保存一段qml里使用opengl shader的代码，由于多平台原因暂时用不了

                            RowLayout {
                                Layout.fillWidth: true
                                height: 60
                                Rectangle {
                                    Layout.margins: 5
                                    radius: 5
                                    width: 40
                                    height: width
                                    Layout.alignment: Qt.AlignVCenter | Qt.AlignLeft
                                    clip: true
                                    layer.enabled: true
                                    layer.effect: ShaderEffect {
                                        readonly property var dataTex: dataCanvas
                                        readonly property real count: dataCanvas.colors.length
                                        fragmentShader: "
varying highp vec2 qt_TexCoord0;
uniform lowp float qt_Opacity;
uniform sampler2D dataTex;
const uniform lowp int count;
void main() {
vec3 col = 0.0;
for (int i = 0; i < count; i++) {
vec4 color = texture2D(dataTex, vec2(i / (float)count + 0.01, 0.0));
vec2 point = texture2D(dataTex, vec2(i / (float)count + 0.01, 1.0)).rg;
float dist = distance(qt_TexCoord0, point);
col += color * (1.0 - dist);
}
gl_FragColor = vec4(col, 1.0);
}
"
                                    }
                                    // Because ShaderEffect doesn't allow passing arrays to shader, we will
                                    // convert arrays to graphical representation and pass them as texture.
                                    Canvas {
                                        id: dataCanvas
                                        readonly property var colors: ["green", "yellow", "cyan", "red"]
                                        readonly property var positions: [Qt.point(
                                                0, 0), Qt.point(parent.width,
                                                                0), Qt.point(
                                                0, parent.height), Qt.point(
                                                parent.width, parent.height)]

                                        height: 2
                                        width: colors.length
                                        antialiasing: false
                                        visible: false

                                        onPaint: {
                                            if (colors.length !== positions.length) {
                                                console.error(
                                                            "Array size of 'colors' doesn't equal array size of 'positions'")
                                                return
                                            }

                                            var ctx = getContext("2d")
                                            ctx.reset()
                                            ctx.lineWidth = 1

                                            for (var i = 0; i < colors.length; i++) {
                                                ctx.beginPath()
                                                ctx.strokeStyle = colors[i]
                                                ctx.moveTo(i, 0)
                                                ctx.lineTo(i + 1, 0)
                                                ctx.stroke()
                                                ctx.closePath()

                                                ctx.beginPath()
                                                ctx.strokeStyle = Qt.rgba(
                                                            positions[i].x / parent.width,
                                                            positions[i].y / parent.height,
                                                            0, 1)
                                                ctx.moveTo(i, 1)
                                                ctx.lineTo(i + 1, 1)
                                                ctx.stroke()
                                                ctx.closePath()
                                            }
                                        }
                                    }
                                }