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FTrasform::TransformVector vs FRotator::RotateVector

Hi, I'm trying to understand the fps tutorial code and recently I'm struggling to understand transforms, vectors and rotators.

At one point of the tutorial I arrive that I have a GunOffset, an offset to the point where to fire my projectile.

I want to fire in front of me so I can start taking the world location of the attached camera or of the eyes of my character:

 //fps tutorial
 FRotator CameraRotation;
 FVector CameraLocation;
 GetActorEyesViewPoint(CameraLocation, CameraRotation);
 FRotator SpawnRotation = CameraRotation;
 FVector SpawnLocation = CameraLocation + FTransform(CameraRotation).TransformVector(GunOffset);

 //fps template
 FRotator CameraRotation;
 FVector CameraLocation = GetActorLocation();
 FRotator SpawnRotation = GetControlRotation();
 FVector SpawnLocation = CameraLocation + SpawnRotation.RotateVector(GunOffset);

I don't understand what is the difference doing one way or the other. The vector SpawnLocation is found adding CameraLocation (world) + GunOffset (once world).

FTransform::TransformVector and FRotator::RotateVector seem doing the same thing taking the vector GunOffset and making him world, but meanwhile the FRotator::RotateVector is clear to me (It rotates the vector GunOffset according to the rotator SpawnRotation), the other one isn't.

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asked Mar 10 '15 at 03:16 PM in C++ Programming

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An FRotationMatrix is just an FTransform where you only change the rotation components. When you RotateVector you are transforming the Vector about a RotationMatrix. An FTransform with only the Rotation set is the same thing as a FRotationMatrix, so anyway, they're all the same, RotateVector is just a nice wrapper I suppose.

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answered Mar 10 '15 at 09:51 PM

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