import QtQuick 2.9
import QtGraphicalEffects 1.0

/*!
   An effect for standard Material Design elevation shadows
 */
Item {
    id: effect

    property variant source

    property int elevation: 0

    // Shadow details follow Material Design (taken from Angular Material)
    readonly property var _shadows: [
        [{offset: 0, blur: 0, spread: 0},
         {offset: 0, blur: 0, spread: 0},
         {offset: 0, blur: 0, spread: 0}],

        [{offset: 1, blur: 3, spread: 0},
         {offset: 1, blur: 1, spread: 0},
         {offset: 2, blur: 1, spread: -1}],

        [{offset: 1, blur: 5, spread: 0},
         {offset: 2, blur: 2, spread: 0},
         {offset: 3, blur: 1, spread: -2}],

        [{offset: 1, blur: 8, spread: 0},
         {offset: 3, blur: 4, spread: 0},
         {offset: 3, blur: 3, spread: -2}],

        [{offset: 2, blur: 4, spread: -1},
         {offset: 4, blur: 5, spread: 0},
         {offset: 1, blur: 10, spread: 0}],

        [{offset: 3, blur: 5, spread: -1},
         {offset: 5, blur: 8, spread: 0},
         {offset: 1, blur: 14, spread: 0}],

        [{offset: 3, blur: 5, spread: -1},
         {offset: 6, blur: 10, spread: 0},
         {offset: 1, blur: 18, spread: 0}],

        [{offset: 4, blur: 5, spread: -2},
         {offset: 7, blur: 10, spread: 1},
         {offset: 2, blur: 16, spread: 1}],

        [{offset: 5, blur: 5, spread: -3},
         {offset: 8, blur: 10, spread: 1},
         {offset: 3, blur: 14, spread: 2}],

        [{offset: 5, blur: 6, spread: -3},
         {offset: 9, blur: 12, spread: 1},
         {offset: 3, blur: 16, spread: 2}],

        [{offset: 6, blur: 6, spread: -3},
         {offset: 10, blur: 14, spread: 1},
         {offset: 4, blur: 18, spread: 3}],

        [{offset: 6, blur: 7, spread: -4},
         {offset: 11, blur: 15, spread: 1},
         {offset: 4, blur: 20, spread: 3}],

        [{offset: 7, blur: 8, spread: -4},
         {offset: 12, blur: 17, spread: 2},
         {offset: 5, blur: 22, spread: 4}],

        [{offset: 7, blur: 8, spread: -4},
         {offset: 13, blur: 19, spread: 2},
         {offset: 5, blur: 24, spread: 4}],

        [{offset: 7, blur: 9, spread: -4},
         {offset: 14, blur: 21, spread: 2},
         {offset: 5, blur: 26, spread: 4}],

        [{offset: 8, blur: 9, spread: -5},
         {offset: 15, blur: 22, spread: 2},
         {offset: 6, blur: 28, spread: 5}],

        [{offset: 8, blur: 10, spread: -5},
         {offset: 16, blur: 24, spread: 2},
         {offset: 6, blur: 30, spread: 5}],

        [{offset: 8, blur: 11, spread: -5},
         {offset: 17, blur: 26, spread: 2},
         {offset: 6, blur: 32, spread: 5}],

        [{offset: 9, blur: 11, spread: -5},
         {offset: 18, blur: 28, spread: 2},
         {offset: 7, blur: 34, spread: 6}],

        [{offset: 9, blur: 12, spread: -6},
         {offset: 19, blur: 29, spread: 2},
         {offset: 7, blur: 36, spread: 6}],

        [{offset: 10, blur: 13, spread: -6},
         {offset: 20, blur: 31, spread: 3},
         {offset: 8, blur: 38, spread: 7}],

        [{offset: 10, blur: 13, spread: -6},
         {offset: 21, blur: 33, spread: 3},
         {offset: 8, blur: 40, spread: 7}],

        [{offset: 10, blur: 14, spread: -6},
         {offset: 22, blur: 35, spread: 3},
         {offset: 8, blur: 42, spread: 7}],

        [{offset: 11, blur: 14, spread: -7},
         {offset: 23, blur: 36, spread: 3},
         {offset: 9, blur: 44, spread: 8}],

        [{offset: 11, blur: 15, spread: -7},
         {offset: 24, blur: 38, spread: 3},
         {offset: 9, blur: 46, spread: 8}]
    ]

    readonly property var _shadowColors: [
        Qt.rgba(0,0,0, 0.2),
        Qt.rgba(0,0,0, 0.14),
        Qt.rgba(0,0,0, 0.12)
    ]

    Repeater {
        model: _shadows[elevation]

        delegate: RectangularGlow {
            anchors {
                centerIn: parent
                verticalCenterOffset: modelData.offset
            }

            width: parent.width + 2 * modelData.spread
            height: parent.height + 2 * modelData.spread
            glowRadius: modelData.blur/2
            spread: 0.05
            color: _shadowColors[index]
            cornerRadius: modelData.blur + (effect.source.radius || 0)
        }
    }

    ShaderEffect {
        anchors.fill: parent
        property alias source: effect.source;
    }
}