Function intervalScaleEnsureValidExtent

src/scale/helper.ts:224–277

(
    rawExtent: number[],
    fixMinMax: ScaleExtentFixMinMax,
    rawExtentResult?: ScaleRawExtentResultFinal | NullUndefined
)

 *    in "nice" and "align" ticks.
 */
export function intervalScaleEnsureValidExtent(
    rawExtent: number[],
    fixMinMax: ScaleExtentFixMinMax,
    rawExtentResult?: ScaleRawExtentResultFinal | NullUndefined
): number[] {
    const extent = rawExtent.slice();

    // PENDING:
    //  This implementation is not rigorous, but has long been in use.

    // If extent start and end are same, expand them
    if (extent[0] === extent[1]) {
        // If `containShape`, the extent must be evenly distributed to both sides;
        // otherwise, shape (e.g., bars) may be overflow and clipped.
        const containShapeRequired = rawExtentResult && rawExtentResult.ctnShp;

        if (extent[0] !== 0) {
            // Expand extent
            // Note that extents can be both negative. See #13154
            const expandSize = mathAbs(extent[0]);
            // In the fowllowing case
            //      Axis has been fixed max 100
            //      Plus data are all 100 and axis extent are [100, 100].
            // Extend to the both side will cause expanded max is larger than fixed max.
            // So only expand to the smaller side.
            if (!fixMinMax[1]) {
                extent[1] += expandSize / 2;
                extent[0] -= expandSize / 2;
            }
            else {
                extent[0] -= expandSize / 2;
            }
        }
        else {
            if (containShapeRequired) {
                extent[0] = -1;
                extent[1] = 1;
            }
            else {
                extent[1] = 1;
            }
        }
    }
    // For example, if there are no series data, extent may be `[Infinity, -Infinity]` here.
    if (!isValidNumberForExtent(extent[0]) || !isValidNumberForExtent(extent[1])) {
        extent[0] = 0;
        extent[1] = 1;
    }
    if (extent[1] < extent[0]) {
        extent.reverse();
    }

    return extent;
}

export function extentDiffers(extent1: number[], extent2: number[]): boolean[] {
    return [extent1[0] !== extent2[0], extent1[1] !== extent2[1]];