title: OpenGLES 2.0: gl_VertexID equivalent?
body: <p>I'm trying to create a grid of points by calculating vertex positions dynamically, based on their index in the array of vertices sent to the shader. Is there an equivalent of the gl_VertexID variable that I can call from within my shader? Or another way of accessing their position in the array without having to send more data to the GPU? Thank, Josh.</p>
  
  <p>Here's my vertex shader:</p>
  
  <pre><code>attribute vec4 vertexPosition;
  uniform mat4 modelViewProjectionMatrix;
  vec4 temp;
  uniform float width;
  
  void main()
  {    
      temp = vertexPosition;
  
      // Calculate x and y values based on index:
      temp.y = floor(gl_VertexID/width);
      temp.x = gl_VertexID - width*temp.y;
  
      gl_Position = modelViewProjectionMatrix * temp;
  }
  </code></pre>