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/*

* Version: 1.0

* Author: Yilmaz Kiymaz (@VoxelBoy)

* Purpose: To be able to change the pivot of Game Objects

* without needing to use a separate 3D application.

* License: Free to use and distribute, in both free and commercial projects.

* Do not try to sell as your own work. Simply put, play nice :)

* Contact: VoxelBoy on Unity Forums

*/

/*

* TODO:

* - Doesn't work properly with rotated objects.

* - Can't compensate for the positioning of Mesh Colliders.

* - Need to figure out if the "Instantiating mesh" error in Editor is a big issue, if not, how to supress it.

* - Allowing the pivot to move outside the bounds of the mesh, ideally using the movement gizmo but only affecting the pivot.

*/

using UnityEngine;

using UnityEditor;

public class SetPivot : EditorWindow {

Vector3 p; //Pivot value -1..1, calculated from Mesh bounds

Vector3 last_p; //Last used pivot

GameObject obj; //Selected object in the Hierarchy

MeshFilter meshFilter; //Mesh Filter of the selected object

Mesh mesh; //Mesh of the selected object

Collider col; //Collider of the selected object

bool pivotUnchanged; //Flag to decide when to instantiate a copy of the mesh

[MenuItem ("GameObject/Set Pivot")] //Place the Set Pivot menu item in the GameObject menu

static void Init () {

SetPivot window = (SetPivot)EditorWindow.GetWindow (typeof (SetPivot));

window.RecognizeSelectedObject(); //Initialize the variables by calling RecognizeSelectedObject on the class instance

window.Show ();

}

void OnGUI() {

if(obj) {

if(mesh) {

p.x = EditorGUILayout.Slider("X", p.x, -1.0f, 1.0f);

p.y = EditorGUILayout.Slider("Y", p.y, -1.0f, 1.0f);

p.z = EditorGUILayout.Slider("Z", p.z, -1.0f, 1.0f);

if(p != last_p) { //Detects user input on any of the three sliders

//Only create instance of mesh when user changes pivot

if(pivotUnchanged) mesh = meshFilter.mesh; pivotUnchanged = false;

UpdatePivot();

last_p = p;

}

if(GUILayout.Button("Center")) { //Set pivot to the center of the mesh bounds

//Only create instance of mesh when user changes pivot

if(pivotUnchanged) mesh = meshFilter.mesh; pivotUnchanged = false;

p = Vector3.zero;

UpdatePivot();

last_p = p;

}

GUILayout.Label("Bounds " + mesh.bounds.ToString());

} else {

GUILayout.Label("Selected object does not have a Mesh specified.");

}

} else {

GUILayout.Label("No object selected in Hierarchy.");

}

}

//Achieve the movement of the pivot by moving the transform position in the specified direction

//and then moving all vertices of the mesh in the opposite direction back to where they were in world-space

void UpdatePivot() {

Vector3 diff = Vector3.Scale(mesh.bounds.extents, last_p - p); //Calculate difference in 3d position

obj.transform.position -= Vector3.Scale(diff, obj.transform.localScale); //Move object position by taking localScale into account

//Iterate over all vertices and move them in the opposite direction of the object position movement

Vector3[] verts = mesh.vertices;

for(int i=0; i<verts.Length; i++) {

verts[i] += diff;

}

mesh.vertices = verts; //Assign the vertex array back to the mesh

mesh.RecalculateBounds(); //Recalculate bounds of the mesh, for the renderer's sake

//The 'center' parameter of certain colliders needs to be adjusted

//when the transform position is modified

if(col) {

if(col is BoxCollider) {

((BoxCollider) col).center += diff;

} else if(col is CapsuleCollider) {

((CapsuleCollider) col).center += diff;

} else if(col is SphereCollider) {

((SphereCollider) col).center += diff;

}

}

}

//Look at the object's transform position in comparison to the center of its mesh bounds

//and calculate the pivot values for xyz

void UpdatePivotVector() {

Bounds b = mesh.bounds;

Vector3 offset = -1 * b.center;

p = last_p = new Vector3(offset.x / b.extents.x, offset.y / b.extents.y, offset.z / b.extents.z);

}

//When a selection change notification is received

//recalculate the variables and references for the new object

void OnSelectionChange() {

RecognizeSelectedObject();

}

//Gather references for the selected object and its components

//and update the pivot vector if the object has a Mesh specified

void RecognizeSelectedObject() {

Transform t = Selection.activeTransform;

obj = t ? t.gameObject : null;

if(obj) {

meshFilter = obj.GetComponent(typeof(MeshFilter)) as MeshFilter;

mesh = meshFilter ? meshFilter.sharedMesh : null;

if(mesh)

UpdatePivotVector();

col = obj.GetComponent(typeof(Collider)) as Collider;

pivotUnchanged = true;

} else {

mesh = null;

}

}

}