Introducing: Volume Brushes

[Henry00IS]

SabreCSG Volumes

Brushes can now be turned into Volumes. For example a trigger, a body of water or an area with a strong wind. It's easy to customize and add new volume types through C# that are automatically detected in your project and integrated into SabreCSG's editor.

A collaboration between myself and @kerfuffles.

How do I use it?

Select a primitive brush like a "Cube Brush (2 x 2 x2)" and in the mode of "Add" or "Subtract" set the brush to "Volume". You will see a new section in the inspector where you can select and configure the volume type, for example the "TriggerVolume". Hit the rebuild button and it works out of the box! No further changes are necessary, this workflow makes it incredibly simple to create new volumes in any shape or size.

You can change the brush mode back to "Add" or "Subtract", you can clip volumes in half, it all works like you'd expect.

How does it work?

Primitive brushes are convex. Unity's mesh collider with "Is Trigger" requires meshes to be convex. This shared rule makes brushes a perfect candidate to define areas of space. When you rebuild the volume brushes they generate a game object with a mesh collider trigger using the convex brush mesh.

Each volume type comes in two parts, an editor script that contains a custom inspector and code to add required components to the built volume game objects (e.g. "TriggerVolume", inherits from "Volume").

The second part is the component itself that will be active during play (e.g. "TriggerVolumeComponent" or something else from your project) which is an ordinary MonoBehaviour that receives OnTriggerEnter events by Unity because there is a mesh collider trigger.

How was this implemented (@sabresaurus edition)?

I wanted to implement this new feature with as minimal changes to SabreCSG's core as possible.

First I decided to add a new CSGMode as that made the most sense, there are no subtractive volumes, they aren't additive brushes, they can't be NoCSG, collision is always on but they are triggers so there is no physical collision and they are never visible, so adding another state button like NoCSG made little sense. Even NoCSG could technically be a CSGMode as they can't be subtractive.

BrushBase now has a property called Volume (usually null). This means I can expand the concept and have compound brushes be volumes in the future. Volume is a ScriptableObject that people can inherit from to build their own custom volume types.

In my first attempts I created all volume game objects under the MeshGroup as VolumeMeshes but quickly found that they were deleted on every rebuild just like MaterialMesh and CollisionMesh. When I made a VolumeGroup instead to prevent this I found that Auto Rebuild is unable to keep track of them anyway and I would have to iterate through all built volumes to try and see if it already exists, meaning for 400 volumes I would have to iterate through 400 built volumes leading up to 160,000 iterations and a bunch of checks and additional components that were unnecessary during play just to associate them, it was all a big mess and too slow.

Then I realized I could parent the built volume objects to their volume brushes. In Auto-Rebuild I have the brush transforms that need to be rebuilt, it's a quick single .Find() check to find any existing built volumes. I opted to use this approach. I used a very unique name "SabreCSG: Volume Component (67173f4f-868c-4c70-ae40-335550c8354f)" for the game objects so there's never going to be a conflict. Then I decided to hide them from the hierarchy. I added a checkbox in the SabreCSG preferences so you can manually show them if needed for development purposes. When the brush is no longer a volume I simply delete the volume object and set the Volume property back to null on rebuild.

Once play mode starts I put these volume objects under the MeshGroup, make them visible and editable for the user and they inherit the parent brush name + " (Volume)" so it's quite easy to find them again.

It's incredibly clean, the hierarchy is identical to all previous SabreCSG versions and it's extremely simple to make volumes, this workflow feels amazing and I clean up after myself, there's no invisible garbage. ;)

Important

We are working on some finishing touches. Do not use this in production projects or levels yet as we may introduce some breaking changes to the volume classes! Feedback is very welcome!

Fixes #116.

[sabresaurus]

Hi, fantastic PR. I've given it a try and I have some thoughts:

• Parenting in the brush is inconsistent with MeshGroups, that seems like a fixable problem. It's somewhat confusing to have hidden objects in this way.
• It's a little unclear what volumes are, maybe there should be more of a description on the actual component.
• Force directions should be applied local to the brush, i.e. if you rotate the brush 90 degrees the force direction should be rotated
• If a setting isn't active it should be hidden, e.g. force, etc. Like you do with filter tag
• "Even NoCSG could technically be a CSGMode as they can't be subtractive" - beyond the scope of this PR, but that seems like a great idea!

[Henry00IS]

Most of your notes have been implemented now (as well as what we discussed). I believe inline documentation is beyond the scope of this PR because we should develop a generic system that doesn't get in the way. But I will add a wiki page on Volumes to explain what it is all about, how it works and how to build your own volume types.