| /* |
| * Copyright (c) 2000, 2002, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| #include "AlphaMacros.h" |
| |
| /* |
| * The following equation is used to blend each pixel in a compositing |
| * operation between two images (a and b). If we have Ca (Component of a) |
| * and Cb (Component of b) representing the alpha and color components |
| * of a given pair of corresponding pixels in the two source images, |
| * then Porter & Duff have defined blending factors Fa (Factor for a) |
| * and Fb (Factor for b) to represent the contribution of the pixel |
| * from the corresponding image to the pixel in the result. |
| * |
| * Cresult = Fa * Ca + Fb * Cb |
| * |
| * The blending factors Fa and Fb are computed from the alpha value of |
| * the pixel from the "other" source image. Thus, Fa is computed from |
| * the alpha of Cb and vice versa on a per-pixel basis. |
| * |
| * A given factor (Fa or Fb) is computed from the other alpha using |
| * one of the following blending factor equations depending on the |
| * blending rule and depending on whether we are computing Fa or Fb: |
| * |
| * Fblend = 0 |
| * Fblend = ONE |
| * Fblend = alpha |
| * Fblend = (ONE - alpha) |
| * |
| * The value ONE in these equations represents the same numeric value |
| * as is used to represent "full coverage" in the alpha component. For |
| * example it is the value 0xff for 8-bit alpha channels and the value |
| * 0xffff for 16-bit alpha channels. |
| * |
| * Each Porter-Duff blending rule thus defines a pair of the above Fblend |
| * equations to define Fa and Fb independently and thus to control |
| * the contributions of the two source pixels to the destination pixel. |
| * |
| * Rather than use conditional tests per pixel in the inner loop, |
| * we note that the following 3 logical and mathematical operations |
| * can be applied to any alpha value to produce the result of one |
| * of the 4 Fblend equations: |
| * |
| * Fcomp = ((alpha AND Fk1) XOR Fk2) PLUS Fk3 |
| * |
| * Through appropriate choices for the 3 Fk values we can cause |
| * the result of this Fcomp equation to always match one of the |
| * defined Fblend equations. More importantly, the Fcomp equation |
| * involves no conditional tests which can stall pipelined processor |
| * execution and typically compiles very tightly into 3 machine |
| * instructions. |
| * |
| * For each of the 4 Fblend equations the desired Fk values are |
| * as follows: |
| * |
| * Fblend Fk1 Fk2 Fk3 |
| * ------ --- --- --- |
| * 0 0 0 0 |
| * ONE 0 0 ONE |
| * alpha ONE 0 0 |
| * ONE-alpha ONE -1 ONE+1 |
| * |
| * This gives us the following derivations for Fcomp. Note that |
| * the derivation of the last equation is less obvious so it is |
| * broken down into steps and uses the well-known equality for |
| * two's-complement arithmetic "((n XOR -1) PLUS 1) == -n": |
| * |
| * ((alpha AND 0 ) XOR 0) PLUS 0 == 0 |
| * |
| * ((alpha AND 0 ) XOR 0) PLUS ONE == ONE |
| * |
| * ((alpha AND ONE) XOR 0) PLUS 0 == alpha |
| * |
| * ((alpha AND ONE) XOR -1) PLUS ONE+1 == |
| * ((alpha XOR -1) PLUS 1) PLUS ONE == |
| * (-alpha) PLUS ONE == ONE - alpha |
| * |
| * We have assigned each Porter-Duff rule an implicit index for |
| * simplicity of referring to the rule in parameter lists. For |
| * a given blending operation which uses a specific rule, we simply |
| * use the index of that rule to index into a table and load values |
| * from that table which help us construct the 2 sets of 3 Fk values |
| * needed for applying that blending rule (one set for Fa and the |
| * other set for Fb). Since these Fk values depend only on the |
| * rule we can set them up at the start of the outer loop and only |
| * need to do the 3 operations in the Fcomp equation twice per |
| * pixel (once for Fa and again for Fb). |
| * ------------------------------------------------------------- |
| */ |
| |
| /* |
| * The following definitions represent terms in the Fblend |
| * equations described above. One "term name" is chosen from |
| * each of the following 3 pairs of names to define the table |
| * values for the Fa or the Fb of a given Porter-Duff rule. |
| * |
| * AROP_ZERO the first operand is the constant zero |
| * AROP_ONE the first operand is the constant one |
| * |
| * AROP_PLUS the two operands are added together |
| * AROP_MINUS the second operand is subtracted from the first |
| * |
| * AROP_NAUGHT there is no second operand |
| * AROP_ALPHA the indicated alpha is used for the second operand |
| * |
| * These names expand to numeric values which can be conveniently |
| * combined to produce the 3 Fk values needed for the Fcomp equation. |
| * |
| * Note that the numeric values used here are most convenient for |
| * generating the 3 specific Fk values needed for manipulating images |
| * with 8-bits of alpha precision. But Fk values for manipulating |
| * images with other alpha precisions (such as 16-bits) can also be |
| * derived from these same values using a small amount of bit |
| * shifting and replication. |
| */ |
| #define AROP_ZERO 0x00 |
| #define AROP_ONE 0xff |
| #define AROP_PLUS 0 |
| #define AROP_MINUS -1 |
| #define AROP_NAUGHT 0x00 |
| #define AROP_ALPHA 0xff |
| |
| /* |
| * This macro constructs a single Fcomp equation table entry from the |
| * term names for the 3 terms in the corresponding Fblend equation. |
| */ |
| #define MAKE_AROPS(add, xor, and) { AROP_ ## add, AROP_ ## and, AROP_ ## xor } |
| |
| /* |
| * These macros define the Fcomp equation table entries for each |
| * of the 4 Fblend equations described above. |
| * |
| * AROPS_ZERO Fblend = 0 |
| * AROPS_ONE Fblend = 1 |
| * AROPS_ALPHA Fblend = alpha |
| * AROPS_INVALPHA Fblend = (1 - alpha) |
| */ |
| #define AROPS_ZERO MAKE_AROPS( ZERO, PLUS, NAUGHT ) |
| #define AROPS_ONE MAKE_AROPS( ONE, PLUS, NAUGHT ) |
| #define AROPS_ALPHA MAKE_AROPS( ZERO, PLUS, ALPHA ) |
| #define AROPS_INVALPHA MAKE_AROPS( ONE, MINUS, ALPHA ) |
| |
| /* |
| * This table maps a given Porter-Duff blending rule index to a |
| * pair of Fcomp equation table entries, one for computing the |
| * 3 Fk values needed for Fa and another for computing the 3 |
| * Fk values needed for Fb. |
| */ |
| AlphaFunc AlphaRules[] = { |
| { {0, 0, 0}, {0, 0, 0} }, /* 0 - Nothing */ |
| { AROPS_ZERO, AROPS_ZERO }, /* 1 - RULE_Clear */ |
| { AROPS_ONE, AROPS_ZERO }, /* 2 - RULE_Src */ |
| { AROPS_ONE, AROPS_INVALPHA }, /* 3 - RULE_SrcOver */ |
| { AROPS_INVALPHA, AROPS_ONE }, /* 4 - RULE_DstOver */ |
| { AROPS_ALPHA, AROPS_ZERO }, /* 5 - RULE_SrcIn */ |
| { AROPS_ZERO, AROPS_ALPHA }, /* 6 - RULE_DstIn */ |
| { AROPS_INVALPHA, AROPS_ZERO }, /* 7 - RULE_SrcOut */ |
| { AROPS_ZERO, AROPS_INVALPHA }, /* 8 - RULE_DstOut */ |
| { AROPS_ZERO, AROPS_ONE }, /* 9 - RULE_Dst */ |
| { AROPS_ALPHA, AROPS_INVALPHA }, /*10 - RULE_SrcAtop */ |
| { AROPS_INVALPHA, AROPS_ALPHA }, /*11 - RULE_DstAtop */ |
| { AROPS_INVALPHA, AROPS_INVALPHA }, /*12 - RULE_Xor */ |
| }; |
