title: Reducing SCNGeometry polygon count at runtime
body: <p>I have a 3D model in Blender which has way too many polygons. Unfortunately I cannot use Blender to reduce the polygon count (e.g., through a Decimate modifier) due to Blender's limitations—it cannot apply the modifier to a object with shape keys.</p>
  
  <p>So I was thinking I could probably simplify the mesh programmatically in SceneKit, and maybe export it afterwards.</p>
  
  <p>I think the first step would be to figure out neighboring polygons I could somehow merge, and iteratively do this step. Then I'd enumerate the resulting polygons and figure out which vertex data was actually used, and create a new simplified <code>SCNGeometrySource</code>, and then a re-indexed <code>SCNGeometryElement</code>. Since the Blender shape keys are exported as <code>SCNMorpher</code> target geometries, I'd also have to make the corresponding changes to all of the target geometries so that their source vertex information matches up.</p>
  
  <p>Does that sound reasonable? Is there an algorithm to use for merging neighboring polygons?</p>