Function getRelativePosition

src/helpers/helpers.dom.ts:105–131

(
  event: Event | ChartEvent | TouchEvent | MouseEvent,
  chart: Chart | PrivateChart
)

 */

export function getRelativePosition(
  event: Event | ChartEvent | TouchEvent | MouseEvent,
  chart: Chart | PrivateChart
): { x: number; y: number } {
  if ('native' in event) {
    return event;
  }

  const {canvas, currentDevicePixelRatio} = chart;
  const style = getComputedStyle(canvas);
  const borderBox = style.boxSizing === 'border-box';
  const paddings = getPositionedStyle(style, 'padding');
  const borders = getPositionedStyle(style, 'border', 'width');
  const {x, y, box} = getCanvasPosition(event, canvas);
  const xOffset = paddings.left + (box && borders.left);
  const yOffset = paddings.top + (box && borders.top);

  let {width, height} = chart;
  if (borderBox) {
    width -= paddings.width + borders.width;
    height -= paddings.height + borders.height;
  }
  return {
    x: Math.round((x - xOffset) / width * canvas.width / currentDevicePixelRatio),
    y: Math.round((y - yOffset) / height * canvas.height / currentDevicePixelRatio)
  };
}

function getContainerSize(canvas: HTMLCanvasElement, width: number, height: number): Partial<Scale> {
  let maxWidth: number, maxHeight: number;