Posting the source code for LookRotation for those who need it .

Development Programming & Scripting C++
1

Posting it here as it took me a bit of trouble to figure this out . Seriously , why doesn’t the engine have this already ?



MyLookRotation(FVector lookAt, FVector upDirection)
{


FVector forward = lookAt;
FVector up = upDirection;


forward = forward.GetSafeNormal();
up = up - (forward * FVector::DotProduct(up, forward));
up = up.GetSafeNormal();

///////////////////////





FVector vector = forward.GetSafeNormal();
FVector vector2 = FVector::CrossProduct(up, vector);
FVector vector3 = FVector::CrossProduct(vector, vector2);
float m00 = vector2.X;
float m01 = vector2.Y;
float m02 = vector2.Z;
float m10 = vector3.X;
float m11 = vector3.Y;
float m12 = vector3.Z;
float m20 = vector.X;
float m21 = vector.Y;
float m22 = vector.Z;


float num8 = (m00 + m11) + m22;
FQuat quaternion = FQuat();
if (num8 > 0.0f)
{
    float num = (float)FMath::Sqrt(num8 + 1.0f);
    quaternion.W = num * 0.5f;
    num = 0.5f / num;
    quaternion.X = (m12 - m21) * num;
    quaternion.Y = (m20 - m02) * num;
    quaternion.Z = (m01 - m10) * num;
    return FRotator(quaternion);
}
if ((m00 >= m11) && (m00 >= m22))
{
    float num7 = (float)FMath::Sqrt(((1.0f + m00) - m11) - m22);
    float num4 = 0.5f / num7;
    quaternion.X = 0.5f * num7;
    quaternion.Y = (m01 + m10) * num4;
    quaternion.Z = (m02 + m20) * num4;
    quaternion.W = (m12 - m21) * num4;
    return FRotator(quaternion);
}
if (m11 > m22)
{
    float num6 = (float)FMath::Sqrt(((1.0f + m11) - m00) - m22);
    float num3 = 0.5f / num6;
    quaternion.X = (m10 + m01) * num3;
    quaternion.Y = 0.5f * num6;
    quaternion.Z = (m21 + m12) * num3;
    quaternion.W = (m20 - m02) * num3;
    return FRotator(quaternion);
}
float num5 = (float)FMath::Sqrt(((1.0f + m22) - m00) - m11);
float num2 = 0.5f / num5;
quaternion.X = (m20 + m02) * num2;
quaternion.Y = (m21 + m12) * num2;
quaternion.Z = 0.5f * num5;
quaternion.W = (m01 - m10) * num2;


return FRotator(quaternion);


}
1 Like
2

Is this like the “Find Look at Rotation”?

3

It does. Find Look at Rotation should do what you want. Or you can just do:



FVector newForward = Target - Source;
newForward.Normalize();

const FVector WorldUp(0.0f, 0.0f, 1.0f);

FVector newRight = FVector::Cross(toTarget, WorldUp);
FVector newUp = FVector::Cross(newRight, newForward);

return FTransform(newForward, newRight, newUp, Source);
4

LookAtRotation and LookRotation are different . You would get more explanation of the difference if you check the unity forums .
https://answers.unity.com/questions/…krotation.html

Basically lookrotation creates a rotation using a forward and upward direction as input alone , while lookat explicitly points towards a target location . LookAtRotation has the problem of “flipping” the rotator when the target pass through the source instead of sticking to a specific direction when needed (a specific problem in my case) . LookRotation will make sure the rotation doesn’t have the flipping problem as stated above .

5 

    //return normalized rotator
    static FORCEINLINE FTransform QuatLookXatLocalDirection(const FTransform& LookAtFromTransform, const FVector& LookAtLocalDirection)
    {
        const FQuat Q = FQuat::FindBetweenNormals(FVector(1, 0, 0), LookAtLocalDirection);
        return FTransform((LookAtFromTransform.GetRotation() * Q).GetNormalized(), LookAtFromTransform.GetLocation(), LookAtFromTransform.GetScale3D());
    }

    static FORCEINLINE FTransform QuatLookXatDirection(const FTransform& LookAtFromTransform, const FVector& LookAtDirection)
    {
        const FVector LookAtLocalDirection = (LookAtFromTransform.Inverse().TransformVector(LookAtDirection)).GetSafeNormal();
        return QuatLookXatLocalDirection(LookAtFromTransform, LookAtLocalDirection);
    }

    //return normalized rotator
    static FORCEINLINE FTransform QuatLookXatLocation(const FTransform& LookAtFromTransform, const FVector& LookAtTarget)
    {
        if (!LookAtFromTransform.GetLocation().Equals(LookAtTarget, 0.01f))
        {
            const FVector LookAtLocalDirection = (LookAtFromTransform.Inverse().TransformPositionNoScale(LookAtTarget)).GetSafeNormal();
            return QuatLookXatLocalDirection(LookAtFromTransform, LookAtLocalDirection);
        }
        else
        {
            return LookAtFromTransform;
        }
    }
6

Can someone post a whole script so I can just copy/paste it, please? I`m really need it

7

Just wondering but what are the use cases where LookAtRotation vs. LookRotation would be useful?

8

How does this even get implemented though?