Blender/Custom Collision

Resource Pack for this Tutorial

About

What's a Collision Mesh?

It tells the game what to bump into (and also whether things can swing and bounce, or are like chains, but that's beyond the current scope of the tutorial), and whether to just sit there, or fall, or bounce, or float, etc. So basically, if there is no collision, you can walk through it, and it won't be affected by gravity, and nothing can touch it (kinda like a ghost, but it won't move, and you can't see through it).

Why Custom?

Why make custom collision you say? Well, the answer is simple. Because you don't want to walk through your mesh, or have your mesh bounce in mid-air or other weird problems. Sometimes it's okay to just use collision from another NIF file, but usually you should use custom collision. It is very easy, and does not take long, despite what some people may lead you to believe. It also does not require NifSkope edits.

Starting Off

Have a Mesh

You can't really make your collision mesh until you have a regular mesh, so either make a mesh to use, or download the Tutorial Resources and use those.

First, decide what type of collision you want to use. If it's cylindrical, you want to make a Cylinder. If it's a rectangular prism (i.e. mostly squarish or rectangular), then use Box. If it's a sphere, use Sphere. If it's just some odd shape that needs accurate collision, then use either a Static TriangleMesh, or Convex Hull Polytope.

Making the Collision Mesh

If you downloaded the Tutorial Resources, open chapstick.blend, you want a cylinder.

Cylinder

Make a new cube, as a new object. When you make it, just know that the flat side is pointing toward your camera, so make sure that when you make the cube you are looking at the flat part of your cylinder, like this:

Then, while in edit mode, fit the cube over your cylinder, stretching and scaling all you need, so that it covers it like this:

When it fits perfectly how you want it to, go to object mode, and make any necessary rotations. This must be done in object mode, otherwise the rotation won't work. Go to object options. Change Draw Type to bounds. The default is Box, but you can choose cylinder by changing box to cylinder in the drop down menu to the right, or sphere by choosing sphere.

Convex Hull Polytope

'I recommend Static TriangleMesh instead of Convex Hull'

This is a bit different, but almost as easy. Basically, the idea is that you make a regular mesh (do it all in edit mode, makes it easier on you later), and then make it a Convex Hull Polytope, and oblivion recognizes it as collision. This is only for convex shapes, so you can't make something like a sphere with an inward dent, only an outward dent (and certainly not a Harvey Dent). Please note that this may not catch arrows, so if it needs to catch arrows use Static TriangleMesh instead. So, after you make the shape of it in edit mode, go to Object mode, and do set it to only display bounds, but under Draw Extra, also click Wire.

Then, go to Logic Options, and click bounds, and choose Convex Hull Polytope.

There is another way to do it, which I'll explain later.

Static TriangleMesh

Make a low-poly version of your mesh that you will use as the collision. In most cases it should fit over your mesh fairly smoothly. Don't use too many polygons, or it will slow down your game. Then under object properties set drawmode to bounds, and change box to Polyheder and under Draw Extra choose Wire.

The "Other way to do it"

Make just the mesh shape, and then go to object mode and select it, then go to the scripts window.

Then go to Scripts>>Mesh>>Hull

Choose the appropriate option.

Then go back to the 3d window (the grid icon) and select JUST YOUR MESH. The script created a copy of the mesh on top of yours, that is already set up for you. So, once you are sure you have your mesh selected, delete it, and you should see a wire version of the mesh you made.

That's it. You're done. Give yourself a pat on the back.

I recommend saving the .blend file right now as a backup.

Export Options

*As of Nif Scripts ver. 2.3.5

When you export, make sure you've selected all of your mesh objects first.

Set up your export options like this:

Then, change settings according to this:

1. • Click on clutter if it's something like a potion, or a bottle, or a food, or something else that just lies around and you can kick and throw and whatnot.
   • Click on weapon if it's a weapon.
   • Click on Static if it's something like a building, or a statue.
   • Click on Creature if it's a creature.
2. Choose one of the materials (glass, wood, cloth, etc.). If you don't like those, then you have to change it in NifSkope.

Solid and Hollow determines how the physics settings are calculated, choose the one closest to your mesh.

Then just export!

Advanced NifSkope Physics

Don't like how much it bounces? Want it to never slide down a hill? Or never stop sliding down a hill? You'll have to use NifSkope, but don't worry, it's easy to do this part.

Just select the bhkRigidBody under the bhkCollisionObject, and there are settings in the setting list. I'm not going to explain all of this, because I don't know all of it, but here's a few.

Mass

Makes it heavy or light, big number = heavy. Will affect how well it flies through the air, and how easy it is to pick up

Linear Damping

Higher number will make it move through the air slower horizontally. (ex. side to side)

Angular Damping

Same as linear, but with angles. (ex. throw it up into the air)

Restitution

How bouncy it is. Values over about 3 don't seem to affect it. (i.e. 10,000,000 is no bouncier than 10)

Layer

What type of physics it is (weapon, clutter, etc.)

If you go into the bhkListShape (parented to the bhkCollisionObject), you can change the material. This will change the sounds that play when you hit it with a weapon, or throw it at something, or walk on it. You will also probably need to change it in each individual shape. (In 'ChapstickHavok.blend', there is only one, and it's a bhkCapsuleShape). This will allow you a wider selection of materials that aren't in the blender exporter.

Good luck!

See Also

• Collision in Blender @ NifTools Wiki
• NifSkope: Adding Collision Model