Sloped belts and filters, laid by a 45° drag (t40)

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

docs/DESIGN.md

@@ -388,3 +388,9 @@ above, including:
 - **Upgrade ideas for the drill**: an amplifier, a tuning fork, harmonics. Also a Grav pick
   upgrade tool and mining charges. See `docs/systems/dig-tools.md`.
 - The owner's ideas for later are tasks tagged `idea` in the Backlog of the task board.
+
+- **Sloped belts and filters (t40, 2026-10-25).** The owner asked for belts, then filters, to work
+  diagonally like tubes and walls. A Belt or Filter drag at about 45° lays slope-shaped blocks
+  whose face is a running belt, carrying grains and bars up or down in the drag's direction at
+  flat-belt speed; the face grips its load, so nothing slides back. A sloped filter drops what it
+  passes out underneath and carries the rest. New block codes (19-22), so saves still load.

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, P_TUR, P_TDR, P_TDL, P_TUL, TUBE_PARTS, TUBE_DIRS, IS_TUBE, TDX, TDY, BIT_TIERS, TANK_TIERS, REACH
 
-### src/sim/pieces.js (156 lines)
+### src/sim/pieces.js (176 lines)
 Everything the player can build (PIECES): blocks, machines and molds, with costs and descriptions; filter settings; wall materials and their cost.
-- 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
+- functions: isSlopeBelt, isFilter, isBelt, beltGrade, slopeShape, beltFaceY, beltDirection, 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, BP_BELT_UP, BP_BELT_DOWN, BP_FILTER_UP, BP_FILTER_DOWN, 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.
@@ -260,27 +260,27 @@ Pipes, pumps and outlets: each joined line holds one liquid as a count, not as g
 - functions: sideOf, pipeClosedSide, pipeJoins, rebuildPipes, pipeNetOf, pipeTakeShare, faceCell, pumpDraw, outletPour, pipesTick
 - variables: PIPE_CAP, PUMP_RATE, OUTLET_RATE, PUMP_MAX_T, SIDE_V, PUMP_V, OUTLET_V, pipeNets, pipeNetAt, pipesDirty
 
-### src/sim/machine-tick.js (168 lines)
+### src/sim/machine-tick.js (154 lines)
 Per-tick machine work: steam engines, fans, belts, filters, screw tubes (machinesTick).
 - functions: engineIntake, fanBlow, machinesTick
 
-### src/sim/conveyors.js (147 lines)
+### src/sim/conveyors.js (201 lines)
 How belts, filters and screw tubes 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: carryColumn, beltDrain, launchGrain, rebuildFilters, filterCarry, setFilter, filterRun, roomFor, tubeSpread, tubeIntake, diagonalTubeNext
+- functions: conveyorStep, carryColumn, holdSlopeColumn, beltDrain, launchGrain, rebuildFilters, filterCarry, carryBeltsAndFilters, setFilter, filterRun, roomFor, tubeSpread, tubeIntake, diagonalTubeNext
 - variables: CARRY_DEPTH, filterR, filterL, filtersDirty
 
-### src/sim/blocks.js (208 lines)
+### src/sim/blocks.js (219 lines)
 Building blocks: placing, integrity, removing, lines and rectangles of blocks.
-- functions: blockOf, blockCellList, pieceCost, slopeSeal, slopeSealOwner, wallCells, canPlaceBlock, placeBlock, blockIntegrity, removeWallCell, removeBlock, diagonalDrag, blockLine, blockRect, blockInReach, blockIs, placeBlocks
+- functions: blockOf, blockCellList, pieceCost, setSlopeSeal, 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.
 - 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 (256 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, entTubeAt, entTubeFree, entTubeMove, entTubeLane, entTubeEdge, entTubeEnter, entTubeTick, entDiagonalTubeTick, entTick, entsInCircle, bagAdd, bagTake, giveOrDrop, refundAt, canAfford, payCost, fmtMoney, costText, needText
+- functions: entSolidCell, entSupportCount, entFreeAt, entMark, spawnBar, removeEnt, entTubeAt, entTubeFree, entTubeMove, entTubeLane, entTubeEdge, entTubeEnter, entTubeTick, entDiagonalTubeTick, entSlopeBeltTick, entTick, entsInCircle, bagAdd, bagTake, giveOrDrop, refundAt, canAfford, payCost, fmtMoney, costText, needText
 - variables: BAR_W, BAR_H, entCurM, droppedLast
 
 ### src/sim/tools.js (52 lines)
@@ -356,7 +356,11 @@ Drawing (src/render/): browser only. This file: the renderer state R, colour tab
 Propagated coloured light from glowing and burning cells.
 - functions: builtForLight, looseForLight, computeLight
 
-### src/render/world.js (410 lines)
+### src/render/slope-belts.js (28 lines)
+A slope's band uses world coordinates, so its stripes never restart at block joints.
+- functions: slopeBeltAt, slopeBeltColor
+
+### src/render/world.js (422 lines)
 Scale colour without changing the smooth-look class.
 - functions: fogColor, diagonalTubeJoins, diagonalTubeShape, diagonalTubeBlock, drawWorld
 - variables: TUBE_CLASS, diagonalJoins, diagonalAcross, diagonalAlong, diagonalCap
@@ -374,7 +378,7 @@ Smooth look: WebGL setup, texture uploads, drawing and adaptive resolution.
 - functions: smCompile, smoothAvailable, smUpload, smoothDraw, smoothPace
 - variables: SM, smBytes
 
-### src/render/smooth-shaders.js (366 lines)
+### src/render/smooth-shaders.js (393 lines)
 Smooth shaders: vertex and fragment programs for the rounded world look.
 - variables: SM_VS, SM_FS
 
@@ -430,16 +434,16 @@ 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 (109 lines)
+### src/ui/build-menu.js (111 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 (112 lines)
+### src/ui/selection.js (119 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, pieceCode, turnSlope
 
-### src/ui/selection-pickers.js (59 lines)
+### src/ui/selection-pickers.js (61 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
 - functions: filterChoices, matList, filterParts, filterSentence, applyFilterRun, openFilterPicker, openWallPicker
 
@@ -457,7 +461,7 @@ Keyboard and mouse listeners.
 - functions: isTyping
 - variables: canvas
 
-### src/ui/actions.js (240 lines)
+### src/ui/actions.js (242 lines)
 What input does: overlays, F, pick, copy / cut / paste, undo, building and tool use each frame. Which overlays are on, shown as a coloured frame round the screen and a named badge
 - functions: updateOverlayUI, toggleLens, doInteract, pickUnderCursor, aimBlock, stampOrigin, selModeHeld, startPaste, stopSelectAndPaste, plural, piecesIn, doUndo, endRmbRecord, dragDirFor, blockLabel, primaryPress, primaryRelease, secondaryPress, toolTick
 - variables: ovShown
@@ -467,7 +471,7 @@ Gamepad input.
 - functions: padPressed, pollPad
 - variables: PAD
 
-### src/ui/previews.js (216 lines)
+### src/ui/previews.js (227 lines)
 Cursor previews: shared grid helpers, air streaks and tool preview dispatch.
 - functions: blockRectPx, drawGrid, previewColor, drawAirStreaks, drawReachCircle, drawPreviews, previewBlock
 
@@ -518,6 +522,7 @@ 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_slope_belts.js`: Sloped belts: transport, joins, sorting, persistence and the actual drag controls.
 - `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.
@@ -549,3 +554,4 @@ The frame loop and boot.
 - `tools/scenes/t35-diagonal.js`: Run after clear-sky.js: a belt takes sand from a pile, up a diagonal screw to an upper belt.
 - `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.

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.
 
+## 2026-10-25: t40: sloped belts and filters (Claude Code, Codex)
+
+- Block codes 19-22 (`BP_BELT_UP/DOWN`, `BP_FILTER_UP/DOWN`, `src/sim/pieces.js`): slope-shaped
+  belts and filters whose 45° face runs, laid by a diagonal Belt or Filter drag. `conveyorStep`,
+  `holdSlopeColumn` and a shared front-first order for belts and filters in `src/sim/conveyors.js`;
+  bars in `items.js`; saves, blueprints, undo, hover, previews; `src/render/slope-belts.js`.
+- 90 grains/s flat, up and down for belts and filters; a sloped filter sorted 64/64 with no loss.
+  Seeds 777, 77 and 4242 generate identically.
+- `test/t_slope_belts.js` (32 checks); `run_all.py --browser` ALL PASSED. Art pass follows.
+
 ## 2026-10-25: t35 follow-up: diagonal tube elbows (Claude Code, Codex)
 
 - Diagonal tubes are as thick as straight ones, and an end block joining a straight tube, belt or