GPv3: Vertex groups in GreasePencil data block and conversion #117337

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Lukas Tönne · 2024-01-19T15:33:58+01:00

Lukas Tönne commented

2024-01-19 15:33:58 +01:00

Add a list of vertex group names to GreasePencil data block DNA.
RNA API for vertex group names.
Basic UI for vertex group names.
Extend conversion functions in grease_pencil_convert_legacy.cc:
- copy vertex group names from old bGPdata to new GreasePencil.
- copy vertex group names from old bGPdata to all Drawings in the data block.
  Optimization: skip vertex groups in Drawings where they have no assigned vertices
- copy MDeformVert from bGPDstroke to new CustomData

- Add a list of vertex group names to `GreasePencil` data block DNA. - RNA API for vertex group names. - Basic UI for vertex group names. - Extend conversion functions in `grease_pencil_convert_legacy.cc`: - copy vertex group names from old `bGPdata` to new `GreasePencil`. - copy vertex group names from old `bGPdata` to all `Drawings` in the data block. _Optimization: skip vertex groups in `Drawings` where they have no assigned vertices_ - copy `MDeformVert` from `bGPDstroke` to new `CustomData`

Lukas Tönne added the

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To Do

label 2024-01-19 15:33:58 +01:00

Lukas Tönne added this to the Grease Pencil project 2024-01-19 15:34:01 +01:00

Lukas Tönne added the

labels 2024-01-19 15:34:39 +01:00

Lukas Tönne self-assigned this 2024-01-19 15:34:49 +01:00

Lukas Tönne commented

2024-01-19 16:26:11 +01:00

Adding a conventional DNA ListBase of vertex group names to GreasePencil is not ideal. It raises questions of where data is actually defined. Vertex groups could be added both through the GreasePencil DNA and through the attributes API in Curves, and the respective other side of the data would need to be kept in sync.

A radical solution would be to not store vertex groups in GreasePencil data blocks at all. Each Drawing stores an independent list of vertex groups. This would require adding each vertex group individually to each drawing. Modifiers would not be able to select a vertex group.

Compromise: use Drawings as the primary storage for vertex groups, and derive a cached runtime list in GreasePencil from that data. This has implications for workflow:

Task
Add vertex group	Have to select a drawing first (cannot add vertex group without any drawings!). New vertex groups are not automatically added to all drawings
Remove vertex group	Removed from all drawings
Rename vertex group	Renamed in all drawings
Move vertex group up/down	Meaningless! Order of vertex groups in the runtime cache is arbitrary: Added in the order in which they appear in drawings (first come, first serve). Cache vgroup order does not have to match order in any of the drawings.

Adding a conventional DNA `ListBase` of vertex group names to `GreasePencil` is not ideal. It raises questions of where data is actually defined. Vertex groups could be added both through the `GreasePencil` DNA and through the attributes API in `Curves`, and the respective other side of the data would need to be kept in sync. A radical solution would be to not store vertex groups in `GreasePencil` data blocks at all. Each `Drawing` stores an independent list of vertex groups. This would require adding each vertex group individually to each drawing. Modifiers would not be able to select a vertex group. Compromise: use `Drawings` as the primary storage for vertex groups, and derive a cached runtime list in `GreasePencil` from that data. This has implications for workflow: |Task|| |-|-| |Add vertex group|Have to select a drawing first (cannot add vertex group without any drawings!). New vertex groups are not automatically added to all drawings| |Remove vertex group|Removed from all drawings| |Rename vertex group|Renamed in all drawings| |Move vertex group up/down|Meaningless! Order of vertex groups in the runtime cache is arbitrary: Added in the order in which they appear in drawings (first come, first serve). Cache vgroup order does not have to match order in any of the drawings.|

Hans Goudey commented

2024-01-19 16:59:28 +01:00

A read-only collection property on GreasePencil called all_drawing_vertex_groups seems like a good place to start. That would be used to choose vertex groups in the modifiers.

The property editor will have to be extended to show properties of the active drawing: attributes and vertex groups.

A read-only collection property on `GreasePencil` called `all_drawing_vertex_groups` seems like a good place to start. That would be used to choose vertex groups in the modifiers. The property editor will have to be extended to show properties of the active drawing: attributes and vertex groups.

Sietse Brouwer commented

2024-01-19 22:27:24 +01:00

As I see it, there is no functional relationship between vertex groups and layers (drawings). A vertex group has a 1:n relationship with stroke points. Those points can reside in multiple layers.
A vertex group is really an object-level thing. So storing it at layer level, sounds like a troublesome design to me.

As I see it, there is no functional relationship between vertex groups and layers (drawings). A vertex group has a 1:n relationship with stroke _points_. Those points can reside in multiple layers. A vertex group is really an object-level thing. So storing it at layer level, sounds like a troublesome design to me.

Lukas Tönne commented

2024-01-22 16:44:40 +01:00

At the module meeting we decided to try the "runtime cache" approach:

Authoritative vertex group names are stored per drawing (CurvesGeometry).
List of vertex groups in GreasePencil data block is cached at runtime.
GreasePencil names are used for global ordering between drawings.

At the module meeting we decided to try the "runtime cache" approach: 1. Authoritative vertex group names are stored per drawing (`CurvesGeometry`). 2. List of vertex groups in `GreasePencil` data block is cached at runtime. 3. `GreasePencil` names are used for global ordering between drawings.

Lukas Tönne commented

2024-01-23 15:27:34 +01:00

Vertex groups definitions (bDeformGroup) have a lock_weight flag, which is used to maintain relative weights during editing. With the "drawings own vertex groups" approach this begs the question: do we use the individual flags on the drawings to determine locking state?

As a user-facing editor setting i would expect all drawings to use the same property. But if drawings are the source of truth this could become a bit more difficult. We could apply the same principle as for vertex group names:

Primary storage is on drawings.
After changes the data block property is updated to reflect overall state.
Operators (for setting the flag) apply to all drawings, only indirectly changing the data block property.
If the lock_weight flag is disabled on any drawing it is disabled on the data block too.

Vertex groups definitions (`bDeformGroup`) have a `lock_weight` flag, which is used to maintain relative weights during editing. With the "drawings own vertex groups" approach this begs the question: do we use the individual flags on the drawings to determine locking state? As a user-facing editor setting i would expect all drawings to use the same property. But if drawings are the source of truth this could become a bit more difficult. We could apply the same principle as for vertex group names: - Primary storage is on drawings. - After changes the data block property is updated to reflect overall state. - Operators (for setting the flag) apply to all drawings, only indirectly changing the data block property. - If the `lock_weight` flag is disabled on any drawing it is disabled on the data block too.

Lukas Tönne referenced a pull request that will close this issue

2024-01-29 10:59:59 +01:00

GPv3: Basic vertex group operators #117476

Lukas Tönne referenced this issue from a commit

2024-01-31 17:46:08 +01:00

GPv3: Basic vertex group operators

Lukas Tönne closed this issue

2024-01-31 17:46:09 +01:00

Blender Bot added the

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Resolved

label 2024-01-31 17:46:11 +01:00