Need help with matrices

Development Programming & Scripting
1

Was hoping I wouldn’t have to call for help for this one, but it’s just beyond me. :frowning:

I modified the ShooterGame so that the camera follows a socket, defined on the mesh (it’s a child of the b_head). It’s working, but when the character moves, there is a sort of offset: the 1st person weapon mesh moves opposite to where the character is going. This happens because the camera is no longer fixed, but follows the mesh’s animation.

So, I realized I had to change the OnCameraUpdate() function. That function positions the first person mesh when the camera moves.

Here is my code:

void AShooterCharacter::OnCameraUpdate(const FVector& CameraLocation, const FRotator& CameraRotation)
{
	USkeletalMeshComponent* DefMesh1P = Cast(GetClass()->GetDefaultSubobjectByName(TEXT("PawnMesh1P")));
	const FMatrix DefMeshLS = FRotationTranslationMatrix(DefMesh1P->GetComponentRotation(), CameraLocation + DefMesh1P->RelativeLocation);
	
	const FRotator RotCameraPitch(CameraRotation.Pitch, 0.0f, 0.0f);
	const FRotator RotCameraYaw(0.0f, CameraRotation.Yaw, 0.0f);

	FMatrix LeveledCameraLS = FRotationTranslationMatrix(RotCameraYaw, CameraLocation);
	FMatrix PitchedCameraLS = FRotationMatrix(RotCameraPitch) * LeveledCameraLS;
	const FMatrix MeshRelativeToCamera = DefMeshLS * LeveledCameraLS.InverseSafe();
	const FMatrix PitchedMesh = MeshRelativeToCamera * PitchedCameraLS;
	Mesh1P->SetWorldLocationAndRotation(PitchedMesh.GetOrigin(), PitchedMesh.Rotator());
}

With this code:

  • During movement, the weapon looks perfectly still, it only plays the Mesh1P animation (this is the intended behaviour);
  • If I aim up/down, the Mesh1P updates correctly.
  • But if I look left/right, the Mesh1P doesn’t updates. Its yaw is fixed.

How do I fix the yaw update?

For reference, here’s the original code on ShooterGame. Modified lines are noted with —.

void AShooterCharacter::OnCameraUpdate(const FVector& CameraLocation, const FRotator& CameraRotation)
{
	USkeletalMeshComponent* DefMesh1P = Cast(GetClass()->GetDefaultSubobjectByName(TEXT("PawnMesh1P")));
--- const FMatrix DefMeshLS = FRotationTranslationMatrix(DefMesh1P->RelativeRotation, DefMesh1P->RelativeLocation);
	const FMatrix LocalToWorld = ActorToWorld().ToMatrixWithScale();

	// Mesh rotating code expect uniform scale in LocalToWorld matrix

	const FRotator RotCameraPitch(CameraRotation.Pitch, 0.0f, 0.0f);
	const FRotator RotCameraYaw(0.0f, CameraRotation.Yaw, 0.0f);

--- const FMatrix LeveledCameraLS = FRotationTranslationMatrix(RotCameraYaw, CameraLocation) * LocalToWorld.InverseSafe();
	const FMatrix PitchedCameraLS = FRotationMatrix(RotCameraPitch) * LeveledCameraLS;
	const FMatrix MeshRelativeToCamera = DefMeshLS * LeveledCameraLS.InverseSafe();
	const FMatrix PitchedMesh = MeshRelativeToCamera * PitchedCameraLS;

--- Mesh1P->SetRelativeLocationAndRotation(PitchedMesh.GetOrigin(), PitchedMesh.Rotator());
}
2

I am just trying to provide some pointers in (hopefully) the right direction since I cannot test this myself, but these two lines seem the most interesting to me:

FMatrix PitchedCameraLS = FRotationMatrix(RotCameraPitch) * LeveledCameraLS;

const FMatrix PitchedMesh = MeshRelativeToCamera * PitchedCameraLS;

:slight_smile:

Seems like you need to make another FRotationMatrix for the yaw, and multiply the Pitched Mesh by that as well

const FMatrix YawedCamera = FRotationMatrix(RotCameraYaw);

:slight_smile:

for a grand conclusion of:

const FMatrix PitchedMesh = MeshRelativeToCamera * PitchedCameraLS * YawedCamera;

Note I did not multiply the YawedCamera by LeveledCameraLS;

you could try that as well :slight_smile:

Let me know if this gets you going in the right direction!

Rama

3

No, that didn’t do it. But you did get me in the right direction!

I’ve rewritten everything for clarity. The end result is:

void AShooterCharacter::OnCameraUpdate(const FVector& CameraLocation, const FRotator& CameraRotation)
{
    const FRotator RotCameraPitch(CameraRotation.Pitch, 0.0f, 0.0f);
    const FRotator RotCameraYaw(0.0f, CameraRotation.Yaw, 0.0f);
	USkeletalMeshComponent* DefMesh1P = Cast(GetClass()->GetDefaultSubobjectByName(TEXT("PawnMesh1P")));
    
	const FMatrix CameraTranslationMatrix = FTranslationMatrix(CameraLocation);
	const FMatrix StartingTranslationMatrix = FTranslationMatrix(DefMesh1P->RelativeLocation);
	const FMatrix StartingRotationMatrix = FRotationMatrix(DefMesh1P->RelativeRotation);
    const FMatrix PitchedMatrix = FRotationMatrix(RotCameraPitch);
	const FMatrix YawedMatrix = FRotationMatrix(RotCameraYaw);
    const FMatrix ResultMatrix = StartingTranslationMatrix * StartingRotationMatrix * PitchedMatrix * YawedMatrix * CameraTranslationMatrix;
    Mesh1P->SetWorldLocationAndRotation(ResultMatrix.GetOrigin(), ResultMatrix.Rotator());
}

ResultMatrix = StartingTranslationMatrix (the weapon offset) * StartingRotationMatrix (rotation defined on the component in Blueprint) * PitchedMatrix (camera rotation) * YawedMatrix (camera rotation) * CameraTranslationMatrix (final camera position) is what I wanted to do all along. Can’t believe I spent like 5 hours to figure this out. It’s so clear now!

Thanks Rama!