remesh op: game-LOD TRELLIS heroes — solidify past voxel, voxel remesh, decimate floor 1/3, smart-UV, Cycles bake

Thin-shell physics learned the hard way: fabric thinner than the voxel
perforates in the remesh itself; decimating any thin slab below ~1/3
collapses its surfaces. Verified on the baseball cap: 483k -> 41k tris,
watertight, textured.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

blender_ops.py

@@ -698,5 +698,99 @@ elif OP == 'assemble':
     print(f'assembled body + {len(ARGS) - 2} garment file(s)')
     export(ARGS[1])
 
+elif OP == 'remesh':
+    # remesh <in> <out.glb> <target_tris> [tex_size]
+    #
+    # Game-LOD a TRELLIS hero mesh. Plain Decimate moth-eats TRELLIS output at
+    # ANY ratio (verified 25k and 50k on the baseball cap) because the surface
+    # is a paper-thin double shell — front and back faces collapse into each
+    # other. So: voxel-remesh into one solid watertight skin first (kills the
+    # UVs), decimate THAT, give it fresh smart-project UVs, and Cycles-bake the
+    # original's textured surface back onto it (selected->active). Rigid props
+    # only — vertex weights do not survive; use decimate for rigged meshes.
+    src, out, target = ARGS[0], ARGS[1], int(ARGS[2])
+    tex_size = int(ARGS[3]) if len(ARGS) > 3 else 2048
+    load(src)
+    meshes = [o for o in bpy.data.objects if o.type == 'MESH']
+    orig = max(meshes, key=lambda o: len(o.data.vertices))
+    for o in meshes:
+        if o is not orig:
+            bpy.data.objects.remove(o, do_unlink=True)
+    for o in [o for o in bpy.data.objects if o.type in ('EMPTY', 'ARMATURE')]:
+        bpy.data.objects.remove(o, do_unlink=True)
+    orig.rotation_mode = 'XYZ'
+
+    lod = orig.copy()
+    lod.data = orig.data.copy()
+    lod.name = 'lod'
+    bpy.context.scene.collection.objects.link(lod)
+
+    # Voxel-remesh into ONE solid skin at a voxel fine enough to keep thin
+    # features (brims, straps): 0.8% of bbox — 39mm voxels ate the cap brim
+    # entirely, 8mm kept it. Then decimate no lower than 1/3: below that the
+    # thin solid slab's two surfaces collapse into each other (the same
+    # moth-eating plain Decimate causes). The target is therefore a WISH —
+    # the shell's physics set the floor, and the op reports what it kept.
+    bpy.context.view_layer.objects.active = lod
+    vox = max(orig.dimensions) * 0.008
+    # SOLIDIFY FIRST: TRELLIS fabric is ~2mm thick — anywhere the shell is
+    # thinner than the voxel, the remesh itself perforates (the cap crown
+    # tore at 8mm voxel in every variant while the double-folded brim held).
+    # Thickening the shell past the voxel size guarantees a watertight solid.
+    sol = lod.modifiers.new('sol', 'SOLIDIFY')
+    sol.thickness = vox * 1.6
+    sol.offset = 0.0
+    bpy.ops.object.modifier_apply(modifier='sol')
+    rm = lod.modifiers.new('remesh', 'REMESH')
+    rm.mode = 'VOXEL'
+    rm.voxel_size = vox
+    bpy.ops.object.modifier_apply(modifier='remesh')
+    tris = sum(len(pg.vertices) - 2 for pg in lod.data.polygons)
+    if tris > target:
+        dec = lod.modifiers.new('dec', 'DECIMATE')
+        dec.ratio = max(target / max(tris, 1), 0.33)
+        bpy.ops.object.modifier_apply(modifier='dec')
+
+    bpy.ops.object.select_all(action='DESELECT')
+    lod.select_set(True)
+    bpy.context.view_layer.objects.active = lod
+    bpy.ops.object.mode_set(mode='EDIT')
+    bpy.ops.mesh.select_all(action='SELECT')
+    bpy.ops.uv.smart_project(angle_limit=1.15, island_margin=0.003)
+    bpy.ops.object.mode_set(mode='OBJECT')
+
+    img = bpy.data.images.new('lod_bake', tex_size, tex_size, alpha=False)
+    mat = bpy.data.materials.new('lod_mat')
+    mat.use_nodes = True
+    nt = mat.node_tree
+    bsdf = next(n for n in nt.nodes if n.type == 'BSDF_PRINCIPLED')
+    tn = nt.nodes.new('ShaderNodeTexImage')
+    tn.image = img
+    nt.nodes.active = tn
+    lod.data.materials.clear()
+    lod.data.materials.append(mat)
+
+    sc = bpy.context.scene
+    sc.render.engine = 'CYCLES'
+    sc.cycles.samples = 16                     # flat diffuse transfer needs few samples
+    sc.cycles.device = 'CPU'
+    sc.render.bake.use_selected_to_active = True
+    sc.render.bake.cage_extrusion = max(orig.dimensions) * 0.03
+    sc.render.bake.max_ray_distance = max(orig.dimensions) * 0.08
+    sc.render.bake.use_pass_direct = False
+    sc.render.bake.use_pass_indirect = False
+    bpy.ops.object.select_all(action='DESELECT')
+    orig.select_set(True)
+    lod.select_set(True)
+    bpy.context.view_layer.objects.active = lod
+    bpy.ops.object.bake(type='DIFFUSE')
+    nt.links.new(tn.outputs['Color'], bsdf.inputs['Base Color'])
+    img.pack()
+
+    bpy.data.objects.remove(orig, do_unlink=True)
+    final_tris = sum(len(pg.vertices) - 2 for pg in lod.data.polygons)
+    print(f'remeshed: voxel {vox * 1000:.1f}mm -> {tris:,} tris -> decimated {final_tris:,} tris, baked {tex_size}px')
+    export(out)
+
 else:
     raise SystemExit(f'unknown op {OP}')