Fix #105217: FBX Force Connect Children transforms Objects parented to Bones #105249

Thomas Barlow · 2024-03-21T02:15:16+01:00

Thomas Barlow commented

2024-03-21 02:15:16 +01:00

Force Connect Children can change the length and rotation of imported
bones, which was affecting Objects parented to bones.

This patch updates the correction matrix for child Objects attached to
bones to account for any changes made by forcing children bones to
connect to their parents.

Meshes rigged to bones weren't affected because it was only the rest
pose that was changed.

I rearranged the formula for calculating the correction matrix that was provided in the issue into a form that I find clearer:
$(Translation(bone.tail-bone.head) ⋅ bone.matrix)^{-1} ⋅ bone_matrix$
$= bone.matrix^{-1} ⋅ (Translation(bone.tail-bone.head))^{-1} ⋅ bone_matrix$
= bone.matrix^{-1} ⋅ Translation(bone.head-bone.tail) ⋅ bone\_matrix

$(T(tail-head) ⋅ A)^{-1} ⋅ B$
$= A^{-1} ⋅ (T(tail-head))^{-1} ⋅ B$
= A^{-1} ⋅ T(head-tail) ⋅ B

Force Connect Children can change the length and rotation of imported bones, which was affecting Objects parented to bones. This patch updates the correction matrix for child Objects attached to bones to account for any changes made by forcing children bones to connect to their parents. Meshes rigged to bones weren't affected because it was only the rest pose that was changed. --- I rearranged the formula for calculating the correction matrix that was provided in the issue into a form that I find clearer: $(Translation(bone.tail-bone.head) ⋅ bone.matrix)^{-1} ⋅ bone\_matrix$ $= bone.matrix^{-1} ⋅ (Translation(bone.tail-bone.head))^{-1} ⋅ bone\_matrix$ $= bone.matrix^{-1} ⋅ Translation(bone.head-bone.tail) ⋅ bone\_matrix$ $(T(tail-head) ⋅ A)^{-1} ⋅ B$ $= A^{-1} ⋅ (T(tail-head))^{-1} ⋅ B$ $= A^{-1} ⋅ T(head-tail) ⋅ B$

Thomas Barlow added 1 commit 2024-03-21 02:15:19 +01:00

f3877b4b08 Fix #105217 : FBX Force Connect Children transforms Objects parented to Bones

Force Connect Children can change the length and rotation of imported
bones, which was affecting Objects parented to bones.

This patch updates the correction matrix for child Objects attached to
bones to account for any changes made by forcing children bones to
connect to their parents.

Rigged meshes weren't affected because it was only the rest pose that
was changed.

Thomas Barlow requested review from Bastien Montagne 2024-03-21 03:16:32 +01:00

Bastien Montagne approved these changes 2024-03-21 11:17:58 +01:00

Bastien Montagne left a comment

LGTM

Thomas Barlow added 2 commits 2024-03-22 13:52:18 +01:00

8765a1590d Merge branch 'main' into fbx_105217_force_connect_child_objects

007b22fc23 Increase FBX IO version

Thomas Barlow merged commit 689081bcbb into main

2024-03-22 13:53:55 +01:00

Thomas Barlow referenced this issue from a commit

2024-03-22 13:53:57 +01:00

Fix #105217: FBX Force Connect Children transforms Objects parented to Bones