1 /* 2 * Copyright (c) 1997, 2010, 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.image.ColorModel; 29 import sun.java2d.SunCompositeContext; 30 31 /** 32 * The <code>AlphaComposite</code> class implements basic alpha 33 * compositing rules for combining source and destination colors 34 * to achieve blending and transparency effects with graphics and 35 * images. 36 * The specific rules implemented by this class are the basic set 37 * of 12 rules described in 38 * T. Porter and T. Duff, "Compositing Digital Images", SIGGRAPH 84, 39 * 253-259. 40 * The rest of this documentation assumes some familiarity with the 41 * definitions and concepts outlined in that paper. 42 * 43 * <p> 44 * This class extends the standard equations defined by Porter and 45 * Duff to include one additional factor. 46 * An instance of the <code>AlphaComposite</code> class can contain 47 * an alpha value that is used to modify the opacity or coverage of 48 * every source pixel before it is used in the blending equations. 49 * 50 * <p> 51 * It is important to note that the equations defined by the Porter 52 * and Duff paper are all defined to operate on color components 53 * that are premultiplied by their corresponding alpha components. 54 * Since the <code>ColorModel</code> and <code>Raster</code> classes 55 * allow the storage of pixel data in either premultiplied or 56 * non-premultiplied form, all input data must be normalized into 57 * premultiplied form before applying the equations and all results 58 * might need to be adjusted back to the form required by the destination 59 * before the pixel values are stored. 60 * 61 * <p> 62 * Also note that this class defines only the equations 63 * for combining color and alpha values in a purely mathematical 64 * sense. The accurate application of its equations depends 65 * on the way the data is retrieved from its sources and stored 66 * in its destinations. 67 * See <a href="#caveats">Implementation Caveats</a> 68 * for further information. 69 * 70 * <p> 71 * The following factors are used in the description of the blending 72 * equation in the Porter and Duff paper: 73 * 74 * <blockquote> 75 * <table summary="layout"> 76 * <tr><th align=left>Factor <th align=left>Definition 77 * <tr><td><em>A<sub>s</sub></em><td>the alpha component of the source pixel 78 * <tr><td><em>C<sub>s</sub></em><td>a color component of the source pixel in premultiplied form 79 * <tr><td><em>A<sub>d</sub></em><td>the alpha component of the destination pixel 80 * <tr><td><em>C<sub>d</sub></em><td>a color component of the destination pixel in premultiplied form 81 * <tr><td><em>F<sub>s</sub></em><td>the fraction of the source pixel that contributes to the output 82 * <tr><td><em>F<sub>d</sub></em><td>the fraction of the destination pixel that contributes 83 * to the output 84 * <tr><td><em>A<sub>r</sub></em><td>the alpha component of the result 85 * <tr><td><em>C<sub>r</sub></em><td>a color component of the result in premultiplied form 86 * </table> 87 * </blockquote> 88 * 89 * <p> 90 * Using these factors, Porter and Duff define 12 ways of choosing 91 * the blending factors <em>F<sub>s</sub></em> and <em>F<sub>d</sub></em> to 92 * produce each of 12 desirable visual effects. 93 * The equations for determining <em>F<sub>s</sub></em> and <em>F<sub>d</sub></em> 94 * are given in the descriptions of the 12 static fields 95 * that specify visual effects. 96 * For example, 97 * the description for 98 * <a href="#SRC_OVER"><code>SRC_OVER</code></a> 99 * specifies that <em>F<sub>s</sub></em> = 1 and <em>F<sub>d</sub></em> = (1-<em>A<sub>s</sub></em>). 100 * Once a set of equations for determining the blending factors is 101 * known they can then be applied to each pixel to produce a result 102 * using the following set of equations: 103 * 104 * <pre> 105 * <em>F<sub>s</sub></em> = <em>f</em>(<em>A<sub>d</sub></em>) 106 * <em>F<sub>d</sub></em> = <em>f</em>(<em>A<sub>s</sub></em>) 107 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>*<em>F<sub>s</sub></em> + <em>A<sub>d</sub></em>*<em>F<sub>d</sub></em> 108 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>*<em>F<sub>s</sub></em> + <em>C<sub>d</sub></em>*<em>F<sub>d</sub></em></pre> 109 * 110 * <p> 111 * The following factors will be used to discuss our extensions to 112 * the blending equation in the Porter and Duff paper: 113 * 114 * <blockquote> 115 * <table summary="layout"> 116 * <tr><th align=left>Factor <th align=left>Definition 117 * <tr><td><em>C<sub>sr</sub></em> <td>one of the raw color components of the source pixel 118 * <tr><td><em>C<sub>dr</sub></em> <td>one of the raw color components of the destination pixel 119 * <tr><td><em>A<sub>ac</sub></em> <td>the "extra" alpha component from the AlphaComposite instance 120 * <tr><td><em>A<sub>sr</sub></em> <td>the raw alpha component of the source pixel 121 * <tr><td><em>A<sub>dr</sub></em><td>the raw alpha component of the destination pixel 122 * <tr><td><em>A<sub>df</sub></em> <td>the final alpha component stored in the destination 123 * <tr><td><em>C<sub>df</sub></em> <td>the final raw color component stored in the destination 124 * </table> 125 *</blockquote> 126 * 127 * <h3>Preparing Inputs</h3> 128 * 129 * <p> 130 * The <code>AlphaComposite</code> class defines an additional alpha 131 * value that is applied to the source alpha. 132 * This value is applied as if an implicit SRC_IN rule were first 133 * applied to the source pixel against a pixel with the indicated 134 * alpha by multiplying both the raw source alpha and the raw 135 * source colors by the alpha in the <code>AlphaComposite</code>. 136 * This leads to the following equation for producing the alpha 137 * used in the Porter and Duff blending equation: 138 * 139 * <pre> 140 * <em>A<sub>s</sub></em> = <em>A<sub>sr</sub></em> * <em>A<sub>ac</sub></em> </pre> 141 * 142 * All of the raw source color components need to be multiplied 143 * by the alpha in the <code>AlphaComposite</code> instance. 144 * Additionally, if the source was not in premultiplied form 145 * then the color components also need to be multiplied by the 146 * source alpha. 147 * Thus, the equation for producing the source color components 148 * for the Porter and Duff equation depends on whether the source 149 * pixels are premultiplied or not: 150 * 151 * <pre> 152 * <em>C<sub>s</sub></em> = <em>C<sub>sr</sub></em> * <em>A<sub>sr</sub></em> * <em>A<sub>ac</sub></em> (if source is not premultiplied) 153 * <em>C<sub>s</sub></em> = <em>C<sub>sr</sub></em> * <em>A<sub>ac</sub></em> (if source is premultiplied) </pre> 154 * 155 * No adjustment needs to be made to the destination alpha: 156 * 157 * <pre> 158 * <em>A<sub>d</sub></em> = <em>A<sub>dr</sub></em> </pre> 159 * 160 * <p> 161 * The destination color components need to be adjusted only if 162 * they are not in premultiplied form: 163 * 164 * <pre> 165 * <em>C<sub>d</sub></em> = <em>C<sub>dr</sub></em> * <em>A<sub>d</sub></em> (if destination is not premultiplied) 166 * <em>C<sub>d</sub></em> = <em>C<sub>dr</sub></em> (if destination is premultiplied) </pre> 167 * 168 * <h3>Applying the Blending Equation</h3> 169 * 170 * <p> 171 * The adjusted <em>A<sub>s</sub></em>, <em>A<sub>d</sub></em>, 172 * <em>C<sub>s</sub></em>, and <em>C<sub>d</sub></em> are used in the standard 173 * Porter and Duff equations to calculate the blending factors 174 * <em>F<sub>s</sub></em> and <em>F<sub>d</sub></em> and then the resulting 175 * premultiplied components <em>A<sub>r</sub></em> and <em>C<sub>r</sub></em>. 176 * 177 * <p> 178 * <h3>Preparing Results</h3> 179 * 180 * <p> 181 * The results only need to be adjusted if they are to be stored 182 * back into a destination buffer that holds data that is not 183 * premultiplied, using the following equations: 184 * 185 * <pre> 186 * <em>A<sub>df</sub></em> = <em>A<sub>r</sub></em> 187 * <em>C<sub>df</sub></em> = <em>C<sub>r</sub></em> (if dest is premultiplied) 188 * <em>C<sub>df</sub></em> = <em>C<sub>r</sub></em> / <em>A<sub>r</sub></em> (if dest is not premultiplied) </pre> 189 * 190 * Note that since the division is undefined if the resulting alpha 191 * is zero, the division in that case is omitted to avoid the "divide 192 * by zero" and the color components are left as 193 * all zeros. 194 * 195 * <p> 196 * <h3>Performance Considerations</h3> 197 * 198 * <p> 199 * For performance reasons, it is preferrable that 200 * <code>Raster</code> objects passed to the <code>compose</code> 201 * method of a {@link CompositeContext} object created by the 202 * <code>AlphaComposite</code> class have premultiplied data. 203 * If either the source <code>Raster</code> 204 * or the destination <code>Raster</code> 205 * is not premultiplied, however, 206 * appropriate conversions are performed before and after the compositing 207 * operation. 208 * 209 * <h3><a name="caveats">Implementation Caveats</a></h3> 210 * 211 * <ul> 212 * <li> 213 * Many sources, such as some of the opaque image types listed 214 * in the <code>BufferedImage</code> class, do not store alpha values 215 * for their pixels. Such sources supply an alpha of 1.0 for 216 * all of their pixels. 217 * 218 * <p> 219 * <li> 220 * Many destinations also have no place to store the alpha values 221 * that result from the blending calculations performed by this class. 222 * Such destinations thus implicitly discard the resulting 223 * alpha values that this class produces. 224 * It is recommended that such destinations should treat their stored 225 * color values as non-premultiplied and divide the resulting color 226 * values by the resulting alpha value before storing the color 227 * values and discarding the alpha value. 228 * 229 * <p> 230 * <li> 231 * The accuracy of the results depends on the manner in which pixels 232 * are stored in the destination. 233 * An image format that provides at least 8 bits of storage per color 234 * and alpha component is at least adequate for use as a destination 235 * for a sequence of a few to a dozen compositing operations. 236 * An image format with fewer than 8 bits of storage per component 237 * is of limited use for just one or two compositing operations 238 * before the rounding errors dominate the results. 239 * An image format 240 * that does not separately store 241 * color components is not a 242 * good candidate for any type of translucent blending. 243 * For example, <code>BufferedImage.TYPE_BYTE_INDEXED</code> 244 * should not be used as a destination for a blending operation 245 * because every operation 246 * can introduce large errors, due to 247 * the need to choose a pixel from a limited palette to match the 248 * results of the blending equations. 249 * 250 * <p> 251 * <li> 252 * Nearly all formats store pixels as discrete integers rather than 253 * the floating point values used in the reference equations above. 254 * The implementation can either scale the integer pixel 255 * values into floating point values in the range 0.0 to 1.0 or 256 * use slightly modified versions of the equations 257 * that operate entirely in the integer domain and yet produce 258 * analogous results to the reference equations. 259 * 260 * <p> 261 * Typically the integer values are related to the floating point 262 * values in such a way that the integer 0 is equated 263 * to the floating point value 0.0 and the integer 264 * 2^<em>n</em>-1 (where <em>n</em> is the number of bits 265 * in the representation) is equated to 1.0. 266 * For 8-bit representations, this means that 0x00 267 * represents 0.0 and 0xff represents 268 * 1.0. 269 * 270 * <p> 271 * <li> 272 * The internal implementation can approximate some of the equations 273 * and it can also eliminate some steps to avoid unnecessary operations. 274 * For example, consider a discrete integer image with non-premultiplied 275 * alpha values that uses 8 bits per component for storage. 276 * The stored values for a 277 * nearly transparent darkened red might be: 278 * 279 * <pre> 280 * (A, R, G, B) = (0x01, 0xb0, 0x00, 0x00)</pre> 281 * 282 * <p> 283 * If integer math were being used and this value were being 284 * composited in 285 * <a href="#SRC"><code>SRC</code></a> 286 * mode with no extra alpha, then the math would 287 * indicate that the results were (in integer format): 288 * 289 * <pre> 290 * (A, R, G, B) = (0x01, 0x01, 0x00, 0x00)</pre> 291 * 292 * <p> 293 * Note that the intermediate values, which are always in premultiplied 294 * form, would only allow the integer red component to be either 0x00 295 * or 0x01. When we try to store this result back into a destination 296 * that is not premultiplied, dividing out the alpha will give us 297 * very few choices for the non-premultiplied red value. 298 * In this case an implementation that performs the math in integer 299 * space without shortcuts is likely to end up with the final pixel 300 * values of: 301 * 302 * <pre> 303 * (A, R, G, B) = (0x01, 0xff, 0x00, 0x00)</pre> 304 * 305 * <p> 306 * (Note that 0x01 divided by 0x01 gives you 1.0, which is equivalent 307 * to the value 0xff in an 8-bit storage format.) 308 * 309 * <p> 310 * Alternately, an implementation that uses floating point math 311 * might produce more accurate results and end up returning to the 312 * original pixel value with little, if any, roundoff error. 313 * Or, an implementation using integer math might decide that since 314 * the equations boil down to a virtual NOP on the color values 315 * if performed in a floating point space, it can transfer the 316 * pixel untouched to the destination and avoid all the math entirely. 317 * 318 * <p> 319 * These implementations all attempt to honor the 320 * same equations, but use different tradeoffs of integer and 321 * floating point math and reduced or full equations. 322 * To account for such differences, it is probably best to 323 * expect only that the premultiplied form of the results to 324 * match between implementations and image formats. In this 325 * case both answers, expressed in premultiplied form would 326 * equate to: 327 * 328 * <pre> 329 * (A, R, G, B) = (0x01, 0x01, 0x00, 0x00)</pre> 330 * 331 * <p> 332 * and thus they would all match. 333 * 334 * <p> 335 * <li> 336 * Because of the technique of simplifying the equations for 337 * calculation efficiency, some implementations might perform 338 * differently when encountering result alpha values of 0.0 339 * on a non-premultiplied destination. 340 * Note that the simplification of removing the divide by alpha 341 * in the case of the SRC rule is technically not valid if the 342 * denominator (alpha) is 0. 343 * But, since the results should only be expected to be accurate 344 * when viewed in premultiplied form, a resulting alpha of 0 345 * essentially renders the resulting color components irrelevant 346 * and so exact behavior in this case should not be expected. 347 * </ul> 348 * @see Composite 349 * @see CompositeContext 350 */ 351 352 public final class AlphaComposite implements Composite { 353 /** 354 * Both the color and the alpha of the destination are cleared 355 * (Porter-Duff Clear rule). 356 * Neither the source nor the destination is used as input. 357 *<p> 358 * <em>F<sub>s</sub></em> = 0 and <em>F<sub>d</sub></em> = 0, thus: 359 *<pre> 360 * <em>A<sub>r</sub></em> = 0 361 * <em>C<sub>r</sub></em> = 0 362 *</pre> 363 */ 364 public static final int CLEAR = 1; 365 366 /** 367 * The source is copied to the destination 368 * (Porter-Duff Source rule). 369 * The destination is not used as input. 370 *<p> 371 * <em>F<sub>s</sub></em> = 1 and <em>F<sub>d</sub></em> = 0, thus: 372 *<pre> 373 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em> 374 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em> 375 *</pre> 376 */ 377 public static final int SRC = 2; 378 379 /** 380 * The destination is left untouched 381 * (Porter-Duff Destination rule). 382 *<p> 383 * <em>F<sub>s</sub></em> = 0 and <em>F<sub>d</sub></em> = 1, thus: 384 *<pre> 385 * <em>A<sub>r</sub></em> = <em>A<sub>d</sub></em> 386 * <em>C<sub>r</sub></em> = <em>C<sub>d</sub></em> 387 *</pre> 388 * @since 1.4 389 */ 390 public static final int DST = 9; 391 // Note that DST was added in 1.4 so it is numbered out of order... 392 393 /** 394 * The source is composited over the destination 395 * (Porter-Duff Source Over Destination rule). 396 *<p> 397 * <em>F<sub>s</sub></em> = 1 and <em>F<sub>d</sub></em> = (1-<em>A<sub>s</sub></em>), thus: 398 *<pre> 399 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em> + <em>A<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>) 400 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em> + <em>C<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>) 401 *</pre> 402 */ 403 public static final int SRC_OVER = 3; 404 405 /** 406 * The destination is composited over the source and 407 * the result replaces the destination 408 * (Porter-Duff Destination Over Source rule). 409 *<p> 410 * <em>F<sub>s</sub></em> = (1-<em>A<sub>d</sub></em>) and <em>F<sub>d</sub></em> = 1, thus: 411 *<pre> 412 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>) + <em>A<sub>d</sub></em> 413 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>) + <em>C<sub>d</sub></em> 414 *</pre> 415 */ 416 public static final int DST_OVER = 4; 417 418 /** 419 * The part of the source lying inside of the destination replaces 420 * the destination 421 * (Porter-Duff Source In Destination rule). 422 *<p> 423 * <em>F<sub>s</sub></em> = <em>A<sub>d</sub></em> and <em>F<sub>d</sub></em> = 0, thus: 424 *<pre> 425 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>*<em>A<sub>d</sub></em> 426 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>*<em>A<sub>d</sub></em> 427 *</pre> 428 */ 429 public static final int SRC_IN = 5; 430 431 /** 432 * The part of the destination lying inside of the source 433 * replaces the destination 434 * (Porter-Duff Destination In Source rule). 435 *<p> 436 * <em>F<sub>s</sub></em> = 0 and <em>F<sub>d</sub></em> = <em>A<sub>s</sub></em>, thus: 437 *<pre> 438 * <em>A<sub>r</sub></em> = <em>A<sub>d</sub></em>*<em>A<sub>s</sub></em> 439 * <em>C<sub>r</sub></em> = <em>C<sub>d</sub></em>*<em>A<sub>s</sub></em> 440 *</pre> 441 */ 442 public static final int DST_IN = 6; 443 444 /** 445 * The part of the source lying outside of the destination 446 * replaces the destination 447 * (Porter-Duff Source Held Out By Destination rule). 448 *<p> 449 * <em>F<sub>s</sub></em> = (1-<em>A<sub>d</sub></em>) and <em>F<sub>d</sub></em> = 0, thus: 450 *<pre> 451 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>) 452 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>) 453 *</pre> 454 */ 455 public static final int SRC_OUT = 7; 456 457 /** 458 * The part of the destination lying outside of the source 459 * replaces the destination 460 * (Porter-Duff Destination Held Out By Source rule). 461 *<p> 462 * <em>F<sub>s</sub></em> = 0 and <em>F<sub>d</sub></em> = (1-<em>A<sub>s</sub></em>), thus: 463 *<pre> 464 * <em>A<sub>r</sub></em> = <em>A<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>) 465 * <em>C<sub>r</sub></em> = <em>C<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>) 466 *</pre> 467 */ 468 public static final int DST_OUT = 8; 469 470 // Rule 9 is DST which is defined above where it fits into the 471 // list logically, rather than numerically 472 // 473 // public static final int DST = 9; 474 475 /** 476 * The part of the source lying inside of the destination 477 * is composited onto the destination 478 * (Porter-Duff Source Atop Destination rule). 479 *<p> 480 * <em>F<sub>s</sub></em> = <em>A<sub>d</sub></em> and <em>F<sub>d</sub></em> = (1-<em>A<sub>s</sub></em>), thus: 481 *<pre> 482 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>*<em>A<sub>d</sub></em> + <em>A<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>) = <em>A<sub>d</sub></em> 483 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>*<em>A<sub>d</sub></em> + <em>C<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>) 484 *</pre> 485 * @since 1.4 486 */ 487 public static final int SRC_ATOP = 10; 488 489 /** 490 * The part of the destination lying inside of the source 491 * is composited over the source and replaces the destination 492 * (Porter-Duff Destination Atop Source rule). 493 *<p> 494 * <em>F<sub>s</sub></em> = (1-<em>A<sub>d</sub></em>) and <em>F<sub>d</sub></em> = <em>A<sub>s</sub></em>, thus: 495 *<pre> 496 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>) + <em>A<sub>d</sub></em>*<em>A<sub>s</sub></em> = <em>A<sub>s</sub></em> 497 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>) + <em>C<sub>d</sub></em>*<em>A<sub>s</sub></em> 498 *</pre> 499 * @since 1.4 500 */ 501 public static final int DST_ATOP = 11; 502 503 /** 504 * The part of the source that lies outside of the destination 505 * is combined with the part of the destination that lies outside 506 * of the source 507 * (Porter-Duff Source Xor Destination rule). 508 *<p> 509 * <em>F<sub>s</sub></em> = (1-<em>A<sub>d</sub></em>) and <em>F<sub>d</sub></em> = (1-<em>A<sub>s</sub></em>), thus: 510 *<pre> 511 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>) + <em>A<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>) 512 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>) + <em>C<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>) 513 *</pre> 514 * @since 1.4 515 */ 516 public static final int XOR = 12; 517 518 /** 519 * <code>AlphaComposite</code> object that implements the opaque CLEAR rule 520 * with an alpha of 1.0f. 521 * @see #CLEAR 522 */ 523 public static final AlphaComposite Clear = new AlphaComposite(CLEAR); 524 525 /** 526 * <code>AlphaComposite</code> object that implements the opaque SRC rule 527 * with an alpha of 1.0f. 528 * @see #SRC 529 */ 530 public static final AlphaComposite Src = new AlphaComposite(SRC); 531 532 /** 533 * <code>AlphaComposite</code> object that implements the opaque DST rule 534 * with an alpha of 1.0f. 535 * @see #DST 536 * @since 1.4 537 */ 538 public static final AlphaComposite Dst = new AlphaComposite(DST); 539 540 /** 541 * <code>AlphaComposite</code> object that implements the opaque SRC_OVER rule 542 * with an alpha of 1.0f. 543 * @see #SRC_OVER 544 */ 545 public static final AlphaComposite SrcOver = new AlphaComposite(SRC_OVER); 546 547 /** 548 * <code>AlphaComposite</code> object that implements the opaque DST_OVER rule 549 * with an alpha of 1.0f. 550 * @see #DST_OVER 551 */ 552 public static final AlphaComposite DstOver = new AlphaComposite(DST_OVER); 553 554 /** 555 * <code>AlphaComposite</code> object that implements the opaque SRC_IN rule 556 * with an alpha of 1.0f. 557 * @see #SRC_IN 558 */ 559 public static final AlphaComposite SrcIn = new AlphaComposite(SRC_IN); 560 561 /** 562 * <code>AlphaComposite</code> object that implements the opaque DST_IN rule 563 * with an alpha of 1.0f. 564 * @see #DST_IN 565 */ 566 public static final AlphaComposite DstIn = new AlphaComposite(DST_IN); 567 568 /** 569 * <code>AlphaComposite</code> object that implements the opaque SRC_OUT rule 570 * with an alpha of 1.0f. 571 * @see #SRC_OUT 572 */ 573 public static final AlphaComposite SrcOut = new AlphaComposite(SRC_OUT); 574 575 /** 576 * <code>AlphaComposite</code> object that implements the opaque DST_OUT rule 577 * with an alpha of 1.0f. 578 * @see #DST_OUT 579 */ 580 public static final AlphaComposite DstOut = new AlphaComposite(DST_OUT); 581 582 /** 583 * <code>AlphaComposite</code> object that implements the opaque SRC_ATOP rule 584 * with an alpha of 1.0f. 585 * @see #SRC_ATOP 586 * @since 1.4 587 */ 588 public static final AlphaComposite SrcAtop = new AlphaComposite(SRC_ATOP); 589 590 /** 591 * <code>AlphaComposite</code> object that implements the opaque DST_ATOP rule 592 * with an alpha of 1.0f. 593 * @see #DST_ATOP 594 * @since 1.4 595 */ 596 public static final AlphaComposite DstAtop = new AlphaComposite(DST_ATOP); 597 598 /** 599 * <code>AlphaComposite</code> object that implements the opaque XOR rule 600 * with an alpha of 1.0f. 601 * @see #XOR 602 * @since 1.4 603 */ 604 public static final AlphaComposite Xor = new AlphaComposite(XOR); 605 606 private static final int MIN_RULE = CLEAR; 607 private static final int MAX_RULE = XOR; 608 609 float extraAlpha; 610 int rule; 611 612 private AlphaComposite(int rule) { 613 this(rule, 1.0f); 614 } 615 616 private AlphaComposite(int rule, float alpha) { 617 if (rule < MIN_RULE || rule > MAX_RULE) { 618 throw new IllegalArgumentException("unknown composite rule"); 619 } 620 if (alpha >= 0.0f && alpha <= 1.0f) { 621 this.rule = rule; 622 this.extraAlpha = alpha; 623 } else { 624 throw new IllegalArgumentException("alpha value out of range"); 625 } 626 } 627 628 /** 629 * Creates an <code>AlphaComposite</code> object with the specified rule. 630 * @param rule the compositing rule 631 * @throws IllegalArgumentException if <code>rule</code> is not one of 632 * the following: {@link #CLEAR}, {@link #SRC}, {@link #DST}, 633 * {@link #SRC_OVER}, {@link #DST_OVER}, {@link #SRC_IN}, 634 * {@link #DST_IN}, {@link #SRC_OUT}, {@link #DST_OUT}, 635 * {@link #SRC_ATOP}, {@link #DST_ATOP}, or {@link #XOR} 636 */ 637 public static AlphaComposite getInstance(int rule) { 638 switch (rule) { 639 case CLEAR: 640 return Clear; 641 case SRC: 642 return Src; 643 case DST: 644 return Dst; 645 case SRC_OVER: 646 return SrcOver; 647 case DST_OVER: 648 return DstOver; 649 case SRC_IN: 650 return SrcIn; 651 case DST_IN: 652 return DstIn; 653 case SRC_OUT: 654 return SrcOut; 655 case DST_OUT: 656 return DstOut; 657 case SRC_ATOP: 658 return SrcAtop; 659 case DST_ATOP: 660 return DstAtop; 661 case XOR: 662 return Xor; 663 default: 664 throw new IllegalArgumentException("unknown composite rule"); 665 } 666 } 667 668 /** 669 * Creates an <code>AlphaComposite</code> object with the specified rule and 670 * the constant alpha to multiply with the alpha of the source. 671 * The source is multiplied with the specified alpha before being composited 672 * with the destination. 673 * @param rule the compositing rule 674 * @param alpha the constant alpha to be multiplied with the alpha of 675 * the source. <code>alpha</code> must be a floating point number in the 676 * inclusive range [0.0, 1.0]. 677 * @throws IllegalArgumentException if 678 * <code>alpha</code> is less than 0.0 or greater than 1.0, or if 679 * <code>rule</code> is not one of 680 * the following: {@link #CLEAR}, {@link #SRC}, {@link #DST}, 681 * {@link #SRC_OVER}, {@link #DST_OVER}, {@link #SRC_IN}, 682 * {@link #DST_IN}, {@link #SRC_OUT}, {@link #DST_OUT}, 683 * {@link #SRC_ATOP}, {@link #DST_ATOP}, or {@link #XOR} 684 */ 685 public static AlphaComposite getInstance(int rule, float alpha) { 686 if (alpha == 1.0f) { 687 return getInstance(rule); 688 } 689 return new AlphaComposite(rule, alpha); 690 } 691 692 /** 693 * Creates a context for the compositing operation. 694 * The context contains state that is used in performing 695 * the compositing operation. 696 * @param srcColorModel the {@link ColorModel} of the source 697 * @param dstColorModel the <code>ColorModel</code> of the destination 698 * @return the <code>CompositeContext</code> object to be used to perform 699 * compositing operations. 700 */ 701 public CompositeContext createContext(ColorModel srcColorModel, 702 ColorModel dstColorModel, 703 RenderingHints hints) { 704 return new SunCompositeContext(this, srcColorModel, dstColorModel); 705 } 706 707 /** 708 * Returns the alpha value of this <code>AlphaComposite</code>. If this 709 * <code>AlphaComposite</code> does not have an alpha value, 1.0 is returned. 710 * @return the alpha value of this <code>AlphaComposite</code>. 711 */ 712 public float getAlpha() { 713 return extraAlpha; 714 } 715 716 /** 717 * Returns the compositing rule of this <code>AlphaComposite</code>. 718 * @return the compositing rule of this <code>AlphaComposite</code>. 719 */ 720 public int getRule() { 721 return rule; 722 } 723 724 /** 725 * Returns a similar <code>AlphaComposite</code> object that uses 726 * the specified compositing rule. 727 * If this object already uses the specified compositing rule, 728 * this object is returned. 729 * @return an <code>AlphaComposite</code> object derived from 730 * this object that uses the specified compositing rule. 731 * @param rule the compositing rule 732 * @throws IllegalArgumentException if 733 * <code>rule</code> is not one of 734 * the following: {@link #CLEAR}, {@link #SRC}, {@link #DST}, 735 * {@link #SRC_OVER}, {@link #DST_OVER}, {@link #SRC_IN}, 736 * {@link #DST_IN}, {@link #SRC_OUT}, {@link #DST_OUT}, 737 * {@link #SRC_ATOP}, {@link #DST_ATOP}, or {@link #XOR} 738 * @since 1.6 739 */ 740 public AlphaComposite derive(int rule) { 741 return (this.rule == rule) 742 ? this 743 : getInstance(rule, this.extraAlpha); 744 } 745 746 /** 747 * Returns a similar <code>AlphaComposite</code> object that uses 748 * the specified alpha value. 749 * If this object already has the specified alpha value, 750 * this object is returned. 751 * @return an <code>AlphaComposite</code> object derived from 752 * this object that uses the specified alpha value. 753 * @param alpha the constant alpha to be multiplied with the alpha of 754 * the source. <code>alpha</code> must be a floating point number in the 755 * inclusive range [0.0, 1.0]. 756 * @throws IllegalArgumentException if 757 * <code>alpha</code> is less than 0.0 or greater than 1.0 758 * @since 1.6 759 */ 760 public AlphaComposite derive(float alpha) { 761 return (this.extraAlpha == alpha) 762 ? this 763 : getInstance(this.rule, alpha); 764 } 765 766 /** 767 * Returns the hashcode for this composite. 768 * @return a hash code for this composite. 769 */ 770 public int hashCode() { 771 return (Float.floatToIntBits(extraAlpha) * 31 + rule); 772 } 773 774 /** 775 * Determines whether the specified object is equal to this 776 * <code>AlphaComposite</code>. 777 * <p> 778 * The result is <code>true</code> if and only if 779 * the argument is not <code>null</code> and is an 780 * <code>AlphaComposite</code> object that has the same 781 * compositing rule and alpha value as this object. 782 * 783 * @param obj the <code>Object</code> to test for equality 784 * @return <code>true</code> if <code>obj</code> equals this 785 * <code>AlphaComposite</code>; <code>false</code> otherwise. 786 */ 787 public boolean equals(Object obj) { 788 if (!(obj instanceof AlphaComposite)) { 789 return false; 790 } 791 792 AlphaComposite ac = (AlphaComposite) obj; 793 794 if (rule != ac.rule) { 795 return false; 796 } 797 798 if (extraAlpha != ac.extraAlpha) { 799 return false; 800 } 801 802 return true; 803 } 804 805 }