[BUG] "ComposeTransform" completely broken in 4.17 and 4.18

Development Programming & Scripting Blueprint
, , , , , ,
1

A very simple example. A.transform * B.transform does not work correctly.

1204×522 135 KB

1248×702 153 KB

error in calculating the quaternion of rotation

absolutely the same thing happens if the function is written in C ++:

TArray<FTransform> UBaseLibraryBPLibrary::BindChainToParent(const TArray<FTransform> InT, const FTransform parent)
{
	TArray<FTransform> Out;

	for (int I = 0; I < InT.Num(); I++)
	{
		if (I == 0)
		{
			Out.Add(InT[I] * parent);
		}
		else
		{
			Out.Add(InT[I] * Out[I - 1]);
		}
	}

	return Out;
}

in my opinion this is a critical bug.
[project][4]

2

it looks like a typical Gimbal lock error,
which should not arise because the transformation must take place without the participation of Eluer angles.

3

I would like to receive a comment on this error from UE4 staff.
is this behavior a bug? will this bug be fixed?

4

Hey -

I’m looking at the sample project you provided and I wanted to confirm the behavior you’re reporting. Are you referring to positions of the blue/green lines shown in the gif? Can you explain what you feel the expected behavior should be?

5

the position of the TArray depends on the position of the first bone,
and must be constantly relative to the first bone.
, but the rotator at certain positions in the world does not work and gets off to zero.

6

t looks like FTransform * FTransform returns a non-normalized rotator (by design?),
because there is no error with this code:

TArray<FTransform> UMyBlueprintFunctionLibrary::BindChainToParent(const TArray<FTransform> & InT, const FTransform& parent)
{
	TArray<FTransform> Out;
    FTransform t;
	for (int I = 0; I < InT.Num(); I++)
	{
		
		if (I == 0)
		{
			t = (InT[I] * parent);
			t.NormalizeRotation();
			Out.Add(t);
		}
		else
		{
			t = InT[I] * Out[I - 1];
			t.NormalizeRotation();
			Out.Add(t);
		}
	}

	return Out;
}