Update SnippetsForStaticAndSkeletalMeshes.md

Roberto De Ioris · web-flow · commit 8b3a36e4c279 · 2017-09-12T20:36:33.000+02:00
diff --git a/tutorials/SnippetsForStaticAndSkeletalMeshes.md b/tutorials/SnippetsForStaticAndSkeletalMeshes.md
@@ -911,6 +911,7 @@ class ColladaLoader:
         transform.translation = FVector(v0.z, v0.x, v0.y) * self.base_quaternion
         transform.quaternion = FQuat(q0[2], q0[0] * -1, q0[1] * -1, q0[3])
 
+        # each bone in collada is in world position (while unreal wants relative positions), we 'subtract' here the parent position
         relative_transform = transform * parent_transform.inverse()
         
         parent_id = self.skeleton.skeleton_add_bone(node.id, parent_id, relative_transform)
@@ -1017,6 +1018,8 @@ If all goes well you wll end with your model correctly loaded (the screenshot sh
 
 ![Collada](https://github.com/20tab/UnrealEnginePython/blob/master/tutorials/SnippetsForStaticAndSkeletalMeshes_Assets/collada.PNG)
 
+As you could have already noted in the comments, joints/bones matrices in collada files are world-relative, while UE4 expects each bone to be relative to the parent. For this reason we multiply each matrix for the inverse of its parent.
+
 ## SkeletalMesh: Morph Targets
 
 Morph Targets (or Blend Shapes), are a simple form of animation where a specific vertex (and eventually its normal) is translated to a new position. By interpolating the transition from the default position to the new one defined by the morph target, you can generate an animation. Morph Targets are common in facial animations or, more generally, whenever an object must be heavily deformed.
