function getVisualGradient()

in src/chart/line/LineView.ts [276:376]
77 lines of code
26 McCabe index (conditional complexity)

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();

    if (stopLen && colorStops[0].coord > colorStops[stopLen - 1].coord) {
        colorStops.reverse();
        outerColors.reverse();
    }
    const colorStopsInRange = clipColorStops(
        colorStops, coordDim === 'x' ? api.getWidth() : api.getHeight()
    );
    const inRangeStopLen = colorStopsInRange.length;
    if (!inRangeStopLen && stopLen) {
        // All stops are out of range. All will be the same color.
        return colorStops[0].coord < 0
            ? (outerColors[1] ? outerColors[1] : colorStops[stopLen - 1].color)
            : (outerColors[0] ? outerColors[0] : colorStops[0].color);
    }

    const tinyExtent = 10; // Arbitrary value: 10px
    const minCoord = colorStopsInRange[0].coord - tinyExtent;
    const maxCoord = colorStopsInRange[inRangeStopLen - 1].coord + tinyExtent;
    const coordSpan = maxCoord - minCoord;

    if (coordSpan < 1e-3) {
        return 'transparent';
    }

    zrUtil.each(colorStopsInRange, function (stop) {
        stop.offset = (stop.coord - minCoord) / coordSpan;
    });
    colorStopsInRange.push({
        // NOTE: inRangeStopLen may still be 0 if stoplen is zero.
        offset: inRangeStopLen ? colorStopsInRange[inRangeStopLen - 1].offset : 0.5,
        color: outerColors[1] || 'transparent'
    });
    colorStopsInRange.unshift({ // notice newColorStops.length have been changed.
        offset: inRangeStopLen ? colorStopsInRange[0].offset : 0.5,
        color: outerColors[0] || 'transparent'
    });

    const gradient = new graphic.LinearGradient(0, 0, 0, 0, colorStopsInRange, true);
    gradient[coordDim] = minCoord;
    gradient[coordDim + '2' as 'x2' | 'y2'] = maxCoord;

    return gradient;
}