I think that issue of flexibility is created by the fact, that we are asking a grease pencil object to do everything.
If what is expected for performance is use of a 2D buffer from GPU, why making the feature dependent of a 3D object. Especially, at time of Viewport compositor.
I think that some LineArt compositing nodes producing effects in viewport, through viewport compositor, using Z pass, Normal pass, cryptomatte, AOVs and/or a specific viewlayer input should be a target.
That being said, it is great to obtain geometry in 3D space from camera, that can be edited, sculpted, duplicated, animated with offsets in 3D space, converted back into meshes and curves …
3D is part of flexibility.
But I think that would be a mistake to keep everything in Line Art nodes , next to geometry nodes.
That will be redundant and transfer complexity, at modifier stack level, between geometry nodes modifiers and LineArt nodes modifiers, if nodetree were separated.
Can you confirm that proposal is about creating Line Art nodes as a categories of GN nodes ?
What is exposed in you LineArt Segment Vertex node, LineArt Adjust Segment node, LineArt Chain Property node does not seem sufficient to create changes along stroke.
In Curve nodes of geometry nodes, we have a Spline Parameter node that makes this kind of tweaking a piece of cake.
I would expect an Index node, too, to make those nodes work with easy “less/more than integer” setups.
I would expect ability to use those nodes with LineArt Selection node.
To create a Depth Offset or Angle Splitting, we would need GN nodes.
So, I suppose that is the case that we are talking about a category of GN nodes. But I may misunderstand.
Proposal talking about upstream and downstream procedurally generated geometry is not clear.
Are we talking about nodes for a LineArt modifier, that could take a GN modifier as entry, and be followed by another GN modifier ? about a category of GN nodes, for Grease Pencil objects only ? about a category of GN nodes for any object type, where setup used to generate meshes can be reused to influence Line Art Strokes ?
It looks like the last one.
In that case, for meshes, Output should precise GP layer, too, not just GP object.
For GP objects, if GN modifier is added to them, ultimate output expected would be a simple Geometry output, but also with GP layer indication.
At the opposite of tree, I suppose that Edge Marks would be considered as an attribute.
So, LineArt Calculation node should be able to handle named attribute.
It is hard to have an idea if it will be sufficient, if we don’t know what GN nodes will be supported, too.
Currently, stylization is done by GP modifiers more than LineArt modifier.
GN nodes supported have to be able to replace those GP modifiers.
Some of them, like Outline and Envelope, are not so obvious to replace by GN made for meshes or curves.
GP Material tweaking from LineArt modifier is also minimal.
It looks like nodes to tweak a Fill material is out of scope.
But nodes to tweak Stroke material, will there be able to assign a different texture to start/middle/end of stroke ? to enable/disable Holdout, Self Overlap options ? or to change Line type ?
Will there be an extension of abilities of GP materials or do we stay with few basic abilities ?