Function getVisualGradient

src/chart/line/LineView.ts:268–368

(
    data: SeriesData,
    coordSys: Cartesian2D | Polar,
    api: ExtensionAPI
)

}

function getVisualGradient(
    data: SeriesData,
    coordSys: Cartesian2D | Polar,
    api: ExtensionAPI
) {
    const visualMetaList = data.getVisual('visualMeta');
    if (!visualMetaList || !visualMetaList.length || !data.count()) {
        // When data.count() is 0, gradient range can not be calculated.
        return;
    }

    if (coordSys.type !== 'cartesian2d') {
        if (__DEV__) {
            console.warn('Visual map on line style is only supported on cartesian2d.');
        }
        return;
    }

    let coordDim: 'x' | 'y';
    let visualMeta;

    for (let i = visualMetaList.length - 1; i >= 0; i--) {
        const dimInfo = data.getDimensionInfo(visualMetaList[i].dimension);
        coordDim = (dimInfo && dimInfo.coordDim) as 'x' | 'y';
        // Can only be x or y
        if (coordDim === 'x' || coordDim === 'y') {
            visualMeta = visualMetaList[i];
            break;
        }
    }

    if (!visualMeta) {
        if (__DEV__) {
            console.warn('Visual map on line style only support x or y dimension.');
        }
        return;
    }

    // If the area to be rendered is bigger than area defined by LinearGradient,
    // the canvas spec prescribes that the color of the first stop and the last
    // stop should be used. But if two stops are added at offset 0, in effect
    // browsers use the color of the second stop to render area outside
    // LinearGradient. So we can only infinitesimally extend area defined in
    // LinearGradient to render `outerColors`.

    const axis = coordSys.getAxis(coordDim);

    // dataToCoord mapping may not be linear, but must be monotonic.
    const colorStops: ColorStop[] = zrUtil.map(visualMeta.stops, function (stop) {
        // offset will be calculated later.
        return {
            coord: axis.toGlobalCoord(axis.dataToCoord(stop.value)),
            color: stop.color
        } as ColorStop;
    });
    const stopLen = colorStops.length;
    const outerColors = visualMeta.outerColors.slice();