Same-row belt feed into an uphill low end draws as two capped ends (t67)

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

docs/DESIGN.md

@@ -500,6 +500,12 @@ above, including:
   belt one block below an uphill belt's low end also feeds it. The owner first approved a rule
   based only on shape, then found in testing that horizontal → uphill and vertical → diagonal
   didn't join the way the other pieces did.
+- **Warehouses replace the trade dock, eventually (t68, 2026-10-27).** The dock only exists to
+  get selling working for testing; the owner finds it unengaging. The plan: a warehouse at each
+  edge of the map, on indestructible ground, served by a road and trucks. Warehouses accept
+  loose grain as well as packaged goods (pallets, barrels or sacks from packaging machines).
+  Trucks matter to play, not just looks: what's waiting is collected when a truck comes, on its
+  schedule. How the player learns where the warehouses are is still open.
 
 ## Ideas not built yet
 

docs/agent-log.md

@@ -4,6 +4,16 @@ What agents have done, newest first. Add an entry for every piece of work: the d
 note or request it was for, what changed, the files touched, the tests run, and anything left
 open or not verified. Keep each entry short; the git history has the details.
 
+## 2026-10-27: t67 belt drop drawn as two capped ends (Claude Code)
+
+- A flat belt feeding an uphill belt's low end on the same row (and two uphill slopes side by
+  side) stays joined, but grains really drop about 3 grains onto the face there, so it now
+  draws as two capped ends instead of the bridge phase 2b drew (it overlapped and stepped
+  badly). `beltDrop` in `src/render/slope-belts.js` decides it for `slopeBeltConnections` and
+  `flatBeltCaps`; the shader and `world.js` packing went back to their pre-2b versions.
+- Tests: `t_joins.js` and `t_smooth.py` drop checks updated; the existing sand test confirms
+  the same-row feed carries sand up. `python3 test/run_all.py --browser` all passed.
+
 ## 2026-10-27: t67 phase 2b, joins follow the travel direction (Claude Code + Codex)
 
 - The owner tested phase 2: horizontal → uphill and vertical-up → diagonal didn't join like the
@@ -19,9 +29,8 @@ open or not verified. Keep each entry short; the git history has the details.
   `src/render/world.js`, `src/ui/previews.js`, `tools/scenes/joins.js`, tests `t_joins.js`,
   `t_diag_screws.js`, `t_slope_belt_art.js`, `t_smooth.py`, `docs/PROJECT_MAP.md`.
 - Tests: `python3 test/run_all.py --browser` all passed.
-- Open: Codex hit its usage limit before finishing. A flat belt feeding an uphill belt on the
+- Open: Codex hit its usage limit before finishing; the belt drop drawing was finished in the
-  same row is joined but draws badly in the smooth look (overlapping casing, stepped edges;
+  next entry. Not playtested.
-  `shots/joins-belt-drop-smooth.png`). Not playtested; determinism diff not re-run by hand.
 
 ## 2026-10-27: t67 phase 2, screw conveyors follow the join rule (Claude Code + Codex)
 

src/render/slope-belt-shader.js

@@ -23,27 +23,13 @@ vec3 slopeShape(vec2 p, vec2 worldOrigin, float grade, int joins) {
   vec2 axis = vec2(1.0, grade) * 0.70710678;
   vec3 best = slopeStroke(p, a, b, dot(worldOrigin + a, axis));
   if ((joins & 1) != 0) {
-    vec3 h;
+    vec3 h = slopeStroke(p, vec2(-2.0, a.y), a, worldOrigin.x - 2.0);
-    if ((joins & 128) != 0 && grade < 0.0) {
-      h = slopeStroke(p, vec2(-2, 2), vec2(0, 2), worldOrigin.x - 2.0);
-      if (h.x < best.x) best = h;
-      h = slopeStroke(p, vec2(0, 2), vec2(0, a.y), worldOrigin.x);
-      if (h.x < best.x) best = h;
-      h = slopeStroke(p, vec2(0, a.y), a, worldOrigin.x);
-    } else 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;
+    vec3 h = slopeStroke(p, b, vec2(6, b.y), worldOrigin.x + b.x);
-    if ((joins & 128) != 0 && grade > 0.0) {
-      h = slopeStroke(p, b, vec2(4, b.y), worldOrigin.x + b.x);
-      if (h.x < best.x) best = h;
-      h = slopeStroke(p, vec2(4, b.y), vec2(4, 2), worldOrigin.x + 4.0);
-      if (h.x < best.x) best = h;
-      h = slopeStroke(p, vec2(4, 2), vec2(6, 2), worldOrigin.x + 4.0);
-    } else 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;
@@ -91,9 +77,8 @@ const SM_SLOPE_DRAW = `
     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 packedX = int(tag.g * 255.0 + 0.5);
+    int joins = int(tag.a * 255.0 + 0.5);
-    int joins = (int(tag.a * 255.0 + 0.5) & 127) | (packedX & 128);
+    vec2 local = floor(tag.gb * 255.0 + 0.5) - 8.0 + fract(w);
-    vec2 local = vec2(float(packedX & 127), floor(tag.b * 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;

src/render/slope-belts.js

@@ -7,16 +7,26 @@ function slopeBeltConnections(bx, by, code, planned = null) {
     const join = endJoin(bx, by, end, planned);
     if (join < 0) continue;
     const nb = join >> 1, next = planned && planned.get(nb);
-    const slope = isSlopeBelt(next ? next[0] : blockP[nb]) &&
+    const pcode = next ? next[0] : blockP[nb];
-      ((nb / BW) | 0) - by === beltGrade(code) * (nb % BW - bx);
+    const slope = isSlopeBelt(pcode) && ((nb / BW) | 0) - by === beltGrade(code) * (nb % BW - bx);
+    // A same-row feed into a low end drops onto its face: drawn as two capped ends, still joined.
+    if (!slope && beltDrop(nb, by, beltGrade(code) * (end ? 1 : -1) > 0, pcode, join & 1)) continue;
     joins |= (slope ? 4 : 1) << end;
-    if (!slope && beltGrade(code) * (end ? 1 : -1) > 0 &&
-        ((nb / BW) | 0) === by) joins |= 128; // low-end feed drops from the same-row flat
   }
   return joins;
 }
+// Does a same-row join between a piece in row `by` and block nb meet a slope's low end?
+function beltDrop(nb, by, ownLow, pcode, pend) {
+  return ((nb / BW) | 0) === by && (ownLow || beltGrade(pcode) * (pend ? 1 : -1) > 0);
+}
 function flatBeltCaps(b, planned = null) {
-  return 3 ^ pieceJoins(b % BW, (b / BW) | 0, planned);
+  const bx = b % BW, by = (b / BW) | 0;
+  let caps = 0;
+  for (let end = 0; end < 2; end++) {
+    const join = endJoin(bx, by, end, planned), nb = join >> 1, next = planned && planned.get(nb);
+    if (join < 0 || beltDrop(nb, by, false, next ? next[0] : blockP[nb], join & 1)) caps |= 1 << end;
+  }
+  return caps;
 }
 function prepareSlopeBelts(x0, y0, x1, y1) {
   if (slopeBeltJoins.length !== NB) { slopeBeltJoins = new Uint8Array(NB); slopeBeltHalo = new Uint8Array(NB); beltCaps = new Uint8Array(NB); }
@@ -60,19 +70,11 @@ function slopeBeltShape(x, y, b, joins = slopeBeltJoins[b], code = blockP[b]) {
   const origin = (ox + grade * oy) * Math.SQRT1_2;
   slopeBeltSegment(x, y, ax, ay, bx, by, origin + (ax + grade * ay) * Math.SQRT1_2);
   if (joins & 1) {
-    if ((joins & 128) && grade < 0) {
+    slopeBeltSegment(x, y, -2, ay, ax, ay, ox - 2);
-      slopeBeltSegment(x, y, -2, 2, 0, 2, ox - 2);
-      slopeBeltSegment(x, y, 0, 2, 0, ay, ox);
-      slopeBeltSegment(x, y, 0, ay, ax, ay, ox);
-    } else slopeBeltSegment(x, y, -2, ay, ax, ay, ox - 2);
     slopeBeltCorner(x, y, ax, ay, ox + ax);
   }
   if (joins & 2) {
-    if ((joins & 128) && grade > 0) {
+    slopeBeltSegment(x, y, bx, by, 6, by, ox + bx);
-      slopeBeltSegment(x, y, bx, by, 4, by, ox + bx);
-      slopeBeltSegment(x, y, 4, by, 4, 2, ox + 4);
-      slopeBeltSegment(x, y, 4, 2, 6, 2, ox + 4);
-    } else slopeBeltSegment(x, y, bx, by, 6, by, ox + bx);
     slopeBeltCorner(x, y, bx, by, ox + bx);
   }
   return slopeDistance;

src/render/world.js

@@ -279,9 +279,8 @@ function drawWorld() {
           const slopeClass = 23 + (code - BP_BELT_UP) * 2 + dir;
           if (slopeArt) cl = slopeClass;
           const f = isFilter(code) && filterCfg.get(sb), fm = f && f.m.length ? f.m[(Math.floor((x + beltGrade(code) * y) / 2) & 65535) % f.m.length] : 0;
-          // Alpha bit 128 marks slope tags; the spare high bit of local X carries the drop.
           tpx[row + bx] = ((slopeBeltJoins[sb] | 128) << 24) | slopeClass |
-            ((y - ((sb / BW) | 0) * BS + 8) << 16) | (((x - (sb % BW) * BS + 8) | (slopeBeltJoins[sb] & 128)) << 8);
+            ((y - ((sb / BW) | 0) * BS + 8) << 16) | ((x - (sb % BW) * BS + 8) << 8);
           if (slopeArt) { r = fm ? COLR[fm] : 0; g = fm ? COLG[fm] : 0; b = fm ? COLB[fm] : 0; }
         }
         if (slopeDetail && slopeWallOwner >= 0) {

test/t_joins.js

@@ -123,15 +123,15 @@ check('a flat belt picks the same-row uphill inlet before the below-low-end exce
   for(const n of [b,b+1,b-BW+1]){blockP[n]=n===b?BP_BELT:BP_BELT_UP;blockV[n]=1;}
   return endJoin(10,10,1)===(b+1)*2&&endJoin(11,9,0)===-1;
 })()`));
-check('same-row uphill low end draws the drop in placed and planned geometry',run(`(()=>{
+check('same-row uphill low end draws as two capped ends in placed and planned geometry',run(`(()=>{
   blockP.fill(0);blockV.fill(0);const b=10*BW+10;
   const p=new Map([[b,[BP_BELT_UP,1]],[b-1,[BP_BELT,1]]]);
   const j=slopeBeltConnections(10,10,BP_BELT_UP,p);
-  return j===129&&slopeBeltShape(40.5,43,b,j,BP_BELT_UP)<0&&flatBeltCaps(b-1,p)===1;
+  return j===0&&endJoin(10,10,0,p)>=0&&flatBeltCaps(b-1,p)===3;
 })()`));
-check('uphill same-row slope joins draw a high elbow and a low drop',run(`(()=>{
+check('uphill slopes side by side on one row are joined but drawn as two capped ends',run(`(()=>{
   blockP.fill(0);blockV.fill(0);const b=10*BW+10,p=new Map([[b,[BP_BELT_UP,1]],[b+1,[BP_BELT_UP,1]]]);
-  return slopeBeltConnections(10,10,BP_BELT_UP,p)===2&&slopeBeltConnections(11,10,BP_BELT_UP,p)===129;
+  return endJoin(10,10,1,p)>=0&&slopeBeltConnections(10,10,BP_BELT_UP,p)===0&&slopeBeltConnections(11,10,BP_BELT_UP,p)===0;
 })()`));
 // Downhill face-to-face transfers (screens always travel downhill when placed).
 for(const grade of [-1,1])for(const filter of [false,true])for(const outgoing of [false,true])for(const joined of [false,true]) {

test/t_smooth.py

@@ -212,7 +212,7 @@ with sync_playwright() as p:
       } finally {slopeDetailAt=detail;performance.now=now;}
     }""")
     for look, (joined, free) in drops.items():
-        check(f'{look}: the same-row uphill inlet draws its drop above the low face', joined != free and joined[2] < free[2], [joined, free])
+        check(f'{look}: the same-row uphill inlet is a drop, drawn like a free low end', joined == free, [joined, free])
     filter_plans = ev("""() => {
       const saved={...GAME},original=slopeBeltConnections,seen=[];
       try {