1 /*
2 * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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10 *
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15 * accompanied this code).
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24 */
25
26 package java.awt;
27
28 import java.awt.image.ColorModel;
29 import java.lang.annotation.Native;
30 import sun.java2d.SunCompositeContext;
31
32 /**
33 * The <code>AlphaComposite</code> class implements basic alpha
34 * compositing rules for combining source and destination colors
35 * to achieve blending and transparency effects with graphics and
36 * images.
37 * The specific rules implemented by this class are the basic set
38 * of 12 rules described in
39 * T. Porter and T. Duff, "Compositing Digital Images", SIGGRAPH 84,
40 * 253-259.
41 * The rest of this documentation assumes some familiarity with the
42 * definitions and concepts outlined in that paper.
43 *
44 * <p>
45 * This class extends the standard equations defined by Porter and
46 * Duff to include one additional factor.
47 * An instance of the <code>AlphaComposite</code> class can contain
48 * an alpha value that is used to modify the opacity or coverage of
49 * every source pixel before it is used in the blending equations.
50 *
51 * <p>
52 * It is important to note that the equations defined by the Porter
53 * and Duff paper are all defined to operate on color components
54 * that are premultiplied by their corresponding alpha components.
55 * Since the <code>ColorModel</code> and <code>Raster</code> classes
56 * allow the storage of pixel data in either premultiplied or
57 * non-premultiplied form, all input data must be normalized into
58 * premultiplied form before applying the equations and all results
59 * might need to be adjusted back to the form required by the destination
60 * before the pixel values are stored.
61 *
62 * <p>
63 * Also note that this class defines only the equations
64 * for combining color and alpha values in a purely mathematical
65 * sense. The accurate application of its equations depends
66 * on the way the data is retrieved from its sources and stored
67 * in its destinations.
68 * See <a href="#caveats">Implementation Caveats</a>
69 * for further information.
70 *
71 * <p>
72 * The following factors are used in the description of the blending
73 * equation in the Porter and Duff paper:
74 *
75 * <blockquote>
76 * <table summary="layout">
77 * <tr><th align=left>Factor <th align=left>Definition
78 * <tr><td><em>A<sub>s</sub></em><td>the alpha component of the source pixel
79 * <tr><td><em>C<sub>s</sub></em><td>a color component of the source pixel in premultiplied form
80 * <tr><td><em>A<sub>d</sub></em><td>the alpha component of the destination pixel
81 * <tr><td><em>C<sub>d</sub></em><td>a color component of the destination pixel in premultiplied form
82 * <tr><td><em>F<sub>s</sub></em><td>the fraction of the source pixel that contributes to the output
83 * <tr><td><em>F<sub>d</sub></em><td>the fraction of the destination pixel that contributes
84 * to the output
85 * <tr><td><em>A<sub>r</sub></em><td>the alpha component of the result
86 * <tr><td><em>C<sub>r</sub></em><td>a color component of the result in premultiplied form
87 * </table>
88 * </blockquote>
89 *
90 * <p>
91 * Using these factors, Porter and Duff define 12 ways of choosing
92 * the blending factors <em>F<sub>s</sub></em> and <em>F<sub>d</sub></em> to
93 * produce each of 12 desirable visual effects.
94 * The equations for determining <em>F<sub>s</sub></em> and <em>F<sub>d</sub></em>
95 * are given in the descriptions of the 12 static fields
96 * that specify visual effects.
97 * For example,
98 * the description for
99 * <a href="#SRC_OVER"><code>SRC_OVER</code></a>
100 * specifies that <em>F<sub>s</sub></em> = 1 and <em>F<sub>d</sub></em> = (1-<em>A<sub>s</sub></em>).
101 * Once a set of equations for determining the blending factors is
102 * known they can then be applied to each pixel to produce a result
103 * using the following set of equations:
104 *
105 * <pre>
106 * <em>F<sub>s</sub></em> = <em>f</em>(<em>A<sub>d</sub></em>)
107 * <em>F<sub>d</sub></em> = <em>f</em>(<em>A<sub>s</sub></em>)
108 * <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>
109 * <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>
110 *
111 * <p>
112 * The following factors will be used to discuss our extensions to
113 * the blending equation in the Porter and Duff paper:
114 *
115 * <blockquote>
116 * <table summary="layout">
117 * <tr><th align=left>Factor <th align=left>Definition
118 * <tr><td><em>C<sub>sr</sub></em> <td>one of the raw color components of the source pixel
119 * <tr><td><em>C<sub>dr</sub></em> <td>one of the raw color components of the destination pixel
120 * <tr><td><em>A<sub>ac</sub></em> <td>the "extra" alpha component from the AlphaComposite instance
121 * <tr><td><em>A<sub>sr</sub></em> <td>the raw alpha component of the source pixel
122 * <tr><td><em>A<sub>dr</sub></em><td>the raw alpha component of the destination pixel
123 * <tr><td><em>A<sub>df</sub></em> <td>the final alpha component stored in the destination
124 * <tr><td><em>C<sub>df</sub></em> <td>the final raw color component stored in the destination
125 * </table>
126 *</blockquote>
127 *
128 * <h3>Preparing Inputs</h3>
129 *
130 * <p>
131 * The <code>AlphaComposite</code> class defines an additional alpha
132 * value that is applied to the source alpha.
133 * This value is applied as if an implicit SRC_IN rule were first
134 * applied to the source pixel against a pixel with the indicated
135 * alpha by multiplying both the raw source alpha and the raw
136 * source colors by the alpha in the <code>AlphaComposite</code>.
137 * This leads to the following equation for producing the alpha
138 * used in the Porter and Duff blending equation:
139 *
140 * <pre>
141 * <em>A<sub>s</sub></em> = <em>A<sub>sr</sub></em> * <em>A<sub>ac</sub></em> </pre>
142 *
143 * All of the raw source color components need to be multiplied
144 * by the alpha in the <code>AlphaComposite</code> instance.
145 * Additionally, if the source was not in premultiplied form
146 * then the color components also need to be multiplied by the
147 * source alpha.
148 * Thus, the equation for producing the source color components
149 * for the Porter and Duff equation depends on whether the source
150 * pixels are premultiplied or not:
151 *
152 * <pre>
153 * <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)
154 * <em>C<sub>s</sub></em> = <em>C<sub>sr</sub></em> * <em>A<sub>ac</sub></em> (if source is premultiplied) </pre>
155 *
156 * No adjustment needs to be made to the destination alpha:
157 *
158 * <pre>
159 * <em>A<sub>d</sub></em> = <em>A<sub>dr</sub></em> </pre>
160 *
161 * <p>
162 * The destination color components need to be adjusted only if
163 * they are not in premultiplied form:
164 *
165 * <pre>
166 * <em>C<sub>d</sub></em> = <em>C<sub>dr</sub></em> * <em>A<sub>d</sub></em> (if destination is not premultiplied)
167 * <em>C<sub>d</sub></em> = <em>C<sub>dr</sub></em> (if destination is premultiplied) </pre>
168 *
169 * <h3>Applying the Blending Equation</h3>
170 *
171 * <p>
172 * The adjusted <em>A<sub>s</sub></em>, <em>A<sub>d</sub></em>,
173 * <em>C<sub>s</sub></em>, and <em>C<sub>d</sub></em> are used in the standard
174 * Porter and Duff equations to calculate the blending factors
175 * <em>F<sub>s</sub></em> and <em>F<sub>d</sub></em> and then the resulting
176 * premultiplied components <em>A<sub>r</sub></em> and <em>C<sub>r</sub></em>.
177 *
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 * <h3>Performance Considerations</h3>
196 *
197 * <p>
198 * For performance reasons, it is preferable that
199 * <code>Raster</code> objects passed to the <code>compose</code>
200 * method of a {@link CompositeContext} object created by the
201 * <code>AlphaComposite</code> class have premultiplied data.
202 * If either the source <code>Raster</code>
203 * or the destination <code>Raster</code>
204 * is not premultiplied, however,
205 * appropriate conversions are performed before and after the compositing
206 * operation.
207 *
208 * <h3><a name="caveats">Implementation Caveats</a></h3>
209 *
210 * <ul>
211 * <li>
212 * Many sources, such as some of the opaque image types listed
213 * in the <code>BufferedImage</code> class, do not store alpha values
214 * for their pixels. Such sources supply an alpha of 1.0 for
215 * all of their pixels.
216 *
217 * <li>
218 * Many destinations also have no place to store the alpha values
219 * that result from the blending calculations performed by this class.
220 * Such destinations thus implicitly discard the resulting
221 * alpha values that this class produces.
222 * It is recommended that such destinations should treat their stored
223 * color values as non-premultiplied and divide the resulting color
224 * values by the resulting alpha value before storing the color
225 * values and discarding the alpha value.
226 *
227 * <li>
228 * The accuracy of the results depends on the manner in which pixels
229 * are stored in the destination.
230 * An image format that provides at least 8 bits of storage per color
231 * and alpha component is at least adequate for use as a destination
232 * for a sequence of a few to a dozen compositing operations.
233 * An image format with fewer than 8 bits of storage per component
234 * is of limited use for just one or two compositing operations
235 * before the rounding errors dominate the results.
236 * An image format
237 * that does not separately store
238 * color components is not a
239 * good candidate for any type of translucent blending.
240 * For example, <code>BufferedImage.TYPE_BYTE_INDEXED</code>
241 * should not be used as a destination for a blending operation
242 * because every operation
243 * can introduce large errors, due to
244 * the need to choose a pixel from a limited palette to match the
245 * results of the blending equations.
246 *
247 * <li>
248 * Nearly all formats store pixels as discrete integers rather than
249 * the floating point values used in the reference equations above.
250 * The implementation can either scale the integer pixel
251 * values into floating point values in the range 0.0 to 1.0 or
252 * use slightly modified versions of the equations
253 * that operate entirely in the integer domain and yet produce
254 * analogous results to the reference equations.
255 *
256 * <p>
257 * Typically the integer values are related to the floating point
258 * values in such a way that the integer 0 is equated
259 * to the floating point value 0.0 and the integer
260 * 2^<em>n</em>-1 (where <em>n</em> is the number of bits
261 * in the representation) is equated to 1.0.
262 * For 8-bit representations, this means that 0x00
263 * represents 0.0 and 0xff represents
264 * 1.0.
265 *
266 * <li>
267 * The internal implementation can approximate some of the equations
268 * and it can also eliminate some steps to avoid unnecessary operations.
269 * For example, consider a discrete integer image with non-premultiplied
270 * alpha values that uses 8 bits per component for storage.
271 * The stored values for a
272 * nearly transparent darkened red might be:
273 *
274 * <pre>
275 * (A, R, G, B) = (0x01, 0xb0, 0x00, 0x00)</pre>
276 *
277 * <p>
278 * If integer math were being used and this value were being
279 * composited in
280 * <a href="#SRC"><code>SRC</code></a>
281 * mode with no extra alpha, then the math would
282 * indicate that the results were (in integer format):
283 *
284 * <pre>
285 * (A, R, G, B) = (0x01, 0x01, 0x00, 0x00)</pre>
286 *
287 * <p>
288 * Note that the intermediate values, which are always in premultiplied
289 * form, would only allow the integer red component to be either 0x00
290 * or 0x01. When we try to store this result back into a destination
291 * that is not premultiplied, dividing out the alpha will give us
292 * very few choices for the non-premultiplied red value.
293 * In this case an implementation that performs the math in integer
294 * space without shortcuts is likely to end up with the final pixel
295 * values of:
296 *
297 * <pre>
298 * (A, R, G, B) = (0x01, 0xff, 0x00, 0x00)</pre>
299 *
300 * <p>
301 * (Note that 0x01 divided by 0x01 gives you 1.0, which is equivalent
302 * to the value 0xff in an 8-bit storage format.)
303 *
304 * <p>
305 * Alternately, an implementation that uses floating point math
306 * might produce more accurate results and end up returning to the
307 * original pixel value with little, if any, roundoff error.
308 * Or, an implementation using integer math might decide that since
309 * the equations boil down to a virtual NOP on the color values
310 * if performed in a floating point space, it can transfer the
311 * pixel untouched to the destination and avoid all the math entirely.
312 *
313 * <p>
314 * These implementations all attempt to honor the
315 * same equations, but use different tradeoffs of integer and
316 * floating point math and reduced or full equations.
317 * To account for such differences, it is probably best to
318 * expect only that the premultiplied form of the results to
319 * match between implementations and image formats. In this
320 * case both answers, expressed in premultiplied form would
321 * equate to:
322 *
323 * <pre>
324 * (A, R, G, B) = (0x01, 0x01, 0x00, 0x00)</pre>
325 *
326 * <p>
327 * and thus they would all match.
328 *
329 * <li>
330 * Because of the technique of simplifying the equations for
331 * calculation efficiency, some implementations might perform
332 * differently when encountering result alpha values of 0.0
333 * on a non-premultiplied destination.
334 * Note that the simplification of removing the divide by alpha
335 * in the case of the SRC rule is technically not valid if the
336 * denominator (alpha) is 0.
337 * But, since the results should only be expected to be accurate
338 * when viewed in premultiplied form, a resulting alpha of 0
339 * essentially renders the resulting color components irrelevant
340 * and so exact behavior in this case should not be expected.
341 * </ul>
342 * @see Composite
343 * @see CompositeContext
344 */
345
346 public final class AlphaComposite implements Composite {
347 /**
348 * Both the color and the alpha of the destination are cleared
349 * (Porter-Duff Clear rule).
350 * Neither the source nor the destination is used as input.
351 *<p>
352 * <em>F<sub>s</sub></em> = 0 and <em>F<sub>d</sub></em> = 0, thus:
353 *<pre>
354 * <em>A<sub>r</sub></em> = 0
355 * <em>C<sub>r</sub></em> = 0
356 *</pre>
357 */
358 @Native public static final int CLEAR = 1;
359
360 /**
361 * The source is copied to the destination
362 * (Porter-Duff Source rule).
363 * The destination is not used as input.
364 *<p>
365 * <em>F<sub>s</sub></em> = 1 and <em>F<sub>d</sub></em> = 0, thus:
366 *<pre>
367 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>
368 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>
369 *</pre>
370 */
371 @Native public static final int SRC = 2;
372
373 /**
374 * The destination is left untouched
375 * (Porter-Duff Destination rule).
376 *<p>
377 * <em>F<sub>s</sub></em> = 0 and <em>F<sub>d</sub></em> = 1, thus:
378 *<pre>
379 * <em>A<sub>r</sub></em> = <em>A<sub>d</sub></em>
380 * <em>C<sub>r</sub></em> = <em>C<sub>d</sub></em>
381 *</pre>
382 * @since 1.4
383 */
384 @Native public static final int DST = 9;
385 // Note that DST was added in 1.4 so it is numbered out of order...
386
387 /**
388 * The source is composited over the destination
389 * (Porter-Duff Source Over Destination rule).
390 *<p>
391 * <em>F<sub>s</sub></em> = 1 and <em>F<sub>d</sub></em> = (1-<em>A<sub>s</sub></em>), thus:
392 *<pre>
393 * <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>)
394 * <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>)
395 *</pre>
396 */
397 @Native public static final int SRC_OVER = 3;
398
399 /**
400 * The destination is composited over the source and
401 * the result replaces the destination
402 * (Porter-Duff Destination Over Source rule).
403 *<p>
404 * <em>F<sub>s</sub></em> = (1-<em>A<sub>d</sub></em>) and <em>F<sub>d</sub></em> = 1, thus:
405 *<pre>
406 * <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>
407 * <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>
408 *</pre>
409 */
410 @Native public static final int DST_OVER = 4;
411
412 /**
413 * The part of the source lying inside of the destination replaces
414 * the destination
415 * (Porter-Duff Source In Destination rule).
416 *<p>
417 * <em>F<sub>s</sub></em> = <em>A<sub>d</sub></em> and <em>F<sub>d</sub></em> = 0, thus:
418 *<pre>
419 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>*<em>A<sub>d</sub></em>
420 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>*<em>A<sub>d</sub></em>
421 *</pre>
422 */
423 @Native public static final int SRC_IN = 5;
424
425 /**
426 * The part of the destination lying inside of the source
427 * replaces the destination
428 * (Porter-Duff Destination In Source rule).
429 *<p>
430 * <em>F<sub>s</sub></em> = 0 and <em>F<sub>d</sub></em> = <em>A<sub>s</sub></em>, thus:
431 *<pre>
432 * <em>A<sub>r</sub></em> = <em>A<sub>d</sub></em>*<em>A<sub>s</sub></em>
433 * <em>C<sub>r</sub></em> = <em>C<sub>d</sub></em>*<em>A<sub>s</sub></em>
434 *</pre>
435 */
436 @Native public static final int DST_IN = 6;
437
438 /**
439 * The part of the source lying outside of the destination
440 * replaces the destination
441 * (Porter-Duff Source Held Out By Destination rule).
442 *<p>
443 * <em>F<sub>s</sub></em> = (1-<em>A<sub>d</sub></em>) and <em>F<sub>d</sub></em> = 0, thus:
444 *<pre>
445 * <em>A<sub>r</sub></em> = <em>A<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>)
446 * <em>C<sub>r</sub></em> = <em>C<sub>s</sub></em>*(1-<em>A<sub>d</sub></em>)
447 *</pre>
448 */
449 @Native public static final int SRC_OUT = 7;
450
451 /**
452 * The part of the destination lying outside of the source
453 * replaces the destination
454 * (Porter-Duff Destination Held Out By Source rule).
455 *<p>
456 * <em>F<sub>s</sub></em> = 0 and <em>F<sub>d</sub></em> = (1-<em>A<sub>s</sub></em>), thus:
457 *<pre>
458 * <em>A<sub>r</sub></em> = <em>A<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>)
459 * <em>C<sub>r</sub></em> = <em>C<sub>d</sub></em>*(1-<em>A<sub>s</sub></em>)
460 *</pre>
461 */
462 @Native public static final int DST_OUT = 8;
463
464 // Rule 9 is DST which is defined above where it fits into the
465 // list logically, rather than numerically
466 //
467 // public static final int DST = 9;
468
469 /**
470 * The part of the source lying inside of the destination
471 * is composited onto the destination
472 * (Porter-Duff Source Atop Destination rule).
473 *<p>
474 * <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:
475 *<pre>
476 * <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>
477 * <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>)
478 *</pre>
479 * @since 1.4
480 */
481 @Native public static final int SRC_ATOP = 10;
482
483 /**
484 * The part of the destination lying inside of the source
485 * is composited over the source and replaces the destination
486 * (Porter-Duff Destination Atop Source rule).
487 *<p>
488 * <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:
489 *<pre>
490 * <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>
491 * <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>
492 *</pre>
493 * @since 1.4
494 */
495 @Native public static final int DST_ATOP = 11;
496
497 /**
498 * The part of the source that lies outside of the destination
499 * is combined with the part of the destination that lies outside
500 * of the source
501 * (Porter-Duff Source Xor Destination rule).
502 *<p>
503 * <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:
504 *<pre>
505 * <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>)
506 * <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>)
507 *</pre>
508 * @since 1.4
509 */
510 @Native public static final int XOR = 12;
511
512 /**
513 * <code>AlphaComposite</code> object that implements the opaque CLEAR rule
514 * with an alpha of 1.0f.
515 * @see #CLEAR
516 */
517 public static final AlphaComposite Clear = new AlphaComposite(CLEAR);
518
519 /**
520 * <code>AlphaComposite</code> object that implements the opaque SRC rule
521 * with an alpha of 1.0f.
522 * @see #SRC
523 */
524 public static final AlphaComposite Src = new AlphaComposite(SRC);
525
526 /**
527 * <code>AlphaComposite</code> object that implements the opaque DST rule
528 * with an alpha of 1.0f.
529 * @see #DST
530 * @since 1.4
531 */
532 public static final AlphaComposite Dst = new AlphaComposite(DST);
533
534 /**
535 * <code>AlphaComposite</code> object that implements the opaque SRC_OVER rule
536 * with an alpha of 1.0f.
537 * @see #SRC_OVER
538 */
539 public static final AlphaComposite SrcOver = new AlphaComposite(SRC_OVER);
540
541 /**
542 * <code>AlphaComposite</code> object that implements the opaque DST_OVER rule
543 * with an alpha of 1.0f.
544 * @see #DST_OVER
545 */
546 public static final AlphaComposite DstOver = new AlphaComposite(DST_OVER);
547
548 /**
549 * <code>AlphaComposite</code> object that implements the opaque SRC_IN rule
550 * with an alpha of 1.0f.
551 * @see #SRC_IN
552 */
553 public static final AlphaComposite SrcIn = new AlphaComposite(SRC_IN);
554
555 /**
556 * <code>AlphaComposite</code> object that implements the opaque DST_IN rule
557 * with an alpha of 1.0f.
558 * @see #DST_IN
559 */
560 public static final AlphaComposite DstIn = new AlphaComposite(DST_IN);
561
562 /**
563 * <code>AlphaComposite</code> object that implements the opaque SRC_OUT rule
564 * with an alpha of 1.0f.
565 * @see #SRC_OUT
566 */
567 public static final AlphaComposite SrcOut = new AlphaComposite(SRC_OUT);
568
569 /**
570 * <code>AlphaComposite</code> object that implements the opaque DST_OUT rule
571 * with an alpha of 1.0f.
572 * @see #DST_OUT
573 */
574 public static final AlphaComposite DstOut = new AlphaComposite(DST_OUT);
575
576 /**
577 * <code>AlphaComposite</code> object that implements the opaque SRC_ATOP rule
578 * with an alpha of 1.0f.
579 * @see #SRC_ATOP
580 * @since 1.4
581 */
582 public static final AlphaComposite SrcAtop = new AlphaComposite(SRC_ATOP);
583
584 /**
585 * <code>AlphaComposite</code> object that implements the opaque DST_ATOP rule
586 * with an alpha of 1.0f.
587 * @see #DST_ATOP
588 * @since 1.4
589 */
590 public static final AlphaComposite DstAtop = new AlphaComposite(DST_ATOP);
591
592 /**
593 * <code>AlphaComposite</code> object that implements the opaque XOR rule
594 * with an alpha of 1.0f.
595 * @see #XOR
596 * @since 1.4
597 */
598 public static final AlphaComposite Xor = new AlphaComposite(XOR);
599
600 @Native private static final int MIN_RULE = CLEAR;
601 @Native private static final int MAX_RULE = XOR;
602
603 float extraAlpha;
604 int rule;
605
606 private AlphaComposite(int rule) {
607 this(rule, 1.0f);
608 }
609
610 private AlphaComposite(int rule, float alpha) {
611 if (rule < MIN_RULE || rule > MAX_RULE) {
612 throw new IllegalArgumentException("unknown composite rule");
613 }
614 if (alpha >= 0.0f && alpha <= 1.0f) {
615 this.rule = rule;
616 this.extraAlpha = alpha;
617 } else {
618 throw new IllegalArgumentException("alpha value out of range");
619 }
620 }
621
622 /**
623 * Creates an <code>AlphaComposite</code> object with the specified rule.
624 *
625 * @param rule the compositing rule
626 * @return the {@code AlphaComposite} object created
627 * @throws IllegalArgumentException if <code>rule</code> is not one of
628 * the following: {@link #CLEAR}, {@link #SRC}, {@link #DST},
629 * {@link #SRC_OVER}, {@link #DST_OVER}, {@link #SRC_IN},
630 * {@link #DST_IN}, {@link #SRC_OUT}, {@link #DST_OUT},
631 * {@link #SRC_ATOP}, {@link #DST_ATOP}, or {@link #XOR}
632 */
633 public static AlphaComposite getInstance(int rule) {
634 switch (rule) {
635 case CLEAR:
636 return Clear;
637 case SRC:
638 return Src;
639 case DST:
640 return Dst;
641 case SRC_OVER:
642 return SrcOver;
643 case DST_OVER:
644 return DstOver;
645 case SRC_IN:
646 return SrcIn;
647 case DST_IN:
648 return DstIn;
649 case SRC_OUT:
650 return SrcOut;
651 case DST_OUT:
652 return DstOut;
653 case SRC_ATOP:
654 return SrcAtop;
655 case DST_ATOP:
656 return DstAtop;
657 case XOR:
658 return Xor;
659 default:
660 throw new IllegalArgumentException("unknown composite rule");
661 }
662 }
663
664 /**
665 * Creates an <code>AlphaComposite</code> object with the specified rule and
666 * the constant alpha to multiply with the alpha of the source.
667 * The source is multiplied with the specified alpha before being composited
668 * with the destination.
669 *
670 * @param rule the compositing rule
671 * @param alpha the constant alpha to be multiplied with the alpha of
672 * the source. <code>alpha</code> must be a floating point number in the
673 * inclusive range [0.0, 1.0].
674 * @return the {@code AlphaComposite} object created
675 * @throws IllegalArgumentException if
676 * <code>alpha</code> is less than 0.0 or greater than 1.0, or if
677 * <code>rule</code> is not one of
678 * the following: {@link #CLEAR}, {@link #SRC}, {@link #DST},
679 * {@link #SRC_OVER}, {@link #DST_OVER}, {@link #SRC_IN},
680 * {@link #DST_IN}, {@link #SRC_OUT}, {@link #DST_OUT},
681 * {@link #SRC_ATOP}, {@link #DST_ATOP}, or {@link #XOR}
682 */
683 public static AlphaComposite getInstance(int rule, float alpha) {
684 if (alpha == 1.0f) {
685 return getInstance(rule);
686 }
687 return new AlphaComposite(rule, alpha);
688 }
689
690 /**
691 * Creates a context for the compositing operation.
692 * The context contains state that is used in performing
693 * the compositing operation.
694 * @param srcColorModel the {@link ColorModel} of the source
695 * @param dstColorModel the <code>ColorModel</code> of the destination
696 * @return the <code>CompositeContext</code> object to be used to perform
697 * compositing operations.
698 */
699 public CompositeContext createContext(ColorModel srcColorModel,
700 ColorModel dstColorModel,
701 RenderingHints hints) {
702 return new SunCompositeContext(this, srcColorModel, dstColorModel);
703 }
704
705 /**
706 * Returns the alpha value of this <code>AlphaComposite</code>. If this
707 * <code>AlphaComposite</code> does not have an alpha value, 1.0 is returned.
708 * @return the alpha value of this <code>AlphaComposite</code>.
709 */
710 public float getAlpha() {
711 return extraAlpha;
712 }
713
714 /**
715 * Returns the compositing rule of this <code>AlphaComposite</code>.
716 * @return the compositing rule of this <code>AlphaComposite</code>.
717 */
718 public int getRule() {
719 return rule;
720 }
721
722 /**
723 * Returns a similar <code>AlphaComposite</code> object that uses
724 * the specified compositing rule.
725 * If this object already uses the specified compositing rule,
726 * this object is returned.
727 * @return an <code>AlphaComposite</code> object derived from
728 * this object that uses the specified compositing rule.
729 * @param rule the compositing rule
730 * @throws IllegalArgumentException if
731 * <code>rule</code> is not one of
732 * the following: {@link #CLEAR}, {@link #SRC}, {@link #DST},
733 * {@link #SRC_OVER}, {@link #DST_OVER}, {@link #SRC_IN},
734 * {@link #DST_IN}, {@link #SRC_OUT}, {@link #DST_OUT},
735 * {@link #SRC_ATOP}, {@link #DST_ATOP}, or {@link #XOR}
736 * @since 1.6
737 */
738 public AlphaComposite derive(int rule) {
739 return (this.rule == rule)
740 ? this
741 : getInstance(rule, this.extraAlpha);
742 }
743
744 /**
745 * Returns a similar <code>AlphaComposite</code> object that uses
746 * the specified alpha value.
747 * If this object already has the specified alpha value,
748 * this object is returned.
749 * @return an <code>AlphaComposite</code> object derived from
750 * this object that uses the specified alpha value.
751 * @param alpha the constant alpha to be multiplied with the alpha of
752 * the source. <code>alpha</code> must be a floating point number in the
753 * inclusive range [0.0, 1.0].
754 * @throws IllegalArgumentException if
755 * <code>alpha</code> is less than 0.0 or greater than 1.0
756 * @since 1.6
757 */
758 public AlphaComposite derive(float alpha) {
759 return (this.extraAlpha == alpha)
760 ? this
761 : getInstance(this.rule, alpha);
762 }
763
764 /**
765 * Returns the hashcode for this composite.
766 * @return a hash code for this composite.
767 */
768 public int hashCode() {
769 return (Float.floatToIntBits(extraAlpha) * 31 + rule);
770 }
771
772 /**
773 * Determines whether the specified object is equal to this
774 * <code>AlphaComposite</code>.
775 * <p>
776 * The result is <code>true</code> if and only if
777 * the argument is not <code>null</code> and is an
778 * <code>AlphaComposite</code> object that has the same
779 * compositing rule and alpha value as this object.
780 *
781 * @param obj the <code>Object</code> to test for equality
782 * @return <code>true</code> if <code>obj</code> equals this
783 * <code>AlphaComposite</code>; <code>false</code> otherwise.
784 */
785 public boolean equals(Object obj) {
786 if (!(obj instanceof AlphaComposite)) {
787 return false;
788 }
789
790 AlphaComposite ac = (AlphaComposite) obj;
791
792 if (rule != ac.rule) {
793 return false;
794 }
795
796 if (extraAlpha != ac.extraAlpha) {
797 return false;
798 }
799
800 return true;
801 }
802
803 }