Visualisation problem

[jmmm]

Hello everyone!

When I have two pieces in the same place and I try to select any of them, I have a problem with the visualisation of the selection. You'll probably see better in the picture. It's like a render problem.

Screenshot from 2019-09-17 01-48-42.png (168.84 KiB) Viewed 1504 times

How could I fix it?

Thanks

[chrisb]

Hi and welcome to the forum!

There is nothing to be fixed, the effekt is known as z-fighting. If you want to make a single solid you could make Union of these two objects. But beware, usually it is not recommended to use booleans on coplanar faces.

[vocx]

...
When I have two pieces in the same place and I try to select any of them, I have a problem with the visualisation of the selection. You'll probably see better in the picture. It's like a render problem.
...

I can't find the thread where one of the lead FreeCAD developers mentions this problem. It is known as Z-fighting, and it's not an easy to solve problem.

Z indicates the coordinate direction normal to the surface. So, it indicates that both surfaces fight to be on top. In your opinion, which surface should be on top? The two cubes are mathematically defined as having a face in exactly the same Z-coordinate, so how can you tell which should be on top? It's not as simple as saying this one or the other one.

[Joel_graff]

It might be useful to address one case regarding z-fighting (which is nicely illustrated here). That is, where two faces are coplanar, the selected face should always be rendered on top.

I realize this can't be maintained in more complex selection cases (i.e., where multiple coplanar faces are picked), but if it's not a terribly difficult thing to implement in a single select case or a multi-select where no selected faces are coplanar, maybe we should put it on the list.

[chrisb]

That is, where two faces are coplanar, the selected face should always be rendered on top.

I'm not sure about this. For me it is a valuable information to see z-fighting, because it usually is something I don't want. It is either a visibility issue or I have modeled something unwanted. So z-fighting bears soome information in its own.

[bitacovir]

So z-fighting bears soome information in its own.

I agree. it is some kind of clash alert.

[Joel_graff]

I'm not sure about this. For me it is a valuable information to see z-fighting, because it usually is something I don't want. It is either a visibility issue or I have modeled something unwanted. So z-fighting bears soome information in its own.

A good point.

[jmmm]

So z-fighting bears soome information in its own.

I agree. it is some kind of clash alert.

Hello again!

Maybe we could create an optional z-fighting filter. Something like in the picture:

zproblem.png (252.2 KiB) Viewed 1409 times

In this case, you could conserve much information, but also you can disable the filter.

The criteria to render could be the actual selection or the creation order in the tree list.

Thanks for the answers

[chrisb]

Maybe we could create an optional z-fighting filter.

What's bad about seeing it? If it's about selecting one of the two faces it's a different issue, probably similar to selecting something which is not on top at all.

[jmmm]

Maybe we could create an optional z-fighting filter.

What's bad about seeing it? If it's about selecting one of the two faces it's a different issue, probably similar to selecting something which is not on top at all.

Well, I think it's a graphic design question (but I'm not graphic designer ). In the visualisation, you want to show the most relevant information in a graphic simple way. With the z-fighting effect you are using a lot of random graphic dynamic effects only to say that you have two o more things in the same position. But an easy graphic solution is to show only one static uniform effect (a color, a patron, etc) to show the same relevant information. I think it could be less distracting, more predictable, more easy to remember and understand, and in general, more efficient (graphically speaking ).