New surface data-block #100127
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Background
Historically, surfaces, curves, and text object data has been grouped in the
Curve
data-block.This is more of a historical relic than proper design, since there is little similarity in the data stored for each type.
With #95355, we already have a new data-type for curves that doesn't include the other two.
Any development of NURBS surfaces in Blender should probably head in that direction too.
Over the years there have been various attempts to contribute to and improve surfaces in Blender,
but the messy state of the code and design has made this hard.
Proposal
Surface
data-block that holds a grids of control points (separate arrays for positions, weights, and knot spans)Surface data-blocks have an implicit evaluated surface (evaluated after modifiers) (just a
Mesh
internally for now) Surface object supports attributes per control pointSome nodes could output a changed surface, other nodes create meshes or curves, etc.
Surface to Mesh
andSample Surface with UV
are two obvious nodesFuture
"Solid" CAD objects are created with surface patches, so having a proper surface data-block
accessible procedurally opens door for future improvements there. Various libraries like OpenCASCADE
(used by FreeCAD) could be used to manipulate surfaces in Blender. While Blender doesn't need to
become a complete CAD tool, opening up different workflows is a more general improvement for artists too.
Changed status from 'Needs Triage' to: 'Confirmed'
Added subscriber: @HooglyBoogly
Added subscriber: @mod_moder
To clarify, I'm not planning on working on this now, but I'd like to settle on a design so contributors could work on this instead of being turned away. I would be happy to help anyone who wants to work on such a project.
Added subscriber: @rygelXVI
Added subscriber: @Yuro
Added subscriber: @laurynas
Will it be only one grid per data-block or few?
Are weights meant to be in a separate array from positions?
This goes along with the idea of the attribute as a separate data block. How the surface geometry structure is organized will depend on the implementation.
I think it would be more than one grid, like the current surface object, and like the new "Curves" type.
I'd also imagine a similar approach to the curves object-- the control point data for all grids would be stored contiguously in one array.
Yeah, the idea is to move away from using specific structs like
BPoint
and instead use generic types likefloat3
andfloat
.That way if we want to deform the surface control points, we just need to pass the array to a generic function (like in the set position node, etc.)
Added subscriber: @lone_noel
Added subscriber: @xrogueleaderx
Added subscriber: @GeorgiaPacific
Added subscriber: @surfacionado
Hello Hans
we are actually good with just cirrectly rendering Bezier patches
(ie NURBS with maximal number of inserted knots = degree+1 many)
since one can always build spline surfaces in Bezier form (for example using B-splines or Polyhedral Splines).
The question is whether one should do the evaluation and rendering in software (C++)
or
use the tessellation engine (that was introduced for that purpose), i.e. a "shader" program (quite standard)
Hi @surfacionado. In the end I think it would be important to support both. CPU evaluation would be used to interface with other CPU algorithms. GPU evaluation could be used for rendering, and eventually more generic GPU algorithms as we move some other processing to the GPU.
As for spline types, I think the surfaces could support multiple types, just like the curves (#68981, etc.). I wouldn't imagine it would be too complex to have an initial implementation with a simple type like Bezier patches while keeping the possibility of other types open for the future.
That's basically what we have right now with the GPU evaluation of the new
Curves
type anyway.How do we find the Curves implementation in Blender?
If it already uses the Tessellation Engine, it should not be tricky to make the same evaluation sequence happen for Bezier surfaces by seeing how it is linked to the Blender C++ code.
Curves in Blender are undergoing a large rewrite at the moment. To find the new curves type, some terms to search for are
Curves
,CurvesGeometry
,OB_CURVES
. Some related tasks are #68981, #95355, #96455.To use a similar process for surfaces, I do think the first step is a new data-block type as described in this task. It's a bit hard to render arbitrary data without first sending it through depsgraph evaluation.
Added subscriber: @pafurijaz-4
Added subscriber: @Schiette