/*
 * Copyright (C) 2010 Sencha, Inc.
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "config.h"
#include "ContextShadow.h"

namespace WebCore {

ContextShadow::ContextShadow()
    : type(NoShadow)
    , blurRadius(0)
{
}

ContextShadow::ContextShadow(const QColor& c, float r, qreal dx, qreal dy)
    : color(c)
    , blurRadius(qRound(r))
    , offset(dx, dy)
{
    // The type of shadow is decided by the blur radius, shadow offset, and shadow color.
    if (!color.isValid() || !color.alpha()) {
        // Can't paint the shadow with invalid or invisible color.
        type = NoShadow;
    } else if (r > 0) {
        // Shadow is always blurred, even the offset is zero.
        type = BlurShadow;
    } else if (offset.isNull()) {
        // Without blur and zero offset means the shadow is fully hidden.
        type = NoShadow;
    } else {
        if (color.alpha() > 0)
            type = AlphaSolidShadow;
        else
            type = OpaqueSolidShadow;
    }
}

void ContextShadow::clear()
{
    type = NoShadow;
    color = QColor();
    blurRadius = 0;
    offset = QPointF(0, 0);
}

// Instead of integer division, we use 18.14 for fixed-point division.
static const int BlurSumShift = 14;

// Note: image must be RGB32 format
static void blurHorizontal(QImage& image, int radius, bool swap = false)
{
    Q_ASSERT(image.format() == QImage::Format_ARGB32_Premultiplied);

    // See comments in http://webkit.org/b/40793, it seems sensible
    // to follow Skia's limit of 128 pixels of blur radius
    radius = qMin(128, radius);

    int imgWidth = image.width();
    int imgHeight = image.height();

    // Check http://www.w3.org/TR/SVG/filters.html#feGaussianBlur
    // for the approaches when the box-blur radius is even vs odd.
    int dmax = radius >> 1;
    int dmin = qMax(0, dmax - 1 + (radius & 1));

    for (int y = 0; y < imgHeight; ++y) {

        unsigned char* pixels = image.scanLine(y);

        int left;
        int right;
        int pixelCount;
        int prev;
        int next;
        int firstAlpha;
        int lastAlpha;
        int totalAlpha;
        unsigned char* target;
        unsigned char* prevPtr;
        unsigned char* nextPtr;

        int invCount;

        static const int alphaChannel = 3;
        static const int blueChannel = 0;
        static const int greenChannel = 1;

        // For each step, we use sliding window algorithm. This is much more
        // efficient than computing the sum of each pixels covered by the box
        // kernel size for each x.

        // As noted in the SVG filter specification, running box blur 3x
        // approximates a real gaussian blur nicely.

        // Step 1: blur alpha channel and store the result in the blue channel.
        left = swap ? dmax : dmin;
        right = swap ? dmin : dmax;
        pixelCount = left + 1 + right;
        invCount = (1 << BlurSumShift) / pixelCount;
        prev = -left;
        next = 1 + right;
        firstAlpha = pixels[alphaChannel];
        lastAlpha = pixels[(imgWidth - 1) * 4 + alphaChannel];
        totalAlpha = 0;
        for (int i = 0; i < pixelCount; ++i)
            totalAlpha += pixels[qBound(0, i - left, imgWidth - 1) * 4 + alphaChannel];
        target = pixels + blueChannel;
        prevPtr = pixels + prev * 4 + alphaChannel;
        nextPtr = pixels + next * 4 + alphaChannel;
        for (int x = 0; x < imgWidth; ++x, ++prev, ++next, target += 4, prevPtr += 4, nextPtr += 4) {
            *target = (totalAlpha * invCount) >> BlurSumShift;
            int delta = ((next < imgWidth) ? *nextPtr : lastAlpha) -
                        ((prev > 0) ? *prevPtr : firstAlpha);
            totalAlpha += delta;
        }

        // Step 2: blur blue channel and store the result in the green channel.
        left = swap ? dmin : dmax;
        right = swap ? dmax : dmin;
        pixelCount = left + 1 + right;
        invCount = (1 << BlurSumShift) / pixelCount;
        prev = -left;
        next = 1 + right;
        firstAlpha = pixels[blueChannel];
        lastAlpha = pixels[(imgWidth - 1) * 4 + blueChannel];
        totalAlpha = 0;
        for (int i = 0; i < pixelCount; ++i)
            totalAlpha += pixels[qBound(0, i - left, imgWidth - 1) * 4 + blueChannel];
        target = pixels + greenChannel;
        prevPtr = pixels + prev * 4 + blueChannel;
        nextPtr = pixels + next * 4 + blueChannel;
        for (int x = 0; x < imgWidth; ++x, ++prev, ++next, target += 4, prevPtr += 4, nextPtr += 4) {
            *target = (totalAlpha * invCount) >> BlurSumShift;
            int delta = ((next < imgWidth) ? *nextPtr : lastAlpha) -
                        ((prev > 0) ? *prevPtr : firstAlpha);
            totalAlpha += delta;
        }

        // Step 3: blur green channel and store the result in the alpha channel.
        left = dmax;
        right = dmax;
        pixelCount = left + 1 + right;
        invCount = (1 << BlurSumShift) / pixelCount;
        prev = -left;
        next = 1 + right;
        firstAlpha = pixels[greenChannel];
        lastAlpha = pixels[(imgWidth - 1) * 4 + greenChannel];
        totalAlpha = 0;
        for (int i = 0; i < pixelCount; ++i)
            totalAlpha += pixels[qBound(0, i - left, imgWidth - 1) * 4 + greenChannel];
        target = pixels + alphaChannel;
        prevPtr = pixels + prev * 4 + greenChannel;
        nextPtr = pixels + next * 4 + greenChannel;
        for (int x = 0; x < imgWidth; ++x, ++prev, ++next, target += 4, prevPtr += 4, nextPtr += 4) {
            *target = (totalAlpha * invCount) >> BlurSumShift;
            int delta = ((next < imgWidth) ? *nextPtr : lastAlpha) -
                        ((prev > 0) ? *prevPtr : firstAlpha);
            totalAlpha += delta;
        }
    }
}

static void shadowBlur(QImage& image, int radius, const QColor& shadowColor)
{
    blurHorizontal(image, radius);

    QTransform transform;
    transform.rotate(90);
    image = image.transformed(transform);
    blurHorizontal(image, radius, true);
    transform.reset();
    transform.rotate(270);
    image = image.transformed(transform);

    // "Colorize" with the right shadow color.
    QPainter p(&image);
    p.setCompositionMode(QPainter::CompositionMode_SourceIn);
    p.fillRect(image.rect(), shadowColor.rgb());
    p.end();
}

void ContextShadow::drawShadowRect(QPainter* p, const QRectF& rect)
{
    if (type == NoShadow)
        return;

    if (type == BlurShadow) {
        QRectF shadowRect = rect.translated(offset);

        // We expand the area by the blur radius * 2 to give extra space
        // for the blur transition.
        int extra = blurRadius * 2;
        QRectF bufferRect = shadowRect.adjusted(-extra, -extra, extra, extra);
        QRect alignedBufferRect = bufferRect.toAlignedRect();

        QRect clipRect;
        if (p->hasClipping())
            clipRect = p->clipRegion().boundingRect();
        else
            clipRect = p->transform().inverted().mapRect(p->window());

        if (!clipRect.contains(alignedBufferRect)) {

            // No need to have the buffer larger that the clip.
            alignedBufferRect = alignedBufferRect.intersected(clipRect);
            if (alignedBufferRect.isEmpty())
                return;

            // We adjust again because the pixels at the borders are still
            // potentially affected by the pixels outside the buffer.
            alignedBufferRect.adjust(-extra, -extra, extra, extra);
        }

        QImage shadowImage(alignedBufferRect.size(), QImage::Format_ARGB32_Premultiplied);
        shadowImage.fill(Qt::transparent);
        QPainter shadowPainter(&shadowImage);

        shadowPainter.fillRect(shadowRect.translated(-alignedBufferRect.topLeft()), color);
        shadowPainter.end();

        shadowBlur(shadowImage, blurRadius, color);

        p->drawImage(alignedBufferRect.topLeft(), shadowImage);

        return;
    }

    p->fillRect(rect.translated(offset), color);
}


}