   Fragment Shader Distance Gradient
  Hello,I hope I am not repeating a question that already has been answered, but I've checked extensively.I currently am writing an openGL application that renders a 3d model of a brain. This model is at a high poly count, approximately 50,000. My problem is choosing a point, or vertex, at any point on this model and modulating an activation for this point in real-time.I currently have a vertex and fragment shader implemented in GLSL along with having the model render correctly but I cannot get the precision of the gradient I am looking for. Ideally, I would pass the point to a shader, have it calculate if a point is within the radius and then color out accordingly.Using the vertex shader I have a rough circle that has rough variations in color due to the vertex faces and not enough precision.Any help is greatly appreciated from anyone and everyone.   
  I should add that this model does not have a texture, UV coords, associated because I had to export this anatomical model from MATLAB. No texture ever existed.