[Bf-viewport] Viewport and shader system patches

[a.romanov at blend4web.com]

> Adding these Cycles node features to BI seems all reasonable to me,
> particularly if the target would be to unify things more with Cycles
> material nodes instead of adding a completely new system 
>specifically
> for the viewport.
It's very good, because we are primarily interested in such things. 
And patches with support for BI and GLSL could even go into the 2.7 
branch as it does not break backward compatibility, isn't it?

> 
> The issue with incremental changes is that you're also pretty much
> forced to incrementally break compatibility over many Blender
> versions, which is annoying for users. If it was mostly about
> parameters, just adding a new PBR material node would be a good
> solution for compatibility.
> 
Primarily we are interested in the stable branch of viewport 
corresponding to current state of BI. So it could be 2.7 branch with 
simplified material workflow, that could be done by adding a new PBR 
material node.

> But there's issues with the way lights and materials interact, how
> transparency and ray tracing are wrong in subtle ways, distinctions
> between specular/reflection and diffuse/environment light, and more.
> In my experience keeping those exceptions while also adding a new 
>PBR
> mode makes the code extremely complicated.
> 
> I don't want to go into too much detail here, but here's some old
> notes about design issues if you're interested:
> http://wiki.blender.org/index.php/Dev:2.5/Source/ShadingSystem/Implementation
> http://wiki.blender.org/index.php/User:Brecht/RenderIdeas
> 
Thanks for the tip. I need more deeply to learn.

> Anyway, maybe it is fine to incrementally break compatibility during
> the Blender 2.8 release cycle and users will just have to accept 
>that?
> Whatever way we do this, it would still be good to have some kind of
> vision for what the end result should be.
In Blend4Web we keep deprecated features in 3-5 releases and our users 
have time to adjust. But we have releases per month.
It's important to understand exactly what is the aim of the first 
release of 2.8. I'm also not sure I understand. But, from the 
conversation it seems to me that BI should stay.