Resolution Tricks

 Mesh, MV-SL-Tutorials, Tutorials  3 Responses »
Mar 202010
 

In this tutorial, you will learn some tricks to make your sculpties looks better at a distance, including the “shrinkage” trick.

LOD Can Kill

As you already know, sculpted prims switch between three resolutions depending on your camera’s distance from them in Second Life.

Sometimes the difference in resolution makes such minor differences in the sculptie that you can simply ignore it. However, sometimes the lower LOD levels end up looking bizarre, or you may simply want the sculptie to retain its resolution better.

The sculpties in the image above were all the same mesh in Blender, but the sculpt map image was changed to effect how the the resolution held up at different distances. The screenshot was taken with Object Detail in SL’s Preferences turned almost all the way down.

Remember Multires

Before I get into more technical tips and tricks, I want to remind you about the multires feature in Blender. I had you learn about that for a better reason than just to annoy you. Multires corresponds with Second Life’s LOD (Level of Detail) rendering.

If you start off modeling at the 8×8 resolution (level 1) then your sculptie will have a better chance of retaining it’s basic shape. At the 16x 16 resolution, you should try to include as much detail as you can. The 32 x 32 resolution should only add the most nit-picky details.

If you don’t remember anything about multires, go back to the multires tutorial and read up.

Texture Tricks

Often you can make the decreases in resolution less noticeable by using a high-quality texture on your sculpties. Baking on shadows, for instance, helps to visually define a form, which will make your object appear to be higher resolution than if you were relying on Second Life’s realtime shadow rendering.

To learn more about texturing sculpts in Blender, read this other tutorial.

Shrinkage

There is a more technical trick that will actually help keep your sculpt’s shape at greater distances.You can shrink them.

I don’t mean in SL. In Second Life, you’ll actually be making them bigger.

An Explanation

You see… the distance at which your sculpt loses resolution is relative to how large the sculpt is. The larger the sculpt, the farther away your camera can get before it loses resolution.

So, what we want to do is make the sculpt larger, but make it appear to be the same size.

Yeah, I know. Weird. But it can be done. You’ve probably seen sculpts that do something like it. Several of the freebie sculpts floating around don’t quite fit inside the bounding box when you scale them. Have you noticed? You can stretch and stretch these sculpts, but they they never seem like they stretch far enough! Well we’re going to do this on purpose.

Using Primstar

The new Primstar scripts allow you to shrink your sculptie when you bake the sculpt map.  When you bring up the Bake Sculpt Meshes dialog, you’ll see a box on the right marked “Range.”  The default values for each color value (or axis) are 0 to 255.

What you want to do is increase the values on the left and decrease the values on the right by the same amount.  I chose to increase the left values by 55 and decrease the right values by 55, because those numbers are easy to figure out.  (I’m lazy.)  The larger the difference between the original values and the new ones, the more your sculptie will shrink.

Image Editor Method

You can also do the same thing with some sort of image editor like Photoshop and decrease the color contrast. Some experience in Photoshop is recommended, because I’m going to describe how to do things in Photoshop, since I have practically no experience in any other image editing software.

Open your sculpt map in your image editing application. In Photoshop, the next step is to go to Image > Adjustments > Levels. Ignore Input Levels. You want to change Output Levels, and it needs to be changed by the same amount on both sides. The default values are 0 and 255. Once again, I usually change mine to 55 and 200 since those are easy numbers to figure out. And still. the greater the difference in the new values from the default, the more your sculpt will shrink. Once you’ve decided on your values hit ‘OK.’ Your sculpt map will look slightly greyed.

In some programs, you can use Brightness/Contrast and decrease the contrast, but this is less precise, and it doesn’t seem to do the same thing in Photoshop at all.

Upload your sculpt map and apply it to a sculpted prim. You’ll see it shrink. If you have the original sculpt uploaded, try placing the two next to each other, and stretching your shrunken sculpt so it looks the same size as the original. Then zoom out and watch how their resolution changes.

A Word of Warning

Although this is a neat trick, you can decrease the contrast on the sculpt map too much.

First of all, if your sculpt is not made phantom, the collision box will be as large as the bounding box, not the shrunken sculpt, but also, your sculpt can become deformed.

The image on above shows the same set of sculpts as the first image on this page, only with the Object detail in SL’s Preferences turned to Mid. Notice that the first two sculpts look identical. The third is slightly more choppy looking, and the fourth, obviously, is rather deformed. Below is what the sculpt maps look like:

The less contrast there is, the more values start to run into each other and the more choppy your sculpt will be. If you’ve done a good job with multires and texturing, there usually isn’t any reason to even get as shrunken as the third sculpt. Remember to use this trick wisely. Only when you absolutely need it, and only to the degree it’s needed.

Starter 4: Get Familiar With Multires and LOD

 MV-SL-Tutorials, Start Sculpting, Tutorials  24 Responses »
Mar 072010
 

Multires!

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

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

Multires is an option inside Blender that lets you switch to lower levels of mesh detail, which corresponds nicely with Second Life’s LOD.

To make… a box.

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.

REMEMBER to upload your sculpt map with “Lossless Compression” checked!

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.

Tips:

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.