Parents and Pivots
Transformation, Pivots and Parents
If you want to rotate or scale a mesh, or another object, about a point other than its own local origin, you can do so by changing its center of transformation using either a parent or a pivot. Although in general conversation, and in some 3D applications, a center of transformation may be referred to as a pivot point, in Babylon.js the term pivot is used when setting a center of transformation with a specific method. The effects of using a parent or a pivot are different. To obtain behavior similar to the pivot point behavior described in applications such as 3DS Max or Maya, set mesh.parent to act as the pivot point rather than using setPivotPoint.
When the parent property is set on a mesh, transforming the parent applies the same transformations to the child. Translations, rotations, and scaling of the child take place relative to the local origin of the child. Setting the position of the child is relative to the local origin of the parent. In simpler terms, moving the child will not move the parent, and moving the parent will move the child.
Depending on the method used to produce the parent-child relationship, some transformations made to the parent prior to the moment of forming the relationship may also be applied to the children at or after that moment. It usually makes sense not to rotate or move a child before assigning its parent.
When a pivot is set on a mesh, repositioning the mesh will reposition the pivot so that its placement relative to the mesh is not changed. Rotation and scaling of the mesh take place relative to the pivot. More simply, moving the mesh will move the pivot and moving the pivot will not move the mesh.
Using a pivot can be tricky, and a number of methods are available. Some of these methods, but not all, may actually change the local origin of a mesh.
