Status: Initial part of milestone 1 merged into master.

Team

Commissioner: ?
Project leader: @Brecht Van Lommel (brecht)
Project members: @Sebastián Barschkis (sebbas) @Jacques Lucke (JacquesLucke)

Description

Big picture: Volumes need their own native datablock type, so Blender can support other use cases like rendering OpenVDB files or procedurally generating volumes.

Use cases:

• Existing use cases (smoke modifier on mesh).
• OpenVDB file rendering.
• Procedurally generating volumes (part of everything nodes).

Design:

• New Volume datablock (similar to Mesh) with an OpenVDB volume data structure with an arbitrary number of attributes.
• Rendered by Cycles and Eevee, first as dense volume as we have now, and later with native sparse volume rendering.
• Volume objects would have modifiers (add resolution detail, fluid domain modifier, ...)

Engineer plan: ?

Work plan

Milestone 1
Time estimate: 10 workdays to complete implementation, 5 for review/docs/bugs.

Completed for merge into Master.

• New volume object data type, based on OpenVDB grids
  • Support reading OpenVDB files from disk
  • Add New material adds principled volume material
  • Solve problem with not enough FILTER_ID bits
  • Show warning when loading VDB points file
  • Auto rotate object from Y-up to Z-up when file was written by Houdini?
• Rendering of dense grids
  • Cycles
    • Basic integration
    • Use principle volume as default material if no material exists
    • Support different transform per grid
  • Eevee
    • Basic integration
    • Use principle volume as default material if no material exists
    • Support rotation/shear in transform
    • Shader code generation for arbitrary number of grids
    • Support different transform per grid
  • Workbench
    • Basic integration
    • Control over which grids to display (active grid only by default?)
    • Use workbench object color settings
    • Density scale setting
    • Figure out why density changes with object scale
  • Add option to specify volume density in object space
  • D1777: Cycles: implement per shader volume step size.
• Viewport drawing and selection of volume bounds
  • Wireframe bounds display of tree nodes (at intermediate or leaf levels)
  • Points display type, that shows one point per coarse/fine node
  • Selection support (based on wireframe bounds?)
• User interface
  • Open file browser immediately from Add menu
  • VDB / volume file type in the file browser
  • Drag & drop VDB files into 3D viewport
  • Finalize properties editor UI layout
• Python API
  • Grids
  • Transforms
• File loading
  • Error reporting
  • On-demand loading
  • Global cache
• Dependency graph copy-on-write integration
  • Refactor mesh runtime storage to be reusable by other objects types
  • Automatic instancing for objects without modifiers, like meshes
  • Fix runtime backup memory leak
• Volume frame sequences
  • Settings to use single volume or sequence, start, length, offset
  • Dependency graph integration
  • Auto detection of sequences when loading file

Viewport
Time estimate: ?

• Viewport selection by rendering fine boxes when drawing for selection (current volumes can't be selected except through the outliner or the origin point if visible)
• Workbench: additional viewport display options
• Option to use lower resolution volume for viewport display

Rendering
Time estimate: ?

• Option to pick byte/half/float precision for 3D texture in Cycles and Eevee
• Eevee/workbench
  • Share textures in global volume cache
  • Preserve batch cache through display setting changes
  • Sparse grid rendering using NanoVDB
• Cycles
  • Optimize mesh bounds creation by using OpenVDB tree
  • Sparse grid rendering using NanoVDB (D8794)
  • Share 3D images like global volume cache
• Auto complete grid names in shader nodes

Modifiers
Time estimate: ?

• Mesh to Volume modifier
• Points to Volume modifier (from PointCloud or Mesh)
• Volume to Mesh modifier
• Displacement modifier (D9075)
• Texture modifier with blending modes (add, multiply)
• Filter modifier (dilate, erode, blur, sharpen, ...)
• Fluid Simulation modifier, replacing the current modifier on meshes for gasses (not liquids)

Other

• Mantaflow: output OpenVDB files with multiple grids and standard grid names
• VDB tree/voxels API using pyopenvdb
• File packing
• File saving
  • Python API
  • Operator in the UI (unclear where still)
• Grid metadata: show in properties editor
• Support other applications overwriting OpenVDB files open in Blender (T75901)
• Volume edit mode and file saving
• OpenVDB level sets, clusters, perspective transform
• VDB files with modifiers are reloaded whenever parameters are changed, revisit this (memory vs. performance)

Relevant links:

• OpenVDB Official Site
• New Object Types design document
• Code Documentation