Add coordinateSystem property to PerspectiveLens.as

Away3D appears to default to a left-handed coordinate system, but other systems (e.g. Alternativa3D, OpenSceneGraph, etc) defaults to a right-handed projection. For compatibility with such systems I have added an option to PerspectiveLens which allows the handedness of the coordinate system to be switched.

The default state of the projection will not be affected by this change.

Author: ChrisDenham

src/away3d/cameras/lenses/PerspectiveLens.as

@@ -14,7 +14,11 @@ package away3d.cameras.lenses
 		private var _focalLengthInv:Number;
 		private var _yMax:Number;
 		private var _xMax:Number;
+		private var _coordinateSystem:int;
 
+		public static const COORDINATE_SYSTEM_LEFT_HANDED:int = 1;
+		public static const COORDINATE_SYSTEM_RIGHT_HANDED:int = -1;
+
 		/**
 		 * Creates a new PerspectiveLens object.
 		 *
@@ -23,6 +27,7 @@ package away3d.cameras.lenses
 		public function PerspectiveLens(fieldOfView:Number = 60)
 		{
 			super();
+			this.coordinateSystem = COORDINATE_SYSTEM_LEFT_HANDED;
 			this.fieldOfView = fieldOfView;
 		}
 
@@ -97,9 +102,26 @@ package away3d.cameras.lenses
 			clone._near = _near;
 			clone._far = _far;
 			clone._aspectRatio = _aspectRatio;
+			clone._coordinateSystem = _coordinateSystem;
 			return clone;
 		}
 
+		/**
+		 * The handedness of the coordinate system projection.
+		 * The default is COORDINATE_SYSTEM_LEFT_HANDED.
+		 */
+		public function get coordinateSystem():int
+		{
+			return _coordinateSystem;
+		}
+
+		public function set coordinateSystem(value:int):void
+		{
+			if (value == _coordinateSystem) return;
+			_coordinateSystem = value;
+			invalidateMatrix();
+		}
+		
 		/**
 		 * @inheritDoc
 		 */
@@ -150,6 +172,12 @@ package away3d.cameras.lenses
 				raw[uint(14)] = -2*_far*_near/(_far - _near);
 			}
 
+			if (_coordinateSystem == COORDINATE_SYSTEM_RIGHT_HANDED)
+			{
+				// Switch projection transform from left to right handed.
+				raw[uint(5)] = -raw[uint(5)];
+			}
+
 			_matrix.copyRawDataFrom(raw);
 
 			var yMaxFar:Number = _far*_focalLengthInv;