IK Rig

SKIP THIS PART IF YOUR USING META HUMANS

First off we will need an IK Rig for our Character. This Assumes your character is a Proper Humanoid Character and adheres to common game-ready skeletal conventions. If it does not then I can't promise you this setup guide will be appropriate and you may need a higher understanding in regards to how to setup an IK Rig. First we will Right-Click the Skeletal Mesh and go to Create->IK Rig. Open The IK Rig. Use the Auto-Settings (This is not a Comprehensive Guide for IK Rig Building and so we will use the Auto-Method). You should have Bone Chains and your Root should be the Pelvis, Full Body IK should be setup as well. As you can see when I drag the hand ik targets out the entire body will follow it. This is bad for Run-Time Anatomy Corrections because it means that if he's aiming the gun and you adjust the hand so that the stock of the rifle is sitting properly on his shoulder, if the adjustment is big then he will lean as well which we do not want. To correct this we will not use Full Body IK for the Arms, only the legs. We will setup Limb IK solvers for the arms instead. To start, you need to delete the LeftHandIK off the hand_l under the Hierarchy, and then delete the RightHandIK off the hand_r. Under the Solver Stack window, select AddNewSolver->LimbIK, do this twice. We will need one for each arm. With the new LimbIK selected under the Solver Stack, right click on the hand_l bone in the Hierarchy and select 'New IK Goal'. When this window pops up select Assign Goal. This will assign that goal to the LeftArm bone Chains as an IK Target. With the new LimbIK selected under the Solver Stack, right click on the upperarm_l bone and select 'Set Root Bone on Selected Solver'. This will tell the LimbIK solver that the chain ends here, we do not want to include the clavicle because it will do funny things if you move the hand in different directions and it will not constrain it to prevent it from rotating in funny ways. Create another Limb IK, we will do the same thing for the other arm now. With the new LimbIK selected under the Solver Stack, right click on the hand_r bone in the Hierarchy and select 'New IK Goal'. When this window pops up select Assign Goal. This will assign that goal to the RightArm bone Chains as an IK Target. With the new LimbIK selected under the Solver Stack, right click on the upperarm_r bone and select 'Set Root Bone on Selected Solver'. Now you will see that no matter how far away we place our Target, the body will not bend to try and allow the arms to reach it. This is the desired result because otherwise it would cause our entire character to lean.