Chaos Corona for 3ds Max > [Max] Feature Requests

Impact of Mesh Topology on the Refraction Behavior of Glass (Curved Surfaces)

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ATa:
Impact of Mesh Topology on the Refraction Behavior of Glass (Especially Curved Surfaces)
Hello,

I have a question regarding the impact of mesh topology on achieving realistic refraction of glass in Corona. As a professional 3D modeler, I primarily use CAD-based software like Rhino, which doesn’t require extensive adjustments to topology and edge flow, unlike 3ds Max or Blender.

In offline render engines like Corona or V-Ray, achieving accurate light behavior and refraction in glass materials often necessitates using quad meshes, especially on curved surfaces. Adjusting weighted normals or smoothing groups often doesn’t resolve shading issues, leading to jagged and inaccurate refractions. (See attached images: Pic 1 with quad mesh, showing perfect refraction, vs. Pic 2 exported from Rhino without quads, showing jagged refraction.)

When exporting models from Rhino as meshes in FBX or OBJ formats, the resulting meshes are precise but not in quad form. This non-quad topology causes issues with physically accurate refraction in traditional render engines. These refraction shading issues are particularly noticeable on curved surfaces!

My question is: Will the Corona developers consider implementing changes to the light solvers or other algorithms so that accurate refraction of glass does not depend on quad mesh topology? As you can see from the attached images, thanks to the precision of CAD software like Rhino, we can achieve highly precise 3D models that are 3D printable or fabricable, regardless of whether they use quad or non-quad meshes.

It's crucial for render engines to tackle these refraction issues caused by mesh topology. Current solutions, such as the Weight Normal modifier in 3ds Max, are not satisfactory. If Corona can address these challenges, it would allow us to focus more on the quality of render outputs rather than being constrained by mesh topology and normals. CAD applications offer great precision, and it's time for render engines to align with these capabilities and resolve the issues related to quad topology and refraction.

looking forward to the feedback.

James Vella:
Triangulated mesh shouldnt make a difference, It sounds more like your smoothing groups (or some UV error if you are using them).

Quad:


Triangulated:


Quad Wire:


Triangle Wire:

Juraj:
Weighted normals are often weird in Corona, not sure if Corona reads them correctly. It looks correct in viewport, but then Corona often does something else.
I think Pokoy and Romullus have investigated this issue. Too bad because it can often be one-quick solution to shading CAD files. I too work often with Rhino.

ATa:
Thanks, James. As you can see in my render, the reflections are accurate, but the shading issue is related to the refraction behavior. The file "2 mesh.jpeg" is an exported OBJ from Rhino.

ATa:
Yes, exactly, Juraj! The weighted normal modifier not only behaves weirdly in refraction but also ruins reflections. So, I decided not to use it in Corona Render, even though it should be an improvement, but it isn't in fact!

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