CVS EdgeSplit modifier and "Mark Sharp"

I thought I’d create a brief tutorial describing the operation of two features currently in blender CVS: the EdgeSplit modifier in combination with the “Edge Specials” -> “Mark Sharp” menu option.

The EdgeSplit modifier basically splits edges in the mesh according to one of two criteria, selectable by buttons in the modifier panel:

  • “From Edge Angle” - edges will be split if the angle between the two faces that touch that edge is greater than a specified threshold
  • “From Marked As Sharp” - edges will be split if they are marked as sharp (using the “Edge Specials” (Ctrl-E) -> “Mark Sharp” menu option in edit mode)

In this tutorial I will be using just the “From Marked As Sharp” option. The image below shows the EdgeSplit modifier panel settings used.

Why would you want to split edges? So you can control smoothing. Meshes are smoothed by calculating vertex normals based on all the faces that touch each vertex. By splitting edges which should be sharp, faces on opposite sides of those edges no longer touch, so vertex normals are no longer smoothed across those edges. This gives a sharp appearance to those edges.

The first image below shows a mesh in editmode with “Draw Sharp” turned on (Edit buttons -> “Mesh Tools 1” panel). The edges which are marked as sharp are highlighted in red. These edges will be split by the EdgeSplit modifier.

The next image shows the same setup in object mode. Note that the results of the EdgeSplit modifier are visible without rendering, whereas the mesh with Autosmooth applied looks the same as the basic smoothed mesh. The results of the EdgeSplit modifier are also available to export scripts.

The next image shows the render result. Note that the EdgeSplit modifier gives more precise control over which edges are sharp than the Autosmooth modifier. Additionally, you do not have to select a group of faces to be smoothed together - just mark the edges which you want to be sharp.

The blend used to create these images is available at


Hey thats cool, thanks for taking the time to make it nice and clear.

So does split edges sort of have the same effect as selecting part of a mesh and separating it? Like in another tutorial posted somewhere about detail in the game-engine?

Because if it does, it sounds pretty handy!

Yes, it does, with the advantage that instead of having to separate the mesh into regions of smoothness, you can just mark the edges that you want to be sharp.