index.js

pre.addEventListener("click", event => {
    const boundingRect = pre.getBoundingClientRect();

    const scaleX = 64 / boundingRect.width;
    const scaleY = 64 / boundingRect.height;

    const canvasLeft = (event.clientX - boundingRect.left) * scaleX;
    const canvasTop = (event.clientY - boundingRect.top) * scaleY;

    const row = Math.min(Math.floor(canvasTop), 64 - 1);
    const col = Math.min(Math.floor(canvasLeft), 64 - 1);

    contract.call(
      wallet,
      "toggle",
      BigInt(0),
      BigInt(1e7),
      BigInt(0),
      {
        type: "uint32",
        value: row
      },
      {
        type: "uint32",
        value: col
      }
    );
  });