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>

src/sim/pieces.js

@@ -5,6 +5,18 @@
 // stays grain-level; only built pieces snap.
 const BS = 4;
 const BP_WALL = 1, BP_BELT = 2, BP_TUBE = 3, BP_SHAFT = 4, BP_GRATE = 5, BP_GATE = 6, BP_FILTER = 7, BP_PIPE = 8, BP_PUMP = 9, BP_OUTLET = 10, BP_GRIND = 11, BP_SAW = 12, BP_PRESS = 13, BP_RACK = 14;
+const BP_SLOPE_BL = 15, BP_SLOPE_BR = 16, BP_SLOPE_TL = 17, BP_SLOPE_TR = 18;
+function isSlope(c) { return c >= BP_SLOPE_BL && c <= BP_SLOPE_TR; }
+function isWall(c) { return c === BP_WALL || isSlope(c); }
+function slopeCell(c, x, y) {
+  if (c === BP_SLOPE_BR || c === BP_SLOPE_TR) x = 3 - x;
+  if (c === BP_SLOPE_TL || c === BP_SLOPE_TR) y = 3 - y;
+  return y >= x;
+}
+function slopeCode(dx, dy, orientation) {
+  if (!diagonalDrag(dx, dy)) return BP_SLOPE_BL + orientation;
+  return dx * dy > 0 ? (orientation >= 2 ? BP_SLOPE_TR : BP_SLOPE_BL) : (orientation >= 2 ? BP_SLOPE_TL : BP_SLOPE_BR);
+}
 function isPipeCode(c) { return c === BP_PIPE || c === BP_PUMP || c === BP_OUTLET; }
 // Filters: each filter block has a set of materials and a mode. In drop mode (inv 0)
 // the chosen materials fall through and everything else rides along on top; in carry
@@ -39,6 +51,8 @@ const CASH = 255; // stands for money in cost lists
 const PIECES = [
   { id: 'wall', code: BP_WALL, name: 'Wall block', kind: 'block', variants: 'wall',
     desc: 'A solid block. R picks what it is made of: 16 grains of rubble, lumps or chunks, or 2 bars of metal.' },
+  { id: 'slope', code: BP_SLOPE_BL, name: 'Sloped wall', kind: 'block', variants: 'wall',
+    desc: 'A half-block with a flat 45° face. Drag diagonally to make a funnel. R picks the material. T flips a dragged slope; without a drag, T cycles its four corners. Costs and returns 8 grains or 1 bar.' },
   { id: 'belt', code: BP_BELT, name: 'Belt', kind: 'block', cost: [[CASH, 12]], dirs: ['left', 'right'],
     desc: 'Carries loose grains and bars resting on top of it, left or right, in a layer up to a block deep. Water and other liquids drain through it.' },
   { id: 'tube', code: BP_TUBE, name: 'Screw tube', kind: 'block', cost: [[CASH, 25]], dirs: ['up', 'right', 'down', 'left'],
@@ -84,6 +98,7 @@ const PIECES = [
 ];
 const PIECE_BY_ID = {}, PIECE_BY_CODE = [];
 PIECES.forEach((p, i) => { p.index = i; PIECE_BY_ID[p.id] = p; if (p.code) PIECE_BY_CODE[p.code] = p; if (p.kind === 'machine') { p.w = p.bw * BS; p.h = p.bh * BS; } });
+for (let c = BP_SLOPE_BR; c <= BP_SLOPE_TR; c++) PIECE_BY_CODE[c] = PIECE_BY_ID.slope;
 // power per grain of belt / tube (a block is 16 grains)
 const BELT_POWER = 0.03, TUBE_POWER = 0.125, FAN_POWER = 6;
 const WHEEL_K = 0.32, ENGINE_K = 40;