Sloped belts and filters, laid by a 45° drag (t40)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/render/smooth-shaders.js

@@ -51,8 +51,8 @@ float beltSD(vec2 lb, bool endL, bool endR) {
 // the line only rounds off where the whole run ends.
 float beltLineSD(ivec2 c, vec2 lb) {
   int nr = cls(cellAt(tCol, c + ivec2(4, 0))), nl = cls(cellAt(tCol, c - ivec2(4, 0)));
-  return beltSD(lb, isBelt(nl) + isF(nl) < 0.5 && !(nl >= 19 && nl <= 22),
-    isBelt(nr) + isF(nr) < 0.5 && !(nr >= 19 && nr <= 22));
+  return beltSD(lb, isBelt(nl) + isF(nl) < 0.5 && !(nl >= 19 && nl <= 30) && cls(cellAt(tCol, c + ivec2(-4, -4))) < 23,
+    isBelt(nr) + isF(nr) < 0.5 && !(nr >= 19 && nr <= 30) && cls(cellAt(tCol, c + ivec2(4, -4))) < 23);
 }
 // The rubber band of a belt or filter: 1 on a ridge. Ridges travel along the top run one way and
 // back along the bottom.
@@ -352,6 +352,33 @@ void main() {
     }
   }
 
+  // Sloped belts and filters: a continuous running band over a triangular frame.
+  if (nc >= 23 && nc <= 30) {
+    int shape = (nc - 23) / 2;
+    bool mesh = shape >= 2;
+    float grade = (shape == 0 || shape == 2) ? -1.0 : 1.0;
+    float dir = ((nc - 23) % 2) == 1 ? 1.0 : -1.0;
+    vec4 tag = cellAt(tTree, c);
+    vec2 lb = mod(w, 4.0);
+    if (tag.a > 0.4) lb.y += 4.0;
+    float face = grade < 0.0 ? 4.0 - lb.x : lb.x;
+    float depth = (lb.y - face) * 0.70710678;
+    float inside = smoothstep(-px, px, depth);
+    float axis = (w.x + grade * w.y) * 0.5;
+    float rg = step(0.72, fract((axis - dir * uTime * 30.0) * 0.5));
+    vec3 band = bandColor(vec2(axis, 0.5), rg);
+    vec3 frame = vec3(0.18, 0.19, 0.21);
+    float roller = 1.0 - smoothstep(0.32, 0.5, length(vec2(mod(axis, 2.0) - 1.0, depth - 0.95)));
+    frame = mix(frame, vec3(0.50, 0.40, 0.31), roller);
+    if (mesh) {
+      float hole = step(0.48, fract(axis)) * step(0.35, fract(depth * 1.8));
+      band = mix(band, dot(tag.rgb, vec3(1)) > 0.01 ? tag.rgb * 0.7 : vec3(0.28, 0.32, 0.33), hole);
+      frame = mix(C, vec3(0.25, 0.27, 0.30), roller * 0.7);
+    }
+    vec3 belt = mix(band, frame, smoothstep(0.55, 0.75, depth));
+    C = mix(C, belt, inside);
+  }
+
   // ---- light, then the glow of hot things on top
   if (uLightMap.w > 0.5) C *= textureLod(tLight, (q - uLightMap.xy) / uLightMap.z / uLightSize, 0.0).rgb;
   if (uGlowK > 0.0) {