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import QtQuick 2.12
import QtGraphicalEffects.private 1.12

/*!
    \qmltype Glow
    \inqmlmodule QtGraphicalEffects
    \since QtGraphicalEffects 1.0
    \inherits QtQuick2::Item
    \ingroup qtgraphicaleffects-glow
    \brief Generates a blurred and colorized image of the source and places it
    behind the original, giving impression that the source is glowing.

    \table
    \header
        \li Source
        \li Effect applied
    \row
        \li \image Original_butterfly_black.png
        \li \image Glow_butterfly.png
    \endtable

    \section1 Example

    The following example shows how to apply the effect.
    \snippet Glow-example.qml example

*/
Item {
    id: rootItem

    /*!
        This property defines the source item that is going to be used as source
        for the generated glow.

        \note It is not supported to let the effect include itself, for
        instance by setting source to the effect's parent.
    */
    property variant source

    /*!
        Radius defines the softness of the glow. A larger radius causes the
        edges of the glow to appear more blurry.

        The value ranges from 0.0 (no blur) to inf. By default, the property is
        set to \c 0.0 (no blur).

        \table
        \header
        \li Output examples with different radius values
        \li
        \li
        \row
            \li \image Glow_radius1.png
            \li \image Glow_radius2.png
            \li \image Glow_radius3.png
        \row
            \li \b { radius: 0 }
            \li \b { radius: 6 }
            \li \b { radius: 12 }
        \row
            \li \l color: #ffffff
            \li \l color: #ffffff
            \li \l color: #ffffff
        \row
            \li \l spread: 0
            \li \l spread: 0
            \li \l spread: 0
        \endtable
    */
    property real radius: 0.0

    /*!
        This property defines how large part of the glow color is strenghtened
        near the source edges.

        The values range from 0.0 to 1.0. By default, the property is set to \c
        0.5.

        \table
        \header
        \li Output examples with different spread values
        \li
        \li
        \row
            \li \image Glow_spread1.png
            \li \image Glow_spread2.png
            \li \image Glow_spread3.png
        \row
            \li \b { spread: 0.0 }
            \li \b { spread: 0.5 }
            \li \b { spread: 1.0 }
        \row
            \li \l radius: 8
            \li \l radius: 8
            \li \l radius: 8
        \row
            \li \l color: #ffffff
            \li \l color: #ffffff
            \li \l color: #ffffff
        \endtable
    */
    property real spread: 0.0

    /*!
        This property defines the RGBA color value which is used for the glow.

        By default, the property is set to \c "white".

        \table
        \header
        \li Output examples with different color values
        \li
        \li
        \row
            \li \image Glow_color1.png
            \li \image Glow_color2.png
            \li \image Glow_color3.png
        \row
            \li \b { color: #ffffff }
            \li \b { color: #00ff00 }
            \li \b { color: #aa00ff00 }
        \row
            \li \l radius: 8
            \li \l radius: 8
            \li \l radius: 8
        \row
            \li \l spread: 0.5
            \li \l spread: 0.5
            \li \l spread: 0.5
        \endtable

    */
    property color color: "white"

    /*!
        This property allows the effect output pixels to be cached in order to
        improve the rendering performance.

        Every time the source or effect properties are changed, the pixels in
        the cache must be updated. Memory consumption is increased, because an
        extra buffer of memory is required for storing the effect output.

        It is recommended to disable the cache when the source or the effect
        properties are animated.

        By default, the property is set to \c false.

    */
    property bool cached: false

    /*!
        This property determines whether or not the effect has a transparent
        border.

        When set to \c true, the exterior of the item is padded with a 1 pixel
        wide transparent edge, making sampling outside the source texture use
        transparency instead of the edge pixels. Without this property, an
        image which has opaque edges will not get a blurred edge.

        In the snippet below, the Rectangle on the left has transparent borders
        and has blurred edges, whereas the Rectangle on the right does not.

        \snippet Glow-transparentBorder-example.qml example

        \image Glow-transparentBorder.png
    */
    property bool transparentBorder: false

    Loader {
        anchors.fill: parent
        sourceComponent: fastGlow
    }

    Component {
        id: fastGlow
        FastGlow {
            anchors.fill: parent
            source: sourceProxy.output
            blur: Math.pow(rootItem.radius / 64.0, 0.4)
            color: rootItem.color
            cached: rootItem.cached
            spread: rootItem.spread
            transparentBorder: rootItem.transparentBorder
        }
    }

    SourceProxy {
        id: sourceProxy
        input: rootItem.source
        sourceRect: rootItem.transparentBorder ? Qt.rect(-1, -1, parent.width + 2.0, parent.height + 2.0) : Qt.rect(0, 0, 0, 0)
    }
    ShaderEffect {
        anchors.fill: parent
        property variant source: sourceProxy.output
    }
}