How to dynamically adjust the angle of a bone to make it point in the correct direction

Development Programming & Scripting
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1

In a third-person shooter game, I attempted to adjust the right-hand bone to make the weapon point toward the target to some extent.

The basic approach is as follows:

  1. Get the position of the target detected by the raycast. If there is no target, use the endpoint of a ray with a fixed length.
  2. Get the position of the right-hand bone’s transform.
  3. Use FindLookAtRotation to calculate the required RightHandRotation for the right-hand bone.
  4. In the Animation Blueprint, use Transform Bone, apply RightHandRotation, set WorldSpace, and ReplaceExisting.

To some extent, this approach achieves the goal of aligning the X-axis of the bone toward the target.

However, the local coordinate system of my bone does not align with the arm. My arm is roughly on the XZ plane, extending from the upper-right to the lower-left.

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This results in the X-axis being aligned, but the actual palm cannot align correctly.

Is there a way to achieve proper alignment?

2

dont change the bone, add a socket to the bone and change that

3

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Thank you very much for your reply. As I am a beginner, I am still unsure about the specific approach. My RightHandSocket has already been created, which is used to attach the weapon when picked up, and I have adjusted the rotation to ensure the weapon is in the correct position. Are you referring to modifying this socket that is already binding the weapon, or should I create a new socket?

I tried adjusting the socket orientation, but the weapon’s behavior doesn’t seem to be quite right？

FTransform RightHandTransform = PlayerCharacter->GetMesh()
			->GetSocketTransform(FName("RightHandSocket"), RTS_World);
RightHandRotation = UKismetMathLibrary::MakeRotFromY(PlayerCharacter->GetHitTarget() -RightHandTransform.GetLocation()) ;
RightHandTransform.SetRotation(FQuat(RightHandRotation));
4

no worries i might be misunderstanding, in your first pic the X vector doesnt face forward (in relation to the gun) so i though you wanted to rotate that?

5

That’s right. Ideally, I want the gun’s muzzle to align with the target, or at least face in a similar direction, otherwise the bullets will shoot out at an angle completely inconsistent with the muzzle. However, I’m not sure what the exact solution is for this problem.

While looking for solutions, I found that some people adjusted the skeleton to achieve good results. However, the X-axis of my skeleton is not aligned with the arm direction, which means I might need to apply some geometric transformations to achieve a similar effect.

The original code is as follows:

FTransform RightHandTransform = PlayerCharacter->GetMesh()
			->GetSocketTransform(FName(TEXT("右手首")), RTS_World);
		
		RightHandRotation = UKismetMathLibrary::FindLookAtRotation(RightHandTransform.GetLocation(),
			PlayerCharacter->GetHitTarget() ) + FRotator(135.f, 0.f, 0.f);
		
		FTransform MuzzleTipTransform =
			EquippedWeapon -> GetWeaponMesh()->GetSocketTransform(FName("MuzzleFlash"), RTS_World);
		
		FVector MuzzleX(FRotationMatrix(MuzzleTipTransform.GetRotation().Rotator()).GetUnitAxis(EAxis::X));
		FVector PlayerX(FRotationMatrix(RightHandTransform.GetRotation().Rotator()).GetUnitAxis(EAxis::X));
		FVector PlayerY(FRotationMatrix(RightHandTransform.GetRotation().Rotator()).GetUnitAxis(EAxis::Y));
		FVector PlayerZ(FRotationMatrix(RightHandTransform.GetRotation().Rotator()).GetUnitAxis(EAxis::Z));
		
		
		DrawDebugLine(GetWorld(),
			RightHandTransform.GetLocation(), PlayerCharacter->GetHitTarget(), FColor::Yellow);
		DrawDebugLine(GetWorld(),
			RightHandTransform.GetLocation(), RightHandTransform.GetLocation()+1000.f*PlayerX, FColor::Red);
		DrawDebugLine(GetWorld(),
			RightHandTransform.GetLocation(), RightHandTransform.GetLocation()+1000.f*PlayerY, FColor::Green);
		DrawDebugLine(GetWorld(),
			RightHandTransform.GetLocation(), RightHandTransform.GetLocation()+1000.f*PlayerZ, FColor::Blue);
		DrawDebugLine(GetWorld(),
			RightHandTransform.GetLocation(), RightHandTransform.GetLocation()-1000.f*PlayerZ-1000.f*PlayerX, FColor::White);
		DrawDebugLine(GetWorld(),
					MuzzleTipTransform.GetLocation(), MuzzleTipTransform.GetLocation()+1000.f*MuzzleX, FColor::Black);

And the result:

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The white line represents the direction of the palm, while the black line represents the direction of the muzzle.

Then I directly adjusted the rotation. Although the palm is facing the correct direction, it is quite obvious that the other directions are a bit off.

RightHandRotation = UKismetMathLibrary::FindLookAtRotation(RightHandTransform.GetLocation(),
			PlayerCharacter->GetHitTarget() ) + FRotator(135.f, 0.f, 0.f);

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I think this might involve some geometric transformations, but I’m not sure how to do it.

6

if you want the skeleton to roughly face the target i actually modify spine_03, although this does depend on your animations

if its just the weapon i do recommend fixing the socket and then adjusting your weapon mesh so the barrel faces forward, (X axis) just for consistency

if its just for bullets then it doesnt really matter, if you just trace from Muzzle to Target and use the UnitDirection it should be fine

another option is to look into the ControlRig which has an inbuilt Aim function

7

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