source: webkit/trunk/Source/WebCore/css/CSSGradientValue.cpp

/*
 * Copyright (C) 2008-2021 Apple 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.
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#include "config.h"
#include "CSSGradientValue.h"

#include "CSSCalcValue.h"
#include "CSSToLengthConversionData.h"
#include "CSSValueKeywords.h"
#include "ColorInterpolation.h"
#include "GeometryUtilities.h"
#include "GradientImage.h"
#include "NodeRenderStyle.h"
#include "Pair.h"
#include "RenderElement.h"
#include "RenderView.h"
#include "StyleBuilderState.h"
#include <wtf/text/StringBuilder.h>

namespace WebCore {

static inline Ref<Gradient> createGradient(CSSGradientValue& value, RenderElement& renderer, FloatSize size)
{
    if (is<CSSLinearGradientValue>(value))
        return downcast<CSSLinearGradientValue>(value).createGradient(renderer, size);
    if (is<CSSRadialGradientValue>(value))
        return downcast<CSSRadialGradientValue>(value).createGradient(renderer, size);
    return downcast<CSSConicGradientValue>(value).createGradient(renderer, size);
}

RefPtr<Image> CSSGradientValue::image(RenderElement& renderer, const FloatSize& size)
{
    if (size.isEmpty())
        return nullptr;
    bool cacheable = isCacheable() && !renderer.style().hasAppleColorFilter();
    if (cacheable) {
        if (!clients().contains(&renderer))
            return nullptr;
        if (auto* result = cachedImageForSize(size))
            return result;
    }
    auto newImage = GradientImage::create(createGradient(*this, renderer, size), size);
    if (cacheable)
        saveCachedImageForSize(size, newImage);
    return newImage;
}

struct GradientStop {
    Color color;
    std::optional<float> offset;

    bool isSpecified() const { return offset.has_value(); }
    bool isMidpoint() const { return !color.isValid(); }
};

static inline Ref<CSSGradientValue> clone(CSSGradientValue& value)
{
    if (is<CSSLinearGradientValue>(value))
        return downcast<CSSLinearGradientValue>(value).clone();
    if (is<CSSRadialGradientValue>(value))
        return downcast<CSSRadialGradientValue>(value).clone();
    ASSERT(is<CSSConicGradientValue>(value));
    return downcast<CSSConicGradientValue>(value).clone();
}

template<typename Function> void resolveStopColors(Vector<CSSGradientColorStop, 2>& stops, Function&& colorResolveFunction)
{
    for (auto& stop : stops) {
        if (stop.color)
            stop.resolvedColor = colorResolveFunction(*stop.color);
    }
}

bool CSSGradientValue::hasColorDerivedFromElement() const
{
    if (!m_hasColorDerivedFromElement) {
        m_hasColorDerivedFromElement = false;
        for (auto& stop : m_stops) {
            if (stop.color && Style::BuilderState::isColorFromPrimitiveValueDerivedFromElement(*stop.color)) {
                m_hasColorDerivedFromElement = true;
                break;
            }
        }
    }
    return *m_hasColorDerivedFromElement;
}

Ref<CSSGradientValue> CSSGradientValue::valueWithStylesResolved(Style::BuilderState& builderState)
{
    auto result = hasColorDerivedFromElement() ? clone(*this) : Ref { *this };
    resolveStopColors(result->m_stops, [&](const CSSPrimitiveValue& colorValue) {
        return builderState.colorFromPrimitiveValueWithResolvedCurrentColor(colorValue);
    });
    return result;
}

void CSSGradientValue::resolveRGBColors()
{
    resolveStopColors(m_stops, [&](const CSSPrimitiveValue& colorValue) {
        ASSERT(colorValue.isRGBColor());
        return colorValue.color();
    });
}

class LinearGradientAdapter {
public:
    explicit LinearGradientAdapter(Gradient::LinearData& data)
        : m_data(data)
    {
    }

    float gradientLength() const
    {
        auto gradientSize = m_data.point0 - m_data.point1;
        return gradientSize.diagonalLength();
    }
    float maxExtent(float, float) const { return 1; }

    void normalizeStopsAndEndpointsOutsideRange(Vector<GradientStop>& stops, ColorInterpolationMethod)
    {
        float firstOffset = *stops.first().offset;
        float lastOffset = *stops.last().offset;
        if (firstOffset != lastOffset) {
            float scale = lastOffset - firstOffset;

            for (auto& stop : stops)
                stop.offset = (*stop.offset - firstOffset) / scale;

            auto p0 = m_data.point0;
            auto p1 = m_data.point1;
            m_data.point0 = { p0.x() + firstOffset * (p1.x() - p0.x()), p0.y() + firstOffset * (p1.y() - p0.y()) };
            m_data.point1 = { p1.x() + (lastOffset - 1) * (p1.x() - p0.x()), p1.y() + (lastOffset - 1) * (p1.y() - p0.y()) };
        } else {
            // There's a single position that is outside the scale, clamp the positions to 1.
            for (auto& stop : stops)
                stop.offset = 1;
        }
    }

private:
    Gradient::LinearData& m_data;
};

class RadialGradientAdapter {
public:
    explicit RadialGradientAdapter(Gradient::RadialData& data)
        : m_data(data)
    {
    }

    float gradientLength() const { return m_data.endRadius; }

    // Radial gradients may need to extend further than the endpoints, because they have
    // to repeat out to the corners of the box.
    float maxExtent(float maxLengthForRepeat, float gradientLength) const
    {
        if (maxLengthForRepeat > gradientLength)
            return gradientLength > 0 ? maxLengthForRepeat / gradientLength : 0;
        return 1;
    }

    void normalizeStopsAndEndpointsOutsideRange(Vector<GradientStop>& stops, ColorInterpolationMethod colorInterpolationMethod)
    {
        auto numStops = stops.size();

        // Rather than scaling the points < 0, we truncate them, so only scale according to the largest point.
        float firstOffset = 0;
        float lastOffset = *stops.last().offset;
        float scale = lastOffset - firstOffset;

        // Reset points below 0 to the first visible color.
        size_t firstZeroOrGreaterIndex = numStops;
        for (size_t i = 0; i < numStops; ++i) {
            if (*stops[i].offset >= 0) {
                firstZeroOrGreaterIndex = i;
                break;
            }
        }

        if (firstZeroOrGreaterIndex > 0) {
            if (firstZeroOrGreaterIndex < numStops && *stops[firstZeroOrGreaterIndex].offset > 0) {
                float prevOffset = *stops[firstZeroOrGreaterIndex - 1].offset;
                float nextOffset = *stops[firstZeroOrGreaterIndex].offset;

                float interStopProportion = -prevOffset / (nextOffset - prevOffset);
                auto blendedColor = interpolateColors(colorInterpolationMethod, stops[firstZeroOrGreaterIndex - 1].color, 1.0f - interStopProportion, stops[firstZeroOrGreaterIndex].color, interStopProportion);

                // Clamp the positions to 0 and set the color.
                for (size_t i = 0; i < firstZeroOrGreaterIndex; ++i) {
                    stops[i].offset = 0;
                    stops[i].color = blendedColor;
                }
            } else {
                // All stops are below 0; just clamp them.
                for (size_t i = 0; i < firstZeroOrGreaterIndex; ++i)
                    stops[i].offset = 0;
            }
        }

        for (auto& stop : stops)
            *stop.offset /= scale;

        m_data.startRadius *= scale;
        m_data.endRadius *= scale;
    }

private:
    Gradient::RadialData& m_data;
};

class ConicGradientAdapter {
public:
    float gradientLength() const { return 1; }
    float maxExtent(float, float) const { return 1; }

    void normalizeStopsAndEndpointsOutsideRange(Vector<GradientStop>& stops, ColorInterpolationMethod colorInterpolationMethod)
    {
        size_t numStops = stops.size();
        size_t lastStopIndex = numStops - 1;

        std::optional<size_t> firstZeroOrGreaterIndex;
        for (size_t i = 0; i < numStops; ++i) {
            if (*stops[i].offset >= 0) {
                firstZeroOrGreaterIndex = i;
                break;
            }
        }

        if (firstZeroOrGreaterIndex) {
            size_t index = *firstZeroOrGreaterIndex;
            if (index > 0) {
                float previousOffset = *stops[index - 1].offset;
                float nextOffset = *stops[index].offset;

                float interStopProportion = -previousOffset / (nextOffset - previousOffset);
                auto blendedColor = interpolateColors(colorInterpolationMethod, stops[index - 1].color, 1.0f - interStopProportion, stops[index].color, interStopProportion);

                // Clamp the positions to 0 and set the color.
                for (size_t i = 0; i < index; ++i) {
                    stops[i].offset = 0;
                    stops[i].color = blendedColor;
                }
            }
        } else {
            // All stop offsets below 0, clamp them.
            for (auto& stop : stops)
                stop.offset = 0;
        }

        std::optional<size_t> lastOneOrLessIndex;
        for (int i = lastStopIndex; i >= 0; --i) {
            if (*stops[i].offset <= 1) {
                lastOneOrLessIndex = i;
                break;
            }
        }

        if (lastOneOrLessIndex) {
            size_t index = *lastOneOrLessIndex;
            if (index < lastStopIndex) {
                float previousOffset = *stops[index].offset;
                float nextOffset = *stops[index + 1].offset;

                float interStopProportion = (1 - previousOffset) / (nextOffset - previousOffset);
                auto blendedColor = interpolateColors(colorInterpolationMethod, stops[index].color, 1.0f - interStopProportion, stops[index + 1].color, interStopProportion);

                // Clamp the positions to 1 and set the color.
                for (size_t i = index + 1; i < numStops; ++i) {
                    stops[i].offset = 1;
                    stops[i].color = blendedColor;
                }
            }
        } else {
            // All stop offsets above 1, clamp them.
            for (auto& stop : stops)
                stop.offset = 1;
        }
    }
};

template<typename GradientAdapter>
GradientColorStops CSSGradientValue::computeStops(GradientAdapter& gradientAdapter, const CSSToLengthConversionData& conversionData, const RenderStyle& style, float maxLengthForRepeat)
{
    bool hasColorFilter = style.hasAppleColorFilter();

    if (m_gradientType == CSSDeprecatedLinearGradient || m_gradientType == CSSDeprecatedRadialGradient) {
        GradientColorStops::StopVector result;
        result.reserveInitialCapacity(m_stops.size());
        
        for (auto& stop : m_stops) {
            float offset;
            if (stop.position->isPercentage())
                offset = stop.position->floatValue(CSSUnitType::CSS_PERCENTAGE) / 100;
            else
                offset = stop.position->floatValue(CSSUnitType::CSS_NUMBER);

            result.uncheckedAppend({ offset, hasColorFilter ? style.colorByApplyingColorFilter(stop.resolvedColor) : stop.resolvedColor });
        }

        std::stable_sort(result.begin(), result.end(), [] (const GradientColorStop& a, const GradientColorStop& b) {
            return a.offset < b.offset;
        });

        return GradientColorStops::Sorted { WTFMove(result) };
    }

    size_t numStops = m_stops.size();
    Vector<GradientStop> stops(numStops);

    float gradientLength = gradientAdapter.gradientLength();

    for (size_t i = 0; i < numStops; ++i) {
        auto& stop = m_stops[i];

        stops[i].color = hasColorFilter ? style.colorByApplyingColorFilter(stop.resolvedColor) : stop.resolvedColor;

        if (stop.position) {
            auto& positionValue = *stop.position;
            if (positionValue.isPercentage())
                stops[i].offset = positionValue.floatValue(CSSUnitType::CSS_PERCENTAGE) / 100;
            else if (positionValue.isLength() || positionValue.isViewportPercentageLength() || positionValue.isCalculatedPercentageWithLength()) {
                float length;
                if (positionValue.isLength())
                    length = positionValue.computeLength<float>(conversionData);
                else {
                    Ref<CalculationValue> calculationValue { positionValue.cssCalcValue()->createCalculationValue(conversionData) };
                    length = calculationValue->evaluate(gradientLength);
                }
                stops[i].offset = (gradientLength > 0) ? length / gradientLength : 0;
            } else if (positionValue.isAngle())
                stops[i].offset = positionValue.floatValue(CSSUnitType::CSS_DEG) / 360;
            else {
                ASSERT_NOT_REACHED();
                stops[i].offset = 0;
            }
        } else {
            // If the first color-stop does not have a position, its position defaults to 0%.
            // If the last color-stop does not have a position, its position defaults to 100%.
            if (!i)
                stops[i].offset = 0;
            else if (numStops > 1 && i == numStops - 1)
                stops[i].offset = 1;
        }

        // If a color-stop has a position that is less than the specified position of any
        // color-stop before it in the list, its position is changed to be equal to the
        // largest specified position of any color-stop before it.
        if (stops[i].isSpecified() && i > 0) {
            size_t prevSpecifiedIndex;
            for (prevSpecifiedIndex = i - 1; prevSpecifiedIndex; --prevSpecifiedIndex) {
                if (stops[prevSpecifiedIndex].isSpecified())
                    break;
            }

            if (*stops[i].offset < *stops[prevSpecifiedIndex].offset)
                stops[i].offset = stops[prevSpecifiedIndex].offset;
        }
    }

    ASSERT(stops[0].isSpecified() && stops[numStops - 1].isSpecified());

    // If any color-stop still does not have a position, then, for each run of adjacent
    // color-stops without positions, set their positions so that they are evenly spaced
    // between the preceding and following color-stops with positions.
    if (numStops > 2) {
        size_t unspecifiedRunStart = 0;
        bool inUnspecifiedRun = false;

        for (size_t i = 0; i < numStops; ++i) {
            if (!stops[i].isSpecified() && !inUnspecifiedRun) {
                unspecifiedRunStart = i;
                inUnspecifiedRun = true;
            } else if (stops[i].isSpecified() && inUnspecifiedRun) {
                size_t unspecifiedRunEnd = i;

                if (unspecifiedRunStart < unspecifiedRunEnd) {
                    float lastSpecifiedOffset = *stops[unspecifiedRunStart - 1].offset;
                    float nextSpecifiedOffset = *stops[unspecifiedRunEnd].offset;
                    float delta = (nextSpecifiedOffset - lastSpecifiedOffset) / (unspecifiedRunEnd - unspecifiedRunStart + 1);

                    for (size_t j = unspecifiedRunStart; j < unspecifiedRunEnd; ++j)
                        stops[j].offset = lastSpecifiedOffset + (j - unspecifiedRunStart + 1) * delta;
                }

                inUnspecifiedRun = false;
            }
        }
    }

    // Walk over the color stops, look for midpoints and add stops as needed.
    // If mid < 50%, add 2 stops to the left and 6 to the right
    // else add 6 stops to the left and 2 to the right.
    // Stops on the side with the most stops start midway because the curve approximates
    // a line in that region. We then add 5 more color stops on that side to minimize the change
    // how the luminance changes at each of the color stops. We don't have to add as many on the other side
    // since it becomes small which increases the differentation of luminance which hides the color stops.
    // Even with 4 extra color stops, it *is* possible to discern the steps when the gradient is large and has
    // large luminance differences between midpoint and color stop. If this becomes an issue, we can consider
    // making this algorithm a bit smarter.

    // Midpoints that coincide with color stops are treated specially since they don't require
    // extra stops and generate hard lines.
    for (size_t x = 1; x < stops.size() - 1;) {
        if (!stops[x].isMidpoint()) {
            ++x;
            continue;
        }

        // Find previous and next color so we know what to interpolate between.
        // We already know they have a color since we checked for that earlier.
        Color color1 = stops[x - 1].color;
        Color color2 = stops[x + 1].color;
        // Likewise find the position of previous and next color stop.
        float offset1 = *stops[x - 1].offset;
        float offset2 = *stops[x + 1].offset;
        float offset = *stops[x].offset;

        // Check if everything coincides or the midpoint is exactly in the middle.
        // If so, ignore the midpoint.
        if (offset - offset1 == offset2 - offset) {
            stops.remove(x);
            continue;
        }

        // Check if we coincide with the left color stop.
        if (offset1 == offset) {
            // Morph the midpoint to a regular stop with the color of the next color stop.
            stops[x].color = color2;
            continue;
        }

        // Check if we coincide with the right color stop.
        if (offset2 == offset) {
            // Morph the midpoint to a regular stop with the color of the previous color stop.
            stops[x].color = color1;
            continue;
        }

        float midpoint = (offset - offset1) / (offset2 - offset1);
        GradientStop newStops[9];
        if (midpoint > .5f) {
            for (size_t y = 0; y < 7; ++y)
                newStops[y].offset = offset1 + (offset - offset1) * (7 + y) / 13;

            newStops[7].offset = offset + (offset2 - offset) / 3;
            newStops[8].offset = offset + (offset2 - offset) * 2 / 3;
        } else {
            newStops[0].offset = offset1 + (offset - offset1) / 3;
            newStops[1].offset = offset1 + (offset - offset1) * 2 / 3;

            for (size_t y = 0; y < 7; ++y)
                newStops[y + 2].offset = offset + (offset2 - offset) * y / 13;
        }
        // calculate colors
        for (size_t y = 0; y < 9; ++y) {
            float relativeOffset = (*newStops[y].offset - offset1) / (offset2 - offset1);
            float multiplier = std::pow(relativeOffset, std::log(.5f) / std::log(midpoint));
            newStops[y].color = interpolateColors(m_colorInterpolationMethod.method, color1, 1.0f - multiplier, color2, multiplier);
        }

        stops.remove(x);
        stops.insert(x, newStops, 9);
        x += 9;
    }

    numStops = stops.size();

    // If the gradient is repeating, repeat the color stops.
    // We can't just push this logic down into the platform-specific Gradient code,
    // because we have to know the extent of the gradient, and possible move the end points.
    if (m_repeating && numStops > 1) {
        // If the difference in the positions of the first and last color-stops is 0,
        // the gradient defines a solid-color image with the color of the last color-stop in the rule.
        float gradientRange = *stops.last().offset - *stops.first().offset;
        if (!gradientRange) {
            stops.first().offset = 0;
            stops.first().color = stops.last().color;
            stops.shrink(1);
            numStops = 1;
        } else {
            float maxExtent = gradientAdapter.maxExtent(maxLengthForRepeat, gradientLength);

            size_t originalNumStops = numStops;
            size_t originalFirstStopIndex = 0;

            // Work backwards from the first, adding stops until we get one before 0.
            float firstOffset = *stops[0].offset;
            if (firstOffset > 0) {
                float currOffset = firstOffset;
                size_t srcStopOrdinal = originalNumStops - 1;

                while (true) {
                    GradientStop newStop = stops[originalFirstStopIndex + srcStopOrdinal];
                    newStop.offset = currOffset;
                    stops.insert(0, newStop);
                    ++originalFirstStopIndex;
                    if (currOffset < 0)
                        break;

                    if (srcStopOrdinal)
                        currOffset -= *stops[originalFirstStopIndex + srcStopOrdinal].offset - *stops[originalFirstStopIndex + srcStopOrdinal - 1].offset;
                    srcStopOrdinal = (srcStopOrdinal + originalNumStops - 1) % originalNumStops;
                }
            }

            // Work forwards from the end, adding stops until we get one after 1.
            float lastOffset = *stops[stops.size() - 1].offset;
            if (lastOffset < maxExtent) {
                float currOffset = lastOffset;
                size_t srcStopOrdinal = 0;

                while (true) {
                    size_t srcStopIndex = originalFirstStopIndex + srcStopOrdinal;
                    GradientStop newStop = stops[srcStopIndex];
                    newStop.offset = currOffset;
                    stops.append(newStop);
                    if (currOffset > maxExtent)
                        break;
                    if (srcStopOrdinal < originalNumStops - 1)
                        currOffset += *stops[srcStopIndex + 1].offset - *stops[srcStopIndex].offset;
                    srcStopOrdinal = (srcStopOrdinal + 1) % originalNumStops;
                }
            }
        }
    }

    // If the gradient goes outside the 0-1 range, normalize it by moving the endpoints, and adjusting the stops.
    if (stops.size() > 1 && (*stops.first().offset < 0 || *stops.last().offset > 1))
        gradientAdapter.normalizeStopsAndEndpointsOutsideRange(stops, m_colorInterpolationMethod.method);
    
    GradientColorStops::StopVector result;
    result.reserveInitialCapacity(stops.size());
    for (auto& stop : stops)
        result.uncheckedAppend({ *stop.offset, WTFMove(stop.color) });

    return GradientColorStops::Sorted { WTFMove(result) };
}

static float positionFromValue(const CSSPrimitiveValue* value, const CSSToLengthConversionData& conversionData, const FloatSize& size, bool isHorizontal)
{
    if (!value)
        return 0;

    float origin = 0;
    float sign = 1;
    float edgeDistance = isHorizontal ? size.width() : size.height();

    // In this case the center of the gradient is given relative to an edge in the
    // form of: [ top | bottom | right | left ] [ <percentage> | <length> ].
    if (value->isPair()) {
        CSSValueID originID = value->pairValue()->first()->valueID();
        if (originID == CSSValueRight || originID == CSSValueBottom) {
            // For right/bottom, the offset is relative to the far edge.
            origin = edgeDistance;
            sign = -1;
        }
        value = value->pairValue()->second();
    }

    if (value->isNumber())
        return origin + sign * value->floatValue() * conversionData.zoom();

    if (value->isPercentage())
        return origin + sign * value->floatValue() / 100 * edgeDistance;

    if (value->isCalculatedPercentageWithLength())
        return origin + sign * value->cssCalcValue()->createCalculationValue(conversionData)->evaluate(edgeDistance);

    switch (value->valueID()) {
    case CSSValueTop:
        ASSERT(!isHorizontal);
        return 0;
    case CSSValueLeft:
        ASSERT(isHorizontal);
        return 0;
    case CSSValueBottom:
        ASSERT(!isHorizontal);
        return edgeDistance;
    case CSSValueRight:
        ASSERT(isHorizontal);
        return edgeDistance;
    case CSSValueCenter:
        return origin + sign * .5f * edgeDistance;
    default:
        break;
    }

    return origin + sign * value->computeLength<float>(conversionData);
}

// Resolve points/radii to front end values.
static FloatPoint computeEndPoint(const CSSPrimitiveValue* horizontal, const CSSPrimitiveValue* vertical, const CSSToLengthConversionData& conversionData, const FloatSize& size)
{
    return { positionFromValue(horizontal, conversionData, size, true), positionFromValue(vertical, conversionData, size, false) };
}

bool CSSGradientValue::isCacheable() const
{
    if (hasColorDerivedFromElement())
        return false;
    for (auto& stop : m_stops) {
        if (stop.position && stop.position->isFontRelativeLength())
            return false;
    }
    return true;
}

bool CSSGradientValue::knownToBeOpaque(const RenderElement& renderer) const
{
    bool hasColorFilter = renderer.style().hasAppleColorFilter();
    for (auto& stop : m_stops) {
        Color color = stop.resolvedColor;
        if (hasColorFilter)
            renderer.style().appleColorFilter().transformColor(color);
        if (!color.isOpaque())
            return false;
    }
    return true;
}

bool CSSGradientValue::equals(const CSSGradientValue& other) const
{
    return compareCSSValuePtr(m_firstX, other.m_firstX)
        && compareCSSValuePtr(m_firstY, other.m_firstY)
        && compareCSSValuePtr(m_secondX, other.m_secondX)
        && compareCSSValuePtr(m_secondY, other.m_secondY)
        && m_stops == other.m_stops
        && m_gradientType == other.m_gradientType
        && m_repeating == other.m_repeating
        && m_colorInterpolationMethod == other.m_colorInterpolationMethod;
}

static void appendHueInterpolationMethod(StringBuilder& builder, HueInterpolationMethod hueInterpolationMethod)
{
    switch (hueInterpolationMethod) {
    case HueInterpolationMethod::Shorter:
        break;
    case HueInterpolationMethod::Longer:
        builder.append(" longer hue");
        break;
    case HueInterpolationMethod::Increasing:
        builder.append(" increasing hue");
        break;
    case HueInterpolationMethod::Decreasing:
        builder.append(" decreasing hue");
        break;
    case HueInterpolationMethod::Specified:
        builder.append(" specified hue");
        break;
    }
}

static bool appendColorInterpolationMethod(StringBuilder& builder, CSSGradientColorInterpolationMethod colorInterpolationMethod, bool needsLeadingSpace)
{
    return WTF::switchOn(colorInterpolationMethod.method.colorSpace,
        [&] (const ColorInterpolationMethod::HSL& hsl) {
            builder.append(needsLeadingSpace ? " " : "", "in hsl");
            appendHueInterpolationMethod(builder, hsl.hueInterpolationMethod);
            return true;
        },
        [&] (const ColorInterpolationMethod::HWB& hwb) {
            builder.append(needsLeadingSpace ? " " : "", "in hwb");
            appendHueInterpolationMethod(builder, hwb.hueInterpolationMethod);
            return true;
        },
        [&] (const ColorInterpolationMethod::LCH& lch) {
            builder.append(needsLeadingSpace ? " " : "", "in lch");
            appendHueInterpolationMethod(builder, lch.hueInterpolationMethod);
            return true;
        },
        [&] (const ColorInterpolationMethod::Lab&) {
            builder.append(needsLeadingSpace ? " " : "", "in lab");
            return true;
        },
        [&] (const ColorInterpolationMethod::OKLCH& oklch) {
            builder.append(needsLeadingSpace ? " " : "", "in oklch");
            appendHueInterpolationMethod(builder, oklch.hueInterpolationMethod);
            return true;
        },
        [&] (const ColorInterpolationMethod::OKLab&) {
            if (colorInterpolationMethod.defaultMethod != CSSGradientColorInterpolationMethod::Default::OKLab) {
                builder.append(needsLeadingSpace ? " " : "", "in oklab");
                return true;
            }
            return false;
        },
        [&] (const ColorInterpolationMethod::SRGB&) {
            if (colorInterpolationMethod.defaultMethod != CSSGradientColorInterpolationMethod::Default::SRGB) {
                builder.append(needsLeadingSpace ? " " : "", "in srgb");
                return true;
            }
            return false;
        },
        [&] (const ColorInterpolationMethod::SRGBLinear&) {
            builder.append(needsLeadingSpace ? " " : "", "in srgb-linear");
            return true;
        },
        [&] (const ColorInterpolationMethod::XYZD50&) {
            builder.append(needsLeadingSpace ? " " : "", "in xyz-d50");
            return true;
        },
        [&] (const ColorInterpolationMethod::XYZD65&) {
            builder.append(needsLeadingSpace ? " " : "", "in xyz-d65");
            return true;
        }
    );
}

static void appendGradientStops(StringBuilder& builder, const Vector<CSSGradientColorStop, 2>& stops)
{
    for (auto& stop : stops) {
        double position = stop.position->doubleValue(CSSUnitType::CSS_NUMBER);
        if (!position)
            builder.append(", from(", stop.color->cssText(), ')');
        else if (position == 1)
            builder.append(", to(", stop.color->cssText(), ')');
        else
            builder.append(", color-stop(", position, ", ", stop.color->cssText(), ')');
    }
}

template<typename T, typename U> static void appendSpaceSeparatedOptionalCSSPtrText(StringBuilder& builder, const T& a, const U& b)
{
    if (a && b)
        builder.append(a->cssText(), ' ', b->cssText());
    else if (a)
        builder.append(a->cssText());
    else if (b)
        builder.append(b->cssText());
}

static void writeColorStop(StringBuilder& builder, const CSSGradientColorStop& stop)
{
    appendSpaceSeparatedOptionalCSSPtrText(builder, stop.color, stop.position);
}

String CSSLinearGradientValue::customCSSText() const
{
    StringBuilder result;
    if (gradientType() == CSSDeprecatedLinearGradient) {
        result.append("-webkit-gradient(linear, ", firstX()->cssText(), ' ', firstY()->cssText(), ", ", secondX()->cssText(), ' ', secondY()->cssText());
        appendGradientStops(result, stops());
    } else if (gradientType() == CSSPrefixedLinearGradient) {
        if (isRepeating())
            result.append("-webkit-repeating-linear-gradient(");
        else
            result.append("-webkit-linear-gradient(");

        if (m_angle)
            result.append(m_angle->cssText());
        else
            appendSpaceSeparatedOptionalCSSPtrText(result, firstX(), firstY());

        for (auto& stop : stops()) {
            result.append(", ");
            writeColorStop(result, stop);
        }
    } else {
        if (isRepeating())
            result.append("repeating-linear-gradient(");
        else
            result.append("linear-gradient(");

        bool wroteSomething = false;

        if (m_angle && m_angle->computeDegrees() != 180) {
            result.append(m_angle->cssText());
            wroteSomething = true;
        } else if (firstX() || (firstY() && firstY()->valueID() != CSSValueBottom)) {
            result.append("to ");
            appendSpaceSeparatedOptionalCSSPtrText(result, firstX(), firstY());
            wroteSomething = true;
        }

        if (appendColorInterpolationMethod(result, colorInterpolationMethod(), wroteSomething))
            wroteSomething = true;

        for (auto& stop : stops()) {
            if (wroteSomething)
                result.append(", ");
            wroteSomething = true;
            writeColorStop(result, stop);
        }
    }

    result.append(')');
    return result.toString();
}

// Compute the endpoints so that a gradient of the given angle covers a box of the given size.
static void endPointsFromAngle(float angleDeg, const FloatSize& size, FloatPoint& firstPoint, FloatPoint& secondPoint, CSSGradientType type)
{
    // Prefixed gradients use "polar coordinate" angles, rather than "bearing" angles.
    if (type == CSSPrefixedLinearGradient)
        angleDeg = 90 - angleDeg;

    angleDeg = toPositiveAngle(angleDeg);

    if (!angleDeg) {
        firstPoint.set(0, size.height());
        secondPoint.set(0, 0);
        return;
    }

    if (angleDeg == 90) {
        firstPoint.set(0, 0);
        secondPoint.set(size.width(), 0);
        return;
    }

    if (angleDeg == 180) {
        firstPoint.set(0, 0);
        secondPoint.set(0, size.height());
        return;
    }

    if (angleDeg == 270) {
        firstPoint.set(size.width(), 0);
        secondPoint.set(0, 0);
        return;
    }

    // angleDeg is a "bearing angle" (0deg = N, 90deg = E),
    // but tan expects 0deg = E, 90deg = N.
    float slope = tan(deg2rad(90 - angleDeg));

    // We find the endpoint by computing the intersection of the line formed by the slope,
    // and a line perpendicular to it that intersects the corner.
    float perpendicularSlope = -1 / slope;

    // Compute start corner relative to center, in Cartesian space (+y = up).
    float halfHeight = size.height() / 2;
    float halfWidth = size.width() / 2;
    FloatPoint endCorner;
    if (angleDeg < 90)
        endCorner.set(halfWidth, halfHeight);
    else if (angleDeg < 180)
        endCorner.set(halfWidth, -halfHeight);
    else if (angleDeg < 270)
        endCorner.set(-halfWidth, -halfHeight);
    else
        endCorner.set(-halfWidth, halfHeight);

    // Compute c (of y = mx + c) using the corner point.
    float c = endCorner.y() - perpendicularSlope * endCorner.x();
    float endX = c / (slope - perpendicularSlope);
    float endY = perpendicularSlope * endX + c;

    // We computed the end point, so set the second point, 
    // taking into account the moved origin and the fact that we're in drawing space (+y = down).
    secondPoint.set(halfWidth + endX, halfHeight - endY);
    // Reflect around the center for the start point.
    firstPoint.set(halfWidth - endX, halfHeight + endY);
}

Ref<Gradient> CSSLinearGradientValue::createGradient(RenderElement& renderer, const FloatSize& size)
{
    ASSERT(!size.isEmpty());

    const RenderStyle* rootStyle = nullptr;
    if (auto* documentElement = renderer.document().documentElement())
        rootStyle = documentElement->renderStyle();

    CSSToLengthConversionData conversionData(renderer.style(), rootStyle, renderer.parentStyle(), &renderer.view(), renderer.generatingElement());

    FloatPoint firstPoint;
    FloatPoint secondPoint;
    if (m_angle) {
        float angle = m_angle->floatValue(CSSUnitType::CSS_DEG);
        endPointsFromAngle(angle, size, firstPoint, secondPoint, gradientType());
    } else {
        switch (gradientType()) {
        case CSSDeprecatedLinearGradient:
            firstPoint = computeEndPoint(firstX(), firstY(), conversionData, size);
            if (secondX() || secondY())
                secondPoint = computeEndPoint(secondX(), secondY(), conversionData, size);
            else {
                if (firstX())
                    secondPoint.setX(size.width() - firstPoint.x());
                if (firstY())
                    secondPoint.setY(size.height() - firstPoint.y());
            }
            break;
        case CSSPrefixedLinearGradient:
            firstPoint = computeEndPoint(firstX(), firstY(), conversionData, size);
            if (firstX())
                secondPoint.setX(size.width() - firstPoint.x());
            if (firstY())
                secondPoint.setY(size.height() - firstPoint.y());
            break;
        case CSSLinearGradient:
            if (firstX() && firstY()) {
                // "Magic" corners, so the 50% line touches two corners.
                float rise = size.width();
                float run = size.height();
                if (firstX() && firstX()->valueID() == CSSValueLeft)
                    run *= -1;
                if (firstY() && firstY()->valueID() == CSSValueBottom)
                    rise *= -1;
                // Compute angle, and flip it back to "bearing angle" degrees.
                float angle = 90 - rad2deg(atan2(rise, run));
                endPointsFromAngle(angle, size, firstPoint, secondPoint, gradientType());
            } else if (firstX() || firstY()) {
                secondPoint = computeEndPoint(firstX(), firstY(), conversionData, size);
                if (firstX())
                    firstPoint.setX(size.width() - secondPoint.x());
                if (firstY())
                    firstPoint.setY(size.height() - secondPoint.y());
            } else
                secondPoint.setY(size.height());
            break;
        default:
            ASSERT_NOT_REACHED();
        }
    }

    Gradient::LinearData data { firstPoint, secondPoint };
    LinearGradientAdapter adapter { data };
    auto stops = computeStops(adapter, conversionData, renderer.style(), 1);

    return Gradient::create(WTFMove(data), colorInterpolationMethod().method, GradientSpreadMethod::Pad, WTFMove(stops));
}

bool CSSLinearGradientValue::equals(const CSSLinearGradientValue& other) const
{
    return CSSGradientValue::equals(other) && compareCSSValuePtr(m_angle, other.m_angle);
}

String CSSRadialGradientValue::customCSSText() const
{
    StringBuilder result;

    if (gradientType() == CSSDeprecatedRadialGradient) {
        result.append("-webkit-gradient(radial, ", firstX()->cssText(), ' ', firstY()->cssText(), ", ", m_firstRadius->cssText(),
            ", ", secondX()->cssText(), ' ', secondY()->cssText(), ", ", m_secondRadius->cssText());
        appendGradientStops(result, stops());
    } else if (gradientType() == CSSPrefixedRadialGradient) {
        if (isRepeating())
            result.append("-webkit-repeating-radial-gradient(");
        else
            result.append("-webkit-radial-gradient(");

        if (firstX() || firstY())
            appendSpaceSeparatedOptionalCSSPtrText(result, firstX(), firstY());
        else
            result.append("center");

        if (m_shape || m_sizingBehavior) {
            result.append(", ");
            if (m_shape)
                result.append(m_shape->cssText(), ' ');
            else
                result.append("ellipse ");
            if (m_sizingBehavior)
                result.append(m_sizingBehavior->cssText());
            else
                result.append("cover");
        } else if (m_endHorizontalSize && m_endVerticalSize)
            result.append(", ", m_endHorizontalSize->cssText(), ' ', m_endVerticalSize->cssText());

        for (auto& stop : stops()) {
            result.append(", ");
            writeColorStop(result, stop);
        }
    } else {
        if (isRepeating())
            result.append("repeating-radial-gradient(");
        else
            result.append("radial-gradient(");

        bool wroteSomething = false;

        // The only ambiguous case that needs an explicit shape to be provided
        // is when a sizing keyword is used (or all sizing is omitted).
        if (m_shape && m_shape->valueID() != CSSValueEllipse && (m_sizingBehavior || (!m_sizingBehavior && !m_endHorizontalSize))) {
            result.append("circle");
            wroteSomething = true;
        }

        if (m_sizingBehavior && m_sizingBehavior->valueID() != CSSValueFarthestCorner) {
            if (wroteSomething)
                result.append(' ');
            result.append(m_sizingBehavior->cssText());
            wroteSomething = true;
        } else if (m_endHorizontalSize) {
            if (wroteSomething)
                result.append(' ');
            result.append(m_endHorizontalSize->cssText());
            if (m_endVerticalSize)
                result.append(' ', m_endVerticalSize->cssText());
            wroteSomething = true;
        }

        if ((firstX() && !firstX()->isCenterPosition()) || (firstY() && !firstY()->isCenterPosition())) {
            if (wroteSomething)
                result.append(' ');
            result.append("at ");
            appendSpaceSeparatedOptionalCSSPtrText(result, firstX(), firstY());
            wroteSomething = true;
        }

        if (appendColorInterpolationMethod(result, colorInterpolationMethod(), wroteSomething))
            wroteSomething = true;

        if (wroteSomething)
            result.append(", ");

        bool wroteFirstStop = false;
        for (auto& stop : stops()) {
            if (wroteFirstStop)
                result.append(", ");
            wroteFirstStop = true;
            writeColorStop(result, stop);
        }
    }

    result.append(')');
    return result.toString();
}

float CSSRadialGradientValue::resolveRadius(CSSPrimitiveValue& radius, const CSSToLengthConversionData& conversionData, float* widthOrHeight)
{
    float result = 0;
    if (radius.isNumber())
        result = radius.floatValue() * conversionData.zoom();
    else if (widthOrHeight && radius.isPercentage())
        result = *widthOrHeight * radius.floatValue() / 100;
    else if (widthOrHeight && radius.isCalculatedPercentageWithLength()) {
        auto expression = radius.cssCalcValue()->createCalculationValue(conversionData);
        result = expression->evaluate(*widthOrHeight);
    }
    else
        result = radius.computeLength<float>(conversionData);
    return result;
}

static float distanceToClosestCorner(const FloatPoint& p, const FloatSize& size, FloatPoint& corner)
{
    FloatPoint topLeft;
    float topLeftDistance = FloatSize(p - topLeft).diagonalLength();

    FloatPoint topRight(size.width(), 0);
    float topRightDistance = FloatSize(p - topRight).diagonalLength();

    FloatPoint bottomLeft(0, size.height());
    float bottomLeftDistance = FloatSize(p - bottomLeft).diagonalLength();

    FloatPoint bottomRight(size.width(), size.height());
    float bottomRightDistance = FloatSize(p - bottomRight).diagonalLength();

    corner = topLeft;
    float minDistance = topLeftDistance;
    if (topRightDistance < minDistance) {
        minDistance = topRightDistance;
        corner = topRight;
    }

    if (bottomLeftDistance < minDistance) {
        minDistance = bottomLeftDistance;
        corner = bottomLeft;
    }

    if (bottomRightDistance < minDistance) {
        minDistance = bottomRightDistance;
        corner = bottomRight;
    }
    return minDistance;
}

static float distanceToFarthestCorner(const FloatPoint& p, const FloatSize& size, FloatPoint& corner)
{
    FloatPoint topLeft;
    float topLeftDistance = FloatSize(p - topLeft).diagonalLength();

    FloatPoint topRight(size.width(), 0);
    float topRightDistance = FloatSize(p - topRight).diagonalLength();

    FloatPoint bottomLeft(0, size.height());
    float bottomLeftDistance = FloatSize(p - bottomLeft).diagonalLength();

    FloatPoint bottomRight(size.width(), size.height());
    float bottomRightDistance = FloatSize(p - bottomRight).diagonalLength();

    corner = topLeft;
    float maxDistance = topLeftDistance;
    if (topRightDistance > maxDistance) {
        maxDistance = topRightDistance;
        corner = topRight;
    }

    if (bottomLeftDistance > maxDistance) {
        maxDistance = bottomLeftDistance;
        corner = bottomLeft;
    }

    if (bottomRightDistance > maxDistance) {
        maxDistance = bottomRightDistance;
        corner = bottomRight;
    }
    return maxDistance;
}

// Compute horizontal radius of ellipse with center at 0,0 which passes through p, and has
// width/height given by aspectRatio.
static inline float horizontalEllipseRadius(const FloatSize& p, float aspectRatio)
{
    // x^2/a^2 + y^2/b^2 = 1
    // a/b = aspectRatio, b = a/aspectRatio
    // a = sqrt(x^2 + y^2/(1/r^2))
    return std::hypot(p.width(), p.height() * aspectRatio);
}

// FIXME: share code with the linear version
Ref<Gradient> CSSRadialGradientValue::createGradient(RenderElement& renderer, const FloatSize& size)
{
    ASSERT(!size.isEmpty());

    const RenderStyle* rootStyle = nullptr;
    if (auto* documentElement = renderer.document().documentElement())
        rootStyle = documentElement->renderStyle();

    CSSToLengthConversionData conversionData(renderer.style(), rootStyle, renderer.parentStyle(), &renderer.view(), renderer.generatingElement());

    FloatPoint firstPoint = computeEndPoint(firstX(), firstY(), conversionData, size);
    if (!firstX())
        firstPoint.setX(size.width() / 2);
    if (!firstY())
        firstPoint.setY(size.height() / 2);

    FloatPoint secondPoint = computeEndPoint(secondX(), secondY(), conversionData, size);
    if (!secondX())
        secondPoint.setX(size.width() / 2);
    if (!secondY())
        secondPoint.setY(size.height() / 2);

    float firstRadius = 0;
    if (m_firstRadius)
        firstRadius = resolveRadius(*m_firstRadius, conversionData);

    float secondRadius = 0;
    float aspectRatio = 1; // width / height.
    if (m_secondRadius)
        secondRadius = resolveRadius(*m_secondRadius, conversionData);
    else if (m_endHorizontalSize) {
        float width = size.width();
        float height = size.height();
        secondRadius = resolveRadius(*m_endHorizontalSize, conversionData, &width);
        if (m_endVerticalSize)
            aspectRatio = secondRadius / resolveRadius(*m_endVerticalSize, conversionData, &height);
        else
            aspectRatio = 1;
    } else {
        enum GradientShape { Circle, Ellipse };
        GradientShape shape = Ellipse;
        if ((m_shape && m_shape->valueID() == CSSValueCircle)
            || (!m_shape && !m_sizingBehavior && m_endHorizontalSize && !m_endVerticalSize))
            shape = Circle;

        enum GradientFill { ClosestSide, ClosestCorner, FarthestSide, FarthestCorner };
        GradientFill fill = FarthestCorner;

        switch (m_sizingBehavior ? m_sizingBehavior->valueID() : 0) {
        case CSSValueContain:
        case CSSValueClosestSide:
            fill = ClosestSide;
            break;
        case CSSValueClosestCorner:
            fill = ClosestCorner;
            break;
        case CSSValueFarthestSide:
            fill = FarthestSide;
            break;
        case CSSValueCover:
        case CSSValueFarthestCorner:
            fill = FarthestCorner;
            break;
        default:
            break;
        }

        // Now compute the end radii based on the second point, shape and fill.

        // Horizontal
        switch (fill) {
        case ClosestSide: {
            float xDist = std::min(secondPoint.x(), size.width() - secondPoint.x());
            float yDist = std::min(secondPoint.y(), size.height() - secondPoint.y());
            if (shape == Circle) {
                float smaller = std::min(xDist, yDist);
                xDist = smaller;
                yDist = smaller;
            }
            secondRadius = xDist;
            aspectRatio = xDist / yDist;
            break;
        }
        case FarthestSide: {
            float xDist = std::max(secondPoint.x(), size.width() - secondPoint.x());
            float yDist = std::max(secondPoint.y(), size.height() - secondPoint.y());
            if (shape == Circle) {
                float larger = std::max(xDist, yDist);
                xDist = larger;
                yDist = larger;
            }
            secondRadius = xDist;
            aspectRatio = xDist / yDist;
            break;
        }
        case ClosestCorner: {
            FloatPoint corner;
            float distance = distanceToClosestCorner(secondPoint, size, corner);
            if (shape == Circle)
                secondRadius = distance;
            else {
                // If <shape> is ellipse, the gradient-shape has the same ratio of width to height
                // that it would if closest-side or farthest-side were specified, as appropriate.
                float xDist = std::min(secondPoint.x(), size.width() - secondPoint.x());
                float yDist = std::min(secondPoint.y(), size.height() - secondPoint.y());

                secondRadius = horizontalEllipseRadius(corner - secondPoint, xDist / yDist);
                aspectRatio = xDist / yDist;
            }
            break;
        }

        case FarthestCorner: {
            FloatPoint corner;
            float distance = distanceToFarthestCorner(secondPoint, size, corner);
            if (shape == Circle)
                secondRadius = distance;
            else {
                // If <shape> is ellipse, the gradient-shape has the same ratio of width to height
                // that it would if closest-side or farthest-side were specified, as appropriate.
                float xDist = std::max(secondPoint.x(), size.width() - secondPoint.x());
                float yDist = std::max(secondPoint.y(), size.height() - secondPoint.y());

                secondRadius = horizontalEllipseRadius(corner - secondPoint, xDist / yDist);
                aspectRatio = xDist / yDist;
            }
            break;
        }
        }
    }

    // computeStops() only uses maxExtent for repeating gradients.
    float maxExtent = 0;
    if (isRepeating()) {
        FloatPoint corner;
        maxExtent = distanceToFarthestCorner(secondPoint, size, corner);
    }

    Gradient::RadialData data { firstPoint, secondPoint, firstRadius, secondRadius, aspectRatio };
    RadialGradientAdapter adapter { data };
    auto stops = computeStops(adapter, conversionData, renderer.style(), maxExtent);

    return Gradient::create(WTFMove(data), colorInterpolationMethod().method, GradientSpreadMethod::Pad, WTFMove(stops));
}

bool CSSRadialGradientValue::equals(const CSSRadialGradientValue& other) const
{
    return CSSGradientValue::equals(other)
        && compareCSSValuePtr(m_shape, other.m_shape)
        && compareCSSValuePtr(m_sizingBehavior, other.m_sizingBehavior)
        && compareCSSValuePtr(m_endHorizontalSize, other.m_endHorizontalSize)
        && compareCSSValuePtr(m_endVerticalSize, other.m_endVerticalSize);
}

String CSSConicGradientValue::customCSSText() const
{
    StringBuilder result;

    result.append(isRepeating() ? "repeating-conic-gradient(" : "conic-gradient(");

    bool wroteSomething = false;

    if (m_angle && m_angle->computeDegrees()) {
        result.append("from ", m_angle->cssText());
        wroteSomething = true;
    }

    if ((firstX() && !firstX()->isCenterPosition()) || (firstY() && !firstY()->isCenterPosition())) {
        if (wroteSomething)
            result.append(' ');
        result.append("at ");
        appendSpaceSeparatedOptionalCSSPtrText(result, firstX(), firstY());
        wroteSomething = true;
    }

    if (appendColorInterpolationMethod(result, colorInterpolationMethod(), wroteSomething))
        wroteSomething = true;

    if (wroteSomething)
        result.append(", ");

    bool wroteFirstStop = false;
    for (auto& stop : stops()) {
        if (wroteFirstStop)
            result.append(", ");
        wroteFirstStop = true;
        writeColorStop(result, stop);
    }

    result.append(')');
    return result.toString();
}

Ref<Gradient> CSSConicGradientValue::createGradient(RenderElement& renderer, const FloatSize& size)
{
    ASSERT(!size.isEmpty());

    const RenderStyle* rootStyle = nullptr;
    if (auto* documentElement = renderer.document().documentElement())
        rootStyle = documentElement->renderStyle();

    CSSToLengthConversionData conversionData(renderer.style(), rootStyle, renderer.parentStyle(), &renderer.view(), renderer.generatingElement());

    FloatPoint centerPoint = computeEndPoint(firstX(), firstY(), conversionData, size);
    if (!firstX())
        centerPoint.setX(size.width() / 2);
    if (!firstY())
        centerPoint.setY(size.height() / 2);

    float angleRadians = 0;
    if (m_angle)
        angleRadians = m_angle->floatValue(CSSUnitType::CSS_RAD);

    Gradient::ConicData data { centerPoint, angleRadians };
    ConicGradientAdapter adapter;
    auto stops = computeStops(adapter, conversionData, renderer.style(), 1);

    return Gradient::create(WTFMove(data), colorInterpolationMethod().method, GradientSpreadMethod::Pad, WTFMove(stops));
}

bool CSSConicGradientValue::equals(const CSSConicGradientValue& other) const
{
    return CSSGradientValue::equals(other) && compareCSSValuePtr(m_angle, other.m_angle);
}

} // namespace WebCore