CustomConvexShape: add a 3-argument constructor

src/main/java/com/jme3/bullet/collision/shapes/CustomConvexShape.java

@@ -75,6 +75,27 @@ protected Vector3f initialValue() {
     // *************************************************************************
     // constructors
 
+    /**
+     * Instantiate a custom collision shape with the specified extents. Subclass
+     * constructors should also invoke {@code setScaledInertia()}.
+     *
+     * @param xHalfExtent the desired half extent on the local X axis, for
+     * scale=(1,1,1) and margin=0 (>0)
+     * @param yHalfExtent the desired half extent on the local Y axis, for
+     * scale=(1,1,1) and margin=0 (>0)
+     * @param zHalfExtent the desired half extent on the local Z axis, for
+     * scale=(1,1,1) and margin=0 (>0)
+     */
+    protected CustomConvexShape(
+            float xHalfExtent, float yHalfExtent, float zHalfExtent) {
+        Validate.positive(xHalfExtent, "X half extent");
+        Validate.positive(yHalfExtent, "Y half extent");
+        Validate.positive(zHalfExtent, "Z half extent");
+
+        this.halfExtents = new Vector3f(xHalfExtent, yHalfExtent, zHalfExtent);
+        createShape();
+    }
+
     /**
      * Instantiate a custom collision shape with the specified extents. Subclass
      * constructors should also invoke {@code setScaledInertia()}.