Screw conveyors join across the corner to diagonals (t62)

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

docs/PROJECT_MAP.md

@@ -134,6 +134,7 @@ dist/, shots/         build output and screenshots (not committed)
 
 - **The pixel look:**
   - `drawWorld` (`src/render/world.js`) fills one pixel per grain;
+  - `diagonal-screws.js` shares screw join and casing geometry between pixels, smooth shading tags and previews;
   - `computeLight` (`light.js`) adds coloured light;
   - overlays (machines, molds, the bot, rain, arrows) are drawn on the 2D canvas afterwards
     (`machines.js`, `overlays.js`).
@@ -264,9 +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 (194 lines)
+### src/sim/conveyors.js (208 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, diagonalScrewNext
+- functions: conveyorStep, carryColumn, beltDrain, launchGrain, rebuildFilters, filterCarry, carryBeltsAndFilters, setFilter, filterRun, roomFor, screwSpread, screwIntake, straightScrewNext, diagonalScrewNext
 - variables: CARRY_DEPTH, filterR, filterL, filtersDirty
 
 ### src/sim/slope-conveyors.js (230 lines)
@@ -283,7 +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 (288 lines)
+### src/sim/items.js (295 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
@@ -366,11 +367,15 @@ 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/world.js (458 lines)
-Scale colour without changing the smooth-look class.
-- functions: fogColor, diagonalScrewJoins, diagonalScrewShape, diagonalScrewBlock, drawWorld
+### src/render/diagonal-screws.js (74 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
 
+### src/render/world.js (402 lines)
+Scale colour without changing the smooth-look class.
+- functions: fogColor, drawWorld
+
 ### src/render/machines.js (256 lines)
 Machine overlays: fans, engines, silo and the rest, drawn on top of the world.
 - functions: cellRect, drawHazardRims, drawMachines, drawProcBlocks, drawSilo, drawSiloPixel, drawSiloWindow, drawRackBlocks
@@ -388,7 +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 (369 lines)
+### src/render/smooth-shaders.js (373 lines)
 Smooth shaders: vertex and fragment programs for the rounded world look.
 - variables: SM_VS, SM_FS
 
@@ -481,7 +486,7 @@ Gamepad input.
 - functions: padPressed, pollPad
 - variables: PAD
 
-### src/ui/previews.js (250 lines)
+### src/ui/previews.js (239 lines)
 Cursor previews: shared grid helpers, air streaks and tool preview dispatch.
 - functions: blockRectPx, drawGrid, previewColor, drawAirStreaks, drawReachCircle, drawPreviews, previewBlock
 
@@ -572,3 +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.

docs/agent-log.md

@@ -4,6 +4,21 @@ 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 screw conveyor joins (Claude Code + Codex)
+
+- Straight screws touching a diagonal's end only at the corner now join, in both looks and in
+  ghosts/previews, and grains and bars cross the joint. Same-row joins were already elbows.
+  Also removed the seam across the top of connected elbows in the smooth look.
+- Files: new `src/render/diagonal-screws.js` (join and casing geometry moved out of
+  `src/render/world.js`), `src/render/smooth-shaders.js`, `src/ui/previews.js`,
+  `src/sim/conveyors.js` (`straightScrewNext`), `src/sim/machine-tick.js`, `src/sim/items.js`,
+  `src/manifest.json`, `docs/PROJECT_MAP.md`, `tools/scenes/t62-joins.js`, tests
+  `test/t_diag_screws.js`, `test/t_smooth.py`.
+- Tests: `python3 test/run_all.py --browser` all passed; determinism diff showed only timing
+  lines and the new checks.
+- Open: the corner join doesn't check that the straight piece ends there, so a straight run
+  passing over the diagonal's corner also draws a jog. Not playtested by hand.
+
 ## 2026-10-27: t66 dev console in every build (Claude Code)
 
 - Owner decision: the console ships in production too, with a warning when it's turned on that

src/manifest.json

@@ -43,6 +43,7 @@
     "render/setup.js",
     "render/light.js",
     "render/slope-belts.js",
+    "render/diagonal-screws.js",
     "render/world.js",
     "render/machines.js",
     "render/overlays.js",

src/render/diagonal-screws.js

@@ -0,0 +1,74 @@
+// 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
+const SCREW_CLASS = new Uint8Array(15); SCREW_CLASS[1] = 9; SCREW_CLASS[4] = 10; SCREW_CLASS[2] = 11; SCREW_CLASS[3] = 12;
+for (let p = P_SCREW_UR; p <= P_SCREW_UL; p++) SCREW_CLASS[p] = 19 + p - P_SCREW_UR;
+// 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.
+  const dy = v === 4 || v === 6 ? -1 : 1;
+  let joins = 0;
+  for (let end = 0; end < 2; end++) {
+    const side = end ? 1 : -1, nx = bx + side, ny = by + side * dy;
+    const nb = ny * BW + nx, next = planned && planned.get(nb);
+    const nc = next ? next[0] : blockP[nb], nv = next ? next[1] : blockV[nb];
+    if (nx >= 0 && ny >= 0 && nx < BW && ny < BH &&
+        nc === BP_SCREW && nv >= 4 && (nv === 4 || nv === 6) === (dy < 0)) continue;
+    let join = 0;
+    for (const dir of [side > 0 ? 1 : 3, side * dy > 0 ? 2 : 0]) {
+      const x = bx + SCREW_DIRS[dir][0], y = by + SCREW_DIRS[dir][1];
+      if (x < 0 || y < 0 || x >= BW || y >= BH) continue;
+      const n = y * BW + x, next = planned && planned.get(n);
+      const code = next ? next[0] : blockP[n], nv = next ? next[1] : blockV[n];
+      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;
+  }
+  return joins;
+}
+// Scratch coordinates shared by the pixel shading; no allocations in the grain loop.
+let diagonalAcross = 0, diagonalAlong = 0, diagonalCap = 0;
+function diagonalScrewShape(x, y, b, v, joins) {
+  const lx = x - (b % BW) * BS - 2, ly = y - ((b / BW) | 0) * BS - 2;
+  let best = Infinity;
+  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 dy = join >= 5 ? (join === 6 ? side * slope : 0) : 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 - ox) * dx + (ly - oy) * dy, across = -(lx - ox) * dy + (ly - oy) * dx;
+    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) {
+      best = sd; diagonalAcross = side * across < 0 ? -radius : radius;
+      diagonalAlong = ((b % BW) * BS + 2 + (((b / BW) | 0) * BS + 2) * (v === 4 || v === 6 ? -1 : 1)) * Math.SQRT1_2 + side * along; diagonalCap = joins & (64 << end) ? cap : -10;
+    }
+  }
+  return best;
+}
+function diagonalScrewBlock(x, y, smooth) {
+  const i = y * W + x, own = (y >> 2) * BW + (x >> 2);
+  if (part[i] >= P_SCREW_UR && part[i] <= P_SCREW_UL) return own;
+  if (mat[i] !== EMPTY || part[i] || mach[i] || occ[i] || blockP[own]) return -1;
+  let best = smooth ? 0.75 : 0, found = -1;
+  for (let k = 0; k < 4; k++) {
+    const bx = (x >> 2) + (k === 0 ? -1 : k === 1 ? 1 : 0);
+    const by = (y >> 2) + (k === 2 ? -1 : k === 3 ? 1 : 0);
+    if (bx < 0 || by < 0 || bx >= BW || by >= BH) continue;
+    const b = by * BW + bx, v = blockV[b];
+    if (blockP[b] !== BP_SCREW || v < 4) continue;
+    const joins = diagonalJoins[b] === undefined ? diagonalScrewJoins(bx, by, v) : diagonalJoins[b];
+    const sd = diagonalScrewShape(x + 0.5, y + 0.5, b, v, joins);
+    if (sd <= best) { best = sd; found = b; }
+  }
+  return found;
+}

src/render/smooth-shaders.js

@@ -265,10 +265,14 @@ ${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);
-        float t = dot(local, ray), cross2 = dot(local, vec2(-ray.y, ray.x));
+        vec2 offset = join == 5 ? vec2(0, side * d.y * 4.0) : join == 6 ? vec2(side * 4.0, 0) : vec2(0);
+        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);
-        float sd = max(radius - 2.0, join != 0 || (joins & (64 << end)) != 0 ? cap : -10.0);
+        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) {
           screwSD = sd;
           a = 2.0 + (side * cross2 < 0.0 ? -radius : radius);

src/render/world.js

@@ -2,71 +2,6 @@
 function fogColor(c, k) { return (c & 0xff000000) | (((c >>> 16 & 255) * k) << 16) | (((c >>> 8 & 255) * k) << 8) | ((c & 255) * k); }
 // drawWorld: the per-grain pixel buffer (pixel look), also the input of the smooth look.
 // ---------- World pixels ----------
-// smooth-look class of a screw conveyor cell by direction: 9 up, 10 right, 11 down, 12 left
-const SCREW_CLASS = new Uint8Array(15); SCREW_CLASS[1] = 9; SCREW_CLASS[4] = 10; SCREW_CLASS[2] = 11; SCREW_CLASS[3] = 12;
-for (let p = P_SCREW_UR; p <= P_SCREW_UL; p++) SCREW_CLASS[p] = 19 + p - P_SCREW_UR;
-// Drawing only: the four transport lanes remain in the square block.
-let diagonalJoins = new Uint8Array(0);
-function diagonalScrewJoins(bx, by, v, planned = null) {
-  // Low/high three bits select the two edge exits; bits 6/7 mark free-end collars.
-  const dy = v === 4 || v === 6 ? -1 : 1;
-  let joins = 0;
-  for (let end = 0; end < 2; end++) {
-    const side = end ? 1 : -1, nx = bx + side, ny = by + side * dy;
-    const nb = ny * BW + nx, next = planned && planned.get(nb);
-    const nc = next ? next[0] : blockP[nb], nv = next ? next[1] : blockV[nb];
-    if (nx >= 0 && ny >= 0 && nx < BW && ny < BH &&
-        nc === BP_SCREW && nv >= 4 && (nv === 4 || nv === 6) === (dy < 0)) continue;
-    let join = 0;
-    for (const dir of [side > 0 ? 1 : 3, side * dy > 0 ? 2 : 0]) {
-      const x = bx + SCREW_DIRS[dir][0], y = by + SCREW_DIRS[dir][1];
-      if (x < 0 || y < 0 || x >= BW || y >= BH) continue;
-      const n = y * BW + x, next = planned && planned.get(n);
-      const code = next ? next[0] : blockP[n], nv = next ? next[1] : blockV[n];
-      if ((code === BP_SCREW && nv < 4 && (nv & 1) === (dir & 1)) ||
-          ((code === BP_BELT || code === BP_FILTER) && (dir & 1))) { join = dir + 1; break; }
-    }
-    joins |= join << (end * 3);
-    if (!join) joins |= 64 << end;
-  }
-  return joins;
-}
-// Scratch coordinates shared by the pixel shading; no allocations in the grain loop.
-let diagonalAcross = 0, diagonalAlong = 0, diagonalCap = 0;
-function diagonalScrewShape(x, y, b, v, joins) {
-  const lx = x - (b % BW) * BS - 2, ly = y - ((b / BW) | 0) * BS - 2;
-  let best = Infinity;
-  for (let end = 0; end < 2; end++) {
-    const join = (joins >> (end * 3)) & 7, side = end ? 1 : -1;
-    const dx = join ? SCREW_DIRS[join - 1][0] : side * Math.SQRT1_2;
-    const dy = join ? SCREW_DIRS[join - 1][1] : side * (v === 4 || v === 6 ? -1 : 1) * Math.SQRT1_2;
-    const along = lx * dx + ly * dy, across = -lx * dy + ly * dx;
-    const radius = Math.hypot(across, Math.min(0, along)), cap = along - (join ? 2 : 2 * Math.SQRT2);
-    const sd = Math.max(radius - 2, join || (joins & (64 << end)) ? cap : -10);
-    if (sd < best) {
-      best = sd; diagonalAcross = side * across < 0 ? -radius : radius;
-      diagonalAlong = ((b % BW) * BS + 2 + (((b / BW) | 0) * BS + 2) * (v === 4 || v === 6 ? -1 : 1)) * Math.SQRT1_2 + side * along; diagonalCap = joins & (64 << end) ? cap : -10;
-    }
-  }
-  return best;
-}
-function diagonalScrewBlock(x, y, smooth) {
-  const i = y * W + x, own = (y >> 2) * BW + (x >> 2);
-  if (part[i] >= P_SCREW_UR && part[i] <= P_SCREW_UL) return own;
-  if (mat[i] !== EMPTY || part[i] || mach[i] || occ[i] || blockP[own]) return -1;
-  let best = smooth ? 0.75 : 0, found = -1;
-  for (let k = 0; k < 4; k++) {
-    const bx = (x >> 2) + (k === 0 ? -1 : k === 1 ? 1 : 0);
-    const by = (y >> 2) + (k === 2 ? -1 : k === 3 ? 1 : 0);
-    if (bx < 0 || by < 0 || bx >= BW || by >= BH) continue;
-    const b = by * BW + bx, v = blockV[b];
-    if (blockP[b] !== BP_SCREW || v < 4) continue;
-    const joins = diagonalJoins[b] === undefined ? diagonalScrewJoins(bx, by, v) : diagonalJoins[b];
-    const sd = diagonalScrewShape(x + 0.5, y + 0.5, b, v, joins);
-    if (sd <= best) { best = sd; found = b; }
-  }
-  return found;
-}
 function drawWorld() {
   const bw = R.bw, bh = R.bh, px = R.px;
   R.vx0 = Math.floor(R.camX); R.vy0 = Math.floor(R.camY);
@@ -404,9 +339,18 @@ function drawWorld() {
       let tr = 90, tg = 190, tb = 230;
       if (blocked) { tr = 230; tg = 70; tb = 60; }
       else if (isWall(code) && WALL_OF[v]) { const wm = WALL_OF[v]; tr = (COLR[wm] + 90) / 2; tg = (COLG[wm] + 190) / 2; tb = (COLB[wm] + 230) / 2; }
-      const slope = isSlopeBelt(code), joins = slope ? slopeBeltConnections(gbx, gby, code, ghostBlocks) : 0;
-      for (let dy = slope ? -9 : 0; dy < (slope ? 8 : BS); dy++) for (let dx = slope ? -5 : 0; dx < (slope ? 9 : BS); dx++) {
+      const slope = isSlopeBelt(code), diagonal = code === BP_SCREW && v >= 4;
+      const joins = slope ? slopeBeltConnections(gbx, gby, code, ghostBlocks) : diagonal ? diagonalScrewJoins(gbx, gby, v, ghostBlocks) : 0;
+      for (let dy = slope ? -9 : diagonal ? -4 : 0; dy < (slope || diagonal ? 8 : BS); dy++) for (let dx = slope ? -5 : diagonal ? -4 : 0; dx < (slope ? 9 : diagonal ? 8 : BS); dx++) {
         let sd = 0;
+        if (diagonal) {
+          const x = gbx * BS + dx, y = gby * BS + dy;
+          if (x < 0 || y < 0 || x >= W || y >= H) continue;
+          const i = y * W + x, n = (y >> 2) * BW + (x >> 2);
+          if (n !== b && (mat[i] !== EMPTY || part[i] || mach[i] || occ[i] || blockP[n])) continue;
+          sd = diagonalScrewShape(x + 0.5, y + 0.5, b, v, joins);
+          if (sd > 0) continue;
+        }
         if (slope) {
           const x = gbx * BS + dx, y = gby * BS + dy;
           if (x < 0 || y < 0 || x >= W || y >= H) continue;
@@ -421,7 +365,7 @@ function drawWorld() {
         const sx = gbx * BS + dx - vx0, sy = gby * BS + dy - vy0;
         if (sx < 0 || sy < 0 || sx >= bw || sy >= bh) continue;
         const k = sy * bw + sx, c = px[k];
-        const edge = slope ? sd > -0.8 : dx === 0 || dy === 0 || dx === BS - 1 || dy === BS - 1;
+        const edge = slope || diagonal ? sd > -0.8 : dx === 0 || dy === 0 || dx === BS - 1 || dy === BS - 1;
         const a = edge ? (((dx + dy + pulse) & 3) === 0 ? 0.85 : 0.6) : 0.28;
         const pr = c & 255, pg = (c >> 8) & 255, pb = (c >> 16) & 255;
         px[k] = (sm ? 0x04000000 : 0xff000000) | ((pb + (tb - pb) * a) << 16) | ((pg + (tg - pg) * a) << 8) | (pr + (tr - pr) * a);

src/sim/conveyors.js

@@ -176,6 +176,20 @@ 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) {

src/sim/items.js

@@ -90,6 +90,13 @@ 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);

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) : i + dj;
+      const dest = dx && dy ? diagonalScrewNext(i, p) : straightScrewNext(i, p);
       if (dest < 0) continue;
       const nx = dest % W, ny = (dest / W) | 0;
       if (nx < 0 || ny < 0 || nx >= W || ny >= H) continue;

src/ui/previews.js

@@ -182,27 +182,16 @@ function previewBlock(code, x, y, w, h, stroke = false, direction = -1, bx = -1,
   const ctx = R.ctx;
   if (code === BP_SCREW && direction >= 4) {
     const joins = bx >= 0 ? diagonalScrewJoins(bx, by, direction, planned) : 0;
-    const points = [];
-    for (let end = 0; end < 2; end++) {
-      const join = (joins >> (end * 3)) & 7, side = end ? 1 : -1;
-      const d = join ? SCREW_DIRS[join - 1] : [side, side * (direction === 4 || direction === 6 ? -1 : 1)];
-      points.push([d[0] * w / 2, d[1] * h / 2]);
+    const scale = w / BS, step = SET.look === "smooth" ? 0.25 : 1;
+    const b = bx >= 0 ? by * BW + bx : 0, ox = (b % BW) * BS, oy = ((b / BW) | 0) * BS;
+    ctx.beginPath();
+    for (let yy = -4; yy < 8; yy += step) for (let xx = -4; xx < 8; xx += step) {
+      const sd = diagonalScrewShape(ox + xx + step / 2, oy + yy + step / 2, b, direction, joins);
+      if (sd <= 0 && (!stroke || sd > -step * 1.5)) ctx.rect(x + xx * scale, y + yy * scale, step * scale, step * scale);
     }
-    const r = w / 2, a = points[0], b = points[1];
-    const al = Math.hypot(...a), bl = Math.hypot(...b);
-    const n0 = [a[1] / al, -a[0] / al], n1 = [-b[1] / bl, b[0] / bl];
-    const turn = n0[0] * n1[1] - n0[1] * n1[0], dot = n0[0] * n1[0] + n0[1] * n1[1];
-    ctx.save(); ctx.translate(x + w / 2, y + h / 2); ctx.beginPath();
-    ctx.moveTo(a[0] + n0[0] * r, a[1] + n0[1] * r);
-    if (turn >= 0) ctx.lineTo((n0[0] + n1[0]) * r / (1 + dot), (n0[1] + n1[1]) * r / (1 + dot));
-    else ctx.arc(0, 0, r, Math.atan2(n0[1], n0[0]), Math.atan2(n1[1], n1[0]), true);
-    ctx.lineTo(b[0] + n1[0] * r, b[1] + n1[1] * r);
-    ctx.lineTo(b[0] - n1[0] * r, b[1] - n1[1] * r);
-    if (turn <= 0) ctx.lineTo(-(n0[0] + n1[0]) * r / (1 + dot), -(n0[1] + n1[1]) * r / (1 + dot));
-    else ctx.arc(0, 0, r, Math.atan2(-n1[1], -n1[0]), Math.atan2(-n0[1], -n0[0]), true);
-    ctx.lineTo(a[0] - n0[0] * r, a[1] - n0[1] * r); ctx.closePath();
-    if (stroke) ctx.stroke(); else ctx.fill();
-    ctx.restore(); return;
+    if (stroke) { const fill = ctx.fillStyle; ctx.fillStyle = ctx.strokeStyle; ctx.fill(); ctx.fillStyle = fill; }
+    else ctx.fill();
+    return;
   }
   if (isSlopeBelt(code)) {
     const b = by * BW + bx, joins = bx >= 0 ? slopeBeltConnections(bx, by, code, planned) : 0;

test/t_diag_screws.js

@@ -48,6 +48,39 @@ for (const v of [4, 5, 6, 7]) {
   const joined = drain(c,500);
   check(`direction ${v}: straight to diagonal to straight`,joined.out===16 && joined.leaks===0,JSON.stringify(joined));
 }
+// Corner-adjacent joints: all axes, both ends, grains and queued bars.
+function cornerLine(v, vertical = false) {
+  const s = line(v), vv = vertical ? (s.dy < 0 ? 0 : 2) : (s.dx > 0 ? 1 : 3);
+  const tx = s.bx-s.dx, ty = s.by-s.dy, hx = s.head+s.dx, hy = s.hy+s.dy;
+  run(`for(let k=0;k<3;k++) {
+    placeBlock(BP_SCREW,${vv},${tx}-k*${vertical?0:s.dx},${ty}-k*${vertical?s.dy:0},true);
+    placeBlock(BP_SCREW,${vv},${hx}+k*${vertical?0:s.dx},${hy}+k*${vertical?s.dy:0},true);
+  }`);
+  return {...s, tail:tx-2*(vertical?0:s.dx), by:ty-2*(vertical?s.dy:0),
+    head:hx+2*(vertical?0:s.dx), hy:hy+2*(vertical?s.dy:0)};
+}
+for(const v of [4,5,6,7]) for(const vertical of [false,true]) {
+  const s=cornerLine(v,vertical);
+  rect(run,s.tail*4,s.by*4,s.tail*4+3,s.by*4+3,run("SAND"));
+  const r=run(`(()=>{let out=0,leak=0;for(let k=0;k<700;k++){
+    simTick();
+    for(const f of flyers)if(f.m===SAND){
+      if(${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)};})()`);
+  check(`corner ${vertical?"vertical":"horizontal"} joins ${v} carry every grain to the far mouth`,r.out===16 && !r.leak,JSON.stringify(r));
+  cornerLine(v,vertical);
+  putBar(s.tail*4,s.by*4); putBar(s.tail*4,s.by*4+2);
+  const bars=run(`(()=>{let out=0,overlap=false;for(let k=0;k<700;k++){
+    simTick();
+    for(let a=0;a<ents.length;a++)for(let b=0;b<a;b++) {
+      const e=ents[a],f=ents[b];if(e.ix<f.ix+4 && f.ix<e.ix+4 && e.iy<f.iy+2 && f.iy<e.iy+2)overlap=true;
+    }
+    if(mat.some((m,i)=>occ[i] && (PH[m]===PH_SOLID || PH[m]===PH_POWDER)))overlap=true;
+    for(const e of ents.slice())if(${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);}
+  }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 = [];
 for (const v of [0, 4, 5]) {
@@ -169,7 +202,17 @@ for(const [dx,dy,v] of [[5,-4,4],[4,5,5],[-5,4,6],[-4,-5,7]]) {
   check(`direction ${v} lays a corner-touching diagonal run`,run(`blockLine(20,20,${20+dx},${20+dy},true).every(([x,y],k)=>x===20+k*${Math.sign(dx)} && y===20+k*${Math.sign(dy)})`));
 }
 // End elbows follow the adjoining straight piece's axis, regardless of flow direction.
+run(fs.readFileSync('src/render/diagonal-screws.js', 'utf8'));
 run(fs.readFileSync('src/render/world.js', 'utf8'));
+for (const v of [4,5,6,7]) for (const end of [-1,1]) for (let dir=0;dir<4;dir++) {
+  fresh();
+  const slope=v===4 || v===6?-1:1, nx=20+end, ny=20+end*slope, shift=end>0?3:0;
+  run(`placeBlock(BP_SCREW,${v},20,20,true);placeBlock(BP_SCREW,${dir},${nx},${ny},true);`);
+  const expected=dir&1?5:6;
+  check(`corner ${v} end ${end} straight ${dir} selects a closed elbow`,run(`(()=>{const j=diagonalScrewJoins(20,20,${v});return (j>>${shift}&7)===${expected} && !(j&${end>0?128:64});})()`));
+  check(`corner ${v} end ${end} straight ${dir} meets all four mouth lanes`,run(`(()=>{const j=diagonalScrewJoins(20,20,${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']) {
   if (code !== 'BP_SCREW' && !(dir & 1)) continue;
   fresh();

test/t_smooth.py

@@ -97,6 +97,34 @@ 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.
+    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={};
+      for(const look of ["pixel","smooth"]) {
+        SET.look=look;SM.scale=1;drawWorld();
+        const bad=[];
+        for(const j of T62_JOINTS) {
+          const slope=j.v===4 || j.v===6?-1:1;
+          const end=j.end*SCREW_DIRS[j.v][0];
+          const dx=j.vertical?0:end,dy=j.vertical?end*slope:0;
+          const ox=j.corner && j.vertical?end*4:0,oy=j.corner && !j.vertical?end*slope*4:0;
+          for(const side of [-1,1])for(const along of [-0.3,0.3]) {
+            const x=j.bx*4+2+ox+dx*(2+along)-dy*side*1.6;
+            const y=j.by*4+2+oy+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)]);
+          }
+        }
+        out[look]=bad;
+      }return out;
+    }''')
+    for look, bad in mouths.items():
+        check(f"{look}: all 64 screw joints have closed casing across both mouth edges", 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

@@ -0,0 +1,26 @@
+// 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.
+money = 50000;
+for (let y = 64; y < 280; y++) for (let x = 112; x < 456; x++) {
+  const i = y * W + x;
+  setCell(i, EMPTY, 20, 0); bgm[i] = 0;
+}
+for (let x = 112; x < 456; x++) surfY[x] = 280;
+window.T62_JOINTS = [];
+for (let row = 0; row < 4; row++) for (let col = 0; col < 8; col++) {
+  const v = 4 + row, [dx, dy] = SCREW_DIRS[v], vertical = !!(col & 2), corner = !!(col & 1);
+  const x = 33 + col * 10 + (dx < 0 ? 4 : 0), y = 23 + row * 12 + (dy < 0 ? 4 : 0);
+  const sv = vertical ? (dy < 0 ? 0 : 2) : (dx > 0 ? 1 : 3), straight = col < 4 ? sv : (sv + 2) % 4;
+  for (let k = 0; k < 3; k++) placeBlock(BP_SCREW, v, x + k * dx, y + k * dy, true);
+  for (const end of [-1, 1]) {
+    const ex = x + (end > 0 ? 2 * dx : 0), ey = y + (end > 0 ? 2 * dy : 0);
+    const nx = ex + (vertical && !corner ? 0 : end * dx), ny = ey + (!vertical && !corner ? 0 : end * dy);
+    for (let k = 0; k < 2; k++) placeBlock(BP_SCREW, straight, nx + (vertical ? 0 : k * end * dx), ny + (vertical ? k * end * dy : 0), true);
+    T62_JOINTS.push({v, end, vertical, corner, straight, bx:ex, by:ey});
+  }
+}
+updateRoof();
+window.CAM = [284, 168];
+drawBot = () => {};