title: opengl - point sprites rendering problem
body: <p>I'm trying to render point sprites but I get points. Where is the problem ? (changing a color via glUniform3f works)</p>
  
  <p>Vertex shader:</p>
  
  <pre><code>private static String vertexShader =
  "#version 330" + "\n" +
  "layout (location = 0) in vec4 position;" + "\n" +
  "uniform mat4 pMatrix;" + "\n" +
  "uniform mat4 mMatrix;" + "\n" +
  "void main()" + "\n" +
  "{" + "\n" +
  "gl_Position = pMatrix * mMatrix * position;" + "\n" +
  "}";
  </code></pre>
  
  <p>Fragment shader:</p>
  
  <pre><code>private static String fragmentShader =
  "#version 330" + "\n" +
  "out vec4 vFragColor;" + "\n" +
  "uniform vec3 Color;" + "\n" +
  "uniform vec3 lightDir;" + "\n" +
  "void main()" + "\n" +
  "{" + "\n" +
  "vec3 N;" + "\n" +
  "N.xy = gl_PointCoord* 2.0 - vec2(1.0);" + "\n" +    
  "float mag = dot(N.xy, N.xy);" + "\n" +
  "if (mag &gt; 1.0) discard;" + "\n" +   
  "N.z = sqrt(1.0-mag);" + "\n" +
  "float diffuse = max(0.0, dot(lightDir, N));" + "\n" +
  "vFragColor = vec4(Color,1) * diffuse;" + "\n" +
  "}";
  </code></pre>
  
  <p>Rendering:</p>
  
  <pre><code>gl.glUseProgram(shaderProgramID);
  gl.glUniformMatrix4fv(projectionMatrixUniform, 1, false, projectionMatrix, 0);
  gl.glUniformMatrix4fv(modelViewMatrixUniform, 1, false, modelViewMatrix, 0);
  gl.glUniform3f(colorUniform, 1.0f, 0.0f, 0.0f);
  gl.glUniform3f(lightDirUniform, 0.0f, 0.0f, 1.0f);
  gl.glBindBuffer(GL3.GL_ARRAY_BUFFER, vbo[0]);
  gl.glEnableVertexAttribArray(0);
  gl.glVertexAttribPointer(0, 4, GL3.GL_FLOAT, false, 0, 0);
  gl.glDrawArrays(GL3.GL_POINTS, 0, n_particles);
  gl.glDisableVertexAttribArray(0);
  gl.glUseProgram(0);
  </code></pre>