[Bf-viewport] Proper handling of normals

[Light BWK]

Hi,

I would like to talk about the state of normals handling for the
viewport project. Current viewport & BI, when normals are edited, many
things will cause the edited normal to fail and showing artifacts.

The first way that edited normals will fail is when any modifier is
present. I have personally confirmed it with few other artists that
object modifiers in generate, deform & modify categories, will cause
unpredictable normal behavior.

The second way that edited normals will fail: when using standard
shaders in BI. The problem is worsen when cast/self shadow is turn on.

For the new viewport, many artists are requesting normals to be
available as multi channel data like any other data in object data tab
(vertex group, Shape keys, UV maps, Vertex color).

Thanks,
WK Bong