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How to get current "Target Arm Length" of camera spring arm in Third Person Blueprint Template?


In UE4 Third Person Blueprint Template, I am trying to get the value of Camera Boom's Target Arm Length.

Using the very simple BP below, I am printing the value on screen at every tick.

alt text

Problem: When the Camera Boom collides with any object in scene, camera zoom in/out to the character just as expected. But, the value of Target Arm Length somehow never changes!

Question: Is this normal? If yes, what parameter should I check for getting the distance between Camera Boom and the character?

Product Version: Not Selected
simplebp.png (1.1 MB)
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asked Oct 06 '14 at 05:08 PM in Blueprint Scripting

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avatar image Dynamo Oct 06 '14 at 05:16 PM
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2 answers: sort voted first


from my undestanding the code, the Target Arm Length always remain the same, but take a look on the:

 void USpringArmComponent::UpdateDesiredArmLocation(bool bDoTrace, bool bDoLocationLag, bool bDoRotationLag, float DeltaTime)

This function updates protected members (RelativeSocketLocation, RelativeSocketRotation) of spring arm component:

// Form a transform for new world transform for camera FTransform WorldCamTM(DesiredRot, ResultLoc); // Convert to relative to component FTransform RelCamTM = WorldCamTM.GetRelativeTransform(ComponentToWorld);

 // Update socket location/rotation
 RelativeSocketLocation = RelCamTM.GetLocation();
 RelativeSocketRotation = RelCamTM.GetRotation();


And they are exposed in BP with "GetSocketTransform" function. You can try call "GetSocketTransform" with RTS_Component parameter and obtain position then compute length of this vector.

 FTransform USpringArmComponent::GetSocketTransform(FName InSocketName, ERelativeTransformSpace TransformSpace) const
     FTransform RelativeTransform(RelativeSocketRotation, RelativeSocketLocation);
         case RTS_World:
             return RelativeTransform * ComponentToWorld;
         case RTS_Actor:
             if( const AActor* Actor = GetOwner() )
                 FTransform SocketTransform = RelativeTransform * ComponentToWorld;
                 return SocketTransform.GetRelativeTransform(Actor->GetTransform());
         case RTS_Component:
             return RelativeTransform;
     return RelativeTransform;



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answered Oct 06 '14 at 07:24 PM

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avatar image Dynamo Oct 06 '14 at 08:08 PM

Great idea!

Thank you very much Pierdek.

It works :-)

ps: Would you please convert your reply into an answer, so that I can click the checkmark to mark your answer accepted?

avatar image MeshMyster Dec 14 '15 at 12:30 AM

Can you add a blueprint function that returns the current length of the spring arm when it's being pushed?

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Here's a way using blueprints. You could probably use a property of the SpringArm itself (instead of "Sphere") to make this more portable.

here's another way, using blueprints

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answered May 28 '16 at 02:59 AM

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avatar image NamInUz Jul 19 '17 at 05:58 PM

and you can use length squared to optimize it

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