title: Scaling around a specific point in 2d coordinate system
body: <p>Below is an image my coordinate system: 
  <a href="https://i.stack.imgur.com/rWoEx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rWoEx.png" alt="enter image description here"></a></p>
  
  <p>What I am trying to do is that I want to start scaling around a specific point in the canvas, the scaling works fine but my problem is that I don't know how to calculate how much to move the canvas while scaling, note that I am not using canvas.scale.</p>
  
  <p>I am simply increasing the distance between each 2 units in the system while scaling and it's working just fine.  </p>
  
  <p>So is there any equation that can help me find out how much to offset the canvas while scaling at specific point?</p>
  
  <p>Suppose I want to scale around point(0,4) how to know how much to move the canvas while scaling? </p>