title: Android Gauge Animation Question
body: <p>Okay so i've been trying to do this for a couple of days and i am getting no where. So i have the following two images:</p>
  
  <p>The First is a RPM Gauge</p>
  
  <p><img src="https://i.stack.imgur.com/T46nQ.png" alt="RPM Gauge"></p>
  
  <p>The Second image is a full white graphic representing rpm gauge being full:</p>
  
  <p><img src="https://i.stack.imgur.com/4pk84.png" alt="Full Gauge"></p>
  
  <p>I want to do the following:</p>
  
  <ol>
  <li>ask the user for an RPM input, if for example they enter 1.2 the gauge will fill up as follows:</li>
  </ol>
  
  <p><img src="https://i.stack.imgur.com/U6yZS.png" alt="output"></p>
  
  <p>I have the user input working i need help with the animation. Here is what i have tried:</p>
  
  <ol>
  <li>I have tried using PorterDuff but it also clips the gauge in the background not just the white bar</li>
  <li>I've tried splitting the image into little bitmaps and store them into arrays so that i can recall    parts but this was slow and often crashed</li>
  <li>I made some progress by applying the Gauge first to the canvas then saving the canvas: canvas.save(); then clipping a path on the white image then restoring the canvas. However i do not know how to clip in a circular fashion starting from bottom left to a 180 degress to the bottom right (CW). Is this the best way? </li>
  </ol>
  
  <p>I know there is probably an easier or more efficient way of doing this i just don't have a clue. Anyone with any good ideas?</p>
  
  <p>*Note all images are PNG's</p>
  
  <p>Thanks in advance!</p>