feat: retire the gantry and billboard districts and light the rest as steel

src/scene/world/districts.ts

@@ -18,8 +18,6 @@ import { WORLD_DEPTH, WORLD_FAR_Z } from './metrics';
  * like the expressway furniture. Districts at rest are hidden, so only the
  * current chapter's pieces cost draw calls. */
 export type DistrictPiece =
-  | 'gantry'
-  | 'billboard'
   | 'rack-row'
   | 'mast'
   | 'workshop'
@@ -34,7 +32,7 @@ interface Placement {
   /** Yaw in radians, applied before mirroring. */
   ry?: number;
   s?: number;
-  /** Extra vertical stretch (gantries clear the chase camera). */
+  /** Extra vertical stretch (the arch clears the chase camera). */
   sy?: number;
 }
 
@@ -42,18 +40,10 @@ interface Placement {
 export const DISTRICT_PRESENCE: Readonly<
   Record<DistrictPiece, Partial<Record<SectionId, number>>>
 > = {
-  gantry: {
-    profile: 1,
-    experience: 1,
-    infrastructure: 1,
-    'selected-builds': 1,
-    'additional-work': 1,
-    toolkit: 1,
-  },
-  billboard: { profile: 1, experience: 1 },
+  // Pieces rise fully or not at all: a part-raised piece is squashed flat.
   'rack-row': { infrastructure: 1 },
-  mast: { infrastructure: 0.75, toolkit: 1 },
-  workshop: { 'selected-builds': 1, 'additional-work': 0.5 },
+  mast: { infrastructure: 1, toolkit: 1 },
+  workshop: { 'selected-builds': 1 },
   crane: { 'selected-builds': 1, 'additional-work': 1 },
   container: { 'additional-work': 1 },
   arch: { contact: 1 },
@@ -67,14 +57,6 @@ const span = (count: number, from: number, to: number) =>
 function placementsFor(piece: DistrictPiece, dense: boolean): Placement[] {
   const n = (full: number) => (dense ? full : Math.ceil(full / 2));
   switch (piece) {
-    case 'gantry':
-      return span(n(3), -70, -70 - WORLD_DEPTH).map((z) => ({ x: 0, z, sy: 1.42 }));
-    case 'billboard':
-      return span(n(10), -40, -40 - WORLD_DEPTH).map((z, i) => ({
-        x: (i % 2 ? 1 : -1) * 16,
-        z,
-        ry: (i % 2 ? 1 : -1) * 0.28,
-      }));
     case 'rack-row':
       return span(n(18), -26, -26 - WORLD_DEPTH).flatMap((z, i) => {
         const side = i % 2 ? 1 : -1;
@@ -194,17 +176,28 @@ export function createDistricts(
           varying float vHeight;
           void main() {
             ${FADES}
+            // Opaque dark steel, like the sign truss: fades dissolve through a
+            // fixed screen-door pattern instead of alpha, so pieces never read
+            // as translucent sheets over the sky and the sun.
+            float cover = fade * smoothstep(0.0, 0.25, vRise);
+            vec2 cell = mod(floor(gl_FragCoord.xy), 4.0);
+            float threshold = (mod(cell.x + cell.y * 2.0, 4.0) * 4.0 + mod(cell.y, 2.0) * 2.0 + mod(cell.x, 2.0) + 0.5) / 16.0;
+            if (cover < threshold) discard;
             vec3 n = normalize(cross(dFdx(vWorld), dFdy(vWorld)));
             float key = max(0.0, dot(n, normalize(vec3(-0.45, 0.85, 0.35))));
-            float rim = pow(1.0 - abs(n.y), 3.0) * 0.5;
-            vec3 color = vec3(0.03, 0.016, 0.05) + vec3(0.085, 0.06, 0.14) * key;
-            color += uAccent * rim * 0.06 * (0.4 + 0.6 * smoothstep(0.0, 12.0, vHeight));
-            gl_FragColor = vec4(color, fade * smoothstep(0.0, 0.25, vRise));
+            float fill = max(0.0, dot(n, normalize(vec3(0.6, 0.2, -0.4))));
+            vec3 color = vec3(0.022, 0.018, 0.034) + vec3(0.07, 0.06, 0.1) * key + vec3(0.02, 0.015, 0.035) * fill;
+            // Emissive edge: the silhouette catches the chapter colour, and
+            // the tops of the pieces carry a thin lit band.
+            float rim = pow(1.0 - abs(dot(n, normalize(cameraPosition - vWorld))), 4.0);
+            float crown = smoothstep(0.92, 1.0, n.y) * smoothstep(1.0, 6.0, vHeight);
+            color += uAccent * (rim * 0.22 + crown * 0.05);
+            gl_FragColor = vec4(color, 1.0);
             #include <tonemapping_fragment>
             #include <colorspace_fragment>
           }
         `,
-        transparent: true,
+        transparent: false,
         depthWrite: true,
         side: THREE.DoubleSide,
       }),
@@ -253,7 +246,7 @@ export function createDistricts(
     const entry = state.get(piece);
     if (!entry) return;
     const placements = placementsFor(piece, quality.postEffects);
-    const accentMix = piece === 'gantry' || piece === 'arch' || piece === 'billboard' ? 1 : 0.35;
+    const accentMix = piece === 'arch' ? 1 : 0.35;
     for (const [geometry, material] of [
       [body, bodyMaterial(entry.rise)],
       [light, lightMaterial(entry.rise, accentMix)],