path: root/src/effects/LinearGradient.qml

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import QtQuick 2.0
import "private"

/*!
    \qmltype LinearGradient
    \inqmlmodule QtGraphicalEffects
    \since QtGraphicalEffects 1.0
    \inherits QtQuick2::Item
    \ingroup qtgraphicaleffects-gradient
    \brief Draws a linear gradient.

    A gradient is defined by two or more colors, which are blended seamlessly.
    The colors start from the given start point and end to the given end point.

    \table
    \header
        \li Effect applied
    \row
        \li \image LinearGradient.png
    \endtable

    \section1 Example

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

*/
Item {
    id: rootItem

    /*!
        This property defines the starting point where the color at gradient
        position of 0.0 is rendered. Colors at larger position values are
        rendered linearly towards the end point. The point is given in pixels
        and the default value is Qt.point(0, 0). Setting the default values for
        the start and \l{LinearGradient::end}{end} results in a full height
        linear gradient on the y-axis.

        \table
        \header
        \li Output examples with different start values
        \li
        \li
        \row
            \li \image LinearGradient_start1.png
            \li \image LinearGradient_start2.png
            \li \image LinearGradient_start3.png
        \row
            \li \b { start: QPoint(0, 0) }
            \li \b { start: QPoint(150, 150) }
            \li \b { start: QPoint(300, 0) }
        \row
            \li \l end: QPoint(300, 300)
            \li \l end: QPoint(300, 300)
            \li \l end: QPoint(300, 300)
        \endtable

    */
    property variant start: Qt.point(0, 0)

    /*!
        This property defines the ending point where the color at gradient
        position of 1.0 is rendered. Colors at smaller position values are
        rendered linearly towards the start point. The point is given in pixels
        and the default value is Qt.point(0, height). Setting the default values
        for the \l{LinearGradient::start}{start} and end results in a full
        height linear gradient on the y-axis.

        \table
        \header
        \li Output examples with different end values
        \li
        \li
        \row
            \li \image LinearGradient_end1.png
            \li \image LinearGradient_end2.png
            \li \image LinearGradient_end3.png
        \row
            \li \b { end: Qt.point(300, 300) }
            \li \b { end: Qt.point(150, 150) }
            \li \b { end: Qt.point(300, 0) }
        \row
            \li \l start: Qt.point(0, 0)
            \li \l start: Qt.point(0, 0)
            \li \l start: Qt.point(0, 0)
        \endtable

    */
    property variant end: Qt.point(0, height)

    /*!
        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 defines the item that is going to be filled with gradient.
        Source item gets rendered into an intermediate pixel buffer and the
        alpha values from the result are used to determine the gradient's pixels
        visibility in the display. The default value for source is undefined and
        in that case whole effect area is filled with gradient.

        \table
        \header
        \li Output examples with different source values
        \li
        \li
        \row
            \li \image LinearGradient_maskSource1.png
            \li \image LinearGradient_maskSource2.png
        \row
            \li \b { source: undefined }
            \li \b { source: Image { source: images/butterfly.png } }
        \row
            \li \l start: Qt.point(0, 0)
            \li \l start: Qt.point(0, 0)
        \row
            \li \l end: Qt.point(300, 300)
            \li \l end: Qt.point(300, 300)
        \endtable

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


    /*!
        A gradient is defined by two or more colors, which are blended
        seamlessly. The colors are specified as a set of GradientStop child
        items, each of which defines a position on the gradient from 0.0 to 1.0
        and a color. The position of each GradientStop is defined by the
        position property, and the color is definded by the color property.

        \table
        \header
        \li Output examples with different gradient values
        \li
        \li
        \row
            \li \image LinearGradient_gradient1.png
            \li \image LinearGradient_gradient2.png
            \li \image LinearGradient_gradient3.png
            \row
            \li \b {gradient:} \code
    Gradient {
      GradientStop { position: 0.000
      color: Qt.rgba(1, 0, 0, 1) }
      GradientStop { position: 0.167;
      color: Qt.rgba(1, 1, 0, 1) }
      GradientStop { position: 0.333;
      color: Qt.rgba(0, 1, 0, 1) }
      GradientStop { position: 0.500;
      color: Qt.rgba(0, 1, 1, 1) }
      GradientStop { position: 0.667;
      color: Qt.rgba(0, 0, 1, 1) }
      GradientStop { position: 0.833;
      color: Qt.rgba(1, 0, 1, 1) }
      GradientStop { position: 1.000;
      color: Qt.rgba(1, 0, 0, 1) }
    }
        \endcode
            \li \b {gradient:} \code
    Gradient {
      GradientStop { position: 0.0
      color: "#F0F0F0"
      }
      GradientStop { position: 0.5
      color: "#000000"
      }
      GradientStop { position: 1.0
      color: "#F0F0F0"
      }
    }
        \endcode
            \li \b {gradient:} \code
    Gradient {
      GradientStop { position: 0.0
        color: "#00000000"
      }
      GradientStop { position: 1.0
        color: "#FF000000"
      }
    }
        \endcode
        \row
            \li \l start: Qt.point(0, 0)
            \li \l start: Qt.point(0, 0)
            \li \l start: Qt.point(0, 0)
        \row
            \li \l end: Qt.point(300, 300)
            \li \l end: Qt.point(300, 300)
            \li \l end: Qt.point(300, 300)
        \endtable

    */
    property Gradient gradient: Gradient {
        GradientStop { position: 0.0; color: "white" }
        GradientStop { position: 1.0; color: "black" }
    }

    SourceProxy {
        id: maskSourceProxy
        input: rootItem.source
    }

    ShaderEffectSource {
        id: gradientSource
        sourceItem: Rectangle {
            width: 16
            height: 256
            gradient: rootItem.gradient
            smooth: true
        }
        smooth: true
        hideSource: true
        visible: false
    }

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

    ShaderEffect {
        id: shaderItem

        anchors.fill: parent

        property variant source: gradientSource
        property variant maskSource: maskSourceProxy.output
        property variant startPoint: Qt.point(start.x / width, start.y / height)
        property real dx: end.x - start.x
        property real dy: end.y - start.y
        property real l: 1.0 / Math.sqrt(Math.pow(dx / width, 2.0) + Math.pow(dy / height, 2.0))
        property real angle: Math.atan2(dx, dy)
        property variant matrixData: Qt.point(Math.sin(angle), Math.cos(angle))

        vertexShader: "
            attribute highp vec4 qt_Vertex;
            attribute highp vec2 qt_MultiTexCoord0;
            uniform highp mat4 qt_Matrix;
            varying highp vec2 qt_TexCoord0;
            varying highp vec2 qt_TexCoord1;
            uniform highp vec2 startPoint;
            uniform highp float l;
            uniform highp vec2 matrixData;

            void main() {
                highp mat2 rot = mat2(matrixData.y, -matrixData.x,
                                      matrixData.x,  matrixData.y);

                qt_TexCoord0 = qt_MultiTexCoord0;

                qt_TexCoord1 = qt_MultiTexCoord0 * l;
                qt_TexCoord1 -= startPoint * l;
                qt_TexCoord1 *= rot;

                gl_Position = qt_Matrix * qt_Vertex;
            }
        "

        fragmentShader: maskSource == undefined ? noMaskShader : maskShader

        onFragmentShaderChanged: lChanged()

        property string maskShader: "
            uniform lowp sampler2D source;
            uniform lowp sampler2D maskSource;
            uniform lowp float qt_Opacity;
            varying highp vec2 qt_TexCoord0;
            varying highp vec2 qt_TexCoord1;

            void main() {
                lowp vec4 gradientColor = texture2D(source, qt_TexCoord1);
                lowp float maskAlpha = texture2D(maskSource, qt_TexCoord0).a;
                gl_FragColor = gradientColor * maskAlpha * qt_Opacity;
            }
        "

        property string noMaskShader: "
            uniform lowp sampler2D source;
            uniform lowp float qt_Opacity;
            varying highp vec2 qt_TexCoord1;

            void main() {
                gl_FragColor = texture2D(source, qt_TexCoord1) * qt_Opacity;
            }
        "
    }
}