title: Texture with transparent areas renders the areas as black - how do I make them transparent?
body: <p>I have a very simple 2d square, which I render a game sprite onto from a texture.  This all works quite well, except that the areas that should be transparent in the texture are rendered as black.  How do I render those transparent areas to show the objects behind the square (in this case, the background)?</p>
  
  <hr>
  
  <p>Incase relevant, here's the simple fragment Shader:</p>
  
  <pre><code>uniform sampler2D uTexture;
  varying vec2 vImagePosition;
  void main(){
      gl_FragColor =  texture2D(uTexture, vImagePosition);
  }
  </code></pre>
  
  <p>And the vertex Shader:</p>
  
  <pre><code>attribute vec4 aPosition;
  attribute vec2 aImagePosition;
  uniform mat4 uMVPMatrix;
  varying vec2 vImagePosition;
  void main(){
      gl_Position = uMVPMatrix*aPosition;
      vImagePosition = aImagePosition;
  }
  </code></pre>