2023-10-30 Line Art

Meetings
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Future Line Art Design

Meeting at the Blender HQ after the Blender Conference 2023. The goal of the meeting was to discuss the porting of existing Line Art Modifier, the node-based- Line Art and their relation with the Geometry Nodes and the on-going Grease Pencil task force.

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Left-to-right: Vivien, Brecht, Falk, Hans, Jacques, Sebastian, Simon, Yiming - off-camera: Dalai.

Attendees:

  • Brecht Van Lommel
  • Dalai Felinto
  • Falk David
  • Hans Goudey
  • Jacques Lucke
  • Sebastian Parborg
  • Simon Thommes
  • Vivien Lulkowski
  • Yiming Wu

Who uses Line Art?

Use Cases

  • Less common in western world?
    • Manga
    • Mechanical renderings
    • Architectural lines

Shortcomings and workarounds

  • Grease pencil aliasing issue
  • Referencing of scene/object geometry
  • Filtering logic is too complex and isn’t used
  • The modifier UI is very complex

Future of Freestyle

  • Initially Line Art was meant as a replacement for Freestyle.
  • The goal was to have feature partity. The main missing thing is the style of the strokes, which was suplemented with some grease pencil modifiers, but 1 to 1 feature parity wasn’t achieved.
  • Freestyle doesn’t work as well for mechanical renderings and is missing some features.
  • Freestyle is slower and uses more memory.
  • Are people still using freestyle?
    • Yes, some people are

Grease Pencil 3

The first goal is porting the existing modifier. This should be simple since the only part that interacts with grease pencil is the final output conversion.

Baking operators also need to be ported.

Plan of Attack

  • Yiming will be able to spend time helping the grease pencil 3.0 project generally.
  • A line art project wouldn’t start before the GPv3 project is finished

Node Based Line Art Design

  • The end goal is to replace freestyle and the existing line art modifier.
    • The rendering of grease pencil needs some improvements to address that goal as well
  • Use-cases presented by Vivien
    • Outlines around shadows
    • Offsetting painterly generated lines around shapes
  • Building block nodes
    • The exact design of nodes is still undecided
    • One main difficulty is the acceleration data structures used across multiple operations-- particularly a 2D lookup structure. The same acceleration data may be necessary across multiple builtin nodes, and it would be good to avoid rebuilding it.
    • Nodes
      • “Line Visibility”?
      • Chaining?
      • Smoothing?
    • If they are useful independently they could be released earlier.
    • But the goal is to work on a use-case basis and for them add their needed building-blocks.
  • Node group bundles
    • These node groups use building block nodes under the hood, but present a simplified use case for artists
    • Bundles
      • Simple thick line
      • Technical drawing (dashed invisble geometry, extension lines)
      • Anime
  • Modifiers
    • Will most likely overlap with the node group assets

Next Steps

  • Define the high-level node groups (inputs and outputs) for specific art styles
    • Different high-level node groups for different art styles.
    • Show what should come in and out of each one.
    • This will be used to define together what the building-blocks should be.
  • Collect use-case scene examples.
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It would be brilliant if the Blender Developers could add ‘Canvases’ in Blender. These ‘Canvases’ would be used to collate LineArt camera views onto one sheet (and include drawing borders). If used in conjunction with the CAD addons (MeasureIt_Arch, BelnderBIM, PRJ Addon, TechSec etc.) then Blender could have a way of making technical drawings without having to resort to using a third party program such as Inkscape.

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At this time LineArt redesign is in its first steps, but it would be important to always include in the design the ability to convert the lines generated by LineArt into Grease Pencil Strokes. The ability to get strokes that can be edited is a unique capability of Blender and should not be missed. Many users use the geometry generated by LineArt as the basis of an animation that is then retouched manually. This capability makes Grease Pencil LineArt tool unique and will not exist if you decide to work only in a rendering engine like FreeStyle.

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Some input about Freestyle & GP LineArt:

  • Freestyle often creates cleaner geometry (removing doubles, chaining, ability to filter out short lines…) this is especially important when exporting geometry to SVG or other formats
  • Freestyle has the ability to color strokes from the material color, something which is not possible at all currently with LineArt

So IMHO LineArt can’t preplace Freestyle at the moment and Freestyle is still used.

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