excalidraw/src/scene/zoom.ts

export function getZoomOrigin(canvas: HTMLCanvasElement | null) {
  if (canvas === null) {
    return { x: 0, y: 0 };
  }
  const context = canvas.getContext("2d");
  if (context === null) {
    return { x: 0, y: 0 };
  }

  const normalizedCanvasWidth = canvas.width / context.getTransform().a;
  const normalizedCanvasHeight = canvas.height / context.getTransform().d;

  return {
    x: normalizedCanvasWidth / 2,
    y: normalizedCanvasHeight / 2,
  };
}

export function getNormalizedZoom(zoom: number): number {
  const normalizedZoom = parseFloat(zoom.toFixed(2));
  const clampedZoom = Math.max(0.1, Math.min(normalizedZoom, 2));
  return clampedZoom;
}