dm-sdf-to-mesh-tool-pattern

name	DM SDF-to-Mesh Tool Pattern
description	Reference for the SDF-to-Mesh conversion tool. Covers where meshing belongs (dedicated tool, NOT render pipeline), the mesher API, output format, and how to create a Part.Shape from mesh data.

DM SDF-to-Mesh Tool Pattern

Meshing is an explicit user action, not a render-time side effect. The render pipeline uses GPU ray marching for real-time visualization. When the user needs a triangle mesh (for export, CNC, 3D printing, or FreeCAD Part operations), they invoke the SDF-to-Mesh tool.

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Architecture

Render pipeline (real-time):
  SdfField → GPU ray march shader → screen pixels
  NO meshing in this path.

SDF-to-Mesh tool (explicit action):
  SdfField → Mesher → (verts, indices) → Part.Shape
  User triggers this via command button.

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Mesher API

from core.dm_mesher import get_active_mesher

mesher = get_active_mesher(type_override=None)
result = mesher.mesh(field, cell_size=1.0)
# Returns: (flat_verts, flat_idx) or None
#   flat_verts: (N, 3) float32 — vertex positions
#   flat_idx:   (M,) int32 — [v0, v1, v2, -1, ...] with -1 sentinels

Mesher Types

Value	Name	Class
0	Marching Cubes	MarchingCubesMesher
1	Adaptive MC	AdaptiveMCMesher
2	Surface Nets	SurfaceNetsMesher
3	Dual Contouring	DualContouringMesher

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Converting Mesh to Part.Shape

import Mesh
import Part

def triangles_to_shape(flat_verts, flat_idx):
    idx = flat_idx.reshape(-1, 4)[:, :3]  # (N_tris, 3)
    facets = []
    for tri in idx:
        v0, v1, v2 = flat_verts[tri[0]], flat_verts[tri[1]], flat_verts[tri[2]]
        facets.append([tuple(v0), tuple(v1), tuple(v2)])
    mesh = Mesh.Mesh(facets)
    shape = Part.Shape()
    shape.makeShapeFromMesh(mesh.Topology, 0.1)
    try:
        return Part.makeSolid(shape)
    except Exception:
        return shape

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Existing Command: CommandSDFToShape

File: commands/cmd_sdf_export.py

This command already implements the SDF-to-Mesh flow. It:

1. Gets the selected SDF object's SdfField
2. Calls get_active_mesher().mesh(field, cell_size)
3. Converts to Part.Shape via Mesh.Mesh
4. Creates a new Part::Feature in the document

This is the correct location for meshing. The render pipeline (dm_object.py:execute()) should NOT call meshers.

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What to Remove from Render Pipeline

In dm_object.py:execute(), the mesh-mode branch (lines 378-390) calls get_active_mesher().mesh() during document recompute. This must be removed so that execute() only sets fp.Shape = Part.Shape() for sdf objects, regardless of render mode.

The DMViewProvider.updateData() mesh handoff to DMRenderer.update_sdf_mesh() also becomes dead code once meshing is removed from execute().

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Files to Read Before Editing

1. commands/cmd_sdf_export.py — existing SDF-to-Shape command
2. core/dm_object.py:369-407 — execute() with mesh-in-render-pipeline (to be cleaned)
3. core/dm_mesher.py — mesher implementations
4. core/dm_renderer.py:192-240 — mesh rendering nodes (to be removed)