Diagonal screw tubes, laid by a 45° drag (t35)

- Tubes run in eight directions: a drag at about 45° lays a diagonal run, R cycles all eight.
- Diagonal runs carry grains at the straight rate (120 grains/s), join straight tubes and belts,
  keep grains in at the corners, pass water, and carry bars level.
- New part ids 11-14 (saved ids are never renumbered); tube checks use an IS_TUBE table.
- New test/t_diag_tubes.js (85 checks).

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

src/sim/items.js

@@ -5,7 +5,7 @@
 // its cells as solid (occ).
 const BAR_W = 4, BAR_H = 2;
 let entCurM = 0; // the bar being moved, so a filter can let its own kind of bar through
-function entSolidCell(j) { const m = mat[j], p = part[j]; return occ[j] || PH[m] === PH_SOLID || PH[m] === PH_POWDER || (p !== 0 && (p <= P_GRATE || (p === P_FILTER && !filterPassAt(entCurM, j)))); }
+function entSolidCell(j) { const m = mat[j], p = part[j]; return occ[j] || PH[m] === PH_SOLID || PH[m] === PH_POWDER || (p !== 0 && (IS_TUBE[p] || p === P_GRATE || (p === P_FILTER && !filterPassAt(entCurM, j)))); }
 function entSupportCount(x, y) {
   if (y + BAR_H >= H) return BAR_W;
   let n = 0;
@@ -42,23 +42,27 @@ function removeEnt(e) { entMark(e, 0); const k = ents.indexOf(e); if (k >= 0) en
 function entTubeAt(x, y) {
   if (x < 0 || y < 0 || x + BAR_W > W || y + BAR_H > H) return 0;
   for (let yy = y; yy < y + BAR_H; yy++) for (let xx = x; xx < x + BAR_W; xx++) {
-    const p = part[yy * W + xx]; if (p < P_TU || p > P_TR) return 0;
+    const p = part[yy * W + xx]; if (!IS_TUBE[p]) return 0;
   }
   return part[(y + 1) * W + x + 1];
 }
 function entTubeFree(x, y, tubeOnly = false) {
   if (x < 0 || y < 0 || x + BAR_W > W || y + BAR_H > H) return false;
   for (let yy = y; yy < y + BAR_H; yy++) for (let xx = x; xx < x + BAR_W; xx++) {
-    const j = yy * W + xx, p = part[j], tube = p >= P_TU && p <= P_TR;
+    const j = yy * W + xx, p = part[j], tube = IS_TUBE[p];
     // gas and liquid don't stop a bar, in a tube or in the open
     if (occ[j] || (mat[j] !== EMPTY && PH[mat[j]] !== PH_GAS && PH[mat[j]] !== PH_LIQUID) || (tubeOnly ? !tube : !tube && entSolidCell(j))) return false;
   }
   return true;
 }
 // Check the swept rectangle too: a snap must never jump through a grain or another bar.
-function entTubeMove(e, x, y, tubeOnly = false) {
+function entTubeMove(e, x, y, tubeOnly = false, mouth = false) {
   if (!entTubeFree(x, y, tubeOnly)) return false;
-  for (let yy = Math.min(e.iy, y); yy <= Math.max(e.iy, y); yy++)
+  if (mouth) {
+    // Lift clear of the receiving belt before sliding over it; check both legs before moving.
+    for (let yy = Math.min(e.iy, y); yy <= Math.max(e.iy, y); yy++) if (!entTubeFree(e.ix, yy)) return false;
+    for (let xx = Math.min(e.ix, x); xx <= Math.max(e.ix, x); xx++) if (!entTubeFree(xx, y)) return false;
+  } else for (let yy = Math.min(e.iy, y); yy <= Math.max(e.iy, y); yy++)
     for (let xx = Math.min(e.ix, x); xx <= Math.max(e.ix, x); xx++) if (!entTubeFree(xx, yy)) return false;
   e.x = e.ix = x; e.y = e.iy = y; e.vx = e.vy = 0; return true;
 }
@@ -72,7 +76,7 @@ function entTubeEnter(e, dx, dy) {
     const i = entTubeEdge(e, dx, dy, k);
     if (i < 0) continue;
     const xx = i % W, yy = (i / W) | 0;
-    const p = part[i]; if (p < P_TU || p > P_TR || (!dx && TDX[p]) || dx * TDX[p] + dy * TDY[p] < 0) continue;
+    const p = part[i]; if (!IS_TUBE[p] || (!dx && TDX[p]) || dx * TDX[p] + dy * TDY[p] < 0) continue;
     // Vertical screws require the full width; horizontal screws use the nearest two-row lane.
     const x = (xx & ~3), y = entTubeLane(yy, e.iy);
     if (entTubeMove(e, x, TDX[p] || dy ? y : e.iy, true)) return true;
@@ -84,13 +88,14 @@ function entTubeTick(e, p) {
   const ci = (e.iy + 1) * W + e.ix + 1;
   if ((tick & 1) || netSat(ci) <= 0 || rnd() > netSat(ci)) return;
   const dx = TDX[p], dy = TDY[p];
+  if (dx && dy) { entDiagonalTubeTick(e, p); return; }
   let x = e.ix + dx, y = e.iy + dy, next = 0, ax = 0, ay = 0;
   for (let k = 0; k < (dx ? BAR_H : BAR_W); k++) {
     const i = entTubeEdge(e, dx, dy, k);
     if (i < 0) return;
     const xx = i % W, yy = (i / W) | 0;
     const q = part[i];
-    if (q >= P_TU && q <= P_TR && q !== p) { next = q; ax = xx; ay = yy; break; }
+    if (IS_TUBE[q] && q !== p) { next = q; ax = xx; ay = yy; break; }
   }
   if (next) {
     if (TDX[next] === -dx && TDY[next] === -dy) return;
@@ -105,6 +110,25 @@ function entTubeTick(e, p) {
   for (let yy = y; yy < y + BAR_H; yy++) for (let xx = x; xx < x + BAR_W; xx++) if (part[yy * W + xx]) return;
   if (entTubeMove(e, x, y)) { e.vx = dx ? dx * 0.5 : (rnd() - 0.5) * 0.4; e.vy = dy * 0.6; stats.moved++; }
 }
+// A horizontal bar stays whole: one diagonal block per four screw beats.
+function entDiagonalTubeTick(e, p) {
+  if (tick & 7) return;
+  const dx = TDX[p], dy = TDY[p], bx = e.ix & ~3, by = e.iy & ~3, lane = e.iy & 3;
+  for (const [ox, oy] of [[dx, dy], [dx, 0], [0, dy]]) {
+    const x = bx + ox * BS, y = by + oy * BS + lane, q = entTubeAt(x, y);
+    if (!q) continue;
+    if (TDX[q] * dx + TDY[q] * dy < 0) return;
+    if (entTubeMove(e, x, y, true)) stats.moved++;
+    return;
+  }
+  const x = bx + dx * BS;
+  let y = by + dy * BS + lane;
+  const belt = y >= 0 && y < H ? mat[y * W + x] : EMPTY;
+  if (dy > 0 && (belt === BELTL || belt === BELTR)) y = (y & ~3) - BAR_H;
+  if (!entTubeFree(x, y)) return;
+  for (let yy = y; yy < y + BAR_H; yy++) for (let xx = x; xx < x + BAR_W; xx++) if (part[yy * W + xx]) return;
+  if (entTubeMove(e, x, y, false, dy < 0)) { e.vx = dx * 0.5; e.vy = dy * 0.6; stats.moved++; }
+}
 function entTick() {
   for (let k = ents.length - 1; k >= 0; k--) {
     const e = ents[k];