw new IllegalArgumentException("offsetLimit must be after current position");
356 }
357
358 int charAtMaxAdvance =
359 measurer.getLineBreakIndex(pos, wrappingWidth);
360
361 if (charAtMaxAdvance == limit) {
362 nextOffset = limit;
363 }
364 else if (Character.isWhitespace(measurer.getChars()[charAtMaxAdvance-start])) {
365 nextOffset = breakIter.following(charAtMaxAdvance);
366 }
367 else {
368 // Break is in a word; back up to previous break.
369
370 // NOTE: I think that breakIter.preceding(limit) should be
371 // equivalent to breakIter.last(), breakIter.previous() but
372 // the authors of BreakIterator thought otherwise...
373 // If they were equivalent then the first branch would be
374 // unnecessary.
375 int testPos = charAtMaxAdvance + 1;
376 if (testPos == limit) {
377 breakIter.last();
378 nextOffset = breakIter.previous();
379 }
380 else {
381 nextOffset = breakIter.preceding(testPos);
382 }
383
384 if (nextOffset <= pos) {
385 // first word doesn't fit on line
386 if (requireNextWord) {
387 nextOffset = pos;
388 }
389 else {
390 nextOffset = Math.max(pos+1, charAtMaxAdvance);
391 }
392 }
393 }
394 }
395
396 if (nextOffset > offsetLimit) {
397 nextOffset = offsetLimit;
398 }
399
400 return nextOffset;
401 }
402
403 /**
404 * Returns the next layout, and updates the current position.
405 *
406 * @param wrappingWidth the maximum visible advance permitted for
407 * the text in the next layout
408 * @return a <code>TextLayout</code>, beginning at the current
409 * position, which represents the next line fitting within
410 * <code>wrappingWidth</code>
411 */
412 public TextLayout nextLayout(float wrappingWidth) {
413 return nextLayout(wrappingWidth, limit, false);
414 }
415
416 /**
417 * Returns the next layout, and updates the current position.
418 *
419 * @param wrappingWidth the maximum visible advance permitted
420 * for the text in the next layout
421 * @param offsetLimit the first character that can not be
422 * included in the next layout, even if the text after the limit
423 * would fit within the wrapping width; <code>offsetLimit</code>
424 * must be greater than the current position
425 * @param requireNextWord if <code>true</code>, and if the entire word
426 * at the current position does not fit within the wrapping width,
427 * <code>null</code> is returned. If <code>false</code>, a valid
428 * layout is returned that includes at least the character at the
429 * current position
430 * @return a <code>TextLayout</code>, beginning at the current
431 * position, that represents the next line fitting within
432 * <code>wrappingWidth</code>. If the current position is at the end
433 * of the text used by this <code>LineBreakMeasurer</code>,
434 * <code>null</code> is returned
435 */
436 public TextLayout nextLayout(float wrappingWidth, int offsetLimit,
437 boolean requireNextWord) {
438
439 if (pos < limit) {
440 int layoutLimit = nextOffset(wrappingWidth, offsetLimit, requireNextWord);
441 if (layoutLimit == pos) {
442 return null;
443 }
444
445 TextLayout result = measurer.getLayout(pos, layoutLimit);
446 pos = layoutLimit;
447
448 return result;
449 } else {
450 return null;
451 }
452 }
453
454 /**
455 * Returns the current position of this <code>LineBreakMeasurer</code>.
456 *
457 * @return the current position of this <code>LineBreakMeasurer</code>
458 * @see #setPosition
459 */
460 public int getPosition() {
461 return pos;
462 }
463
464 /**
465 * Sets the current position of this <code>LineBreakMeasurer</code>.
466 *
467 * @param newPosition the current position of this
468 * <code>LineBreakMeasurer</code>; the position should be within the
469 * text used to construct this <code>LineBreakMeasurer</code> (or in
470 * the text most recently passed to <code>insertChar</code>
471 * or <code>deleteChar</code>
472 * @see #getPosition
473 */
474 public void setPosition(int newPosition) {
475 if (newPosition < start || newPosition > limit) {
476 throw new IllegalArgumentException("position is out of range");
477 }
478 pos = newPosition;
479 }
480
481 /**
482 * Updates this <code>LineBreakMeasurer</code> after a single
483 * character is inserted into the text, and sets the current
484 * position to the beginning of the paragraph.
485 *
486 * @param newParagraph the text after the insertion
487 * @param insertPos the position in the text at which the character
488 * is inserted
489 * @throws IndexOutOfBoundsException if <code>insertPos</code> is less
490 * than the start of <code>newParagraph</code> or greater than
491 * or equal to the end of <code>newParagraph</code>
492 * @throws NullPointerException if <code>newParagraph</code> is
493 * <code>null</code>
494 * @see #deleteChar
495 */
496 public void insertChar(AttributedCharacterIterator newParagraph,
497 int insertPos) {
498
499 measurer.insertChar(newParagraph, insertPos);
500
501 limit = newParagraph.getEndIndex();
502 pos = start = newParagraph.getBeginIndex();
503
504 charIter.reset(measurer.getChars(), newParagraph.getBeginIndex());
505 breakIter.setText(charIter);
506 }
507
508 /**
509 * Updates this <code>LineBreakMeasurer</code> after a single
510 * character is deleted from the text, and sets the current
511 * position to the beginning of the paragraph.
512 * @param newParagraph the text after the deletion
513 * @param deletePos the position in the text at which the character
514 * is deleted
515 * @throws IndexOutOfBoundsException if <code>deletePos</code> is
516 * less than the start of <code>newParagraph</code> or greater
517 * than the end of <code>newParagraph</code>
518 * @throws NullPointerException if <code>newParagraph</code> is
519 * <code>null</code>
520 * @see #insertChar
521 */
522 public void deleteChar(AttributedCharacterIterator newParagraph,
523 int deletePos) {
524
525 measurer.deleteChar(newParagraph, deletePos);
526
527 limit = newParagraph.getEndIndex();
528 pos = start = newParagraph.getBeginIndex();
529
530 charIter.reset(measurer.getChars(), start);
531 breakIter.setText(charIter);
532 }
533 }
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