Apologies if there is already a thread discussing non-coplanar quads. However I wanted to open a discussion regarding the use of non-coplanar quads.
I have already read alot of discussions about tris and ngons. But I can’t seem to find much on non-coplanar quads.
So should non planar surfaces be avoided at all costs?
Are there situations when they’re ok?
How be mindful of non planar surfaces when editing mesh?
From my limited experience with blender it seems they’re fine to use if you to use subdivsub, however for low poly whether smooth or flat shading, it is best avoided at all cost as it distorts the shading.
I also noticed when editing vertices it is very difficult avoid non planar surfaces, which makes it difficult to get a model/mesh to follow a particular shape.
would be good to gain insight from more advanced 3d experts
You can’t avoid non planar quads in most objects and they always gonna produce visual distortions with default flat shading because cycles always splits quads into tris for rendering.
They can be removed with smooth shading, also don’t confuse it with subd since subd changes geometry and doesn’t affect shading (it only makes distortions harder to notice since geometry is more dense and quads are smaller).
You can mix and combine various shading types and various modifiers like subd or bevel to get different results, some common examples:
flat shading / no modifiers for buildings in distance (since they mostly consist from flat surfaces)
smooth shading with auto smooth angle / no modifiers for object closer to camera but still far enough to you not notice “artificial” sharp edges
smooth shading / subd modifier for objects what can be in center of shot so you need realistic edges and perfect reflections on glossy surfaces
Alternatively to last you can use smooth shading with auto smooth angle / bevel modifier set to specific angle but that can be complicated to setup for beginner.
Everything gets broken down to tris at rendertime (and this is true for most game engines, so when you get to that point make sure you do all your baking/exporting with a triangulated mesh) But ideally in a perfect world you are going to keep all of your quads as close to planer as you can keep them, this cuts down on stretch distortion and when it comes time for uv mapping there are benefits to having mostly squarish quads.
My rule of thumb is that a model should look ‘alright’ at a distance with flat shading and at most 1 level of subdiv, honestly I would look at some retopology tutorials and spend a weekend playing around with those if you want to get a feel for how much/how little topology you need and how much you can stretch your faces.
Thank you for the explanation. Just one other thing, you mention cycles splits quads into tris for rendering.
So if you wanted to export a very low poly model to a game engine, how would non planar surfaces look in a game engine? (from my understanding game engines also triangulate quads)
Non-planar quads are normal, smooth shading hides the edges between them. It’s severely non-planar quads that cause problems, which are usually caused by bad edge/polygon flow where the structure doesn’t follow the forms. In the example case more geometry was needed to lessen the angle between polygons so that the shading can be more effective.
There are exceptions
Even perfectly planar and convex quads can cause problems with Cycles. It suffers from shadow artifacts with low poly models, which is also known as shadow terminator problem
When triangulation can’t change between applications, you have to triangulate the mesh with actual edges to make sure that doesn’t happen. One such case is when baking normals for an external application, triangulate before baking.
