Corner placements of screw conveyors stay separate ends (t62 follow-up)

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

docs/DESIGN.md

@@ -486,6 +486,11 @@ above, including:
   on warns first that the save will be marked, and the mark stays with the world; any future
   achievements won't unlock in a marked world. Besides money, items and upgrades it may have
   game speed and other things just for fun.
+- **Screw conveyors only join a diagonal on the same row (t62, 2026-10-27).** A straight screw
+  joins a diagonal when it sits right beside the diagonal's end block, and that join is drawn
+  as an elbow. When the diagonal instead starts one block lower or higher, so the two only touch
+  corner to corner, they stay two separate ends and nothing passes between them. The owner tried
+  a corner join and found it looked odd, and building it that way is unusual anyway.
 
 ## Ideas not built yet
 

docs/PROJECT_MAP.md

@@ -265,9 +265,9 @@ Pipes, pumps and outlets: each joined line holds one liquid as a count, not as g
 Per-tick machine work: steam engines, fans, belts, filters, screw conveyors (machinesTick).
 - functions: engineIntake, fanBlow, machinesTick
 
-### src/sim/conveyors.js (208 lines)
+### src/sim/conveyors.js (198 lines)
 How belts, filters and screw conveyors move what is on or in them. What rests on a belt or filter rides along: the whole stack standing on the carrying surface steps one cell toward d together (belts run front of the line first, so the way ahead is clear). If a powder grain is blocked, the load above it stands still and the belt slips underneath. A filter's own material drops through it instead, unless it is already full.
-- functions: conveyorStep, carryColumn, beltDrain, launchGrain, rebuildFilters, filterCarry, carryBeltsAndFilters, setFilter, filterRun, roomFor, screwSpread, screwIntake, straightScrewNext, diagonalScrewNext
+- functions: conveyorStep, carryColumn, beltDrain, launchGrain, rebuildFilters, filterCarry, carryBeltsAndFilters, setFilter, filterRun, roomFor, screwSpread, screwIntake, diagonalScrewNext
 - variables: CARRY_DEPTH, filterR, filterL, filtersDirty
 
 ### src/sim/slope-conveyors.js (230 lines)
@@ -284,7 +284,7 @@ Molds: cavities for castings; ingot troughs empty themselves below. Removal retu
 - functions: moldCellsAt, canPlaceMold, newMoldRecord, addMold, castMix, cavityState, troughState, clearCavity, moldPlugCells, rakeAbove, furnaceJunkHint, unplugMold, ejectIngot, checkMolds, moldAt, tally, collectMold, removeMold
 - variables: DROSS, grains, barWord
 
-### src/sim/items.js (295 lines)
+### src/sim/items.js (288 lines)
 Bars and other loose objects (ents), and the bag: adding, taking, costs and refunds.
 - functions: entSolidCell, entSupportCount, entFreeAt, entMark, spawnBar, removeEnt, entScrewAt, entScrewFree, entScrewMove, entScrewLane, entScrewEdge, entScrewEnter, entScrewTick, entDiagonalScrewTick, entSlopeBeltTick, entTick, entsInCircle, bagAdd, bagTake, giveOrDrop, refundAt, canAfford, payCost, fmtMoney, costText, needText
 - variables: BAR_W, BAR_H, entCurM, droppedLast
@@ -367,7 +367,7 @@ Drawing only: the face stays on its simulation cells; the band hangs below it.
 - functions: slopeBeltConnections, flatBeltCaps, prepareSlopeBelts, slopeBeltSegment, slopeBeltCorner, slopeBeltShape, slopeBeltAt, slopeBeltColor, screenLoaded, slopeWallShape, slopeWallAt, slopeDetailAt, slopePreviewCleat
 - variables: slopeBeltJoins, slopeBeltHalo, beltCaps, slopeAcross, slopeAlong, slopeDistance, slopeWallOwner
 
-### src/render/diagonal-screws.js (74 lines)
+### src/render/diagonal-screws.js (68 lines)
 Screw casing geometry shared by both looks, ghosts and placement previews. smooth-look class of a screw conveyor cell by direction: 9 up, 10 right, 11 down, 12 left
 - functions: diagonalScrewJoins, diagonalScrewShape, diagonalScrewBlock
 - variables: SCREW_CLASS, diagonalJoins, diagonalAcross, diagonalAlong, diagonalCap
@@ -393,7 +393,7 @@ Smooth look: WebGL setup, texture uploads, drawing and adaptive resolution.
 Smooth slope shading, kept beside the shared CPU geometry in slope-belts.js.
 - variables: SM_SLOPE_HELPERS, SM_SLOPE_DRAW
 
-### src/render/smooth-shaders.js (373 lines)
+### src/render/smooth-shaders.js (370 lines)
 Smooth shaders: vertex and fragment programs for the rounded world look.
 - variables: SM_VS, SM_FS
 
@@ -577,4 +577,4 @@ The frame loop and boot.
 - `tools/scenes/t35-joins.js`: Run after clear-sky.js. Paused, empty pipes make casing, flights and mouths easy to inspect.
 - `tools/scenes/t36-funnel.js`: A twelve-block funnel, one block open at the bottom, draining 400 grains of sand.
 - `tools/scenes/t40-sloped-belt.js`: Self-contained: a flat feed climbs, crosses the top, and runs downhill; a filter sorts below.
-- `tools/scenes/t62-joins.js`: Self-contained grid. Rows: UR, DR, DL, UL. Each run has both end joins. Columns: horizontal edge, horizontal corner, vertical edge, vertical corner; repeat those four with the straight travel reversed. Camera fits --zoom 6 --viewport 2100x1300. Run after clear-sky.js or by itself. Empty, paused screws expose the whole casing.
+- `tools/scenes/t62-joins.js`: Self-contained grid. Rows: UR, DR, DL, UL. Each run shows both ends. Columns: horizontal edge, horizontal corner, vertical edge, vertical corner. Corner columns stay unconnected, with two separate ends. Repeat those four with the straight travel reversed. Camera fits --zoom 6 --viewport 2100x1300. Run after clear-sky.js or by itself. Empty, paused screws expose the whole casing.

docs/agent-log.md

@@ -4,6 +4,19 @@ 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: t62 corner placements stay separate (Claude Code + Codex)
+
+- Owner tried the corner join and found the jog odd; decision (recorded in DESIGN.md): only
+  same-row joins connect. Removed join kinds 5/6 and `straightScrewNext`; `diagonalScrewNext`
+  and `entDiagonalScrewTick` now continue across a corner only into a diagonal running the same
+  way, so a corner straight piece no longer receives grains or bars. Kept the shared geometry
+  file and the smooth-look elbow seam fix.
+- Files: `src/render/diagonal-screws.js`, `src/render/smooth-shaders.js`, `src/sim/conveyors.js`,
+  `src/sim/items.js`, `src/sim/machine-tick.js`, `test/t_diag_screws.js`, `test/t_smooth.py`,
+  `tools/scenes/t62-joins.js`, `docs/PROJECT_MAP.md`, `docs/DESIGN.md`.
+- Tests: `python3 test/run_all.py --browser` all passed; determinism diff changed only the
+  replaced corner checks.
+
 ## 2026-10-27: t62 screw conveyor joins (Claude Code + Codex)
 
 - Straight screws touching a diagonal's end only at the corner now join, in both looks and in

src/render/diagonal-screws.js

@@ -5,7 +5,7 @@ for (let p = P_SCREW_UR; p <= P_SCREW_UL; p++) SCREW_CLASS[p] = 19 + p - P_SCREW
 // Drawing only: the four transport lanes remain in the square block.
 let diagonalJoins = new Uint8Array(0);
 function diagonalScrewJoins(bx, by, v, planned = null) {
-  // Three bits per end: 1..4 edge exits, 5/6 corner horizontal/vertical; bits 6/7 are collars.
+  // Three bits per end: 1..4 edge exits; bits 6/7 are collars.
   const dy = v === 4 || v === 6 ? -1 : 1;
   let joins = 0;
   for (let end = 0; end < 2; end++) {
@@ -23,7 +23,6 @@ function diagonalScrewJoins(bx, by, v, planned = null) {
       if ((code === BP_SCREW && nv < 4 && (nv & 1) === (dir & 1)) ||
           ((code === BP_BELT || code === BP_FILTER) && (dir & 1))) { join = dir + 1; break; }
     }
-    if (!join && nx >= 0 && ny >= 0 && nx < BW && ny < BH && nc === BP_SCREW && nv < 4) join = nv & 1 ? 5 : 6;
     joins |= join << (end * 3);
     if (!join) joins |= 64 << end;
   }
@@ -37,15 +36,10 @@ function diagonalScrewShape(x, y, b, v, joins) {
   for (let end = 0; end < 2; end++) {
     const join = (joins >> (end * 3)) & 7, side = end ? 1 : -1;
     const slope = v === 4 || v === 6 ? -1 : 1;
-    const dx = join >= 5 ? (join === 5 ? side : 0) : join ? SCREW_DIRS[join - 1][0] : side * Math.SQRT1_2;
+    const dx = join ? SCREW_DIRS[join - 1][0] : side * Math.SQRT1_2;
-    const dy = join >= 5 ? (join === 6 ? side * slope : 0) : join ? SCREW_DIRS[join - 1][1] : side * slope * Math.SQRT1_2;
+    const dy = join ? SCREW_DIRS[join - 1][1] : side * slope * Math.SQRT1_2;
-    const ox = join === 6 ? side * BS : 0, oy = join === 5 ? side * slope * BS : 0;
+    const along = lx * dx + ly * dy, across = -lx * dy + ly * dx;
-    const along = (lx - ox) * dx + (ly - oy) * dy, across = -(lx - ox) * dy + (ly - oy) * dx;
+    const radius = Math.hypot(across, Math.min(0, along));
-    let radius = Math.hypot(across, Math.min(0, along));
-    if (join >= 5) {
-      const t = Math.max(0, Math.min(1, (lx * ox + ly * oy) / (BS * BS)));
-      radius = Math.min(radius, Math.hypot(lx - ox * t, ly - oy * t));
-    }
     const cap = along - (join ? 2 : 2 * Math.SQRT2);
     const sd = Math.max(radius - 2, join || (joins & (64 << end)) ? cap : -10);
     if (sd < best) {

src/render/smooth-shaders.js

@@ -265,12 +265,9 @@ ${SM_SLOPE_DRAW}
         int join = (joins >> (end * 3)) & 7;
         float side = end == 0 ? -1.0 : 1.0;
         vec2 ray = join == 0 ? vec2(side, side * (nc == 19 || nc == 21 ? -1.0 : 1.0)) * 0.70710678 :
-          join == 5 ? vec2(side, 0) : join == 6 ? vec2(0, side * d.y) :
           join == 1 ? vec2(0, -1) : join == 2 ? vec2(1, 0) : join == 3 ? vec2(0, 1) : vec2(-1, 0);
-        vec2 offset = join == 5 ? vec2(0, side * d.y * 4.0) : join == 6 ? vec2(side * 4.0, 0) : vec2(0);
+        float t = dot(local, ray), cross2 = dot(local, vec2(-ray.y, ray.x));
-        float t = dot(local - offset, ray), cross2 = dot(local - offset, vec2(-ray.y, ray.x));
         float radius = length(vec2(cross2, min(0.0, t))), cap = t - (join == 0 ? 2.82842712 : 2.0);
-        if (join >= 5) radius = min(radius, length(local - offset * clamp(dot(local, offset) / 16.0, 0.0, 1.0)));
         // A connected mouth meets another opaque pipe; fading its edge leaves a seam.
         float sd = max(radius - 2.0, (joins & (64 << end)) != 0 ? cap : -10.0);
         if (sd < screwSD) {

src/sim/conveyors.js

@@ -176,20 +176,6 @@ function screwIntake(i, p, dx, dy) {
   }
 }
 
-// A straight mouth can feed a diagonal tail one block across the corner.
-function straightScrewNext(i, p) {
-  const dx = SCREW_DX[p], dy = SCREW_DY[p], x = i % W, y = (i / W) | 0;
-  const xx = x + dx, yy = y + dy, next = i + dx + dy * W;
-  if (xx < 0 || yy < 0 || xx >= W || yy >= H) return -1;
-  if (((xx >> 2) === (x >> 2) && (yy >> 2) === (y >> 2)) || part[next] || blockP[(yy >> 2) * BW + (xx >> 2)]) return next;
-  for (let side = -1; side <= 1; side += 2) {
-    const nx = xx + (dx ? 0 : side * BS), ny = yy + (dy ? 0 : side * BS);
-    if (nx < 0 || ny < 0 || nx >= W || ny >= H) continue;
-    const j = ny * W + nx, q = part[j];
-    if (SCREW_DX[q] === (dx || side) && SCREW_DY[q] === (dy || side)) return j;
-  }
-  return next;
-}
 // Four lanes cross a block in four beats; the casing carries every lane across the corner.
 // Prefer the next diagonal block, then either straight join, then the open head.
 function diagonalScrewNext(i, p) {
@@ -198,11 +184,15 @@ function diagonalScrewNext(i, p) {
   if (xx < 0 || xx >= W) return -1;
   if ((xx >> 2) === (x >> 2)) return i + dx;
   const yy = y + dy * BS;
-  if (yy >= 0 && yy < H && IS_SCREW[part[yy * W + xx]]) return yy * W + xx;
+  if (yy >= 0 && yy < H) {
+    const q = part[yy * W + xx];
+    if (q >= P_SCREW_UR && q <= P_SCREW_UL && SCREW_DX[q] === dx && SCREW_DY[q] === dy) return yy * W + xx;
+  }
   if (IS_SCREW[part[y * W + xx]]) return y * W + xx;
   if (dy > 0 && yy < H && (mat[yy * W + xx] === BELTL || mat[yy * W + xx] === BELTR)) return ((yy & ~3) - 1) * W + xx;
   const hy = by + (dy > 0 ? BS : -1), hx = bx + (y & 3);
   if (hy >= 0 && hy < H && IS_SCREW[part[hy * W + hx]]) return hy * W + hx;
   // An open mouth discharges along the diagonal, clear of the last block.
-  return yy >= 0 && yy < H ? yy * W + xx : -1;
+  // A corner screw is a separate end, not an open discharge cell.
+  return yy >= 0 && yy < H && !IS_SCREW[part[yy * W + xx]] ? yy * W + xx : -1;
 }

src/sim/items.js

@@ -90,13 +90,6 @@ function entScrewTick(e, p) {
   if ((tick & 1) || netSat(ci) <= 0 || rnd() > netSat(ci)) return;
   const dx = SCREW_DX[p], dy = SCREW_DY[p];
   if (dx && dy) { entDiagonalScrewTick(e, p); return; }
-  const edge = entScrewEdge(e, dx, dy, 0), behind = edge - dx - dy * W;
-  const corner = edge >= 0 ? straightScrewNext(behind, p) : -1;
-  if (corner >= 0 && corner !== edge) {
-    const x = (corner % W) & ~3, y = entScrewLane((corner / W) | 0, e.iy);
-    if (entScrewMove(e, x, y, true)) stats.moved++;
-    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 = entScrewEdge(e, dx, dy, k);
@@ -124,7 +117,7 @@ function entDiagonalScrewTick(e, p) {
   const dx = SCREW_DX[p], dy = SCREW_DY[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 = entScrewAt(x, y);
-    if (!q) continue;
+    if (!q || (ox && oy && (q < P_SCREW_UR || q > P_SCREW_UL || SCREW_DX[q] !== dx || SCREW_DY[q] !== dy))) continue;
     if (SCREW_DX[q] * dx + SCREW_DY[q] * dy < 0) return;
     if (entScrewMove(e, x, y, true)) stats.moved++;
     return;

src/sim/machine-tick.js

@@ -130,7 +130,7 @@ function machinesTick() {
         if (shifted) continue;
       }
       if (x + dx < 0 || x + dx >= W || y + dy < 0 || y + dy >= H) continue;
-      const dest = dx && dy ? diagonalScrewNext(i, p) : straightScrewNext(i, p);
+      const dest = dx && dy ? diagonalScrewNext(i, p) : i + dj;
       if (dest < 0) continue;
       const nx = dest % W, ny = (dest / W) | 0;
       if (nx < 0 || ny < 0 || nx >= W || ny >= H) continue;

test/t_diag_screws.js

@@ -48,38 +48,35 @@ for (const v of [4, 5, 6, 7]) {
   const joined = drain(c,500);
   check(`direction ${v}: straight to diagonal to straight`,joined.out===16 && joined.leaks===0,JSON.stringify(joined));
 }
-// Corner-adjacent joints: all axes, both ends, grains and queued bars.
+// Corner placements are separate mouths, on both axes and in either transfer direction.
-function cornerLine(v, vertical = false) {
+for (const v of [4,5,6,7]) for (const vertical of [false,true]) for (const fromDiagonal of [false,true]) {
-  const s = line(v), vv = vertical ? (s.dy < 0 ? 0 : 2) : (s.dx > 0 ? 1 : 3);
+  fresh();
-  const tx = s.bx-s.dx, ty = s.by-s.dy, hx = s.head+s.dx, hy = s.hy+s.dy;
+  const [dx,dy]=run(`SCREW_DIRS[${v}]`), sv=vertical?(dy<0?0:2):(dx>0?1:3);
-  run(`for(let k=0;k<3;k++) {
+  const sx=20+(fromDiagonal?0:-dx), sy=20+(fromDiagonal?0:-dy);
-    placeBlock(BP_SCREW,${vv},${tx}-k*${vertical?0:s.dx},${ty}-k*${vertical?s.dy:0},true);
+  const tx=20+(fromDiagonal?dx:0), ty=20+(fromDiagonal?dy:0);
-    placeBlock(BP_SCREW,${vv},${hx}+k*${vertical?0:s.dx},${hy}+k*${vertical?s.dy:0},true);
+  const source=fromDiagonal?v:sv, target=fromDiagonal?sv:v;
-  }`);
+  const label=`corner ${vertical?'vertical':'horizontal'} ${v} ${fromDiagonal?'diagonal to straight':'straight to diagonal'}`;
-  return {...s, tail:tx-2*(vertical?0:s.dx), by:ty-2*(vertical?s.dy:0),
+  run(`placeBlock(BP_SCREW,${source},${sx},${sy},true);placeBlock(BP_SCREW,${target},${tx},${ty},true);rebuildPower();`);
-    head:hx+2*(vertical?0:s.dx), hy:hy+2*(vertical?s.dy:0)};
+  rect(run,sx*4,sy*4,sx*4+3,sy*4+3,run('SAND'));
-}
+  const grains=run(`(()=>{let crossed=0;for(let k=0;k<80;k++){
-for(const v of [4,5,6,7]) for(const vertical of [false,true]) {
+    tick+=2;tickStamp++;machinesTick();
-  const s=cornerLine(v,vertical);
+    for(let i=0;i<N;i++)if(mat[i]===SAND){
-  rect(run,s.tail*4,s.by*4,s.tail*4+3,s.by*4+3,run("SAND"));
+      const x=i%W>>2,y=(i/W|0)>>2;
-  const r=run(`(()=>{let out=0,leak=0;for(let k=0;k<700;k++){
+      if(x===${tx} && y===${ty})crossed++;
-    simTick();
+      if(x!==${sx} || y!==${sy})setCell(i,EMPTY,20,0);
-    for(const f of flyers)if(f.m===SAND){
-      if(${vertical ? (s.dy<0?`f.y<${s.hy*4}`:`f.y>=${(s.hy+1)*4}`) : (s.dx<0?`f.x<${s.head*4}`:`f.x>=${(s.head+1)*4}`)})out++;else leak++;
     }flyers=[];
-  }return {out,leak,inside:mat.reduce((n,m)=>n+(m===SAND),0)};})()`);
+  }return crossed;})()`);
-  check(`corner ${vertical?"vertical":"horizontal"} joins ${v} carry every grain to the far mouth`,r.out===16 && !r.leak,JSON.stringify(r));
+  check(`${label} does not pass grains`,grains===0,grains);
-  cornerLine(v,vertical);
+  run('mat.forEach((m,i)=>{if(m===SAND)setCell(i,EMPTY,20,0);});');
-  putBar(s.tail*4,s.by*4); putBar(s.tail*4,s.by*4+2);
+  for(const lane of [0,1,2]) {
-  const bars=run(`(()=>{let out=0,overlap=false;for(let k=0;k<700;k++){
+    putBar(sx*4,sy*4+lane);
-    simTick();
+    const bar=run(`(()=>{const e=ents[0];let crossed=false;for(let k=0;k<80;k++){
-    for(let a=0;a<ents.length;a++)for(let b=0;b<a;b++) {
+      tick+=8;entMark(e,0);entScrewTick(e,SCREW_PARTS[${source}]);entMark(e,1);
-      const e=ents[a],f=ents[b];if(e.ix<f.ix+4 && f.ix<e.ix+4 && e.iy<f.iy+2 && f.iy<e.iy+2)overlap=true;
+      if((e.ix>>2)===${tx} && (e.iy>>2)===${ty})crossed=true;
-    }
+      if(!entScrewAt(e.ix,e.iy))break;
-    if(mat.some((m,i)=>occ[i] && (PH[m]===PH_SOLID || PH[m]===PH_POWDER)))overlap=true;
+    }removeEnt(e);return crossed;})()`);
-    for(const e of ents.slice())if(${vertical ? (s.dy<0?`e.iy+2<=${s.hy*4}`:`e.iy>=${(s.hy+1)*4}`) : (s.dx<0?`e.ix+4<=${s.head*4}`:`e.ix>=${(s.head+1)*4}`)}){out++;removeEnt(e);}
+    check(`${label} does not pass a bar in lane ${lane}`,!bar);
-  }return {out,overlap,left:ents.length};})()`);
+  }
-  check(`corner ${vertical?"vertical":"horizontal"} joins ${v} carry queued bars`,bars.out===2 && !bars.overlap,JSON.stringify(bars));
 }
 // A saturated ten-block line: 80 warmup ticks, then 600 measured ticks at 60 Hz.
 const rates = [];
@@ -208,9 +205,8 @@ for (const v of [4,5,6,7]) for (const end of [-1,1]) for (let dir=0;dir<4;dir++)
   fresh();
   const slope=v===4 || v===6?-1:1, nx=20+end, ny=20+end*slope, shift=end>0?3:0;
   run(`placeBlock(BP_SCREW,${v},20,20,true);placeBlock(BP_SCREW,${dir},${nx},${ny},true);`);
-  const expected=dir&1?5:6;
+  check(`corner ${v} end ${end} straight ${dir} keeps its free-end collar`,run(`(()=>{const j=diagonalScrewJoins(20,20,${v});return (j>>${shift}&7)===0 && !!(j&${end>0?128:64});})()`));
-  check(`corner ${v} end ${end} straight ${dir} selects a closed elbow`,run(`(()=>{const j=diagonalScrewJoins(20,20,${v});return (j>>${shift}&7)===${expected} && !(j&${end>0?128:64});})()`));
+  check(`corner ${v} end ${end} straight ${dir} leaves the free-end geometry unchanged`,run(`(()=>{const b=20*BW+20,j=diagonalScrewJoins(20,20,${v});removeBlock(${nx},${ny});const alone=diagonalScrewJoins(20,20,${v});placeBlock(BP_SCREW,${dir},${nx},${ny},true);return j===alone && [0.5,1.5,2.5,3.5].every(t=>diagonalScrewShape(82+${end}*2,80+t,b,${v},j)===diagonalScrewShape(82+${end}*2,80+t,b,${v},alone));})()`));
-  check(`corner ${v} end ${end} straight ${dir} meets all four mouth lanes`,run(`(()=>{const j=diagonalScrewJoins(20,20,${v});return [0.5,1.5,2.5,3.5].every(t=>diagonalScrewShape(${dir&1?82+end*1.99:"80+t+"+end*4},${dir&1?"80+t+"+end*slope*4:82+end*slope*1.99},20*BW+20,${v},j)<=0);})()`));
   check(`corner ${v} end ${end} straight ${dir} planned joins match placed joins`,run(`(()=>{const j=diagonalScrewJoins(20,20,${v});removeBlock(${nx},${ny});return diagonalScrewJoins(20,20,${v},new Map([[${ny}*BW+${nx},[BP_SCREW,${dir}]]]))===j;})()`));
 }
 for (const v of [4,5,6,7]) for (let dir=0;dir<4;dir++) for (const code of ['BP_SCREW','BP_BELT','BP_FILTER']) {

test/t_smooth.py

@@ -97,34 +97,58 @@ with sync_playwright() as p:
     }''')
     check('sidewall stays behind the grain colour in pixels and smooth',
           wall and wall['colors'][0] == wall['colors'][1] and wall['grainClass'] == 2, wall)
-    # All 64 straight/diagonal mouths must have copper casing on both sides of the join.
+    # Edge joins keep closed elbows; corner placements match two isolated free ends.
     pg.set_viewport_size({"width": 2100, "height": 1300})
     ev("part.fill(0); blockP.fill(0); occ.fill(0); mach.fill(0); ents=[]; ghostBlocks.clear();")
     ev("() => {" + (root / "tools/scenes/t62-joins.js").read_text() + "}")
     mouths = ev('''() => {
       SET.zoom=6; SET.lighting="off"; SET.glow="off"; resizeRender();
       bot.x=CAM[0]-bot.w/2;bot.y=CAM[1]-bot.h/2;snapCamera();
-      const out={};
+      const now=performance.now.bind(performance),frozen=now();
-      for(const look of ["pixel","smooth"]) {
+      performance.now=()=>frozen;
-        SET.look=look;SM.scale=1;drawWorld();
+      try {
-        const bad=[];
+        const out={};
-        for(const j of T62_JOINTS) {
+        const draw=()=>{SM.scale=1;drawWorld();};
-          const slope=j.v===4 || j.v===6?-1:1;
+        for(const look of ["pixel","smooth"]) {
-          const end=j.end*SCREW_DIRS[j.v][0];
+          SET.look=look;draw();
-          const dx=j.vertical?0:end,dy=j.vertical?end*slope:0;
+          const bad=[];
-          const ox=j.corner && j.vertical?end*4:0,oy=j.corner && !j.vertical?end*slope*4:0;
+          for(const j of T62_JOINTS) {
-          for(const side of [-1,1])for(const along of [-0.3,0.3]) {
+            const slope=j.v===4 || j.v===6?-1:1;
-            const x=j.bx*4+2+ox+dx*(2+along)-dy*side*1.6;
+            const end=j.end*SCREW_DIRS[j.v][0];
-            const y=j.by*4+2+oy+dy*(2+along)+dx*side*1.6;
+            const dx=j.vertical?0:end,dy=j.vertical?end*slope:0;
-            const p=worldToScreenPx(x,y),c=R.ctx.getImageData(Math.floor(p.x),Math.floor(p.y),1,1).data;
+            if(j.corner)continue;
-            if(!(c[0]>c[1]*1.15 && c[1]>c[2]*1.1))bad.push([j,x,y,Array.from(c)]);
+            for(const side of [-1,1])for(const along of [-0.3,0.3]) {
+              const x=j.bx*4+2+dx*(2+along)-dy*side*1.6;
+              const y=j.by*4+2+dy*(2+along)+dx*side*1.6;
+              const p=worldToScreenPx(x,y),c=R.ctx.getImageData(Math.floor(p.x),Math.floor(p.y),1,1).data;
+              if(!(c[0]>c[1]*1.15 && c[1]>c[2]*1.1))bad.push([j,x,y,Array.from(c)]);
+            }
           }
-        }
+          const sample=(bx,by)=>{
-        out[look]=bad;
+            const colors=[];
-      }return out;
+            for(let y=0;y<4;y++)for(let x=0;x<4;x++) {
+              const p=worldToScreenPx(bx*4+x+0.5,by*4+y+0.5);
+              colors.push(...R.ctx.getImageData(Math.floor(p.x),Math.floor(p.y),1,1).data);
+            }return colors.join(',');
+          };
+          for(const j of T62_JOINTS.filter(j=>j.corner)) {
+            const [dx,dy]=SCREW_DIRS[j.v],sx=j.bx+j.end*dx,sy=j.by+j.end*dy;
+            const collar=sample(j.bx,j.by),straight=sample(sx,sy);
+            const joins=diagonalScrewJoins(j.bx,j.by,j.v),end=j.end*dx>0?1:0;
+            if(!(joins & (64<<end)) || (joins>>(end*3)&7))bad.push(['missing collar',j]);
+            removeBlock(sx,sy);draw();
+            if(sample(j.bx,j.by)!==collar)bad.push(['diagonal differs from isolated end',j]);
+            placeBlock(BP_SCREW,j.straight,sx,sy,true);
+            removeBlock(j.bx,j.by);draw();
+            if(sample(sx,sy)!==straight)bad.push(['straight differs from normal end',j]);
+            placeBlock(BP_SCREW,j.v,j.bx,j.by,true);draw();
+          }
+          out[look]=bad;
+        }return out;
+      } finally {performance.now=now;}
     }''')
     for look, bad in mouths.items():
-        check(f"{look}: all 64 screw joints have closed casing across both mouth edges", not bad, bad[:2])
+        check(f"{look}: edge elbows stay closed and corners show two separate free ends", not bad, bad[:2])
     # a browser without hardware drawing gets the pixel look and a note
     pg2 = b.new_page(viewport={'width': 800, 'height': 500})
     pg2.add_init_script('localStorage.clear();')

tools/scenes/t62-joins.js

@@ -1,6 +1,7 @@
-// Self-contained grid. Rows: UR, DR, DL, UL. Each run has both end joins.
+// Self-contained grid. Rows: UR, DR, DL, UL. Each run shows both ends.
-// Columns: horizontal edge, horizontal corner, vertical edge, vertical corner;
+// Columns: horizontal edge, horizontal corner, vertical edge, vertical corner.
-// repeat those four with the straight travel reversed. Camera fits --zoom 6 --viewport 2100x1300.
+// Corner columns stay unconnected, with two separate ends.
+// Repeat those four with the straight travel reversed. Camera fits --zoom 6 --viewport 2100x1300.
 // Run after clear-sky.js or by itself. Empty, paused screws expose the whole casing.
 money = 50000;
 for (let y = 64; y < 280; y++) for (let x = 112; x < 456; x++) {