OTOY Forums

I have one semi-transparent (glass) mesh that is boolean substracted from a lower terrain mesh
This means that the base of glass mesh object exactly fits the top of terrain mesh object , so there are two coincident polygons, with different materials defining the junction of the two.

How do I prevent shadows and flickering appearing at the interface of the two adjacent meshes as a result?

I cannot either separate or push the two meshes together so that they no longer share a surface - because the junction is (and needs to be) live - per ArchiCAD normal SEO methodology. If I adjust the terrain, I want the glass to automatically follow.

Is there a materials based solution?

Note, a workaround (not at all ideal) in ArchiCAD , when the glass mesh is a CADimage site planning envelope, is to review the boolean operations on the glass mesh, and delete the one where the main ground mesh is subtracted from glass mesh. This removes the coincident polygons issue in Octane, but it also messes up linework where the cut line of glass envelope should be showing as it follows ground mesh top surface.

Really looking for a more elegant solution

You can try reducing the Ray Epsilon to the lowest value possible (but that might cause artifacts in other parts of the scene). Unfortunately you need to avoid having vertices with the same position which belong to 2 different objects, otherwise you will get these artifacts.

Paul

face_off wrote:You can try reducing the Ray Epsilon to the lowest value possible (but that might cause artifacts in other parts of the scene). Unfortunately you need to avoid having vertices with the same position which belong to 2 different objects, otherwise you will get these artifacts.

Paul

Thanks Paul.
I had tried that, but no improvement - the shadows just changed position.

This issue seems to come up often in one form or another, so it would be great if there was a way for Octane to ignore or switch off coincident polygons, using materials priority to decide which ones get switched off. Appreciate this feature may not want to be switched on by default, given the processing time required to detect coincident polygons.
Have other gaming engines perhaps solved this problem already? - these days I notice flickering is quite uncommon in 3D games, and assume not all of that is down to perfect modelling - if so, would Cuda cores be good at handling this?

I think vertices in the same position in a game would be unlikely. Given the float point precision, it is incredibly hard to have vertices in the same position, unless you actually duplicate the vertices (which is what is happening in this case). It is an issue you would need to take up with OTOY, since it is a core render engine problem.

Sorry I can't be more help.

Paul

Hi Paul. I think having exactly matching vertices would be a special (and rare) case, but having co-planar (or even near co-planar) polygons more generally that results in problems is not so uncommon.

I recall seeing flickering in 3D games when this used to occur through some error of modelling, but not so much in recent years - hence my speculation that some method exists to automatically detect or suppress them.

Will post a request to Otoy developers.

PK,

in this case you could potentially add a simple mid-grey image into the displacement channel of the "soil" material and give it a 1mm displacement value so that it would get pushed/pulled away from the intersecting face of the glass volumes you've used to do your boolean operations? You'll just need to look at the +/- direction the faces move in as well as the mid-level values to make sure you don't get opening corners in the soil material as a result. Also, you'll need to "Follow the Smoothed" normal, and make sure you're welding the vertices.

Cheers, Dan.

Daniel_Ward wrote:PK,

in this case you could potentially add a simple mid-grey image into the displacement channel of the "soil" material and give it a 1mm displacement value so that it would get pushed/pulled away from the intersecting face of the glass volumes you've used to do your boolean operations? You'll just need to look at the +/- direction the faces move in as well as the mid-level values to make sure you don't get opening corners in the soil material as a result. Also, you'll need to "Follow the Smoothed" normal, and make sure you're welding the vertices.

Cheers, Dan.

Thanks Dan - sounds like a promising idea.