Related to my previous question’s scenario Expose FBoneReference to Blueprint - C++ - Epic Developer Community Forums
I have two transform in world space A (Red), B (Blue) and I’d like to compute a relative transform (r) as if B would be the children of A.
// Pseudo code
FTransform r = B - A;
Then later, I’d like find where would B be according to a third transform C (world space)
// Pseudo code
FTransform D = r + C;
Can anyone tell me if is there any builtin math with Matrix/Transform in UE4 or do I need to find my own solution?
The relative transform of B to A is:
Br = B * inv(A)
The world transform of relative transform is:
Bw = Br * A
I might be wrong but…
Bw = Br * A = B * inv(A) * A = B * I = B
Which doesn’t look right, this should do the trick though:
Bw = A * Br
FTransforms are applied left-to-right in my limited UE4 experience.
Bw = Br * A = B * inv(A) * A = B * I = B
That’s exactly how I understood a question. If you didn’t change B or A transforms, than Bw should be equal to initial B.
Ah yes, I fail at reading 
Thank you guys! I did not know that the order in which you apply them changes the result.
This indeed did the tick
Bw = Br * A
