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Revision as of 01:25, 20 January 2011

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Updated to the latest version of Blender with plugins. Tried to improve readability and added some more explanations.
imported>DragoonWraith
(→‎Making the Collision Mesh: no need to link repeatedly)
imported>Bruneauinfo
(Updated to the latest version of Blender with plugins. Tried to improve readability and added some more explanations.)
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[http://www.fileplanet.com/191690/190000/fileinfo/Blender-Havok-Tutorial-Resource-Pack Resource Pack for this Tutorial]
==Introduction==
 
If you've decided you'd like to make custom objects for Oblivion using Blender (weapons, armor, furniture, buildings, etc) at some point you will realize the need to implement what is called a Collision Mesh to make your items behave naturally within the game world. This article introduces a basic method through simple examples for making custom collision meshes.


==About==
===What's a Collision Mesh?===
===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).
A collision mesh tells the game how objects interact with each other in the game world. What happens when an object bumps into another object? Do they swing and bounce? Is an object solid and unmovable? Can an object fall, float, roll, etc. Without a collision mesh there is no collision which means objects, like the player, can pass right through them. Without a collision mesh your creations won't be affected by gravity and can't be touched. So if you want your work to be useful in the game you'll need to learn the simple process of creating collision meshes in Blender.


===Why Custom?===
===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 [[Glossary#N|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.
Why make custom collision meshes? Is it possible to reuse collision meshes from another object? Certainly collision meshes can be reused from other objects. However, the process of making collision meshes yourself is pretty simple. Properly sized and shaped collision meshes will reduce or eliminate clipping. Knowing how they are made means you can customize your collision mesh specifically for your project. You'll also have a much easier time troubleshooting problems should they arise in testing your mods in the game.  


=====Notes=====


==Starting Off==
* Custom collisions do not ''require'' [[NifSkope]] edits.
===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 [http://www.fileplanet.com/190119/190000/fileinfo/Oblivion---Blender-Havok-Tutorial-UESP-Resource-Pack Tutorial Resources] and use those.
==Prerequisites==


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.
This article of course assumes you've installed Blender and know how to use the software. If not then you need to go here first : [http://www.tesnexus.com/downloads/file.php?id=12248 TESNexus] Follow the installation instructions exactly for your OS. Once you gain some [http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro experience using Blender] return to this article.


===Making the Collision Mesh===
This article also includes a resource pack. You may find it handy if you're relatively new to Blender : [http://www.fileplanet.com/190119/190000/fileinfo/Oblivion---Blender-Havok-Tutorial-UESP-Resource-Pack Tutorial Resources]


If you downloaded the Tutorial Resources, open '''chapstick.blend''', you want a cylinder.
==Making the Collision Mesh==


====Cylinder====
====Open a Mesh in Blender====
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:


[[Image:BlenderCollisionExample1.png]]
Specifically you need an object mesh from the resource pack listed above - open '''chapstick.blend''' in Blender. You won't be able to create your collision mesh until you have an object mesh that needs one.
 
The type of collision you use will be based on the shape of your object mesh as well as what your object represents in the game world. If your object is the inside of a room, for example, you would want your collision mesh to be slightly smaller than your object mesh. Otherwise objects might clip into the wall. If on the other hand your object is a stone wall or a sword you will want your collision mesh to be slightly larger than the object mesh so objects don't clip into it.  


Then, while in edit mode, fit the cube over your cylinder, stretching and scaling all you need, so that it covers it like this:
Another consideration is the shape of your object mesh. If your object is a cylinder (like the tube of ChapStick in the example below) you'll want to make a Cylinder collision mesh. If your object is a rectangular prism - mostly squarish or rectangular - then you'll use a Box. If it's a sphere, then a Sphere. However, if it's an odd shape that needs accurate collision you'll use a Static TriangleMesh.


[[Image:BlenderCollisionExample2.png]]
=====Notes=====


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.
*You should give your object mesh a name in the Object Panel under Objects and Links. The two meshes could very well look almost identical in Blender. Naming your object mesh (and later your collision mesh) will help cut down on confusion when you're wondering if you've selected the correct one during an edit operation.  


[[Image:BlenderCollisionExample3.png]]
*Along with the above note it's also a good idea to open an Outliner window for a similar reason.


====Convex Hull Polytope====
====The Collision Mesh====


'I recommend Static TriangleMesh instead of Convex Hull'
This may sound a little counterintuitive, but a cylindrical collision starts out in the shape of a cube. In Blender create a cube as a new object. The photo below shows the cube just created being positioned over the end of the ChapStick cylinder which appears in the photo as a circle. This is precisely where you want it. <br /><br />


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.
[[Image:BlenderCollisionExample1.png]]


Then, go to Logic Options, and click bounds, and choose Convex Hull Polytope.
<br /> The goal is to encapsulate the tube of ChapStick inside the cube by extruding the cube over the body of the ChapStick cylinder and then resizing the cube so it fits snuggly. <br /><br />


There is another way to do it, which I'll explain later.
[[Image:BlenderCollisionExample2.png]]


====Static TriangleMesh====
=====Notes=====


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 faces of the cube are opaque in the picture. The next photo gives a little more insight into how the Chapstick tube should be positioned within the cube.


[[Image:BlenderCollisionStaticMeshExample1.png]]
====Create the Collision====


====The "Other way to do it"====
When you're happy with your collision mesh go to a Buttons Window in Blender and select the Object Panel (or Press F7 while hovering your mouse in a Buttons Window)
Under '''Draw>Drawtype''' select '''Bounds'''. Under '''Draw>Draw Extra''' you will see a select box with the default setting set to '''Box'''. Since the ChapStick tube is in the shape of a cylinder you will want to select '''Cylinder'''. Do this now.
<br /><br />


Make just the mesh shape, and then go to object mode and select it, then go to the scripts window.
[[Image:BlenderCollisionExample3.png|680px|]]<br />


[[Image:BlenderCollisionExample5.png]]
====Other Collision Shapes====


Then go to Scripts>>Mesh>>Hull
The steps for other shapes are for the most part identical to the example above. The only difference would be what you selected under '''Draw>Draw Extra'''. If your object was a box you would select '''Box'''. If your object was a sphere you would select '''Sphere'''. A pyramid like shape would use '''Pyramid'''.


Choose the appropriate option.
====Static TriangleMesh====


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.
There is at least one other option for creating your collision mesh using what's called Static TriangleMesh.  


That's it. You're done. Give yourself a pat on the back.
Similar to the steps above you make a low-poly version of your object mesh to use as the collision mesh. Optimally, it should fit over your object mesh as smoothly as possible. Just don't use too many polygons, or it will slow down your game. Next, in the Object Panel under '''Draw>Drawtype''' set drawmode to Bounds, and set the select box to '''Polyheder'''. Under '''Draw Extra''' choose '''Wire'''.<br /><br />
 
[[Image:BlenderCollisionStaticMeshExample1.png]]


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


==Export Options==
==Export Options==
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Set up your export options like this:
Set up your export options like this:


[[Image:BlenderCollisionExample6.png]]
[[Image:BlenderCollisionExample6.png |680px|]]


Then, change settings according to this:
Then, change settings according to this:
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