Loop Normals - I

A first patch of loop normals work.

[b.mont29, 2013-11-01 14:51:50]

On 2013/11/01 13:29:25, b.mont29 wrote:

This patch adds several things:

* calc_normals_tangent() mesh API compute tangent space for each loop of the
tri/quad faces, similar to calc_normals_split(), in a temp CDLayer.

* Objects now have two new options, a flag (OB_USE_LOOPNORMALS) to enable loop
normals use, and an angle threshold to automatically "sharpen" edges above that
value.

* These options are used to optionally compute a loop normal CDLayer at the end
of the modifier stack.

* Support to "tessellated loop normals" was also added.

* Basic viewport shading support was also added.

* In edit mode, we can preview loop normals the same way we do with face/vertex
ones.

Notes:
* Viewport drawing is basic for now (only working with VBOs), as I didn’t want
to mess too much with draw code (because of the pending GSoc branch) - in any
case, adapting to new code should not be a problem, it just features a third way
to get vertices' normals.
* Preview not working correctly with subdiv dm currently (probably because of
custom drawing code?), normals are correctly computed though.
* In general, this is kind of draft patch, would need polishing in any case (UI
needs work, new icon for loop, position of loop checkbox/angle threshold not
definitive, etc.).
* I still have to figure a good way to make render engines use this new data,
would also allow us to get rid (actually, replace) the Normals panel in Mesh
buttons.