Cannon Grip

Rotate objects with a swivelled mount around an anchor point via VRC Pickup grips, synced using Smart Object Sync.

Installing

Make sure to add Maellon’s Listing since this package depends on Smart Object Sync.

Then head to my VCC Listing and follow the instructions there.

Contributing

This project uses custom git filters to reduce the amount of noise generated by Udon and UdonSharp. These filters are not required in order to contribute, though without them all UdonSharp asset files will show as modified and those “changes” should not be committed.

Learning

This package also contains an extra file about Quaternion math in Unity, in the hopes of providing intuition when working with them.

Setup

There’s 3 scripts:

• CannonGripRestrictor
• CannonAimAndRotationConstraint
• CannonSpecializedConstraint

CannonGripRestrictor

This script is to be put on a vrc pickup.

• Said pickup is the object the player will grab in order to aim a cannon
• It should be placed at the back of the cannon, somewhere where it makes sense for there to be a grip on the cannon
• It should be invisible, yet placed inside of the geometry of the cannon
• The pickup should for most use cases (like for cannons) also be synced, the script supports
  • VRC Object Sync
  • Smart Object Sync
  • Most likely Light Sync too, though it is untested

This script does two things:

• When a player picked up the grip, moved it around, and then drops it, the script moves the grip back into the cannon, where it was placed initially
• When a player moves the grip too far away from the cannon, it gets dropped and moved back automatically

VRC Pickup and Rigidbody

• The Rigidbody should
  • not have gravity
  • be kinematic
• The VRC Pickup should
  • have a very short proximity of <= 0.1
  • have exact grip enabled, without any exact grip transform referenced. What this does is it prevents the pickup from moving towards the hand upon being picked up, especially good for desktop

Constraints

No matter which constraint approach is used, the CannonGripRestrictor should be used for all of them when setting up an aim-able cannon.

The constraints are responsible for actually rotating the cannon based on the grips movement. In this document a setup with a cannon and a mount it is mounted in will be described, such that the cannon can be aimed horizontally and vertically where the mount only rotates around one axis. In other words it will behave as though the mount is enabling horizontal rotation while the cannon rotates with the mount but the cannon can also rotate/tilt vertically.

VRC/Unity Constraints

It is possible to use the existing constraints provided by Unity and VRChat. For this setup, have a hierarchy as follows:

Cannon
┣╸Mount (the up (green arrow) direction must be the literal up)
┣╸Cannon (the up (green arrow) direction must be the literal up)
┗╸Grip

Where:

• Mount has a rotation constraint with Cannon as the target with locked rotation around the Y axis
• Cannon has an aim constraint with Grip as the target
• Grip
  • has the CannonGripRestrictor with Cannon as To Snap To
  • has VRCObjectSync or SmartObjectSync on it

CannonAimAndRotationConstraint

This is effectively the exact same as VRC/Unity Constraints, except that if one wanted to have a different constraint setup, well that is possible when using VRC/Unity Constraints, whereas this script is specifically made to perform a rotation and aim constraint. The upside is that this script has no constant performance cost while constraints do.

Requires Smart Object Sync.

Hierarchy:

Cannon
┣╸Constraint (doesn't matter where this object is)
┣╸Mount (the up (green arrow) direction must be the literal up)
┣╸Cannon (the up (green arrow) direction must be the literal up)
┗╸Grip

Where:

• Constraint has the CannonAimAndRotationConstraint script on it
  • with Grip as Obj Sync
  • with Mount as To Rotate
  • with Cannon as To Aim
• Grip
  • has the CannonGripRestrictor with Cannon as To Snap To
  • has the SmartObjectSync on it

CannonSpecializedConstraint

This script is quite notably different in that it has the option to define limits for how much the grip is allowed to be rotated/moved to the left, right, down and up, each of those direction defined as separate angular limits.

Hierarchy:

Cannon
┣╸Constraint (doesn't matter where this object is)
┣╸Mount (all 3 directions, up, forward and right, must be clean)
┃ ┗╸Cannon (the rotation does not matter)
┗╸Grip

Where:

• Constraint has the CannonSpecializedConstraint script on it
  • with Grip as Obj Sync
  • with Mount as Mount
  • with Cannon as Cannon
• Grip
  • has the CannonGripRestrictor with Cannon as To Snap To
  • has the SmartObjectSync on it