src/core/SkUnPreMultiply.cpp

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
#include "SkUnPreMultiply.h"
#include "SkColorPriv.h"

SkColor SkUnPreMultiply::PMColorToColor(SkPMColor c) {
    const unsigned a = SkGetPackedA32(c);
    const Scale scale = GetScale(a);
    return SkColorSetARGB(a,
                          ApplyScale(scale, SkGetPackedR32(c)),
                          ApplyScale(scale, SkGetPackedG32(c)),
                          ApplyScale(scale, SkGetPackedB32(c)));
}

const uint32_t SkUnPreMultiply::gTable[] = {
    0x00000000, 0xFF000000, 0x7F800000, 0x55000000, 0x3FC00000, 0x33000000, 0x2A800000, 0x246DB6DB,
    0x1FE00000, 0x1C555555, 0x19800000, 0x172E8BA3, 0x15400000, 0x139D89D9, 0x1236DB6E, 0x11000000,
    0x0FF00000, 0x0F000000, 0x0E2AAAAB, 0x0D6BCA1B, 0x0CC00000, 0x0C249249, 0x0B9745D1, 0x0B1642C8,
    0x0AA00000, 0x0A333333, 0x09CEC4EC, 0x0971C71C, 0x091B6DB7, 0x08CB08D4, 0x08800000, 0x0839CE74,
    0x07F80000, 0x07BA2E8C, 0x07800000, 0x07492492, 0x07155555, 0x06E45307, 0x06B5E50D, 0x0689D89E,
    0x06600000, 0x063831F4, 0x06124925, 0x05EE23B9, 0x05CBA2E9, 0x05AAAAAB, 0x058B2164, 0x056CEFA9,
    0x05500000, 0x05343EB2, 0x0519999A, 0x05000000, 0x04E76276, 0x04CFB2B8, 0x04B8E38E, 0x04A2E8BA,
    0x048DB6DB, 0x0479435E, 0x0465846A, 0x045270D0, 0x04400000, 0x042E29F8, 0x041CE73A, 0x040C30C3,
    0x03FC0000, 0x03EC4EC5, 0x03DD1746, 0x03CE540F, 0x03C00000, 0x03B21643, 0x03A49249, 0x03976FC6,
    0x038AAAAB, 0x037E3F20, 0x03722983, 0x03666666, 0x035AF287, 0x034FCACE, 0x0344EC4F, 0x033A5441,
    0x03300000, 0x0325ED09, 0x031C18FA, 0x0312818B, 0x03092492, 0x03000000, 0x02F711DC, 0x02EE5847,
    0x02E5D174, 0x02DD7BAF, 0x02D55555, 0x02CD5CD6, 0x02C590B2, 0x02BDEF7C, 0x02B677D4, 0x02AF286C,
    0x02A80000, 0x02A0FD5C, 0x029A1F59, 0x029364D9, 0x028CCCCD, 0x0286562E, 0x02800000, 0x0279C952,
    0x0273B13B, 0x026DB6DB, 0x0267D95C, 0x026217ED, 0x025C71C7, 0x0256E62A, 0x0251745D, 0x024C1BAD,
    0x0246DB6E, 0x0241B2F9, 0x023CA1AF, 0x0237A6F5, 0x0232C235, 0x022DF2DF, 0x02293868, 0x02249249,
    0x02200000, 0x021B810F, 0x021714FC, 0x0212BB51, 0x020E739D, 0x020A3D71, 0x02061862, 0x02020408,
    0x01FE0000, 0x01FA0BE8, 0x01F62762, 0x01F25214, 0x01EE8BA3, 0x01EAD3BB, 0x01E72A08, 0x01E38E39,
    0x01E00000, 0x01DC7F11, 0x01D90B21, 0x01D5A3EA, 0x01D24925, 0x01CEFA8E, 0x01CBB7E3, 0x01C880E5,
    0x01C55555, 0x01C234F7, 0x01BF1F90, 0x01BC14E6, 0x01B914C2, 0x01B61EED, 0x01B33333, 0x01B05161,
    0x01AD7943, 0x01AAAAAB, 0x01A7E567, 0x01A5294A, 0x01A27627, 0x019FCBD2, 0x019D2A20, 0x019A90E8,
    0x01980000, 0x01957741, 0x0192F685, 0x01907DA5, 0x018E0C7D, 0x018BA2E9, 0x018940C5, 0x0186E5F1,
    0x01849249, 0x018245AE, 0x01800000, 0x017DC11F, 0x017B88EE, 0x0179574E, 0x01772C23, 0x01750750,
    0x0172E8BA, 0x0170D045, 0x016EBDD8, 0x016CB157, 0x016AAAAB, 0x0168A9B9, 0x0166AE6B, 0x0164B8A8,
    0x0162C859, 0x0160DD68, 0x015EF7BE, 0x015D1746, 0x015B3BEA, 0x01596596, 0x01579436, 0x0155C7B5,
    0x01540000, 0x01523D04, 0x01507EAE, 0x014EC4EC, 0x014D0FAC, 0x014B5EDD, 0x0149B26D, 0x01480A4B,
    0x01466666, 0x0144C6B0, 0x01432B17, 0x0141938C, 0x01400000, 0x013E7064, 0x013CE4A9, 0x013B5CC1,
    0x0139D89E, 0x01385831, 0x0136DB6E, 0x01356246, 0x0133ECAE, 0x01327A97, 0x01310BF6, 0x012FA0BF,
    0x012E38E4, 0x012CD45A, 0x012B7315, 0x012A150B, 0x0128BA2F, 0x01276276, 0x01260DD6, 0x0124BC45,
    0x01236DB7, 0x01222222, 0x0120D97D, 0x011F93BC, 0x011E50D8, 0x011D10C5, 0x011BD37A, 0x011A98EF,
    0x0119611A, 0x01182BF3, 0x0116F970, 0x0115C988, 0x01149C34, 0x0113716B, 0x01124925, 0x01112359,
    0x01100000, 0x010EDF12, 0x010DC087, 0x010CA458, 0x010B8A7E, 0x010A72F0, 0x01095DA9, 0x01084AA0,
    0x010739CE, 0x01062B2E, 0x01051EB8, 0x01041466, 0x01030C31, 0x01020612, 0x01010204, 0x01000000
};

#ifdef BUILD_DIVIDE_TABLE
void SkUnPreMultiply_BuildTable() {
    for (unsigned i = 0; i <= 255; i++) {
        uint32_t scale;

        if (0 == i) {
            scale = 0;
        } else {
            scale = ((255 << 24) + (i >> 1)) / i;
        }

        SkDebugf(" 0x%08X,", scale);
        if ((i & 7) == 7) {
            SkDebugf("\n");
        }

        // test the result
        for (int j = 1; j <= i; j++) {
            uint32_t test = (j * scale + (1 << 23)) >> 24;
            uint32_t div = roundf(j * 255.0f / i);
            int diff = SkAbs32(test - div);
            SkASSERT(diff <= 1 && test <= 255);
        }
    }
}
#endif