A Blender specific question - edge sharpening

[Nacy Nightfire]

I'd appreciate it very much if someone could explain the difference of each of these modeling treatment of edges and pe impact of each option, I'm a bit confused here:

- Splitting the seam so its unattached geometry

- Flat shading

- Marking seams as "sharp"

- Using the "edge crease" function

- Modeling in close edges or alternatively using Loopcut/slide to add a loop and slide it close to the edge you want to keep sharp

I used edge crease on the following model, but I'm not sure that was the most efficient method pe wise.

 

[Drongle McMahon]

Smooth vertices have s single normal that is used in all the triangles that meet there. For sharp edges the normal at the vertex position has to be different for triangles on either side. In the SL internal format, this ,eans storing the vertex data twice which will increase the download weight, and thus usually the PE. Sharp edges cost more. This all happens transparently whichver method use to make the sharp edges. However. so will cost even more....

- Splitting the seam so its unattached geometry

Assuming you mean producing two edge loops with duplicated vertices belonging to two separate unconnected meshes. This is what actually happens when you use Edge->Mark Sharp and apply the edge-split modifier using just marked as sharp and not by angle. It is probably better to use the modifier and keep the edges unsplit until it is applied during the Collada export (check apply modifiers). That way, you don't have to be careful to always move the superimposed vertices together.

- Flat shading

Is this "solid" in Blender 2.49? Giving faceted appeareance? If so, this is fine as far as it goes, but does not give the same level as control as the edge split modifier. You usually can't get exectly what you want. It ends up with the same duplication of vertex data as the latter, so there is no saving by using this inn prefrerence.

- Marking seams as "sharp"

Yes. See above. This is the best way in my view. It requires the edge-split modifier. Note that if you apply the modifier before export you will get actual vertex duplication that will make editing more difficult. You can see the effect of the modifier in the 3D view without having to apply it. Note that the edges marked as sharp do not have to be UV seams. These are quite separate thingss. However, since both have the same effect of vertex duplication, increasingt PE, there might be some saving if the same edges are used for both when it is convenient.

- Using the "edge crease" function

Not so sure. Is this while using the subsurf modifier? I have not tested that. Someone else can answer.

- Modeling in close edges or alternatively using Loopcut/slide to add a loop and slide it close to the edge you want to keep sharp

This is like the vertex collapsing method you have to use with sculpties. This method should be avoided. It leaves zero area faces and you have to deal with the UV map as well as the vertices. The zero area faces may be culled during upload or may cause errors, or it may leave the redundant geometry intact, I don't know. When the edge split modifier allows you to achieve the desired result without these problems there is no reason to use this approach.

[Nacy Nightfire]

Thanks a gazillion Drongle.  That gets me well on my way. I'll do more research now that I have a better understanding of the differences and I'll expecially get a handle on "edge crease" and report back.  I'm sure this is useful info for alot of folks.

 Circular/rounded modeling shapes need more verts to hold up their shape which is costly, but the sharpen effect for edges adds to the cost also.  It makes my head spin.

[Nacy Nightfire]

You are correct about the edge crease function "weighting" subsurfed model edges, which means I was using it  incorrectly on a model that was not subsurfed =(.

 

http://download.blender.org/documentation/htmlI/ch07s02.html

 

The fog is lifting.

[Ashasekayi Ra]

Just a side note, the edge split modifier combined with "mark sharp" can also be used for more than just sharpening edges. You can use it to seperate parts of the model so that you can add more detail where it's needed while keeping another part unaltered.

[Nacy Nightfire]

Thanks Ashasekayi, that's extreamly helpful!

[Ashasekayi Ra]

Welcome Nacy ^^