// Smooth slope shading, kept beside the shared CPU geometry in slope-belts.js.
const SM_SLOPE_HELPERS = `
// The same rounded strokes as slopeBeltShape; y/z carry distance along/across the band.
vec3 slopeStroke(vec2 p, vec2 a, vec2 b, float origin) {
  vec2 ray = b - a; float len = length(ray); ray /= len;
  float along = dot(p - a, ray), across = dot(p - a, vec2(-ray.y, ray.x));
  vec2 q = abs(vec2(along - len * 0.5, across)) - vec2(len * 0.5 - 0.75, 1.1);
  float sd = length(max(q, 0.0)) + min(max(q.x, q.y), 0.0) - 0.75;
  return vec3(sd, origin + along, across + 2.0);
}
vec3 slopeCorner(vec2 p, vec2 a, float origin) {
  vec2 d = p - a; float radius = length(d);
  return vec3(radius - 1.85, origin + d.x, 2.0 + d.y);
}
vec3 slopeShape(vec2 p, vec2 worldOrigin, float grade, int joins) {
  if ((joins & 64) != 0) p.y -= 0.45;
  float sy = grade < 0.0 ? 4.0 : 0.0;
  vec2 a = vec2(-grade * 1.30814755, sy + 1.30814755), b = vec2(4.0 - grade * 1.30814755, 4.0 - sy + 1.30814755);
  if ((joins & 1) != 0) { a.y = sy + 2.0; a.x = (a.y - sy - 2.61629509) / grade; }
  else if ((joins & 4) != 0) a -= vec2(4.0, grade * 4.0);
  if ((joins & 2) != 0) { b.y = 6.0 - sy; b.x = (b.y - sy - 2.61629509) / grade; }
  else if ((joins & 8) != 0) b += vec2(4.0, grade * 4.0);
  vec2 axis = vec2(1.0, grade) * 0.70710678;
  vec3 best = slopeStroke(p, a, b, dot(worldOrigin + a, axis));
  if ((joins & 1) != 0) {
    vec3 h = slopeStroke(p, vec2(-2.0, a.y), a, worldOrigin.x - 2.0);
    if (h.x < best.x) best = h;
    h = slopeCorner(p, a, worldOrigin.x + a.x);
    if (h.x < best.x) best = h;
  }
  if ((joins & 2) != 0) {
    vec3 h = slopeStroke(p, b, vec2(6, b.y), worldOrigin.x + b.x);
    if (h.x < best.x) best = h;
    h = slopeCorner(p, b, worldOrigin.x + b.x);
    if (h.x < best.x) best = h;
  }
  return best;
}
`;

const SM_SLOPE_DRAW = `
  if (nc == 31 || nc == 32) {
    vec4 tag = cellAt(tTree, c);
    float grade = nc == 31 ? -1.0 : 1.0;
    vec2 local = floor(tag.gb * 255.0 + 0.5) - 8.0 + fract(w);
    float sy = grade < 0.0 ? 4.0 : 0.0;
    float foot = (local.x + grade * (local.y - sy)) * 0.5;
    float depth = (grade * local.x - local.y + sy) * 0.70710678;
    int wallFlags = int(tag.a * 255.0 + 0.5);
    float ends = max((wallFlags & 8) == 0 ? -foot : -100.0, (wallFlags & 16) == 0 ? foot - 4.0 : -100.0);
    float sd = max(ends * 1.41421356, max(-depth, depth - ${CLEAT_HEIGHT.toFixed(1)}));
    float phase = float(wallFlags & 7);
    float wave = 0.5 + 0.5 * sin((foot + w.x - local.x - phase) * 3.14159265);
    vec3 rubber = mix(vec3(0.20,0.22,0.25), vec3(0.25,0.27,0.31), wave);
    C = mix(C, rubber, 1.0 - smoothstep(-px, px, sd));
    // the ribs, where the simulation has them: rubber bars standing straight out of the belt,
    // one every ${CLEAT_SPACING} face cells, moved along by the belt's phase
    float dirS = (wallFlags & 32) != 0 ? 1.0 : -1.0;
    float rc = (w.x - local.x) + foot - (grade < 0.0 ? 1.0 : 0.0) - dirS * phase;
    float off = (mod(rc + ${(CLEAT_SPACING / 2).toFixed(1)}, ${CLEAT_SPACING.toFixed(1)}) - ${(CLEAT_SPACING / 2).toFixed(1)}) * 1.41421356;
    float ribTop = ${((2 * CLEAT_REACH + 1) * Math.SQRT1_2).toFixed(3)};
    float rd = length(vec2(off, depth - clamp(depth, 0.0, ribTop))) - 0.5;
    vec3 rib = mix(vec3(0.50,0.52,0.56), vec3(0.70,0.72,0.76), smoothstep(ribTop - 1.2, ribTop, depth));
    rib *= mix(0.78, 1.0, smoothstep(-0.5, 0.2, off * -dirS * grade));
    C = mix(C, rib, 1.0 - smoothstep(-px, px, rd));
  }

  // Slopes use the flat belt's band, rollers and mesh in coordinates along the run.
  if ((nc == 2 || (nc >= 23 && nc <= 30)) &&
      (int(cellAt(tTree, c).a * 255.0 + 0.5) & 128) != 0 &&
      cellAt(tTree, c).r * 255.0 >= 22.5 && cellAt(tTree, c).r * 255.0 <= 30.5) {
    int slopeClass = int(cellAt(tTree, c).r * 255.0 + 0.5);
    int shape = (slopeClass - 23) / 2;
    bool mesh = shape >= 2;
    float grade = (shape == 0 || shape == 2) ? -1.0 : 1.0;
    float dir = ((slopeClass - 23) % 2) == 1 ? 1.0 : -1.0;
    vec4 tag = cellAt(tTree, c);
    int joins = int(tag.a * 255.0 + 0.5);
    vec2 local = floor(tag.gb * 255.0 + 0.5) - 8.0 + fract(w);
    vec3 shapePos = slopeShape(local, w - local, grade, joins);
    float sd = shapePos.x, axis = shapePos.y, depth = shapePos.z;
    float time = !mesh && (joins & 16) != 0 ? uTime : 0.0;
    vec2 lb = vec2(axis, depth), alongWorld = vec2(axis, depth);
    float rg = step(0.72, fract((axis - dir * (depth < 2.0 ? 1.0 : -1.0) * time * 30.0) * 0.5));
    vec3 belt;
    if (-sd < (mesh ? 1.1 : 0.8)) {
      belt = mesh ? mix(vec3(0.22,0.25,0.29), vec3(0.48,0.53,0.59), depth < 2.0 ? 0.85 : 0.35) : bandColor(lb, rg);
      belt *= mix(0.55, 1.0, smoothstep(0.0, max(px * 1.4, 0.12), -sd));
    } else if (mesh) {
      vec2 cg = abs(fract(alongWorld) - 0.5);
      float bw2 = max(px * 0.9, 0.09);
      float hole = 1.0 - smoothstep(0.5 - bw2 - px, 0.5 - bw2, max(cg.x, cg.y));
      vec3 steel = dot(own.rgb, vec3(1)) > 0.01 ? mix(vec3(0.42, 0.44, 0.5), own.rgb, 0.4) : vec3(0.42, 0.44, 0.5);
      belt = mix(steel * 0.78, C * 0.8, hole);
    } else {
      vec2 dv = vec2(mod(axis, 2.0) - 1.0, depth - 2.0);
      float rd = length(dv);
      belt = vec3(0.15, 0.16, 0.18);
      if (rd < 0.95) {
        float ang = atan(dv.y, dv.x) - dir * time * 30.0 / 0.95;
        float spoke = smoothstep(0.55, 0.85, cos(ang * 3.0));
        belt = mix(vec3(0.5, 0.36, 0.25), vec3(0.72, 0.53, 0.36), 0.5 + 0.5 * dot(normalize(dv + 1e-4), vec2(-0.6, -0.8)) * smoothstep(0.2, 0.95, rd));
        belt *= mix(1.0, 0.72, spoke * smoothstep(0.25, 0.4, rd));
        belt *= mix(1.0, 0.55, smoothstep(0.82, 0.95, rd));
      }
    }
    C = mix(C, belt, 1.0 - smoothstep(-px, px, sd));
  }
`;