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 * Copyright (c) 2008, Google Inc. All rights reserved.
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 * modification, are permitted provided that the following conditions are
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 * 
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 * in the documentation and/or other materials provided with the
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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 */

#include "config.h"
#include "Gradient.h"

#include "CSSParser.h"
#include "GraphicsContext.h"

#include "SkGradientShader.h"
#include "SkiaUtils.h"

namespace WebCore {

void Gradient::platformDestroy()
{
    if (m_gradient)
        m_gradient->safeUnref();
    m_gradient = 0;
}

static inline U8CPU F2B(float x)
{
    return static_cast<int>(x * 255);
}

static SkColor makeSkColor(float a, float r, float g, float b)
{
    return SkColorSetARGB(F2B(a), F2B(r), F2B(g), F2B(b));
}

// Determine the total number of stops needed, including pseudo-stops at the
// ends as necessary.
static size_t totalStopsNeeded(const Gradient::ColorStop* stopData, size_t count)
{
    const Gradient::ColorStop* stop = stopData;
    size_t countUsed = count;
    if (count < 1 || stop->stop > 0.0)
        countUsed++;
    stop += count - 1;
    if (count < 2 || stop->stop < 1.0)
        countUsed++;
    return countUsed;
}

// Collect sorted stop position and color information into the pos and colors 
// buffers, ensuring stops at both 0.0 and 1.0.  The buffers must be large
// enough to hold information for all stops, including the new endpoints if
// stops at 0.0 and 1.0 aren't already included.
static void fillStops(const Gradient::ColorStop* stopData,
                       size_t count, SkScalar* pos, SkColor* colors)
{ 
    const Gradient::ColorStop* stop = stopData;
    size_t start = 0;
    if (count < 1) {
        // A gradient with no stops must be transparent black.
        pos[0] = WebCoreFloatToSkScalar(0.0);
        colors[0] = makeSkColor(0.0, 0.0, 0.0, 0.0);
        start = 1;
    } else if (stop->stop > 0.0) {
        // Copy the first stop to 0.0. The first stop position may have a slight
        // rounding error, but we don't care in this float comparison, since
        // 0.0 comes through cleanly and people aren't likely to want a gradient
        // with a stop at (0 + epsilon).
        pos[0] = WebCoreFloatToSkScalar(0.0);
        colors[0] = makeSkColor(stop->alpha, stop->red, stop->green, stop->blue);
        start = 1;
    }

    for (size_t i = start; i < start + count; i++) {
        pos[i] = WebCoreFloatToSkScalar(stop->stop);
        colors[i] = makeSkColor(stop->alpha, stop->red, stop->green, stop->blue);
        ++stop;
    }

    // Copy the last stop to 1.0 if needed.  See comment above about this float
    // comparison.
    if (count < 1 || (--stop)->stop < 1.0) {
        pos[start + count] = WebCoreFloatToSkScalar(1.0);
        colors[start + count] = colors[start + count - 1];
    }
}

static inline bool compareStops(const Gradient::ColorStop& a, const Gradient::ColorStop& b)
{
    return a.stop < b.stop;
}

SkShader* Gradient::platformGradient()
{
    if (m_gradient)
        return m_gradient;

    // FIXME: This and compareStops() are also in Gradient.cpp and
    // CSSGradientValue.cpp; probably should refactor in WebKit.
    if (!m_stopsSorted) {
        if (m_stops.size())
            std::stable_sort(m_stops.begin(), m_stops.end(), compareStops);
        m_stopsSorted = true;
    }
    size_t countUsed = totalStopsNeeded(m_stops.data(), m_stops.size());
    ASSERT(countUsed >= 2);
    ASSERT(countUsed >= m_stops.size());

    // FIXME: Why is all this manual pointer math needed?!
    SkAutoMalloc storage(countUsed * (sizeof(SkColor) + sizeof(SkScalar)));
    SkColor* colors = (SkColor*)storage.get();
    SkScalar* pos = (SkScalar*)(colors + countUsed);

    fillStops(m_stops.data(), m_stops.size(), pos, colors);

    if (m_radial) {
        // FIXME: CSS radial Gradients allow an offset focal point (the
        // "start circle"), but skia doesn't seem to support that, so this just
        // ignores m_p0/m_r0 and draws the gradient centered in the "end
        // circle" (m_p1/m_r1).
        // See http://webkit.org/blog/175/introducing-css-gradients/ for a
        // description of the expected behavior.
        m_gradient = SkGradientShader::CreateRadial(m_p1,
            WebCoreFloatToSkScalar(m_r1), colors, pos,
            static_cast<int>(countUsed), SkShader::kClamp_TileMode);
    } else {
        SkPoint pts[2] = { m_p0, m_p1 };
        m_gradient = SkGradientShader::CreateLinear(pts, colors, pos,
            static_cast<int>(countUsed), SkShader::kClamp_TileMode);
    }

    return m_gradient;
}

void Gradient::fill(GraphicsContext* context, const FloatRect& rect)
{
    context->setFillGradient(this);
    context->fillRect(rect);
}

} // namespace WebCore
