If I attach objects together in 3DSMAX, what happens to their UV's?

Bletzkarn

I want to attach small objects together to reduce draw calls in EU4. However does that mean their UV's will all have to exist on the same UV map?

I have several fasteners. I want to make a UV once and duplicate them, then attach them together. They should all share that UV right? Then if I want to add a different type of fastener I would have to add it to the existing UV?

mephi100fel

Yes, but no..
You need everything nice packed together tight? I want to believe that it's not textured yet) 
1. Check UV of the each separate object. You can add unwrap UV modifier to modifier stack of each object and then see how parts looks. 
2. When you will attach for example couple of objects I believe you will see intersection of different UVs 
It's easy to fix - pack button or manually.
Can you share more information about your situation? Screens, etc? 

JordanN

I'm not sure what the results will happen in UE4, but in 3DS Max I'm actually doing this technique with brick planes I have.

I'm randomizing brick patterns by hand for a house so I have multiple planes and then I welded them together (so no light leaks). I've found so far the UV integrity remains in tact. Moving/scaling vertices around only messes with my brick patterns (I made 4 of them that share a single UV map).

Bletzkarn

mephi100fel said:

Yes, but no..
You need everything nice packed together tight? I want to believe that it's not textured yet) 
1. Check UV of the each separate object. You can add unwrap UV modifier to modifier stack of each object and then see how parts looks. 
2. When you will attach for example couple of objects I believe you will see intersection of different UVs 
It's easy to fix - pack button or manually.
Can you share more information about your situation? Screens, etc? 

Okay.

To recap: 

- I want to import a model into UE4 that has lots of repeating parts.
- UE4 requires less draw calls if these parts are joined into a single mesh.
- UE4 also requires a light map UVmap or else all lighting on the model will build incorrectly.
- In 3DSMAX, all items that would have the same material I am trying to put into 1 mesh.
- However because of repetition, it's easier to UVmap them BEFORE dupilcation.
- The problem is when you try to attach identical meshes with a unique one.

Now you have 2 options:

Individually Unwrap the UV for EVERY component.
Leave the meshes separate.

What would be ideal is to somehow "add" the UV's of both meshes without reconstructing them.


Unfortunetly, due to the lightmap, UV's generally can't share the same space.

ActionDawg

The lightmap UVs are often separate from the regular UVs. You can have many UV channels for one mesh.

Bletzkarn

somedoggy said:

The lightmap UVs are often separate from the regular UVs. You can have many UV channels for one mesh.

My question should be;

Can UV's overlap in the lightmap channel?

Eric Chadwick

Yes. But it will create artifacts, because each overlapped uv will try to store its lighting, causing overlaps. Lightmap will just store the last one that was rendered.

If you know the mesh elements will always be lit the same, you can do a little trick of offsetting all but one overlapping uv, offset them all exactly 1 uv unit. Just leave 1 of the uvs behind. Then all those meshes will receive exactly the same lightmap. Pretty rare though, usually lighting is not symmetrical.

If the fasteners are small, may be better to uv the whole assembly (whole wall unit) as one in the lightmap. Then you get more consistent lighting across the surface. Instead of fasteners getting pixelly shadowing.

Bletzkarn

Eric Chadwick said:

Yes. But it will create artifacts, because each overlapped uv will try to store its lighting, causing overlaps. Lightmap will just store the last one that was rendered.

If you know the mesh elements will always be lit the same, you can do a little trick of offsetting all but one overlapping uv, offset them all exactly 1 uv unit. Just leave 1 of the uvs behind. Then all those meshes will receive exactly the same lightmap. Pretty rare though, usually lighting is not symmetrical.

If the fasteners are small, may be better to uv the whole assembly (whole wall unit) as one in the lightmap. Then you get more consistent lighting across the surface. Instead of fasteners getting pixelly shadowing.

Thank you for the concise answer. 

Yes I think this is the best option to get good lighting. It's for an archvis project so I want it to be fairly high quality. Okay so it requires more work to individually unwrap the fasteners 1 by 1, but will lead to higher quality.