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SimpleCADAPI-master/examples/15_cached_mesh_obj_export.py

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+"""Example 15: export an internal cached mesh as OBJ.
+
+Run from the repository root with:
+    uv run python examples/15_cached_mesh_obj_export.py
+
+This is a developer-facing example for the mesh-cache groundwork. It
+intentionally does not call the public STL exporter. Instead it builds a normal
+SimpleCAD solid, reads the framework's internal cached mesh, and writes a common
+Wavefront OBJ mesh file from that pure triangle data.
+
+Application code should not depend on ``simplecadapi._mesh``. Future structural
+checking APIs will consume the same internal mesh cache without exposing mesh
+extraction to framework users.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import simplecadapi as scad
+import simplecadapi._mesh as internal_mesh
+
+
+OUT_DIR = Path("examples/out/cached_mesh_obj_export")
+
+
+def build_demo_solid() -> scad.Solid:
+    """Build a small bracket-like solid using only normal modeling APIs."""
+
+    base = scad.make_box_rsolid(
+        width=34.0,
+        height=20.0,
+        depth=6.0,
+        bottom_face_center=(0.0, 0.0, 0.0),
+    )
+    through_hole = scad.make_cylinder_rsolid(
+        radius=4.0,
+        height=12.0,
+        bottom_face_center=(0.0, 0.0, -3.0),
+        axis=(0.0, 0.0, 1.0),
+    )
+    mount_slot = scad.make_box_rsolid(
+        width=8.0,
+        height=24.0,
+        depth=10.0,
+        bottom_face_center=(10.0, 0.0, -2.0),
+    )
+    boss = scad.make_cylinder_rsolid(
+        radius=7.0,
+        height=5.0,
+        bottom_face_center=(-10.0, 0.0, 6.0),
+        axis=(0.0, 0.0, 1.0),
+    )
+
+    bracket = scad.cut_rsolid(
+        base,
+        through_hole,
+        mount_slot,
+        skip_non_intersecting=False,
+    )
+    bracket = scad.union_rsolid([bracket, boss])
+    return scad.apply_tag(shape=bracket, tag="role.cached_mesh_obj_demo")
+
+
+def write_cached_mesh_obj(solid: scad.Solid, path: Path) -> internal_mesh.TriMesh:
+    """Write a Solid's internal cached mesh to Wavefront OBJ."""
+
+    mesh = internal_mesh.cached_mesh(solid)
+    if mesh is None:
+        detail = internal_mesh.mesh_error(solid) or "no internal mesh cache"
+        raise RuntimeError(f"Solid has no cached mesh: {detail}")
+
+    lines = [
+        "# OBJ written from SimpleCAD internal cached mesh",
+        "# This example intentionally bypasses scad.export_stl(...).",
+    ]
+    for x, y, z in mesh.vertices:
+        lines.append(f"v {x:.9g} {y:.9g} {z:.9g}")
+    for a, b, c in mesh.triangles:
+        lines.append(f"f {int(a) + 1} {int(b) + 1} {int(c) + 1}")
+
+    path.write_text("\n".join(lines) + "\n", encoding="utf-8")
+    return mesh
+
+
+def main() -> None:
+    OUT_DIR.mkdir(parents=True, exist_ok=True)
+    solid = build_demo_solid()
+    obj_path = OUT_DIR / "cached_mesh_bracket.obj"
+    mesh = write_cached_mesh_obj(solid=solid, path=obj_path)
+    lower, upper = mesh.bounds
+
+    print("volume", round(solid.get_volume(), 3))
+    print("faces", len(solid.get_faces()))
+    print("mesh", f"vertices={mesh.vertex_count}", f"triangles={mesh.triangle_count}")
+    print("bounds", f"min={tuple(round(v, 3) for v in lower)}", f"max={tuple(round(v, 3) for v in upper)}")
+    print("wrote_obj", obj_path)
+
+
+if __name__ == "__main__":
+    main()