path: root/src/effects/GaussianBlur.qml

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import QtQuick 2.0
import "private"

/*!
    \qmltype GaussianBlur
    \inqmlmodule QtGraphicalEffects
    \since QtGraphicalEffects 1.0
    \inherits QtQuick2::Item
    \ingroup qtgraphicaleffects-blur
    \brief Applies a higher quality blur effect.

    GaussianBlur effect softens the image by blurring it with an algorithm that
    uses the Gaussian function to calculate the effect. The effect produces
    higher quality than \l{QtGraphicalEffects1::FastBlur}{FastBlur}, but is
    slower to render.

    \table
    \header
        \li Source
        \li Effect applied
    \row
        \li \image Original_bug.png
        \li \image GaussianBlur_bug.png
    \endtable

    \section1 Example

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

*/
Item {
    id: rootItem

    /*!
        This property defines the source item that is going to be blurred.

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

    /*!
        This property defines the distance of the neighboring pixels which
        affect the blurring of an individual pixel. A larger radius increases
        the blur effect.

        Depending on the radius value, value of the
        \l{GaussianBlur::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 GaussianBlur_radius1.png
            \li \image GaussianBlur_radius2.png
            \li \image GaussianBlur_radius3.png
        \row
            \li \b { radius: 0 }
            \li \b { radius: 4 }
            \li \b { radius: 8 }
        \row
            \li \l samples: 16
            \li \l samples: 16
            \li \l samples: 16
        \row
            \li \l deviation: 3
            \li \l deviation: 3
            \li \l deviation: 3
        \endtable

    */
    property real radius: 0.0

    /*!
        This property defines how many samples are taken per pixel when 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.

    */
    property int samples: 0

    /*!
        This property is a parameter to the gaussian function that is used when
        calculating neighboring pixel weights for the blurring. A larger
        deviation causes image to appear more blurry, but it also reduces the
        quality of the blur. A very large deviation value causes the effect to
        look a bit similar to what, for exmple, a box blur algorithm produces. A
        too small deviation values makes the effect insignificant for the pixels
        near the radius.

        \inlineimage GaussianBlur_deviation_graph.png
        \caption The image above shows the Gaussian function with two different
        deviation values, yellow (1) and cyan (2.7). The y-axis shows the
        weights, the x-axis shows the pixel distance.

        The value ranges from 0.0 (no deviation) to inf (maximum deviation). By
        default, devaition is binded to radius. When radius increases, deviation
        is automatically increased linearly. With the radius value of 8, the
        deviation default value becomes approximately 2.7034. This value
        produces a compromise between the blur quality and overall blurriness.

        \table
        \header
        \li Output examples with different deviation values
        \li
        \li
        \row
            \li \image GaussianBlur_deviation1.png
            \li \image GaussianBlur_deviation2.png
            \li \image GaussianBlur_deviation3.png
        \row
            \li \b { deviation: 1 }
            \li \b { deviation: 2 }
            \li \b { deviation: 4 }
        \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
        \endtable

    */
    property real deviation: (radius + 1) / 3.3333

    /*!
        This property defines the blur behavior near the edges of the item,
        where the pixel blurring is affected by the pixels outside the source
        edges.

        If the property is set to \c true, the pixels outside the source are
        interpreted to be transparent, which is similar to OpenGL
        clamp-to-border extension. The blur is expanded slightly outside the
        effect item area.

        If the property is set to \c false, the pixels outside the source are
        interpreted to contain the same color as the pixels at the edge of the
        item, which is similar to OpenGL clamp-to-edge behavior. The blur does
        not expand outside the effect item area.

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

        \table
        \header
        \li Output examples with different transparentBorder values
        \li
        \li
        \row
            \li \image GaussianBlur_transparentBorder1.png
            \li \image GaussianBlur_transparentBorder2.png
        \row
            \li \b { transparentBorder: false }
            \li \b { transparentBorder: true }
        \row
            \li \l radius: 8
            \li \l radius: 8
        \row
            \li \l samples: 16
            \li \l samples: 16
        \row
            \li \l deviation: 2.7
            \li \l deviation: 2.7
        \endtable

    */
    property bool transparentBorder: 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

    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)
    }

    ShaderEffectSource {
        id: cacheItem
        anchors.fill: verticalBlur
        visible: rootItem.cached
        smooth: true
        sourceItem: verticalBlur
        live: true
        hideSource: visible
    }

    GaussianDirectionalBlur {
        id: verticalBlur
        x: transparentBorder ? -maximumRadius - 1 : 0
        y: transparentBorder ? -maximumRadius - 1 : 0
        width: horizontalBlur.width
        height: horizontalBlur.height

        horizontalStep: 0.0
        verticalStep: 1.0 / parent.height

        source: ShaderEffectSource {
            id: horizontalBlurSource
            sourceItem: horizontalBlur
            hideSource: true
            visible: false
            smooth: true
        }

        deviation: rootItem.deviation
        radius: rootItem.radius
        maximumRadius: rootItem.samples * 0.5
        transparentBorder: rootItem.transparentBorder
    }

    GaussianDirectionalBlur {
        id: horizontalBlur
        width: transparentBorder ? parent.width + 2 * maximumRadius + 2 : parent.width
        height: transparentBorder ? parent.height + 2 * maximumRadius + 2  : parent.height

        horizontalStep: 1.0 / parent.width
        verticalStep: 0.0

        source: sourceProxy.output
        deviation: rootItem.deviation
        radius: rootItem.radius
        maximumRadius: rootItem.samples / 2.0
        transparentBorder: rootItem.transparentBorder
    }
}