BGE: Allow access to light shadow settings with python

This patch adds a new API which allow us to access light shadow settings from python. The new API can be used to write custom GLSL materials with shadows.

Reviewers: brecht, kupoman, agoose77, panzergame, campbellbarton, moguri, hg1

Reviewed By: agoose77, panzergame, campbellbarton, moguri, hg1

Projects: #game_engine

Differential Revision: https://developer.blender.org/D1690

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

@@ -48,6 +48,78 @@ base class --- :class:`KX_GameObject`
 
       :type: float
 
+   .. attribute:: shadowClipStart
+
+      The shadowmap clip start, below which objects will not generate shadows.
+
+      :type: float (read only)
+
+   .. attribute:: shadowClipEnd
+
+      The shadowmap clip end, beyond which objects will not generate shadows.
+
+      :type: float (read only)
+
+   ..attribute:: shadowFrustumSize
+
+      Size of the frustum used for creating the shadowmap.
+
+      :type: float (read only)
+
+   ..attribute:: shadowBindId
+
+      The OpenGL shadow texture bind number/id.
+
+      :type: int (read only)
+
+   ..attribute:: shadowMapType
+
+      The shadow shadow map type (0 -> Simple; 1 -> Variance)
+
+      :type: int (read only)
+
+   ..attribute:: shadowBias
+
+      The shadow buffer sampling bias.
+
+      :type: float (read only)
+
+   ..attribute:: shadowBleedBias
+
+      The bias for reducing light-bleed on variance shadow maps.
+
+      :type: float (read only)
+
+   ..attribute:: useShadow
+
+      Returns True if the light has Shadow option activated, else returns False.
+
+      :type: boolean (read only)
+
+   .. attribute:: shadowColor
+
+      The color of this light shadows. Black = (0.0, 0.0, 0.0), White = (1.0, 1.0, 1.0).
+
+      :type: :class:`mathutils.Color` (read only)
+
+   .. attribute:: shadowMatrix
+
+      Matrix that converts a vector in camera space to shadow buffer depth space.
+
+      Computed as:
+          mat4_perspective_to_depth * mat4_lamp_to_perspective * mat4_world_to_lamp * mat4_cam_to_world.
+
+      mat4_perspective_to_depth is a fixed matrix defined as follow:
+
+          0.5 0.0 0.0 0.5
+          0.0 0.5 0.0 0.5
+          0.0 0.0 0.5 0.5
+          0.0 0.0 0.0 1.0
+      Note:
+          There is one matrix of that type per lamp casting shadow in the scene.
+
+      :type: Matrix4x4 (read only)
+
    .. attribute:: distance
 
       The maximum distance this light can illuminate. (SPOT and NORMAL lights only).