Sloped walls with a flat 45° face, and diagonal wall lines (t36)

- New Sloped wall piece: a half-block triangle in any wall material, at half a wall's cost.
  Dragging walls or slopes at about 45° lays a diagonal line; the drag picks the slope's
  orientation and T flips or turns it.
- Each slope fills one cell past its corner, so a diagonal run is sealed against grains and water.
- New test/t_slopes.js: a slope funnel passes 400/400 sand (square steps 379/400).

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

docs/DESIGN.md

@@ -364,6 +364,15 @@ above, including:
   tick, nearest first (a Huge world is fully started after 17 s), and flying toward areas still
   waiting starts them. Nothing is skipped: the same settling happens, spread out.
 
+- **Sloped walls and diagonal wall lines (t36, 2026-10-25).** The owner wanted funnel walls that
+  material slides down instead of catching on block steps. A Sloped wall is a half-block triangle
+  with a flat 45° face, in four orientations, built of any wall material at half a wall block's
+  cost. Dragging walls or slopes at about 45° lays a diagonal line; for slopes the drag direction
+  picks the orientation (solid side below) and T flips it, or turns a single piece. Each slope
+  also fills one cell past its corner so a diagonal run is sealed (grains move diagonally and
+  would otherwise slip through where two pieces meet). Square walls placed diagonally still
+  touch only at corners and leak there, like any square blocks.
+
 ## Ideas not built yet
 
 - **Concrete**, as a stronger wall material from rubble.

docs/PROJECT_MAP.md

@@ -205,10 +205,10 @@ Material definitions: ids, properties and metal families. ids, and drill/tank ti
 Material tables: typed properties, casting groups, flags, parts and tool tiers. Typed property tables
 - variables: PH, DENS, KC, ICAP, CASTMETAL, METAL_TIER, SOLIDMETAL, F_NAT, F_CAST, F_BURN, P_NONE, P_TU, P_TD, P_TL, P_TR, P_GRATE, P_GOPEN, P_WHEEL, P_INTAKE, P_FILTER, P_PIPE, TDX, TDY, BIT_TIERS, TANK_TIERS, REACH
 
-### src/sim/pieces.js (143 lines)
+### src/sim/pieces.js (158 lines)
 Everything the player can build (PIECES): blocks, machines and molds, with costs and descriptions; filter settings; wall materials and their cost.
-- functions: isPipeCode, filterable, cleanFilterCfg, filterRec, filterPassAt, filterInfo, sameFilter, wallCost
-- variables: BS, BP_WALL, BP_BELT, BP_TUBE, BP_SHAFT, BP_GRATE, BP_GATE, BP_FILTER, BP_PIPE, BP_PUMP, BP_OUTLET, BP_GRIND, BP_SAW, BP_PRESS, BP_RACK, filterCfg, WALL_OF, WALL_LIST, BAR_OF, GRAINS_PER_BAR, POWER_FREE, CASH, PIECES, PIECE_BY_ID, PIECE_BY_CODE, BELT_POWER, TUBE_POWER, FAN_POWER, WHEEL_K, ENGINE_K, MOLDS
+- functions: isSlope, isWall, slopeCell, slopeCode, isPipeCode, filterable, cleanFilterCfg, filterRec, filterPassAt, filterInfo, sameFilter, wallCost
+- variables: BS, BP_WALL, BP_BELT, BP_TUBE, BP_SHAFT, BP_GRATE, BP_GATE, BP_FILTER, BP_PIPE, BP_PUMP, BP_OUTLET, BP_GRIND, BP_SAW, BP_PRESS, BP_RACK, BP_SLOPE_BL, BP_SLOPE_BR, BP_SLOPE_TL, BP_SLOPE_TR, filterCfg, WALL_OF, WALL_LIST, BAR_OF, GRAINS_PER_BAR, POWER_FREE, CASH, PIECES, PIECE_BY_ID, PIECE_BY_CODE, BELT_POWER, TUBE_POWER, FAN_POWER, WHEEL_K, ENGINE_K, MOLDS
 
 ### src/sim/economy.js (152 lines)
 Money, prices, market saturation, the trade dock, buyer and builder orders.
@@ -269,9 +269,9 @@ How belts, filters and screw tubes move what is on or in them. What rests on a b
 - functions: carryColumn, beltDrain, launchGrain, rebuildFilters, filterCarry, setFilter, filterRun, roomFor, tubeSpread, tubeIntake
 - variables: CARRY_DEPTH, filterR, filterL, filtersDirty
 
-### src/sim/blocks.js (156 lines)
+### src/sim/blocks.js (208 lines)
 Building blocks: placing, integrity, removing, lines and rectangles of blocks.
-- functions: blockOf, blockCellList, pieceCost, canPlaceBlock, placeBlock, blockIntegrity, removeWallCell, removeBlock, blockLine, blockRect, blockInReach, blockIs, placeBlocks
+- functions: blockOf, blockCellList, pieceCost, slopeSeal, slopeSealOwner, wallCells, canPlaceBlock, placeBlock, blockIntegrity, removeWallCell, removeBlock, diagonalDrag, blockLine, blockRect, blockInReach, blockIs, placeBlocks
 
 ### src/sim/molds.js (317 lines)
 Molds: cavities for castings; ingot troughs empty themselves below. Removal returns set metal.
@@ -356,7 +356,7 @@ Drawing (src/render/): browser only. This file: the renderer state R, colour tab
 Propagated coloured light from glowing and burning cells.
 - functions: builtForLight, computeLight
 
-### src/render/world.js (321 lines)
+### src/render/world.js (330 lines)
 Scale colour without changing the smooth-look class.
 - functions: fogColor, drawWorld
 - variables: TUBE_CLASS
@@ -374,7 +374,7 @@ Smooth look: WebGL setup, texture uploads, drawing and adaptive resolution.
 - functions: smCompile, smoothAvailable, smUpload, smoothDraw, smoothPace
 - variables: SM, smBytes
 
-### src/render/smooth-shaders.js (330 lines)
+### src/render/smooth-shaders.js (337 lines)
 Smooth shaders: vertex and fragment programs for the rounded world look.
 - variables: SM_VS, SM_FS
 
@@ -430,14 +430,14 @@ Notebook blueprints: starter designs, saved library and code sharing.
 The tool hotbar and what is selected.
 - functions: renderHotbar, toolId, steering, modShift, grainAt, selectTool, bagMaterials, blowList, blowAllList, blowingAll, piece
 
-### src/ui/build-menu.js (104 lines)
+### src/ui/build-menu.js (105 lines)
 The build menu along the bottom: categories, piece tiles and their icons.
 - functions: pieceIcon, catOf, selectBuildCat, cycleBuildCat, buildVariantChips, renderBuildBar, setupBuildBar
 - variables: BUILD_CATS, BUILD_ORDER, PIECE_ICONS, lastBuildKey, lastBuildMenu
 
-### src/ui/selection.js (96 lines)
+### src/ui/selection.js (107 lines)
 Tool selection: cycling, drill tuning, piece variants and costs.
-- functions: pieceSize, pieceUsesWall, setDrillWidth, tuneUnderCursor, cycleItem, cycleWall, rotate, toggleBlow, pickFilterUnderCursor, toggleFilterMat, setBrush, pieceV, pieceExtra, filterBlockAt, chipCost, pieceCostNow
+- functions: pieceSize, pieceUsesWall, setDrillWidth, tuneUnderCursor, cycleItem, cycleWall, rotate, toggleBlow, pickFilterUnderCursor, toggleFilterMat, setBrush, pieceV, pieceExtra, filterBlockAt, chipCost, pieceCostNow, pieceCode, turnSlope
 
 ### src/ui/selection-pickers.js (59 lines)
 Selection pickers: filter rules, filter settings and wall materials. What a filter can hold: loose things and bars you have found, plus anything it already holds
@@ -467,9 +467,9 @@ Gamepad input.
 - functions: padPressed, pollPad
 - variables: PAD
 
-### src/ui/previews.js (192 lines)
+### src/ui/previews.js (203 lines)
 Cursor previews: shared grid helpers, air streaks and tool preview dispatch.
-- functions: blockRectPx, drawGrid, previewColor, drawAirStreaks, drawReachCircle, drawPreviews
+- functions: blockRectPx, drawGrid, previewColor, drawAirStreaks, drawReachCircle, drawPreviews, previewBlock
 
 ### src/ui/preview-drill.js (104 lines)
 Drill previews: shaken rock cracks, pulse wavefronts and aiming fan. Rock the drill has shaken but not yet broken shows cracks, more and finer as it nears breaking. Each crack is a contour line of a noise field (marching squares, cell by cell), so the lines run on unbroken from one cell to the next and look like real fractures, not a pattern.
@@ -517,6 +517,7 @@ The frame loop and boot.
 - `test/t_pipes.js`: Pipes, pumps and outlets move liquids; the Grinder grinds waste rock for trace ore.
 - `test/t_racks.js`: Rack intake, FIFO storage, gate, removal and saved-state validation.
 - `test/t_sim_optimizations.js`: Optimized paths must match the full roof scan and the original heat loop exactly.
+- `test/t_slopes.js`: Sloped walls: flow, sealed joints, building, refunds and persistence.
 - `test/t_smooth.py`: The smooth look: the WebGL pass compiles, draws, falls back cleanly, and the thermal lens still works.
 - `test/t_stone.js`: Uses for waste rock and sand: glass bricks from a fan furnace, the Saw, the silo and builders' orders.
 - `test/t_water.js`: Water conservation, settling, ledge pouring, boundaries, pipes and phase changes. Tall worlds keep geothermal heat out of the ponds.
@@ -544,3 +545,4 @@ The frame loop and boot.
 - `tools/scenes/silo.js`: Run after clear-sky.js; leave paused so the open gate keeps its demonstration charge.
 - `tools/scenes/stone-uses.js`: The stone and sand machines: a half-full silo with its gate open over a belt, a stone cutter fed with rubble, and cut stone and glass brick walls. Run clear-sky.js first, e.g. python3 tools/shot.py /tmp/stone.png --setup tools/scenes/clear-sky.js --js "$(cat tools/scenes/stone-uses.js)" --ticks 240 --zoom 7
 - `tools/scenes/t33-ground.js`: Paused dug pocket: copper ore, rubble and dirt against stone, granite and dirt. Use --js "..." to set daylight or R.lens after this setup; CAM frames the pocket.
+- `tools/scenes/t36-funnel.js`: A twelve-block funnel, one block open at the bottom, draining 400 grains of sand.

docs/agent-log.md

@@ -4,6 +4,17 @@ 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.
 
+## 2026-10-25: t36: sloped walls and diagonal wall lines (Claude Code, Codex)
+
+- `BP_SLOPE_BL`..`BP_SLOPE_TR` (15-18) in `src/sim/pieces.js` (`isSlope`, `isWall`, `slopeCell`,
+  `slopeCode`); `src/sim/blocks.js`: half cost and refund, `slopeSeal` corner cell and
+  `slopeSealOwner`, `diagonalDrag` and `blockLine(.., diagonal)`. Build menu, T key
+  (`turnSlope`), previews, copy/paste, undo, blueprints, hover, both looks.
+- `test/t_slopes.js`: funnel 400/400 sand (square steps 379/400), water 400/400, no leaks in all
+  four orientations from both sides, bars slide, every wall material; play.py menu and diagonal
+  drag. Seeds unchanged. `run_all.py --browser` ALL PASSED. Screenshots
+  `shots/t36-funnel-*.png`, scene `tools/scenes/t36-funnel.js`.
+
 ## 2026-10-25: t33: loose grains and solid ground look different (Claude Code, Codex)
 
 - Smooth look (`src/render/smooth-shaders.js`): natural ground gets a soft seam where it meets