title: Cannot get pass through geometry shader working
body: <p>I have a VBO with points in it, that I can render fine with a vertex and fragment shader, but when I add a pass through geometry shader, I see nothing.  I'm using MRT for glow, but in this example I don't touch it.</p>
  
  <p>From what I've seen on other posts, it looks like there may be issues with passing values from one stage to another, so I removed all my varyings but it still does not work.</p>
  
  <p>I set up the program parameters after linking - hopefully that's alright.</p>
  
  <p>Any ideas why disabling the geometry shader produces white particles, but enabling it shows nothing?</p>
  
  <p>VERTEX SHADER:</p>
  
  <pre><code>#version 120
  attribute vec3 position;
  uniform mat4 projectionMatrix;
  uniform mat4 modelViewMatrix;
  
  void main()
  {
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1);
  }
  </code></pre>
  
  <p>FRAGMENT SHADER:</p>
  
  <pre><code>#version 120
  
  void main()
  {
      gl_FragData[0] = vec4(1.f, 1.f, 1.f, 1.f);
      gl_FragData[1] = vec4(0.f, 0.f, 0.f, 0.f);
  }
  </code></pre>
  
  <p>GEOMETRY SHADER:</p>
  
  <pre><code>#version 120
  #extension GL_EXT_geometry_shader4: enable
  
  uniform mat4 projectionMatrix;
  uniform mat4 modelViewMatrix;
  
  void main(void)
  {
      for (int i = 0; i &lt; gl_VerticesIn; i++)
      {
          gl_Position = gl_PositionIn[i];
          EmitVertex();
      }
          EndPrimitive();
  }
  </code></pre>
  
  <p>Setting up params (after program linking, program is resources.particleprogram)</p>
  
  <pre><code>glProgramParameteriEXT(resources.particleprogram, GL_GEOMETRY_INPUT_TYPE_EXT, GL_POINTS);
  glProgramParameteriEXT(resources.particleprogram, GL_GEOMETRY_OUTPUT_TYPE_EXT, GL_POINTS);
  glProgramParameteriEXT(resources.particleprogram, GL_GEOMETRY_VERTICES_OUT_EXT, 4);
  </code></pre>