Allow PlainGeometry initialization from Geometry

This allows access to vertices etc. generated by geometry creator
classes.

Author: vidartf

js/scripts/three-class-config.js

@@ -267,6 +267,7 @@ module.exports = {
             morphNormals: new Types.Array(),
             skinWeights: new Types.Array(),
             skinIndices: new Types.Array(),
+            _ref_geometry: new Types.ThreeType('Geometry', {allowNull: false}),
         },
     },
     InstancedBufferAttribute: {

js/src/geometries/PlainGeometry.js

@@ -6,6 +6,30 @@ var PlainGeometryModel = AutogenPlainGeometryModel.extend({
     constructThreeObject: function() {
 
         var result = new THREE.Geometry();
+
+        var ref = this.get('_ref_geometry');
+        if (ref) {
+            return ref.initPromise.bind(this).then(function() {
+                result.copy(ref.obj);
+
+                // A bit of a hack:
+                // Sync out all copied properties before returning
+                this.obj = result;
+                var old_three = this.props_created_by_three;
+                this.props_created_by_three = {};
+                [
+                    'name', 'colors', 'faces', 'vertices', 'faceVertexUvs', 'morphTargets',
+                    'morphNormals', 'skinWeights', 'skinIndices', 'lineDistances',
+                    'boundingBox', 'boundingSphere'
+                ].forEach(key => {
+                    this.props_created_by_three[key] = true;
+                });
+                this.syncToModel();
+                this.props_created_by_three = old_three;
+                return result;
+            });
+        }
+
         return Promise.resolve(result);
 
     },

pythreejs/geometries/PlainGeometry.py

@@ -0,0 +1,18 @@
+
+from .PlainGeometry_autogen import PlainGeometry as PlainGeometryBase
+
+
+class PlainGeometry(PlainGeometryBase):
+
+    @classmethod
+    def from_geometry(cls, geometry):
+        """Creates a PlainGeometry of another geometry.
+
+        NOTE:
+        The PlainGeometry will copy the arrays from the source geometry.abs
+        To avoid this, use PlainBufferGeometry (TODO).
+        """
+        return cls(_ref_geometry=geometry)
+
+
+