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 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 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="../lang/Character.html#supplementary"> supplementary 321 * characters</a>. To support all Unicode characters, including 322 * supplementary characters, use the {@link #charWidth(int)} method. 323 * 324 * @param ch the character to be measured 325 * @return the advance width of the specified character 326 * in the {@code Font} described by this 327 * {@code FontMetrics} object. 328 * @see #charsWidth(char[], int, int) 329 * @see #stringWidth(String) 330 */ 331 public int charWidth(char ch) { 332 if (ch < 256) { 333 return getWidths()[ch]; 334 } 335 char[] data = {ch}; 336 return charsWidth(data, 0, 1); 337 } 338 339 /** 340 * Returns the total advance width for showing the specified 341 * {@code String} in this {@code Font}. The advance 342 * is the distance from the leftmost point to the rightmost point 343 * on the string's baseline. 344 * <p> 345 * Note that the advance of a {@code String} is 346 * not necessarily the sum of the advances of its characters. 347 * @param str the {@code String} to be measured 348 * @return the advance width of the specified {@code String} 349 * in the {@code Font} described by this 350 * {@code FontMetrics}. 351 * @throws NullPointerException if str is null. 352 * @see #bytesWidth(byte[], int, int) 353 * @see #charsWidth(char[], int, int) 354 * @see #getStringBounds(String, Graphics) 355 */ 356 public int stringWidth(String str) { 357 int len = str.length(); 358 char[] data = new char[len]; 359 str.getChars(0, len, data, 0); 360 return charsWidth(data, 0, len); 361 } 362 363 /** 364 * Returns the total advance width for showing the specified array 365 * of characters in this {@code Font}. The advance is the 366 * distance from the leftmost point to the rightmost point on the 367 * string's baseline. The advance of a {@code String} 368 * is not necessarily the sum of the advances of its characters. 369 * This is equivalent to measuring a {@code String} of the 370 * characters in the specified range. 371 * @param data the array of characters to be measured 372 * @param off the start offset of the characters in the array 373 * @param len the number of characters to be measured from the array 374 * @return the advance width of the subarray of the specified 375 * {@code char} array in the font described by 376 * this {@code FontMetrics} object. 377 * @throws NullPointerException if {@code data} is null. 378 * @throws IndexOutOfBoundsException if the {@code off} 379 * and {@code len} arguments index characters outside 380 * the bounds of the {@code data} array. 381 * @see #charWidth(int) 382 * @see #charWidth(char) 383 * @see #bytesWidth(byte[], int, int) 384 * @see #stringWidth(String) 385 */ 386 public int charsWidth(char[] data, int off, int len) { 387 return stringWidth(new String(data, off, len)); 388 } 389 390 /** 391 * Returns the total advance width for showing the specified array 392 * of bytes in this {@code Font}. The advance is the 393 * distance from the leftmost point to the rightmost point on the 394 * string's baseline. The advance of a {@code String} 395 * is not necessarily the sum of the advances of its characters. 396 * This is equivalent to measuring a {@code String} of the 397 * characters in the specified range. 398 * @param data the array of bytes to be measured 399 * @param off the start offset of the bytes in the array 400 * @param len the number of bytes to be measured from the array 401 * @return the advance width of the subarray of the specified 402 * {@code byte} array in the {@code Font} 403 * described by 404 * this {@code FontMetrics} object. 405 * @throws NullPointerException if {@code data} is null. 406 * @throws IndexOutOfBoundsException if the {@code off} 407 * and {@code len} arguments index bytes outside 408 * the bounds of the {@code data} array. 409 * @see #charsWidth(char[], int, int) 410 * @see #stringWidth(String) 411 */ 412 @SuppressWarnings("deprecation") 413 public int bytesWidth(byte[] data, int off, int len) { 414 return stringWidth(new String(data, 0, off, len)); 415 } 416 417 /** 418 * Gets the advance widths of the first 256 characters in the 419 * {@code Font}. The advance is the 420 * distance from the leftmost point to the rightmost point on the 421 * character's baseline. Note that the advance of a 422 * {@code String} is not necessarily the sum of the advances 423 * of its characters. 424 * @return an array storing the advance widths of the 425 * characters in the {@code Font} 426 * described by this {@code FontMetrics} object. 427 */ 428 public int[] getWidths() { 429 int[] widths = new int[256]; 430 for (char ch = 0 ; ch < 256 ; ch++) { 431 widths[ch] = charWidth(ch); 432 } 433 return widths; 434 } 435 436 /** 437 * Checks to see if the {@code Font} has uniform line metrics. A 438 * composite font may consist of several different fonts to cover 439 * various character sets. In such cases, the 440 * {@code FontLineMetrics} objects are not uniform. 441 * Different fonts may have a different ascent, descent, metrics and 442 * so on. This information is sometimes necessary for line 443 * measuring and line breaking. 444 * @return {@code true} if the font has uniform line metrics; 445 * {@code false} otherwise. 446 * @see java.awt.Font#hasUniformLineMetrics() 447 */ 448 public boolean hasUniformLineMetrics() { 449 return font.hasUniformLineMetrics(); 450 } 451 452 /** 453 * Returns the {@link LineMetrics} object for the specified 454 * {@code String} in the specified {@link Graphics} context. 455 * @param str the specified {@code String} 456 * @param context the specified {@code Graphics} context 457 * @return a {@code LineMetrics} object created with the 458 * specified {@code String} and {@code Graphics} context. 459 * @see java.awt.Font#getLineMetrics(String, FontRenderContext) 460 */ 461 public LineMetrics getLineMetrics( String str, Graphics context) { 462 return font.getLineMetrics(str, myFRC(context)); 463 } 464 465 /** 466 * Returns the {@link LineMetrics} object for the specified 467 * {@code String} in the specified {@link Graphics} context. 468 * @param str the specified {@code String} 469 * @param beginIndex the initial offset of {@code str} 470 * @param limit the end offset of {@code str} 471 * @param context the specified {@code Graphics} context 472 * @return a {@code LineMetrics} object created with the 473 * specified {@code String} and {@code Graphics} context. 474 * @see java.awt.Font#getLineMetrics(String, int, int, FontRenderContext) 475 */ 476 public LineMetrics getLineMetrics( String str, 477 int beginIndex, int limit, 478 Graphics context) { 479 return font.getLineMetrics(str, beginIndex, limit, myFRC(context)); 480 } 481 482 /** 483 * Returns the {@link LineMetrics} object for the specified 484 * character array in the specified {@link Graphics} context. 485 * @param chars the specified character array 486 * @param beginIndex the initial offset of {@code chars} 487 * @param limit the end offset of {@code chars} 488 * @param context the specified {@code Graphics} context 489 * @return a {@code LineMetrics} object created with the 490 * specified character array and {@code Graphics} context. 491 * @see java.awt.Font#getLineMetrics(char[], int, int, FontRenderContext) 492 */ 493 public LineMetrics getLineMetrics(char [] chars, 494 int beginIndex, int limit, 495 Graphics context) { 496 return font.getLineMetrics( 497 chars, beginIndex, limit, myFRC(context)); 498 } 499 500 /** 501 * Returns the {@link LineMetrics} object for the specified 502 * {@link CharacterIterator} in the specified {@link Graphics} 503 * context. 504 * @param ci the specified {@code CharacterIterator} 505 * @param beginIndex the initial offset in {@code ci} 506 * @param limit the end index of {@code ci} 507 * @param context the specified {@code Graphics} context 508 * @return a {@code LineMetrics} object created with the 509 * specified arguments. 510 * @see java.awt.Font#getLineMetrics(CharacterIterator, int, int, FontRenderContext) 511 */ 512 public LineMetrics getLineMetrics(CharacterIterator ci, 513 int beginIndex, int limit, 514 Graphics context) { 515 return font.getLineMetrics(ci, beginIndex, limit, myFRC(context)); 516 } 517 518 /** 519 * Returns the bounds of the specified {@code String} in the 520 * specified {@code Graphics} context. The bounds is used 521 * to layout the {@code String}. 522 * <p>Note: The returned bounds is in baseline-relative coordinates 523 * (see {@link java.awt.FontMetrics class notes}). 524 * @param str the specified {@code String} 525 * @param context the specified {@code Graphics} context 526 * @return a {@link Rectangle2D} that is the bounding box of the 527 * specified {@code String} in the specified 528 * {@code Graphics} context. 529 * @see java.awt.Font#getStringBounds(String, FontRenderContext) 530 */ 531 public Rectangle2D getStringBounds( String str, Graphics context) { 532 return font.getStringBounds(str, myFRC(context)); 533 } 534 535 /** 536 * Returns the bounds of the specified {@code String} in the 537 * specified {@code Graphics} context. The bounds is used 538 * to layout the {@code String}. 539 * <p>Note: The returned bounds is in baseline-relative coordinates 540 * (see {@link java.awt.FontMetrics class notes}). 541 * @param str the specified {@code String} 542 * @param beginIndex the offset of the beginning of {@code str} 543 * @param limit the end offset of {@code str} 544 * @param context the specified {@code Graphics} context 545 * @return a {@code Rectangle2D} that is the bounding box of the 546 * specified {@code String} in the specified 547 * {@code Graphics} context. 548 * @see java.awt.Font#getStringBounds(String, int, int, FontRenderContext) 549 */ 550 public Rectangle2D getStringBounds( String str, 551 int beginIndex, int limit, 552 Graphics context) { 553 return font.getStringBounds(str, beginIndex, limit, 554 myFRC(context)); 555 } 556 557 /** 558 * Returns the bounds of the specified array of characters 559 * in the specified {@code Graphics} context. 560 * The bounds is used to layout the {@code String} 561 * created with the specified array of characters, 562 * {@code beginIndex} and {@code limit}. 563 * <p>Note: The returned bounds is in baseline-relative coordinates 564 * (see {@link java.awt.FontMetrics class notes}). 565 * @param chars an array of characters 566 * @param beginIndex the initial offset of the array of 567 * characters 568 * @param limit the end offset of the array of characters 569 * @param context the specified {@code Graphics} context 570 * @return a {@code Rectangle2D} that is the bounding box of the 571 * specified character array in the specified 572 * {@code Graphics} context. 573 * @see java.awt.Font#getStringBounds(char[], int, int, FontRenderContext) 574 */ 575 public Rectangle2D getStringBounds( char [] chars, 576 int beginIndex, int limit, 577 Graphics context) { 578 return font.getStringBounds(chars, beginIndex, limit, 579 myFRC(context)); 580 } 581 582 /** 583 * Returns the bounds of the characters indexed in the specified 584 * {@code CharacterIterator} in the 585 * specified {@code Graphics} context. 586 * <p>Note: The returned bounds is in baseline-relative coordinates 587 * (see {@link java.awt.FontMetrics class notes}). 588 * @param ci the specified {@code CharacterIterator} 589 * @param beginIndex the initial offset in {@code ci} 590 * @param limit the end index of {@code ci} 591 * @param context the specified {@code Graphics} context 592 * @return a {@code Rectangle2D} that is the bounding box of the 593 * characters indexed in the specified {@code CharacterIterator} 594 * in the specified {@code Graphics} context. 595 * @see java.awt.Font#getStringBounds(CharacterIterator, int, int, FontRenderContext) 596 */ 597 public Rectangle2D getStringBounds(CharacterIterator ci, 598 int beginIndex, int limit, 599 Graphics context) { 600 return font.getStringBounds(ci, beginIndex, limit, 601 myFRC(context)); 602 } 603 604 /** 605 * Returns the bounds for the character with the maximum bounds 606 * in the specified {@code Graphics} context. 607 * @param context the specified {@code Graphics} context 608 * @return a {@code Rectangle2D} that is the 609 * bounding box for the character with the maximum bounds. 610 * @see java.awt.Font#getMaxCharBounds(FontRenderContext) 611 */ 612 public Rectangle2D getMaxCharBounds(Graphics context) { 613 return font.getMaxCharBounds(myFRC(context)); 614 } 615 616 private FontRenderContext myFRC(Graphics context) { 617 if (context instanceof Graphics2D) { 618 return ((Graphics2D)context).getFontRenderContext(); 619 } 620 return DEFAULT_FRC; 621 } 622 623 624 /** 625 * Returns a representation of this {@code FontMetrics} 626 * object's values as a {@code String}. 627 * @return a {@code String} representation of this 628 * {@code FontMetrics} object. 629 */ 630 public String toString() { 631 return getClass().getName() + 632 "[font=" + getFont() + 633 "ascent=" + getAscent() + 634 ", descent=" + getDescent() + 635 ", height=" + getHeight() + "]"; 636 } 637 638 /** 639 * Initialize JNI field and method IDs 640 */ 641 private static native void initIDs(); 642 }