[solved] what does new 3D option "Transparent objects" do?

[uwestoehr]

git commit ea8d3bb2 implemented the new option "Transparent objects". What does this exactly do? (I want to describe it in the Wiki.)

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[openBrain]

https://grey.colorado.edu/coin3d/classS ... a156b93863

[uwestoehr]

https://grey.colorado.edu/coin3d/classS ... a156b93863

Thanks. I described this now in the Wiki so far but do not understand the following:

* where in FreeCAD do we have non-solid objects?
* what are "backfacing polygons"?

[openBrain]

* where in FreeCAD do we have non-solid objects?

I think lone faces or meshes are non-solid objects for example

* what are "backfacing polygons"?

I guess this are polygons whose back faces are visible by the user, like the black ones in the case of the issue #4285. But really I'm not sure.

[chrisb]

* where in FreeCAD do we have non-solid objects?

At least faces, not sure whether sketches and wires should count as objects.

[uwestoehr]

I think lone faces or meshes are non-solid objects for example

But why do have faces (2D objects) have 2 different types of polygons that can be rendered in two passes?
For meshes what are the backfacing polygons? I think a mesh is a concatenation of polygons. So is maybe the direction of their normal vector the difference?

[openBrain]

But why do have faces (2D objects) have 2 different types of polygons that can be rendered in two passes?

I don't think they have 2 types of polygon. Just their back face is visible. And (I couldn't explain technically why, we're talking about a GL thing) it seems that rendering them in a one pass process can trigger artifacts (I don't know which ones, I never saw a single one).

For meshes what are the backfacing polygons? I think a mesh is a concatenation of polygons. So is maybe the direction of their normal vector the difference?

That's it. For meshes the back faces are on the "negative side" according the normals.

[uwestoehr]

That's it. For meshes the back faces are on the "negative side" according the normals.

OK, I think I got the idea and try to explain this in the Wiki.

However, maybe Werner has some further input for me?

[openBrain]

Here's an example generated with a transparent mesh cube (top face has been removed, but it doesn't change anything). Artifact is on bottom left of the cube in "one pass" and disappears in "two pass" mode.
HTH

transparent.gif (598.02 KiB) Viewed 607 times

[uwestoehr]

Here's an example generated with a transparent mesh cube

Cool. This explains it better than with words.