title: THREE.SpriteCanvasMaterial not working
body: <p>This code (based on <a href="http://threejs.org/examples/#canvas_particles_shapes" rel="nofollow">this</a> <a href="http://threejs.org/examples/webgl_particles_billboards.html" rel="nofollow">code</a>):</p>
  
  <pre><code>    drawCircle = (context) -&gt;
          pos = 0.5
          radius = 0.5
          context.scale(0.05, -0.05)
          context.beginPath()
          context.arc(pos, pos, radius, 0, 2*Math.PI, false)
          context.fillStyle = 'white'
          context.fill()
  
      m = new THREE.SpriteCanvasMaterial( {program: drawCircle } )
      s = new THREE.Sprite( m )
  </code></pre>
  
  <p>returns an error</p>
  
  <pre><code>    Uncaught TypeError: Cannot read property 'x' of undefined. 
  </code></pre>
  
  <p>In Three.js: line 36534:</p>
  
  <pre><code>    _gl.uniform2f( uniforms.uvScale, material.uvScale.x, material.uvScale.y );
  </code></pre>
  
  <p>It seems that the material uvScale and uvOffset properties are not properly initialized... Why ?
  If I set those properties myself: </p>
  
  <pre><code>    m.uvScale = new THREE.Vector2()
      m.uvOffset = new THREE.Vector2()
  </code></pre>
  
  <p>Errors disappear but I can't see the particles (I don't know where to draw in the canvas, and why should I scale it).</p>