[Bf-cycles] Cycles Standalone

[Brecht Van Lommel]

Hi,

We do indeed need build system work and improvements to the the file format
to make the standalone version usable. I don't think there is any good
standard for the scene file format that is worth trying to support, it will
never be a perfect fit, we need a native file format. Some thoughts on that:


FILE SYNTAX

XML and RIB syntax are well known. JSON is perhaps more readable and less
verbose due to not requiring start+end elements, but also seems a bit out
of place. XML would be easiest as we already have a parser from
OpenImageIO, though perhaps it's not particularly hip to use XML :)

It's mostly a matter of taste I guess, maybe someone can come up with a
good argument for one choice or the other.

SEMANTICS

We do not need an attribute stacks like Renderman does. That's nice if you
really want to construct more complex scenes with just a text editor, but I
don't think that's our target. I rather have a flat list of data with a
unique ID that can reference each other, so instancing is natural and not
conditional on the attribute stack state. The list of data types I imagine
would be:

* output settings
* integrator settings
* camera
* geometry (mesh, curves, .. in external file)
* object (either a geometry instance or parent object with child objects)
* material
* light
* shader

We should make it so that we can have RIB like archives that we can delay
loading once we support that in the core. We have to be a bit careful here
in defining the semantics, so we don't just assume the whole archive is
included in place.

GEOMETRY

Geometry does not need to be in the scene file format, we can reference
external files in some standard format(s) instead. Alembic is quite nice
for this, it supports an object hierarchy and is designed for efficient
loading.

Main problem is that it is a big dependency, and we don't have Blender
export here yet? Perhaps basic .obj and later alembic support is a
reasonable compromise.

SHADERS

Shaders are node based in Cycles and OSL. You would have 3 types of shaders
that all look the same from the outside, as a node with inputs and outputs:
 ** Builtin node
** OSL shader
** Shader group

A material or light would reference such a shader and only have a few extra
properties, most of its behavior is defined by the shader. A shader group
is like a Blender node group and basically a more general type of shader
instance as in Renderman. If we support archives this could be stored in a
separate file but use the same syntax as the scene file format.
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