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Vertex Count Increasing In Unreal Engine

Hi everyone,

So I’ve been importing some models in to Unreal Engine 4. In my modelling application the vertex count stands at 1,498 and the polygon count at 2,442 however when I import the model in to Unreal Engine the vertex count doubles to 4,225, the polygon count remains the same.

This leads me to believe that Unreal Engine duplicates all the vertices that two or more polygons share. I read on the internet that this is called vertex indexing and that when your graphics card renders the model it will only render 1,498 vertices as the modelling application shows and that I shouldn’t worry about it but focus on the polygon count only.

Is this true? Am I importing the model wrong? Whats going on?

Thank you in advance. :slight_smile:

You should not have to worry about the vertex count difference between your modeling app and the game engine (unless you’re searching for optimisations), because they count them in different ways :

  • The modeling apps in general simply counts the total vertices of an object
  • The game engine counts the number of vertices containing “single infos”. When you have an UV seam in the mesh, the corresponding vertex gets doubled (because one vertex index corresponds to only one uv), same for a split normal (hard edge / smoothing group) and material.

Here’s a small article with more explanations about this, and with some tools to get the “good” vertex count in your modeling app : http://wiki.polycount.com/wiki/Polygon_Count#Triangle_Count_vs._Vertex_Count

If you have wrong settings in calculate tangents/normals engine might have to split all edges. This is real problem and can lower performance and make generated LOD’s much worse.

Settings that works for us is to import normals from Blender and recalculate tangents on engine. Also we use MikkTSpace tangent space.

Thanks, this method lowered my vertices count by about ⅓ to 3,571 which will have a big effect on the level as a whole.