gecko/gfx/thebes/src/gfxUtils.cpp

/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
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 *
 * Software distributed under the License is distributed on an "AS IS" basis,
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 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla Corporation code.
 *
 * The Initial Developer of the Original Code is Mozilla Foundation.
 * Portions created by the Initial Developer are Copyright (C) 2010
 * the Initial Developer. All Rights Reserved.
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 * Contributor(s):
 *   Vladimir Vukicevic <vladimir@pobox.com>
 *
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 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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#include "gfxImageSurface.h"
#include "gfxUtils.h"

static PRUint8 sUnpremultiplyTable[256*256];
static PRUint8 sPremultiplyTable[256*256];
static PRBool sTablesInitialized = PR_FALSE;

static const PRUint8 PremultiplyValue(PRUint8 a, PRUint8 v) {
    return sPremultiplyTable[a*256+v];
}

static const PRUint8 UnpremultiplyValue(PRUint8 a, PRUint8 v) {
    return sUnpremultiplyTable[a*256+v];
}

static void
CalculateTables()
{
    // It's important that the array be indexed first by alpha and then by rgb
    // value.  When we unpremultiply a pixel, we're guaranteed to do three
    // lookups with the same alpha; indexing by alpha first makes it likely that
    // those three lookups will be close to one another in memory, thus
    // increasing the chance of a cache hit.

    // Unpremultiply table

    // a == 0 case
    for (PRUint32 c = 0; c <= 255; c++) {
        sUnpremultiplyTable[c] = c;
    }

    for (int a = 1; a <= 255; a++) {
        for (int c = 0; c <= 255; c++) {
            sUnpremultiplyTable[a*256+c] = (PRUint8)((c * 255) / a);
        }
    }

    // Premultiply table

    for (int a = 0; a <= 255; a++) {
        for (int c = 0; c <= 255; c++) {
            sPremultiplyTable[a*256+c] = (a * c + 254) / 255;
        }
    }

    sTablesInitialized = PR_TRUE;
}

void
gfxUtils::PremultiplyImageSurface(gfxImageSurface *aSourceSurface,
                                  gfxImageSurface *aDestSurface)
{
    if (!aDestSurface)
        aDestSurface = aSourceSurface;

    NS_ASSERTION(aSourceSurface->Format() == aDestSurface->Format() &&
                 aSourceSurface->Width() == aDestSurface->Width() &&
                 aSourceSurface->Height() == aDestSurface->Height() &&
                 aSourceSurface->Stride() == aDestSurface->Stride(),
                 "Source and destination surfaces don't have identical characteristics");

    NS_ASSERTION(aSourceSurface->Stride() == aSourceSurface->Width() * 4,
                 "Source surface stride isn't tightly packed");

    // Only premultiply ARGB32
    if (aSourceSurface->Format() != gfxASurface::ImageFormatARGB32) {
        if (aDestSurface != aSourceSurface) {
            memcpy(aDestSurface->Data(), aSourceSurface->Data(),
                   aSourceSurface->Stride() * aSourceSurface->Height());
        }
        return;
    }

    if (!sTablesInitialized)
        CalculateTables();

    PRUint8 *src = aSourceSurface->Data();
    PRUint8 *dst = aDestSurface->Data();

    PRUint32 dim = aSourceSurface->Width() * aSourceSurface->Height();
    for (PRUint32 i = 0; i < dim; ++i) {
#ifdef IS_LITTLE_ENDIAN
        PRUint8 b = *src++;
        PRUint8 g = *src++;
        PRUint8 r = *src++;
        PRUint8 a = *src++;

        *dst++ = PremultiplyValue(a, b);
        *dst++ = PremultiplyValue(a, g);
        *dst++ = PremultiplyValue(a, r);
        *dst++ = a;
#else
        PRUint8 a = *src++;
        PRUint8 r = *src++;
        PRUint8 g = *src++;
        PRUint8 b = *src++;

        *dst++ = a;
        *dst++ = PremultiplyValue(a, r);
        *dst++ = PremultiplyValue(a, g);
        *dst++ = PremultiplyValue(a, b);
#endif
    }
}

void
gfxUtils::UnpremultiplyImageSurface(gfxImageSurface *aSourceSurface,
                                    gfxImageSurface *aDestSurface)
{
    if (!aDestSurface)
        aDestSurface = aSourceSurface;

    NS_ASSERTION(aSourceSurface->Format() == aDestSurface->Format() &&
                 aSourceSurface->Width() == aDestSurface->Width() &&
                 aSourceSurface->Height() == aDestSurface->Height() &&
                 aSourceSurface->Stride() == aDestSurface->Stride(),
                 "Source and destination surfaces don't have identical characteristics");

    NS_ASSERTION(aSourceSurface->Stride() == aSourceSurface->Width() * 4,
                 "Source surface stride isn't tightly packed");

    // Only premultiply ARGB32
    if (aSourceSurface->Format() != gfxASurface::ImageFormatARGB32) {
        if (aDestSurface != aSourceSurface) {
            memcpy(aDestSurface->Data(), aSourceSurface->Data(),
                   aSourceSurface->Stride() * aSourceSurface->Height());
        }
        return;
    }

    if (!sTablesInitialized)
        CalculateTables();

    PRUint8 *src = aSourceSurface->Data();
    PRUint8 *dst = aDestSurface->Data();

    PRUint32 dim = aSourceSurface->Width() * aSourceSurface->Height();
    for (PRUint32 i = 0; i < dim; ++i) {
#ifdef IS_LITTLE_ENDIAN
        PRUint8 b = *src++;
        PRUint8 g = *src++;
        PRUint8 r = *src++;
        PRUint8 a = *src++;

        *dst++ = UnpremultiplyValue(a, b);
        *dst++ = UnpremultiplyValue(a, g);
        *dst++ = UnpremultiplyValue(a, r);
        *dst++ = a;
#else
        PRUint8 a = *src++;
        PRUint8 r = *src++;
        PRUint8 g = *src++;
        PRUint8 b = *src++;

        *dst++ = a;
        *dst++ = UnpremultiplyValue(a, r);
        *dst++ = UnpremultiplyValue(a, g);
        *dst++ = UnpremultiplyValue(a, b);
#endif
    }
}