Irrlicht Engine

This patch adds the following:

* Culling mode: front or back faces.

Currently, irrlicht supports setting in a material if
the back faces are culled or not. Obviously this is not
enough. With this patch, the culling mode can be set on
a driver level.

* Clipping planes.

Currently, irrlicht does not support user clipping
planes. All drivers support at mimimum 6 of those so
it's a shame that the user can't set them at will. This
patch adds this functionality on the camera level, i.e.
you set the clipping planes per-camera.

* View matrix affector.

Currently, it is not possible in irrlicht to alter
the camera's view matrix. That is because the view
matrix is recalculated each frame in
CCameraSceneNode::OnPreRender(). This patch adds the
ability for the user to set a matrix ("view matrix
affector") per-camera which is multiplied with the
camera's view matrix each frame, after the view matrix
is calculated.

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I must say that this is the first patch I ever did for
irrlicht which supports not only the opengl driver but
the d3d9 and d3d8 ones :).
Of course someone with more experience should check the
validity of the patch for the d3d drivers.

Finally, this patch was created while developing the
following demo:
http://irrlicht.sourceforge.net/phpBB2/viewtopic.php?t=16546