path: root/src/effects/Glow.qml

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import QtQuick 2.0
import "private"

/*!
    \qmltype Glow
    \inqmlmodule QtGraphicalEffects 1.0
    \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.

    By default effect produces a high quality glow image, thus the rendering
    speed of the effect may not be the highest possible. The rendering speed is
    reduced especially if the glow edges are heavily softened. For use cases
    that require faster rendering speed and the highest possible visual quality
    is not necessary, property \l{Glow::fast}{fast} can be set to true.

    \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.

        Depending on the radius value, value of the \l{Glow::samples}{samples}
        should be set to sufficiently large to ensure the visual quality.

        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 samples: 24
            \li \l samples: 24
            \li \l samples: 24
        \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 many samples are taken per pixel when edge
        softening blur calculation is done. Larger value produces better
        quality, but is slower to render.

        Ideally, this value should be twice as large as the highest required
        radius value, for example, if the radius is animated between 0.0 and
        4.0, samples should be set to 8.

        The value ranges from 0 to 32. By default, the property is set to \c 0.

        This property is not intended to be animated. Changing this property may
        cause the underlying OpenGL shaders to be recompiled.

        When \l fast property is set to true, this property has no effect.

    */
    property int samples: 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 samples: 16
            \li \l samples: 16
            \li \l samples: 16
        \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 samples: 16
            \li \l samples: 16
            \li \l samples: 16
        \row
            \li \l spread: 0.5
            \li \l spread: 0.5
            \li \l spread: 0.5
        \endtable

    */
    property color color: "white"

    /*!
        This property selects the blurring algorithm that is used to produce the
        softness for the effect. Setting this to true enables fast algorithm,
        setting value to false produces higher quality result.

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

        \table
        \header
        \li Output examples with different fast values
        \li
        \li
        \row
            \li \image Glow_fast1.png
            \li \image Glow_fast2.png
        \row
            \li \b { fast: false }
            \li \b { fast: true }
        \row
            \li \l radius: 16
            \li \l radius: 16
        \row
            \li \l samples: 24
            \li \l samples: 24
        \row
            \li \l color: #ffffff
            \li \l color: #ffffff
        \row
            \li \l spread: 0.3
            \li \l spread: 0.3
        \endtable
    */
    property bool fast: false

    /*!
        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
    property bool transparentBorder: false

    Loader {
        anchors.fill: parent
        sourceComponent: rootItem.fast ? fastGlow : gaussianGlow
    }

    Component {
        id: gaussianGlow
        GaussianGlow {
            anchors.fill: parent
            source: sourceProxy.output
            radius: rootItem.radius
            maximumRadius: rootItem.samples * 0.5
            color: rootItem.color
            cached: rootItem.cached
            spread: rootItem.spread
            transparentBorder: rootItem.transparentBorder
        }
    }

    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
    }
}