J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2000-2002 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | #include "AlphaMacros.h" |
| 27 | |
| 28 | /* |
| 29 | * The following equation is used to blend each pixel in a compositing |
| 30 | * operation between two images (a and b). If we have Ca (Component of a) |
| 31 | * and Cb (Component of b) representing the alpha and color components |
| 32 | * of a given pair of corresponding pixels in the two source images, |
| 33 | * then Porter & Duff have defined blending factors Fa (Factor for a) |
| 34 | * and Fb (Factor for b) to represent the contribution of the pixel |
| 35 | * from the corresponding image to the pixel in the result. |
| 36 | * |
| 37 | * Cresult = Fa * Ca + Fb * Cb |
| 38 | * |
| 39 | * The blending factors Fa and Fb are computed from the alpha value of |
| 40 | * the pixel from the "other" source image. Thus, Fa is computed from |
| 41 | * the alpha of Cb and vice versa on a per-pixel basis. |
| 42 | * |
| 43 | * A given factor (Fa or Fb) is computed from the other alpha using |
| 44 | * one of the following blending factor equations depending on the |
| 45 | * blending rule and depending on whether we are computing Fa or Fb: |
| 46 | * |
| 47 | * Fblend = 0 |
| 48 | * Fblend = ONE |
| 49 | * Fblend = alpha |
| 50 | * Fblend = (ONE - alpha) |
| 51 | * |
| 52 | * The value ONE in these equations represents the same numeric value |
| 53 | * as is used to represent "full coverage" in the alpha component. For |
| 54 | * example it is the value 0xff for 8-bit alpha channels and the value |
| 55 | * 0xffff for 16-bit alpha channels. |
| 56 | * |
| 57 | * Each Porter-Duff blending rule thus defines a pair of the above Fblend |
| 58 | * equations to define Fa and Fb independently and thus to control |
| 59 | * the contributions of the two source pixels to the destination pixel. |
| 60 | * |
| 61 | * Rather than use conditional tests per pixel in the inner loop, |
| 62 | * we note that the following 3 logical and mathematical operations |
| 63 | * can be applied to any alpha value to produce the result of one |
| 64 | * of the 4 Fblend equations: |
| 65 | * |
| 66 | * Fcomp = ((alpha AND Fk1) XOR Fk2) PLUS Fk3 |
| 67 | * |
| 68 | * Through appropriate choices for the 3 Fk values we can cause |
| 69 | * the result of this Fcomp equation to always match one of the |
| 70 | * defined Fblend equations. More importantly, the Fcomp equation |
| 71 | * involves no conditional tests which can stall pipelined processor |
| 72 | * execution and typically compiles very tightly into 3 machine |
| 73 | * instructions. |
| 74 | * |
| 75 | * For each of the 4 Fblend equations the desired Fk values are |
| 76 | * as follows: |
| 77 | * |
| 78 | * Fblend Fk1 Fk2 Fk3 |
| 79 | * ------ --- --- --- |
| 80 | * 0 0 0 0 |
| 81 | * ONE 0 0 ONE |
| 82 | * alpha ONE 0 0 |
| 83 | * ONE-alpha ONE -1 ONE+1 |
| 84 | * |
| 85 | * This gives us the following derivations for Fcomp. Note that |
| 86 | * the derivation of the last equation is less obvious so it is |
| 87 | * broken down into steps and uses the well-known equality for |
| 88 | * two's-complement arithmetic "((n XOR -1) PLUS 1) == -n": |
| 89 | * |
| 90 | * ((alpha AND 0 ) XOR 0) PLUS 0 == 0 |
| 91 | * |
| 92 | * ((alpha AND 0 ) XOR 0) PLUS ONE == ONE |
| 93 | * |
| 94 | * ((alpha AND ONE) XOR 0) PLUS 0 == alpha |
| 95 | * |
| 96 | * ((alpha AND ONE) XOR -1) PLUS ONE+1 == |
| 97 | * ((alpha XOR -1) PLUS 1) PLUS ONE == |
| 98 | * (-alpha) PLUS ONE == ONE - alpha |
| 99 | * |
| 100 | * We have assigned each Porter-Duff rule an implicit index for |
| 101 | * simplicity of referring to the rule in parameter lists. For |
| 102 | * a given blending operation which uses a specific rule, we simply |
| 103 | * use the index of that rule to index into a table and load values |
| 104 | * from that table which help us construct the 2 sets of 3 Fk values |
| 105 | * needed for applying that blending rule (one set for Fa and the |
| 106 | * other set for Fb). Since these Fk values depend only on the |
| 107 | * rule we can set them up at the start of the outer loop and only |
| 108 | * need to do the 3 operations in the Fcomp equation twice per |
| 109 | * pixel (once for Fa and again for Fb). |
| 110 | * ------------------------------------------------------------- |
| 111 | */ |
| 112 | |
| 113 | /* |
| 114 | * The following definitions represent terms in the Fblend |
| 115 | * equations described above. One "term name" is chosen from |
| 116 | * each of the following 3 pairs of names to define the table |
| 117 | * values for the Fa or the Fb of a given Porter-Duff rule. |
| 118 | * |
| 119 | * AROP_ZERO the first operand is the constant zero |
| 120 | * AROP_ONE the first operand is the constant one |
| 121 | * |
| 122 | * AROP_PLUS the two operands are added together |
| 123 | * AROP_MINUS the second operand is subtracted from the first |
| 124 | * |
| 125 | * AROP_NAUGHT there is no second operand |
| 126 | * AROP_ALPHA the indicated alpha is used for the second operand |
| 127 | * |
| 128 | * These names expand to numeric values which can be conveniently |
| 129 | * combined to produce the 3 Fk values needed for the Fcomp equation. |
| 130 | * |
| 131 | * Note that the numeric values used here are most convenient for |
| 132 | * generating the 3 specific Fk values needed for manipulating images |
| 133 | * with 8-bits of alpha precision. But Fk values for manipulating |
| 134 | * images with other alpha precisions (such as 16-bits) can also be |
| 135 | * derived from these same values using a small amount of bit |
| 136 | * shifting and replication. |
| 137 | */ |
| 138 | #define AROP_ZERO 0x00 |
| 139 | #define AROP_ONE 0xff |
| 140 | #define AROP_PLUS 0 |
| 141 | #define AROP_MINUS -1 |
| 142 | #define AROP_NAUGHT 0x00 |
| 143 | #define AROP_ALPHA 0xff |
| 144 | |
| 145 | /* |
| 146 | * This macro constructs a single Fcomp equation table entry from the |
| 147 | * term names for the 3 terms in the corresponding Fblend equation. |
| 148 | */ |
| 149 | #define MAKE_AROPS(add, xor, and) { AROP_ ## add, AROP_ ## and, AROP_ ## xor } |
| 150 | |
| 151 | /* |
| 152 | * These macros define the Fcomp equation table entries for each |
| 153 | * of the 4 Fblend equations described above. |
| 154 | * |
| 155 | * AROPS_ZERO Fblend = 0 |
| 156 | * AROPS_ONE Fblend = 1 |
| 157 | * AROPS_ALPHA Fblend = alpha |
| 158 | * AROPS_INVALPHA Fblend = (1 - alpha) |
| 159 | */ |
| 160 | #define AROPS_ZERO MAKE_AROPS( ZERO, PLUS, NAUGHT ) |
| 161 | #define AROPS_ONE MAKE_AROPS( ONE, PLUS, NAUGHT ) |
| 162 | #define AROPS_ALPHA MAKE_AROPS( ZERO, PLUS, ALPHA ) |
| 163 | #define AROPS_INVALPHA MAKE_AROPS( ONE, MINUS, ALPHA ) |
| 164 | |
| 165 | /* |
| 166 | * This table maps a given Porter-Duff blending rule index to a |
| 167 | * pair of Fcomp equation table entries, one for computing the |
| 168 | * 3 Fk values needed for Fa and another for computing the 3 |
| 169 | * Fk values needed for Fb. |
| 170 | */ |
| 171 | AlphaFunc AlphaRules[] = { |
| 172 | { {0, 0, 0}, {0, 0, 0} }, /* 0 - Nothing */ |
| 173 | { AROPS_ZERO, AROPS_ZERO }, /* 1 - RULE_Clear */ |
| 174 | { AROPS_ONE, AROPS_ZERO }, /* 2 - RULE_Src */ |
| 175 | { AROPS_ONE, AROPS_INVALPHA }, /* 3 - RULE_SrcOver */ |
| 176 | { AROPS_INVALPHA, AROPS_ONE }, /* 4 - RULE_DstOver */ |
| 177 | { AROPS_ALPHA, AROPS_ZERO }, /* 5 - RULE_SrcIn */ |
| 178 | { AROPS_ZERO, AROPS_ALPHA }, /* 6 - RULE_DstIn */ |
| 179 | { AROPS_INVALPHA, AROPS_ZERO }, /* 7 - RULE_SrcOut */ |
| 180 | { AROPS_ZERO, AROPS_INVALPHA }, /* 8 - RULE_DstOut */ |
| 181 | { AROPS_ZERO, AROPS_ONE }, /* 9 - RULE_Dst */ |
| 182 | { AROPS_ALPHA, AROPS_INVALPHA }, /*10 - RULE_SrcAtop */ |
| 183 | { AROPS_INVALPHA, AROPS_ALPHA }, /*11 - RULE_DstAtop */ |
| 184 | { AROPS_INVALPHA, AROPS_INVALPHA }, /*12 - RULE_Xor */ |
| 185 | }; |