Surface flow – why it matters

Often when someone new to 3D shows their first model online, the form lacks definition and the whole thing looks a bit play-doughy.  And if they show the model wireframe, you can see the construction may have lots of polygons but the distribution is not even nor does it flow with the shape.  It’s often because they construct the model without changing surface flow.
Surface flow is directed with either the edges between the polygons or by polygons themselves – the same thing really.  It is usually called edgeflow.

Benefits of good edgeflow

  • more definition with less polygons, an optimized mesh
  • better deformation in animation (if built with anatomy in mind)
  • better shading

surf.flow good flows

I’ve prepared some examples, an organic shape done in two ways:
1.  with edges directing the flow
2.  no flow directions made

First image is our example shape, a cute  nose.

surf.flow nosepolys

Here it is as a basemesh and same with subdivision(control cage showing).  The nose has 42 polygons.  Now lets try achieve same shape and definition without any  flow direction – starting with 42 polys.

no surface flow, examples

As you can see, results don’t get much better with more polygons, somewhat worse in fact.  The model becomes difficult to work with.  Yet I’d still have to increase polycount to achieve the same definition we get with directed surface flow.  You CAN get good results this way in a sculpting program, working with thousands or millions polygons, but to get anything out that you can use in any other program, or animate for that matter,  you have to reconstruct the model surface flow.

surf.flow mouth exampleAnimated models benefit from good surface flow when flow is correct in places where the deformation happens, like around the mouth.  See the pic.  And sorry but I shan’t torture myself by building a poor mesh for comparison.  Just imagine a  rough head shaped tube here with a polygon or few pulled in for the mouth.  If you think that’s bad, imagine what happens when it is animated.

Good surface flow also improves shading simply because having a flow that defines the shape nicely from the ground up, you have every big and small part of said mesh aligned along the shape and not against it.  Also with good flow you do not have mesh issues(poles, etc.). When virtual light rays hit those parts, they reflect and refract as they should.  Shading, that is highlights and shadows and all, looks like it should.  I have no solid proof on this, but can say from experience that models with good edgeflow render better.

To conclude building without edgeflow is harder, needs more polygons and renders worse. Our nose is not the best example, but the difference should be apparent in the render below. Left nose is with good edgeflow, right is without.

comparing model with good surface-flow and other without

Besides the bit about animation, all of the above also applies to hard surfaces models, not just character models.  So model with directed flows, model well.  We’ll go into edgeloops and modeling for animation later.

This whole article, the concept, is one of those things I wish somebody had explained to me a long long time ago.  So here it is, in my words.  I hope somebody out there benefits from it.  If you found the article useful, or if you think it’s all nonsense, please comment – let me know.

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