function line(ctx, x1, y1, x2, y2) {
    ctx.beginPath();
    ctx.moveTo(x1, y1);
    ctx.lineTo(x2, y2);
    ctx.stroke();
}
Add a quadratic curve to the bounding box.
This extends the bounding box to include the entire quadratic curve.
@param {number} x0 - The starting X coordinate.
@param {number} y0 - The starting Y coordinate.
@param {number} x1 - The X coordinate of the control point.
@param {number} y1 - The Y coordinate of the control point.
@param {number} x - The ending X coordinate.
@param {number} y - The ending Y coordinate.