1 /*
2 * Copyright (c) 1995, 2018, Oracle and/or its affiliates. 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
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10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
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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).
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24 */
25
26 package java.awt;
27
28 import java.awt.Graphics2D;
29 import java.awt.font.FontRenderContext;
30 import java.awt.font.LineMetrics;
31 import java.awt.geom.Rectangle2D;
32 import java.text.CharacterIterator;
33
34 /**
35 * The {@code FontMetrics} class defines a font metrics object, which
36 * encapsulates information about the rendering of a particular font on a
37 * particular screen.
38 * <p>
39 * <b>Note to subclassers</b>: Since many of these methods form closed,
40 * mutually recursive loops, you must take care that you implement
41 * at least one of the methods in each such loop to prevent
42 * infinite recursion when your subclass is used.
43 * In particular, the following is the minimal suggested set of methods
44 * to override in order to ensure correctness and prevent infinite
45 * recursion (though other subsets are equally feasible):
46 * <ul>
47 * <li>{@link #getAscent()}
48 * <li>{@link #getLeading()}
49 * <li>{@link #getMaxAdvance()}
50 * <li>{@link #charWidth(char)}
51 * <li>{@link #charsWidth(char[], int, int)}
52 * </ul>
53 * <p>
54 * <img src="doc-files/FontMetrics-1.gif" alt="The letter 'p' showing its 'reference point'"
55 * style="border:15px; float:right; margin: 7px 10px;">
56 * Note that the implementations of these methods are
57 * inefficient, so they are usually overridden with more efficient
58 * toolkit-specific implementations.
59 * <p>
60 * When an application asks to place a character at the position
61 * (<i>x</i>, <i>y</i>), the character is placed so that its
62 * reference point (shown as the dot in the accompanying image) is
63 * put at that position. The reference point specifies a horizontal
64 * line called the <i>baseline</i> of the character. In normal
65 * printing, the baselines of characters should align.
66 * <p>
67 * In addition, every character in a font has an <i>ascent</i>, a
68 * <i>descent</i>, and an <i>advance width</i>. The ascent is the
69 * amount by which the character ascends above the baseline. The
70 * descent is the amount by which the character descends below the
71 * baseline. The advance width indicates the position at which AWT
72 * should place the next character.
73 * <p>
74 * An array of characters or a string can also have an ascent, a
75 * descent, and an advance width. The ascent of the array is the
76 * maximum ascent of any character in the array. The descent is the
77 * maximum descent of any character in the array. The advance width
78 * is the sum of the advance widths of each of the characters in the
79 * character array. The advance of a {@code String} is the
80 * distance along the baseline of the {@code String}. This
81 * distance is the width that should be used for centering or
82 * right-aligning the {@code String}.
83 * <p>Note that the advance of a {@code String} is not necessarily
84 * the sum of the advances of its characters measured in isolation
85 * because the width of a character can vary depending on its context.
86 * For example, in Arabic text, the shape of a character can change
87 * in order to connect to other characters. Also, in some scripts,
88 * certain character sequences can be represented by a single shape,
89 * called a <em>ligature</em>. Measuring characters individually does
90 * not account for these transformations.
91 * <p>Font metrics are baseline-relative, meaning that they are
92 * generally independent of the rotation applied to the font (modulo
93 * possible grid hinting effects). See {@link java.awt.Font Font}.
94 *
95 * @author Jim Graham
96 * @see java.awt.Font
97 * @since 1.0
98 */
99 public abstract class FontMetrics implements java.io.Serializable {
100
101 static {
102 /* ensure that the necessary native libraries are loaded */
103 Toolkit.loadLibraries();
104 if (!GraphicsEnvironment.isHeadless()) {
105 initIDs();
106 }
107 }
108
109 private static final FontRenderContext
110 DEFAULT_FRC = new FontRenderContext(null, false, false);
111
112 /**
113 * The actual {@link Font} from which the font metrics are
114 * created.
115 * This cannot be null.
116 *
117 * @serial
118 * @see #getFont()
119 */
120 protected Font font;
121
122 /*
123 * JDK 1.1 serialVersionUID
124 */
125 private static final long serialVersionUID = 1681126225205050147L;
126
127 /**
128 * Creates a new {@code FontMetrics} object for finding out
129 * height and width information about the specified {@code Font}
130 * and specific character glyphs in that {@code Font}.
131 * @param font the {@code Font}
132 * @see java.awt.Font
133 */
134 protected FontMetrics(Font font) {
135 this.font = font;
136 }
137
138 /**
139 * Gets the {@code Font} described by this
140 * {@code FontMetrics} object.
141 * @return the {@code Font} described by this
142 * {@code FontMetrics} object.
143 */
144 public Font getFont() {
145 return font;
146 }
147
148 /**
149 * Gets the {@code FontRenderContext} used by this
150 * {@code FontMetrics} object to measure text.
151 * <p>
152 * Note that methods in this class which take a {@code Graphics}
153 * parameter measure text using the {@code FontRenderContext}
154 * of that {@code Graphics} object, and not this
155 * {@code FontRenderContext}
156 * @return the {@code FontRenderContext} used by this
157 * {@code FontMetrics} object.
158 * @since 1.6
159 */
160 public FontRenderContext getFontRenderContext() {
161 return DEFAULT_FRC;
162 }
163
164 /**
165 * Determines the <em>standard leading</em> of the
166 * {@code Font} described by this {@code FontMetrics}
167 * object. The standard leading, or
168 * interline spacing, is the logical amount of space to be reserved
169 * between the descent of one line of text and the ascent of the next
170 * line. The height metric is calculated to include this extra space.
171 * @return the standard leading of the {@code Font}.
172 * @see #getHeight()
173 * @see #getAscent()
174 * @see #getDescent()
175 */
176 public int getLeading() {
177 return 0;
178 }
179
180 /**
181 * Determines the <em>font ascent</em> of the {@code Font}
182 * described by this {@code FontMetrics} object. The font ascent
183 * is the distance from the font's baseline to the top of most
184 * alphanumeric characters. Some characters in the {@code Font}
185 * might extend above the font ascent line.
186 * @return the font ascent of the {@code Font}.
187 * @see #getMaxAscent()
188 */
189 public int getAscent() {
190 return font.getSize();
191 }
192
193 /**
194 * Determines the <em>font descent</em> of the {@code Font}
195 * described by this
196 * {@code FontMetrics} object. The font descent is the distance
197 * from the font's baseline to the bottom of most alphanumeric
198 * characters with descenders. Some characters in the
199 * {@code Font} might extend
200 * below the font descent line.
201 * @return the font descent of the {@code Font}.
202 * @see #getMaxDescent()
203 */
204 public int getDescent() {
205 return 0;
206 }
207
208 /**
209 * Gets the standard height of a line of text in this font. This
210 * is the distance between the baseline of adjacent lines of text.
211 * It is the sum of the leading + ascent + descent. Due to rounding
212 * this may not be the same as getAscent() + getDescent() + getLeading().
213 * There is no guarantee that lines of text spaced at this distance are
214 * disjoint; such lines may overlap if some characters overshoot
215 * either the standard ascent or the standard descent metric.
216 * @return the standard height of the font.
217 * @see #getLeading()
218 * @see #getAscent()
219 * @see #getDescent()
220 */
221 public int getHeight() {
222 return getLeading() + getAscent() + getDescent();
223 }
224
225 /**
226 * Determines the maximum ascent of the {@code Font}
227 * described by this {@code FontMetrics} object. No character
228 * extends further above the font's baseline than this height.
229 * @return the maximum ascent of any character in the
230 * {@code Font}.
231 * @see #getAscent()
232 */
233 public int getMaxAscent() {
234 return getAscent();
235 }
236
237 /**
238 * Determines the maximum descent of the {@code Font}
239 * described by this {@code FontMetrics} object. No character
240 * extends further below the font's baseline than this height.
241 * @return the maximum descent of any character in the
242 * {@code Font}.
243 * @see #getDescent()
244 */
245 public int getMaxDescent() {
246 return getDescent();
247 }
248
249 /**
250 * For backward compatibility only.
251 * @return the maximum descent of any character in the
252 * {@code Font}.
253 * @see #getMaxDescent()
254 * @deprecated As of JDK version 1.1.1,
255 * replaced by {@code getMaxDescent()}.
256 */
257 @Deprecated
258 public int getMaxDecent() {
259 return getMaxDescent();
260 }
261
262 /**
263 * Gets the maximum advance width of any character in this
264 * {@code Font}. The advance is the
265 * distance from the leftmost point to the rightmost point on the
266 * string's baseline. The advance of a {@code String} is
267 * not necessarily the sum of the advances of its characters.
268 * @return the maximum advance width of any character
269 * in the {@code Font}, or {@code -1} if the
270 * maximum advance width is not known.
271 */
272 public int getMaxAdvance() {
273 return -1;
274 }
275
276 /**
277 * Returns the advance width of the specified character in this
278 * {@code Font}. The advance is the
279 * distance from the leftmost point to the rightmost point on the
280 * character's baseline. Note that the advance of a
281 * {@code String} is not necessarily the sum of the advances
282 * of its characters.
283 *
284 * <p>This method doesn't validate the specified character to be a
285 * valid Unicode code point. The caller must validate the
286 * character value using {@link
287 * java.lang.Character#isValidCodePoint(int)
288 * Character.isValidCodePoint} if necessary.
289 *
290 * @param codePoint the character (Unicode code point) to be measured
291 * @return the advance width of the specified character
292 * in the {@code Font} described by this
293 * {@code FontMetrics} object.
294 * @see #charsWidth(char[], int, int)
295 * @see #stringWidth(String)
296 */
297 public int charWidth(int codePoint) {
298 if (!Character.isValidCodePoint(codePoint)) {
299 codePoint = 0xffff; // substitute missing glyph width
300 }
301
302 if (codePoint < 256) {
303 return getWidths()[codePoint];
304 } else {
305 char[] buffer = new char[2];
306 int len = Character.toChars(codePoint, buffer, 0);
307 return charsWidth(buffer, 0, len);
308 }
309 }
310
311 /**
312 * Returns the advance width of the specified character in this
313 * {@code Font}. The advance is the
314 * distance from the leftmost point to the rightmost point on the
315 * character's baseline. Note that the advance of a
316 * {@code String} is not necessarily the sum of the advances
317 * of its characters.
318 *
319 * <p><b>Note:</b> This method cannot handle <a
320 * href="../../../java.base/java/lang/Character.html#supplementary">
321 * supplementary characters</a>.
322 * To support all Unicode characters, including
323 * supplementary characters, use the {@link #charWidth(int)} method.
324 *
325 * @param ch the character to be measured
326 * @return the advance width of the specified character
327 * in the {@code Font} described by this
328 * {@code FontMetrics} object.
329 * @see #charsWidth(char[], int, int)
330 * @see #stringWidth(String)
331 */
332 public int charWidth(char ch) {
333 if (ch < 256) {
334 return getWidths()[ch];
335 }
336 char[] data = {ch};
337 return charsWidth(data, 0, 1);
338 }
339
340 /**
341 * Returns the total advance width for showing the specified
342 * {@code String} in this {@code Font}. The advance
343 * is the distance from the leftmost point to the rightmost point
344 * on the string's baseline.
345 * <p>
346 * Note that the advance of a {@code String} is
347 * not necessarily the sum of the advances of its characters.
348 * @param str the {@code String} to be measured
349 * @return the advance width of the specified {@code String}
350 * in the {@code Font} described by this
351 * {@code FontMetrics}.
352 * @throws NullPointerException if str is null.
353 * @see #bytesWidth(byte[], int, int)
354 * @see #charsWidth(char[], int, int)
355 * @see #getStringBounds(String, Graphics)
356 */
357 public int stringWidth(String str) {
358 int len = str.length();
359 char[] data = new char[len];
360 str.getChars(0, len, data, 0);
361 return charsWidth(data, 0, len);
362 }
363
364 /**
365 * Returns the total advance width for showing the specified array
366 * of characters in this {@code Font}. The advance is the
367 * distance from the leftmost point to the rightmost point on the
368 * string's baseline. The advance of a {@code String}
369 * is not necessarily the sum of the advances of its characters.
370 * This is equivalent to measuring a {@code String} of the
371 * characters in the specified range.
372 * @param data the array of characters to be measured
373 * @param off the start offset of the characters in the array
374 * @param len the number of characters to be measured from the array
375 * @return the advance width of the subarray of the specified
376 * {@code char} array in the font described by
377 * this {@code FontMetrics} object.
378 * @throws NullPointerException if {@code data} is null.
379 * @throws IndexOutOfBoundsException if the {@code off}
380 * and {@code len} arguments index characters outside
381 * the bounds of the {@code data} array.
382 * @see #charWidth(int)
383 * @see #charWidth(char)
384 * @see #bytesWidth(byte[], int, int)
385 * @see #stringWidth(String)
386 */
387 public int charsWidth(char[] data, int off, int len) {
388 return stringWidth(new String(data, off, len));
389 }
390
391 /**
392 * Returns the total advance width for showing the specified array
393 * of bytes in this {@code Font}. The advance is the
394 * distance from the leftmost point to the rightmost point on the
395 * string's baseline. The advance of a {@code String}
396 * is not necessarily the sum of the advances of its characters.
397 * This is equivalent to measuring a {@code String} of the
398 * characters in the specified range.
399 * @param data the array of bytes to be measured
400 * @param off the start offset of the bytes in the array
401 * @param len the number of bytes to be measured from the array
402 * @return the advance width of the subarray of the specified
403 * {@code byte} array in the {@code Font}
404 * described by
405 * this {@code FontMetrics} object.
406 * @throws NullPointerException if {@code data} is null.
407 * @throws IndexOutOfBoundsException if the {@code off}
408 * and {@code len} arguments index bytes outside
409 * the bounds of the {@code data} array.
410 * @see #charsWidth(char[], int, int)
411 * @see #stringWidth(String)
412 */
413 @SuppressWarnings("deprecation")
414 public int bytesWidth(byte[] data, int off, int len) {
415 return stringWidth(new String(data, 0, off, len));
416 }
417
418 /**
419 * Gets the advance widths of the first 256 characters in the
420 * {@code Font}. The advance is the
421 * distance from the leftmost point to the rightmost point on the
422 * character's baseline. Note that the advance of a
423 * {@code String} is not necessarily the sum of the advances
424 * of its characters.
425 * @return an array storing the advance widths of the
426 * characters in the {@code Font}
427 * described by this {@code FontMetrics} object.
428 */
429 public int[] getWidths() {
430 int[] widths = new int[256];
431 for (char ch = 0 ; ch < 256 ; ch++) {
432 widths[ch] = charWidth(ch);
433 }
434 return widths;
435 }
436
437 /**
438 * Checks to see if the {@code Font} has uniform line metrics. A
439 * composite font may consist of several different fonts to cover
440 * various character sets. In such cases, the
441 * {@code FontLineMetrics} objects are not uniform.
442 * Different fonts may have a different ascent, descent, metrics and
443 * so on. This information is sometimes necessary for line
444 * measuring and line breaking.
445 * @return {@code true} if the font has uniform line metrics;
446 * {@code false} otherwise.
447 * @see java.awt.Font#hasUniformLineMetrics()
448 */
449 public boolean hasUniformLineMetrics() {
450 return font.hasUniformLineMetrics();
451 }
452
453 /**
454 * Returns the {@link LineMetrics} object for the specified
455 * {@code String} in the specified {@link Graphics} context.
456 * @param str the specified {@code String}
457 * @param context the specified {@code Graphics} context
458 * @return a {@code LineMetrics} object created with the
459 * specified {@code String} and {@code Graphics} context.
460 * @see java.awt.Font#getLineMetrics(String, FontRenderContext)
461 */
462 public LineMetrics getLineMetrics( String str, Graphics context) {
463 return font.getLineMetrics(str, myFRC(context));
464 }
465
466 /**
467 * Returns the {@link LineMetrics} object for the specified
468 * {@code String} in the specified {@link Graphics} context.
469 * @param str the specified {@code String}
470 * @param beginIndex the initial offset of {@code str}
471 * @param limit the end offset of {@code str}
472 * @param context the specified {@code Graphics} context
473 * @return a {@code LineMetrics} object created with the
474 * specified {@code String} and {@code Graphics} context.
475 * @see java.awt.Font#getLineMetrics(String, int, int, FontRenderContext)
476 */
477 public LineMetrics getLineMetrics( String str,
478 int beginIndex, int limit,
479 Graphics context) {
480 return font.getLineMetrics(str, beginIndex, limit, myFRC(context));
481 }
482
483 /**
484 * Returns the {@link LineMetrics} object for the specified
485 * character array in the specified {@link Graphics} context.
486 * @param chars the specified character array
487 * @param beginIndex the initial offset of {@code chars}
488 * @param limit the end offset of {@code chars}
489 * @param context the specified {@code Graphics} context
490 * @return a {@code LineMetrics} object created with the
491 * specified character array and {@code Graphics} context.
492 * @see java.awt.Font#getLineMetrics(char[], int, int, FontRenderContext)
493 */
494 public LineMetrics getLineMetrics(char [] chars,
495 int beginIndex, int limit,
496 Graphics context) {
497 return font.getLineMetrics(
498 chars, beginIndex, limit, myFRC(context));
499 }
500
501 /**
502 * Returns the {@link LineMetrics} object for the specified
503 * {@link CharacterIterator} in the specified {@link Graphics}
504 * context.
505 * @param ci the specified {@code CharacterIterator}
506 * @param beginIndex the initial offset in {@code ci}
507 * @param limit the end index of {@code ci}
508 * @param context the specified {@code Graphics} context
509 * @return a {@code LineMetrics} object created with the
510 * specified arguments.
511 * @see java.awt.Font#getLineMetrics(CharacterIterator, int, int, FontRenderContext)
512 */
513 public LineMetrics getLineMetrics(CharacterIterator ci,
514 int beginIndex, int limit,
515 Graphics context) {
516 return font.getLineMetrics(ci, beginIndex, limit, myFRC(context));
517 }
518
519 /**
520 * Returns the bounds of the specified {@code String} in the
521 * specified {@code Graphics} context. The bounds is used
522 * to layout the {@code String}.
523 * <p>Note: The returned bounds is in baseline-relative coordinates
524 * (see {@link java.awt.FontMetrics class notes}).
525 * @param str the specified {@code String}
526 * @param context the specified {@code Graphics} context
527 * @return a {@link Rectangle2D} that is the bounding box of the
528 * specified {@code String} in the specified
529 * {@code Graphics} context.
530 * @see java.awt.Font#getStringBounds(String, FontRenderContext)
531 */
532 public Rectangle2D getStringBounds( String str, Graphics context) {
533 return font.getStringBounds(str, myFRC(context));
534 }
535
536 /**
537 * Returns the bounds of the specified {@code String} in the
538 * specified {@code Graphics} context. The bounds is used
539 * to layout the {@code String}.
540 * <p>Note: The returned bounds is in baseline-relative coordinates
541 * (see {@link java.awt.FontMetrics class notes}).
542 * @param str the specified {@code String}
543 * @param beginIndex the offset of the beginning of {@code str}
544 * @param limit the end offset of {@code str}
545 * @param context the specified {@code Graphics} context
546 * @return a {@code Rectangle2D} that is the bounding box of the
547 * specified {@code String} in the specified
548 * {@code Graphics} context.
549 * @see java.awt.Font#getStringBounds(String, int, int, FontRenderContext)
550 */
551 public Rectangle2D getStringBounds( String str,
552 int beginIndex, int limit,
553 Graphics context) {
554 return font.getStringBounds(str, beginIndex, limit,
555 myFRC(context));
556 }
557
558 /**
559 * Returns the bounds of the specified array of characters
560 * in the specified {@code Graphics} context.
561 * The bounds is used to layout the {@code String}
562 * created with the specified array of characters,
563 * {@code beginIndex} and {@code limit}.
564 * <p>Note: The returned bounds is in baseline-relative coordinates
565 * (see {@link java.awt.FontMetrics class notes}).
566 * @param chars an array of characters
567 * @param beginIndex the initial offset of the array of
568 * characters
569 * @param limit the end offset of the array of characters
570 * @param context the specified {@code Graphics} context
571 * @return a {@code Rectangle2D} that is the bounding box of the
572 * specified character array in the specified
573 * {@code Graphics} context.
574 * @see java.awt.Font#getStringBounds(char[], int, int, FontRenderContext)
575 */
576 public Rectangle2D getStringBounds( char [] chars,
577 int beginIndex, int limit,
578 Graphics context) {
579 return font.getStringBounds(chars, beginIndex, limit,
580 myFRC(context));
581 }
582
583 /**
584 * Returns the bounds of the characters indexed in the specified
585 * {@code CharacterIterator} in the
586 * specified {@code Graphics} context.
587 * <p>Note: The returned bounds is in baseline-relative coordinates
588 * (see {@link java.awt.FontMetrics class notes}).
589 * @param ci the specified {@code CharacterIterator}
590 * @param beginIndex the initial offset in {@code ci}
591 * @param limit the end index of {@code ci}
592 * @param context the specified {@code Graphics} context
593 * @return a {@code Rectangle2D} that is the bounding box of the
594 * characters indexed in the specified {@code CharacterIterator}
595 * in the specified {@code Graphics} context.
596 * @see java.awt.Font#getStringBounds(CharacterIterator, int, int, FontRenderContext)
597 */
598 public Rectangle2D getStringBounds(CharacterIterator ci,
599 int beginIndex, int limit,
600 Graphics context) {
601 return font.getStringBounds(ci, beginIndex, limit,
602 myFRC(context));
603 }
604
605 /**
606 * Returns the bounds for the character with the maximum bounds
607 * in the specified {@code Graphics} context.
608 * @param context the specified {@code Graphics} context
609 * @return a {@code Rectangle2D} that is the
610 * bounding box for the character with the maximum bounds.
611 * @see java.awt.Font#getMaxCharBounds(FontRenderContext)
612 */
613 public Rectangle2D getMaxCharBounds(Graphics context) {
614 return font.getMaxCharBounds(myFRC(context));
615 }
616
617 private FontRenderContext myFRC(Graphics context) {
618 if (context instanceof Graphics2D) {
619 return ((Graphics2D)context).getFontRenderContext();
620 }
621 return DEFAULT_FRC;
622 }
623
624
625 /**
626 * Returns a representation of this {@code FontMetrics}
627 * object's values as a {@code String}.
628 * @return a {@code String} representation of this
629 * {@code FontMetrics} object.
630 */
631 public String toString() {
632 return getClass().getName() +
633 "[font=" + getFont() +
634 "ascent=" + getAscent() +
635 ", descent=" + getDescent() +
636 ", height=" + getHeight() + "]";
637 }
638
639 /**
640 * Initialize JNI field and method IDs
641 */
642 private static native void initIDs();
643 }