flutter_flutter/engine/platform/graphics/Gradient.cpp

/*
 * Copyright (C) 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
 * Copyright (C) 2007 Alp Toker <alp@atoker.com>
 * Copyright (C) 2013 Google 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 "sky/engine/config.h"
#include "sky/engine/platform/graphics/Gradient.h"

#include "sky/engine/platform/geometry/FloatRect.h"
#include "sky/engine/platform/graphics/GraphicsContext.h"
#include "sky/engine/platform/graphics/skia/SkiaUtils.h"
#include "third_party/skia/include/core/SkColor.h"
#include "third_party/skia/include/core/SkColorShader.h"
#include "third_party/skia/include/core/SkShader.h"
#include "third_party/skia/include/effects/SkGradientShader.h"

typedef Vector<SkScalar, 8> ColorStopOffsetVector;
typedef Vector<SkColor, 8> ColorStopColorVector;

namespace blink {

Gradient::Gradient(const FloatPoint& p0, const FloatPoint& p1)
    : m_p0(p0)
    , m_p1(p1)
    , m_r0(0)
    , m_r1(0)
    , m_aspectRatio(1)
    , m_radial(false)
    , m_stopsSorted(false)
    , m_drawInPMColorSpace(false)
    , m_spreadMethod(SpreadMethodPad)
{
}

Gradient::Gradient(const FloatPoint& p0, float r0, const FloatPoint& p1, float r1, float aspectRatio)
    : m_p0(p0)
    , m_p1(p1)
    , m_r0(r0)
    , m_r1(r1)
    , m_aspectRatio(aspectRatio)
    , m_radial(true)
    , m_stopsSorted(false)
    , m_drawInPMColorSpace(false)
    , m_spreadMethod(SpreadMethodPad)
{
}

Gradient::~Gradient()
{
}

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

void Gradient::addColorStop(const Gradient::ColorStop& stop)
{
    if (m_stops.isEmpty()) {
        m_stopsSorted = true;
    } else {
        m_stopsSorted = m_stopsSorted && compareStops(m_stops.last(), stop);
    }

    m_stops.append(stop);
    m_gradient.clear();
}

void Gradient::sortStopsIfNecessary()
{
    if (m_stopsSorted)
        return;

    m_stopsSorted = true;

    if (!m_stops.size())
        return;

    std::stable_sort(m_stops.begin(), m_stops.end(), compareStops);
}

bool Gradient::hasAlpha() const
{
    for (size_t i = 0; i < m_stops.size(); i++) {
        if (m_stops[i].color.hasAlpha())
            return true;
    }

    return false;
}

void Gradient::setSpreadMethod(GradientSpreadMethod spreadMethod)
{
    // FIXME: Should it become necessary, allow calls to this method after m_gradient has been set.
    ASSERT(!m_gradient);

    if (m_spreadMethod == spreadMethod)
        return;

    m_spreadMethod = spreadMethod;
}

void Gradient::setDrawsInPMColorSpace(bool drawInPMColorSpace)
{
    if (drawInPMColorSpace == m_drawInPMColorSpace)
        return;

    m_drawInPMColorSpace = drawInPMColorSpace;
    m_gradient.clear();
}

void Gradient::setGradientSpaceTransform(const AffineTransform& gradientSpaceTransformation)
{
    if (m_gradientSpaceTransformation == gradientSpaceTransformation)
        return;

    m_gradientSpaceTransformation = gradientSpaceTransformation;
    m_gradient.clear();
}

// 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)
{
    // N.B.: The tests in this function should kept in sync with the ones in
    // fillStops(), or badness happens.
    const Gradient::ColorStop* stop = stopData;
    size_t countUsed = count;
    if (count < 1 || stop->stop > 0.0)
        countUsed++;
    stop += count - 1;
    if (count < 1 || stop->stop < 1.0)
        countUsed++;
    return countUsed;
}

// FIXME: This would be more at home as Color::operator SkColor.
static inline SkColor makeSkColor(const Color& c)
{
    return SkColorSetARGB(c.alpha(), c.red(), c.green(), c.blue());
}

// 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, ColorStopOffsetVector& pos, ColorStopColorVector& 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] = SK_ColorTRANSPARENT;
        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->color);
        start = 1;
    }

    for (size_t i = start; i < start + count; i++) {
        pos[i] = WebCoreFloatToSkScalar(stop->stop);
        colors[i] = makeSkColor(stop->color);
        ++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];
    }
}

SkShader* Gradient::shader()
{
    if (m_gradient)
        return m_gradient.get();

    sortStopsIfNecessary();
    ASSERT(m_stopsSorted);

    size_t countUsed = totalStopsNeeded(m_stops.data(), m_stops.size());
    ASSERT(countUsed >= 2);
    ASSERT(countUsed >= m_stops.size());

    ColorStopOffsetVector pos(countUsed);
    ColorStopColorVector colors(countUsed);
    fillStops(m_stops.data(), m_stops.size(), pos, colors);

    SkShader::TileMode tile = SkShader::kClamp_TileMode;
    switch (m_spreadMethod) {
    case SpreadMethodReflect:
        tile = SkShader::kMirror_TileMode;
        break;
    case SpreadMethodRepeat:
        tile = SkShader::kRepeat_TileMode;
        break;
    case SpreadMethodPad:
        tile = SkShader::kClamp_TileMode;
        break;
    }

    uint32_t shouldDrawInPMColorSpace = m_drawInPMColorSpace ? SkGradientShader::kInterpolateColorsInPremul_Flag : 0;
    if (m_radial) {
        if (aspectRatio() != 1) {
            // CSS3 elliptical gradients: apply the elliptical scaling at the
            // gradient center point.
            m_gradientSpaceTransformation.translate(m_p0.x(), m_p0.y());
            m_gradientSpaceTransformation.scale(1, 1 / aspectRatio());
            m_gradientSpaceTransformation.translate(-m_p0.x(), -m_p0.y());
            ASSERT(m_p0 == m_p1);
        }
        SkMatrix localMatrix = affineTransformToSkMatrix(m_gradientSpaceTransformation);

        // Since the two-point radial gradient is slower than the plain radial,
        // only use it if we have to.
        if (m_p0 == m_p1 && m_r0 <= 0.0f) {
            m_gradient = adoptRef(SkGradientShader::CreateRadial(m_p1.data(), m_r1, colors.data(), pos.data(), static_cast<int>(countUsed), tile, shouldDrawInPMColorSpace, &localMatrix));
        } else {
            // The radii we give to Skia must be positive. If we're given a
            // negative radius, ask for zero instead.
            SkScalar radius0 = m_r0 >= 0.0f ? WebCoreFloatToSkScalar(m_r0) : 0;
            SkScalar radius1 = m_r1 >= 0.0f ? WebCoreFloatToSkScalar(m_r1) : 0;
            m_gradient = adoptRef(SkGradientShader::CreateTwoPointConical(m_p0.data(), radius0, m_p1.data(), radius1, colors.data(), pos.data(), static_cast<int>(countUsed), tile, shouldDrawInPMColorSpace, &localMatrix));
        }
    } else {
        SkPoint pts[2] = { m_p0.data(), m_p1.data() };
        SkMatrix localMatrix = affineTransformToSkMatrix(m_gradientSpaceTransformation);
        m_gradient = adoptRef(SkGradientShader::CreateLinear(pts, colors.data(), pos.data(), static_cast<int>(countUsed), tile, shouldDrawInPMColorSpace, &localMatrix));
    }

    if (!m_gradient) {
        // use last color, since our "geometry" was degenerate (e.g. radius==0)
        m_gradient = adoptRef(new SkColorShader(colors[countUsed - 1]));
    }
    return m_gradient.get();
}

} // namespace blink