BGE performance, 3rd round: culling and rasterizer.

This commit extend the technique of dynamic linked list to the mesh
slots so as to eliminate dumb scan or map lookup. It provides massive 
performance improvement in the culling and in the rasterizer when 
the majority of objects are static.

Other improvements:
- Compute the opengl matrix only for objects that are visible.
- Simplify hash function for GEN_HasedPtr
- Scan light list instead of general object list to render shadows
- Remove redundant opengl calls to set specularity, shinyness and diffuse
  between each mesh slots.
- Cache GPU material to avoid frequent call to GPU_material_from_blender
- Only set once the fixed elements of mesh slot
- Use more inline function

The following table shows the performance increase between 2.48, 1st round
and this round of improvement. The test was done with a scene containing 
40000 objects, of which 1000 are in the view frustrum approximately. The
object are simple textured cube to make sure the GPU is not the bottleneck.
As some of the rasterizer processing time has moved under culling, I present
the sum of scenegraph(includes culling)+rasterizer time

Scenegraph+rasterizer(ms)       2.48      1st round       3rd round

All objects static,            323.0           86.0             7.2
all visible, 1000 in 
the view frustrum

All objects static,            219.0           49.7             N/A(*)
all invisible.

All objects moving,            323.0          105.6            34.7
all visible, 1000 in 
the view frustrum

Scene destruction              40min          40min              4s

(*) : this time is not representative because the frame rate was at 60fps.
      In that case, the GPU holds down the GE by frame sync. By design, the
      overhead of the rasterizer is 0 when the the objects are invisible. 

This table shows a global speed up between 9x and 45x compared to 2.48a
for scenegraph, culling and rasterizer overhead. The speed up goes much
higher when objects are invisible.

An additional 2-4x speed up is possible in the scenegraph by upgrading
the Moto library to use Eigen2 BLAS library instead of C++ classes but
the scenegraph is already so fast that it is not a priority right now.

Next speed up in logic: many things to do there...

1 files changed, 7 insertions, 2 deletions

diff --git a/source/kernel/gen_system/GEN_HashedPtr.cpp b/source/kernel/gen_system/GEN_HashedPtr.cpp
index 6dbed1fb7a8..ff9de465a34 100644
--- a/source/kernel/gen_system/GEN_HashedPtr.cpp
+++ b/source/kernel/gen_system/GEN_HashedPtr.cpp
@@ -40,11 +40,12 @@
 // is a 32-bit integer, use all the bits of the pointer as long
 // as possible.
 //
-
+#if 1
 unsigned int GEN_Hash(void * inDWord)
 {
 	uintptr_t key = (uintptr_t)inDWord;
-
+#if 0
+	// this is way too complicated
 	key += ~(key << 16);
 	key ^=  (key >>  5);
 	key +=  (key <<  3);
@@ -53,4 +54,8 @@ unsigned int GEN_Hash(void * inDWord)
 	key ^=  (key >> 17);
 
   	return (unsigned int)(key & 0xffffffff);
+#else
+	return (unsigned int)(key ^ (key>>4));
+#endif
 }
+#endif
\ No newline at end of file