Function setSectorTextRotation

src/label/sectorLabel.ts:192–261

(
    sector: Sector,
    textPosition: T,
    positionMapping: (seriesLabelPosition: T) => SectorTextPosition,
    rotateType: number | 'auto'
)

}

export function setSectorTextRotation<T extends (string | (number | string)[])>(
    sector: Sector,
    textPosition: T,
    positionMapping: (seriesLabelPosition: T) => SectorTextPosition,
    rotateType: number | 'auto'
) {
    if (isNumber(rotateType)) {
        // user-set rotation
        sector.setTextConfig({
            rotation: rotateType
        });
        return;
    }
    else if (isArray(textPosition)) {
        // user-set position, use 0 as auto rotation
        sector.setTextConfig({
            rotation: 0
        });
        return;
    }

    const shape = sector.shape;
    const startAngle = shape.clockwise ? shape.startAngle : shape.endAngle;
    const endAngle = shape.clockwise ? shape.endAngle : shape.startAngle;
    const middleAngle = (startAngle + endAngle) / 2;

    let anchorAngle;
    const mappedSectorPosition = positionMapping(textPosition);
    switch (mappedSectorPosition) {
        case 'startArc':
        case 'insideStartArc':
        case 'middle':
        case 'insideEndArc':
        case 'endArc':
            anchorAngle = middleAngle;
            break;

        case 'startAngle':
        case 'insideStartAngle':
            anchorAngle = startAngle;
            break;

        case 'endAngle':
        case 'insideEndAngle':
            anchorAngle = endAngle;
            break;

        default:
            sector.setTextConfig({
                rotation: 0
            });
            return;
    }

    let rotate = Math.PI * 1.5 - anchorAngle;
    /**
     * TODO: labels with rotate > Math.PI / 2 should be rotate another
     * half round flipped to increase readability. However, only middle