gameplay: designated street crossing — zebra markings, corridor cut, up-facing street

- street_mesh.py: continental zebra markings (0.5 m bars, 0.5 m gaps, 3 m
  band) at all three signalised crossings, triangles not quads (FBX SDK
  refuses to triangulate the crown-twisted quads), stripes +6 cm above the
  DEM so they stay above the road surface; winding flipped so every street
  surface faces up (road/sidewalks/markings were 100% down-facing and
  invisible in engine once the terrain stopped covering them).
- terrain_from_dem.py: cut a 10.7 m corridor around the Hollywood Blvd
  centreline so road, kerbs and sidewalks are not buried under the terrain;
  sidewalks themselves cover the transition band, walk-check stays at 0 holes.
- Blender builders save with a writability guard + fatal failure: *.blend
  is LFS-lockable and checks out read-only; a failed save previously left
  downstream steps building from stale files.
- ue_import_site.py: Crossing_Markings imports with no collision (paint on
  the road); ue_build_demo_map.py stages it and chmods the lockable .umap
  before saving (save_map silently returned False on read-only maps).
- ue_build_review_map.py: demo-crossing camera moved to the real crossing
  (s=130.1 m -> UE -24291,-1340) and fixed the ensure_writable path (was
  missing the .umap suffix, so the chmod never fired).

Art/blender/site/export_site_fbx.py

@@ -17,7 +17,7 @@ import sys
 import bpy
 
 MESHES = ("Terrain_DEM", "Road_Hollywood", "Sidewalk_South", "Sidewalk_North",
-          "Kerb_South", "Kerb_North")
+          "Kerb_South", "Kerb_North", "Crossing_Markings")
 
 
 def main():

Art/blender/site/site_assembly.py

@@ -63,6 +63,7 @@ APPEND = {
     "Art/blender/terrain/terrain-2026-11-06.blend": ["Terrain_DEM"],
     "Art/blender/street/street-2026-11-06.blend": [
         "Road_Hollywood", "Sidewalk_South", "Sidewalk_North", "Kerb_South", "Kerb_North",
+        "Crossing_Markings",
     ],
 }
 BLOCKOUT = "Art/blender/blockout/blockout-2026-11-06.blend"
@@ -193,7 +194,14 @@ def main():
 
     out = os.path.abspath(args.out)
     os.makedirs(os.path.dirname(out), exist_ok=True)
-    bpy.ops.wm.save_as_mainfile(filepath=out)
+    # *.blend is LFS-lockable, so a fresh checkout marks it read-only. Make it
+    # writable again or the save fails and downstream steps build from a stale
+    # file — which is worse than failing here.
+    if os.path.exists(out) and not os.access(out, os.W_OK):
+        os.chmod(out, 0o644)
+    result = bpy.ops.wm.save_as_mainfile(filepath=out)
+    if result != {"FINISHED"}:
+        raise RuntimeError(f"could not save {out}: {result}")
     print(f"saved {out}")
 
 

Art/blender/street/street_mesh.py

@@ -148,7 +148,10 @@ def strip(rows, offsets, z_at, name, material):
     for r in range(len(rows) - 1):
         for c in range(cols - 1):
             i = r * cols + c
-            faces.append((i, i + 1, i + cols + 1, i + cols))
+            # Winding faces up: the natural (i, i+1, i+cols+1, i+cols) order
+            # produces downward normals (every surface faced the ground and was
+            # invisible in engine until the terrain corridor cut exposed it).
+            faces.append((i, i + cols, i + cols + 1, i + 1))
     mesh = bpy.data.meshes.new(name)
     mesh.from_pydata(verts, [], faces)
     mesh.update()
@@ -239,7 +242,7 @@ def main():
             verts.extend([(x, y, z_road), (x, y, z_walk)])
         for idx in range(len(rows) - 1):
             i = idx * 2
-            faces.append((i, i + 2, i + 3, i + 1))
+            faces.append((i, i + 1, i + 3, i + 2))
         mesh = bpy.data.meshes.new(name)
         mesh.from_pydata(verts, [], faces)
         mesh.update()
@@ -259,24 +262,34 @@ def main():
     paint.diffuse_color = (0.85, 0.85, 0.85, 1.0)
 
     def crossing_band(s_c):
+        # Stripes are emitted as two triangles each: the road crown makes the
+        # quad non-planar and the FBX SDK refuses to triangulate it on import
+        # ("unable to triangulate mesh" — the mesh is omitted entirely).
         zone = 3.0        # band length along the road, m
         w, g = 0.5, 0.5   # stripe width / gap, m
         span = (SOUTH_GUTTER + 0.2, NORTH_GUTTER - 0.2)
         verts, faces = [], []
         n = int(zone // (w + g))
+        covered = n * w + (n - 1) * g   # actual stripe coverage, centred on s_c
         for k in range(n):
-            s0 = s_c - zone / 2 + k * (w + g)
+            s0 = s_c - covered / 2 + k * (w + g)
             corners = []
+            base_idx = len(verts)  # verts grows only after the stripe is sampled
             for s_edge in (s0, s0 + w):
                 base, normal, _ = at(s_edge)
                 for off in span:
                     x = base[0] + off * normal[0]
                     y = base[1] + off * normal[1]
-                    corners.append((len(verts), (x, y, (dem_z(x, y) or 0.0) + 0.03)))
+                    # +6 cm above the DEM = 4 cm above the road surface: the road
+                    # interpolates the DEM along 1 m rows while the markings sample
+                    # only their own corners, so a 1 cm lift left parts of the
+                    # stripes sunk under the road and invisible in game.
+                    corners.append((base_idx + len(corners), (x, y, (dem_z(x, y) or 0.0) + 0.06)))
             # corners order: (s0,off_s), (s0,off_n), (s1,off_s), (s1,off_n)
             idx = [c[0] for c in corners]
             verts.extend(c[1] for c in corners)
-            faces.append((idx[0], idx[1], idx[3], idx[2]))
+            faces.append((idx[0], idx[3], idx[1]))
+            faces.append((idx[0], idx[2], idx[3]))
         mesh = bpy.data.meshes.new("Crossing_Markings")
         mesh.from_pydata(verts, [], faces)
         mesh.update()
@@ -303,7 +316,14 @@ def main():
 
     out = os.path.abspath(args.out)
     os.makedirs(os.path.dirname(out), exist_ok=True)
-    bpy.ops.wm.save_as_mainfile(filepath=out)
+    # *.blend is LFS-lockable, so a fresh checkout marks it read-only. Make it
+    # writable again or the save fails and downstream steps build from a stale
+    # file — which is worse than failing here.
+    if os.path.exists(out) and not os.access(out, os.W_OK):
+        os.chmod(out, 0o644)
+    result = bpy.ops.wm.save_as_mainfile(filepath=out)
+    if result != {"FINISHED"}:
+        raise RuntimeError(f"could not save {out}: {result}")
     print(f"saved {out}")
 
 

Art/blender/terrain/terrain_from_dem.py

@@ -53,6 +53,9 @@ def parse_args():
     ap.add_argument("--ymax", type=float, default=110.0)
     ap.add_argument("--osm", default=None,
                     help="OSM extract; building outlines are cut out so rooftops never become terrain")
+    ap.add_argument("--corridor", type=float, default=10.7,
+                    help="half-width in m of the Hollywood Blvd corridor to cut out so the "
+                         "street meshes (road, kerbs, sidewalks) are not buried under the terrain")
     return ap.parse_args(argv)
 
 
@@ -110,6 +113,30 @@ def pts_flat(ring):
     return ring
 
 
+def centreline_polyline(osm_path):
+    """Hollywood Blvd centreline as a local-frame polyline (Highland -> Orange)."""
+    nodes, ways = oc.load(osm_path)
+    line, _, _, _, _ = oc.block_extent(
+        nodes, ways, "Hollywood Boulevard", "North Orange Drive", "North Highland Avenue")
+    utm = project_to_utm(line, find_proj())
+    return [(e - ORIGIN_E, n - ORIGIN_N) for e, n in utm]
+
+
+def dist_to_polyline(x, y, pts):
+    best = float("inf")
+    for (ax, ay), (bx, by) in zip(pts, pts[1:]):
+        dx, dy = bx - ax, by - ay
+        l2 = dx * dx + dy * dy
+        if l2 == 0.0:
+            continue
+        t = max(0.0, min(1.0, ((x - ax) * dx + (y - ay) * dy) / l2))
+        px, py = ax + t * dx, ay + t * dy
+        d = (x - px) ** 2 + (y - py) ** 2
+        if d < best:
+            best = d
+    return best ** 0.5
+
+
 def inside(x, y, ring):
     """Ray casting point-in-polygon."""
     hit = False
@@ -146,9 +173,12 @@ def main():
           f"X {args.xmin}..{args.xmax}, Y {args.ymin}..{args.ymax}")
 
     polys = []
+    corridor = None
     if args.osm:
         polys = building_polygons(args.osm)
         print(f"masking {len(polys)} building footprints")
+        corridor = centreline_polyline(args.osm)
+        print(f"cutting {args.corridor} m corridor around the Hollywood Blvd centreline")
 
     verts = []
     ok = []
@@ -168,6 +198,10 @@ def main():
                 verts.append((x, y, 0.0))
                 ok.append(False)
                 continue
+            if corridor is not None and dist_to_polyline(x, y, corridor) <= args.corridor:
+                verts.append((x, y, 0.0))
+                ok.append(False)
+                continue
             z = values[ri * width + ci]
             if nodata is not None and z == nodata:
                 verts.append((x, y, 0.0))
@@ -212,7 +246,14 @@ def main():
 
     out = os.path.abspath(args.out)
     os.makedirs(os.path.dirname(out), exist_ok=True)
-    bpy.ops.wm.save_as_mainfile(filepath=out)
+    # *.blend is LFS-lockable, so a fresh checkout marks it read-only. Make it
+    # writable again or the save fails and downstream steps build from a stale
+    # file — which is worse than failing here.
+    if os.path.exists(out) and not os.access(out, os.W_OK):
+        os.chmod(out, 0o644)
+    result = bpy.ops.wm.save_as_mainfile(filepath=out)
+    if result != {"FINISHED"}:
+        raise RuntimeError(f"could not save {out}: {result}")
     print(f"saved {out}")