title: How to draw rectangle over canvas
body: <p>i'm receving from webserver part of image, let say 600px x 600px, which i'm drawing in canvas.</p>
  <p>The real size of image is let say 600px x 1200px(height).</p>
  <p>I need to create scrollbar over canvas. After i will drag scrollbar i will count, how many pixels i've moved scrollbar, send to server information and i will receive other portion of picture (600x600px) but scrolled.
  The mechanism is done by me, but i need to draw scrollbar over canvas.</p>
  <pre><code>&lt;b-card&gt;
    &lt;div id=&quot;image&quot;&gt;
      &lt;canvas
        id=&quot;canvasId&quot;
        ref=&quot;canRef&quot;
        @mousedown=&quot;clickMe&quot;
        @mouseup=&quot;scrollOff&quot;
        @mousemove=&quot;scrollMe&quot;
      /&gt;
    &lt;/div&gt;
  &lt;/b-card&gt;
  </code></pre>
  <p>How to draw scroll bar on the right side of canvas?</p>