In older versions of these tutorials, I introduced LOD and multires in a short section in the previous tutorial. However, with the new Primstar scripts, I’ve decided to create a separate and more detailed tutorial on this rather important topic.
LOD stands for Level of Detail, and refers to a function of Second Life, OpenSim, or any other game where a mesh becomes less detailed the further away you get from it. This is important in games as it helps decrease the resources needed to render the game’s graphics.
Multires is an option inside Blender that lets you switch to lower levels of mesh detail, which corresponds nicely with Second Life’s LOD.
There is a certain set of video tutorials that explain multires by having the viewers create a box. Although a box might be a silly example, it serves the purpose, and it introduces some useful editing techniques.
So I’m going to use the box example, but with a few variations that I think make it easier. So go back into blender. Delete your old sculpt, and if you’d like, save the file as something new.
Now create a new sculpt mesh. Make it a cylinder with multires subdivision, just like the previous one. In the Edit Buttons, click “Set Solid” (marked in green) to give the mesh sharp edges instead of smooth ones.
Now switch to the top view (NUM7), go into edit mode (TAB), then deselect everything (A). Then with the Box Select tool (B) select the bottom part of the circle, like the first image below. Then, making sure proportional falloff is OFF, press S to scale, Y to scale along the Y axis, then press 0, then ENTER. You should end up with a straight line of vertices, like the second image below.
Now select some vertices on one side and press S, X, 0 to make on of the sides of our box. Keep doing this until you have a square or rectangle that looks something like the third image above.
Now lets also cap off the top and bottom. To do this, go to the front view (NUM1) and select the top and bottom edge loops. Then press S, SHIFT-Z, 0. This scales everything except the Z axis down to a point.
Then make sure the top a bottom are flat. Use the Box Select tool to select the top point you just made and the next edge loop and scale Z to 0. (S, Z, 0) Do the same for the bottom.
Note: To anyone with OCD, I apologize for my terrible box. As you can see, it isn’t very even. I did this on purpose, though. Lets bake this sculpt and upload it to the grid.
Tada! Up close, this cube looks pretty good, right? But as we zoom further away, the corners start doing weird things. You’ve probably seen similar behavior in a lot of sculpties in Second Life. (Though hopefully not on anything as simple as a box!)
So what do we do about it?
A Better Box
Go back to blender and in Edit Mode, find the tab labeled “Multires”. If you look for the ‘level’ button, (marked in green) You’ll see that currently, you are on multires level 3.
What does this mean? Well… click on the left side of this button to switch to level 2, then level 1. You’ll see your cube lose a lot of its vertices, and as you can see from the picture on the left, my cube no longer looks like a cube. It looks exactly how it looked in world when I zoomed out.
So what would happen if I made it look like a cube at Multires level 1? Lets do that.
I even decided to line up the middle vertices to make it look pretty. Anyway. Lets switch back to level 2.
Woah. Hey what happened here?
Well, Blender multires likes to help “correct” your mesh if one multires level is very different from another. Level 1 may have been that perfect box, but level 3 was still the old box, so Blender tried to create a “happy medium.”
In a lot of cases this behavior is what you want, but sometimes, especially with geometric shapes, you don’t want this at all.
So… lets fix this. Hit CTRL-Z to undo, going back to our nice level1 box.
Now since Blender still thinks multires level 3 and 2 should be our old box, the easiest way to fix it is to delete the higher levels. In the multires tab, find the button called “Del Higher” (marked in green) and click it to get rid of the higher levels. All of the options below should vanish. Next, click on the drop box currently marked “Catmull-Clark” and switch it to “Simple Subdiv.”
What does that mean?
The options in the drop box are different methods of subdividing a mesh. Simple subdivision adds vertices by dividing each edge exactly in half. This is good for meshes with a lot of straight edges.
Catmull-Clark is fairly well-known algorithm developed by Edwin Catmull (of Pixar) and Jim Clark (see Wikipedia). I don’t know the technical details of how it works. Only that it’s currently the best algorithm for smoothing a mesh.
So with Simple Subdiv selected, click “Add Level” twice, and you should get something that looks like this from the top.
Now if you bake the sculptie and upload it to the grid, you’ll have a cube that holds up well, even at a distance.
Personally, I’m feeling lazy, so I’m not going to upload it. _I_ know it would hold up. You’re probably convinced too, and I don’t really have any practical use for this sculpted cube.
Don’t consider the time wasted, though. You’ve learned some valuable skills and a VERY valuable lesson. Right?
Just in case you need a reminder, here it is again:
The moral of the story, and some tips
The box held up better when built at a lower multires level, and the same is true of ALL other sculpties.
If a sculpt is simple enough, like most organic shapes, I’ll start sculpting it at multires level 1. For more complex sculpties, like furniture, I’ll start with multires level 2. I never, ever, EVER start with multires level 3. Sure, you can make really complex sculpties at that level, but if your object turns into a birds nest when you walk three feet away, it’s not really worth it.
START WITH A LOWER MULTIRES LEVEL. This ONE principle leads to better LOD and cleaner meshes. While there are other tricks that can help along side it, nothing can substitute for it.
Working from a lower multires level is actually useful for more than just LOD. It lets you establish the basic shape of a sculpt while you have less vertices to worry about. Ultimately, this can help you create a cleaner sculptie.
Sometimes adding a multires level with Catmull-Clark subdivision will smooth out a sculpt too much for what you need. When this is the case, try using Simple Subdivision, then click the “smooth” button in the Mesh Tools panel to round things out a little. This also works if only part of the mesh needs to be smooth. Just select the vertices you want to round out and click the smooth button a few times.