BGE: Finally adding support for additive layer blending.

Currently this is only for the Python API. The logic brick will be updated in a future commit.

doc/python_api/rst/bge.logic.rst

@@ -1114,6 +1114,19 @@ See :class:`bge.types.KX_GameObject.playAction`
    
    :value: 2
 
+.. _gameobject-playaction-blend:
+
+.. data:: KX_ACTION_BLEND_BLEND
+
+   Blend layers using linear interpolation
+
+   :value: 0
+
+.. data:: KX_ACTION_BLEND_ADD
+
+   Adds the layers together
+
+   :value: 1
 
 -------------
 Mouse Buttons

doc/python_api/rst/bge_types/bge.types.KX_GameObject.rst

@@ -776,7 +776,7 @@ base class --- :class:`SCA_IObject`
       Return the value matching key, or the default value if its not found.
       :return: The key value or a default.
 
-   .. method:: playAction(name, start_frame, end_frame, layer=0, priority=0, blendin=0, play_mode=ACT_MODE_PLAY, layer_weight=0.0, ipo_flags=0, speed=1.0)
+   .. method:: playAction(name, start_frame, end_frame, layer=0, priority=0, blendin=0, play_mode=KX_ACTION_MODE_PLAY, layer_weight=0.0, ipo_flags=0, speed=1.0, blend_mode=KX_ACTION_BLEND_BLEND)
 
       Plays an action.
       
@@ -794,12 +794,14 @@ base class --- :class:`SCA_IObject`
       :type blendin: float
       :arg play_mode: the play mode
       :type play_mode: one of :ref:`these constants <gameobject-playaction-mode>`
-      :arg layer_weight: how much of the previous layer to use for blending (0 = add)
+      :arg layer_weight: how much of the previous layer to use for blending
       :type layer_weight: float
       :arg ipo_flags: flags for the old IPO behaviors (force, etc)
       :type ipo_flags: int bitfield
       :arg speed: the playback speed of the action as a factor (1.0 = normal speed, 2.0 = 2x speed, etc)
       :type speed: float
+	  :arg blend_mode: how to blend this layer with previous layers
+	  :type blend_mode: one of :ref:`these constants <gameobject-playaction-blend>`
 
    .. method:: stopAction(layer=0)