Let a tile report a touch instead of blocking it (#160)

A tile could be solid, one-way and scaled, but not report without
blocking. Water, lava, spikes or a goal zone needed a trigger object
of their own laid over the map. Now a tile has a switch Trigger, and
the collision events name the tile and the cell they met.

- A tile has the switch "Trigger (reports, never blocks)" under
  Solid. Its cells hold nothing up: no Move, no falling body, no
  ray. They raise On collision enter, stay and exit with the tilemap
  as other.
- The three events have the outputs tile, cell x and cell y. Without
  a tile, tile is empty and the cell is -1, -1.
- The three events have the input per cell. Off, the default, gives
  one event per area: cells of the same tile that touch side by
  side. On gives one event per cell.
- The scene view outlines trigger cells in yellow like a trigger
  collider, merged to rectangles but never with solid cells.
- Is touching with the map counts trigger tiles, and Set tile works
  while the game runs.
- Both systems find the touches with the same overlap check in
  runtime/systems/tileTriggers.ts, not through the physics engine.

Decided here:

- Trigger wins over Solid. A tile with both does not block, as with
  a collider.
- Water beside lava is two areas, and so are two ponds that touch
  only at a corner.
- An area names the cell nearest to the centre of the collider, and
  on exit the cell it named last.
- The solid cells of a map still do not name their tile.
- Normal, impulse and point are 0, as with a trigger collider.
- Collision scale and outlines shape a trigger cell like a solid
  one. One-way, friction and bounciness have no effect.

Tests:
- Gate on stein2: 205 files, 3104 tests (3067 + 37), exit 0
- e2e 39,40: 106 checks. e2e 1-8,39-43: 490 checks. Both on
  melektaus-atx. No full run, the sum of 1648 (1645 + 3) is
  reckoned and CI measures it.
- 37 unit tests in tests/core/tile-triggers.test.ts, nearly all
  against both systems
- Three e2e checks with a real mouse in block 40l-iv
- 24 unit counter-probes fail tests. Two did not at first, tests
  were added for them.
- Two browser counter-probes fail their checks
- Two screenshots looked at (yellow outline, the node with per cell)

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

src/core/graph/GraphInterpreter.ts

@@ -120,6 +120,17 @@ export class GraphInterpreter {
     this.follow(node, port, ctx, 0);
   }
 
+  /**
+   * A data input of an event node, read ahead of its pulse: what decides whether the event concerns
+   * the node at all (#160). Null for an input the node does not have.
+   */
+  eventInput(node: GraphNode, key: string, ctx: NodeContext): Value {
+    this.frame = this.emptyFrame(this.graph);
+    this.steps = 0;
+    const port = this.def(node)?.inputs.find((p) => p.key === key);
+    return port ? this.inputValue(node, port, ctx) : null;
+  }
+
   /**
    * The `On state entered` / `On state exited` nodes watching one machine. A node whose machine
    * input carries a running value rather than a pick has no state outputs at all, so it is never

src/core/graph/nodes/action/tileNodes.ts

@@ -7,7 +7,7 @@ import { cellToWorld, worldToCell } from '../../../model/liveTilemap';
 import { worldMatrixOf } from '../../NodeContext';
 import type { NodeDef, PortDef } from '../../NodeRegistry';
 import { asEntity, asNumber, asString, type Value } from '../../values';
-import { bool, exec, int, num, obj } from '../shared';
+import { bool, exec, int, num, obj, tilePort } from '../shared';
 
 /** The layer by name, picked from the layers of every map in the project; none = the first. */
 const layerPort = (): PortDef => ({
@@ -17,14 +17,6 @@ const layerPort = (): PortDef => ({
   field: { key: 'layer', label: 'Layer', kind: 'tileLayer', default: '' },
 });
 
-/** A tile asset; unconnected, it shows the tile picker, and none chosen empties the cell. */
-const tilePort = (key = 'tile', label = key): PortDef => ({
-  key,
-  label,
-  type: 'string',
-  field: { key, label: 'Tile', kind: 'asset', default: '', assetTypes: ['tile'] },
-});
-
 const CELL_INPUTS: readonly PortDef[] = [int('cellX', 0, 'cell x'), int('cellY', 0, 'cell y')];
 
 /** A cell counts in whole columns and rows, so a fraction arriving over an edge is floored. */

src/core/graph/nodes/events/OnCollisionEnter.ts

@@ -1,6 +1,6 @@
 import type { NodeDef } from '../../NodeRegistry';
 import { hiddenOrder, orderParam } from '../../eventOrder';
-import { collisionOutputs, contactOutputs } from '../shared';
+import { collisionOutputs, contactOutputs, perCellPort, tileOutputs } from '../shared';
 
 export const OnCollisionEnter: NodeDef = {
   type: 'OnCollisionEnter',
@@ -9,9 +9,11 @@ export const OnCollisionEnter: NodeDef = {
   description:
     'Runs once when a collider of the owner starts overlapping another collider. While playing, ' +
     'normal x/y point from the other collider towards the own one, impulse says how hard they met and ' +
-    'point x/y where (all 0 for a trigger).',
-  inputs: [],
-  outputs: [...collisionOutputs(), ...contactOutputs()],
+    'point x/y where (all 0 for a trigger). Walking onto a trigger tile of a tilemap runs it too, with ' +
+    'the tile and its cell: once for a whole stretch of touching cells of that tile, or with "per cell" ' +
+    'for every cell.',
+  inputs: [perCellPort()],
+  outputs: [...collisionOutputs(), ...contactOutputs(), ...tileOutputs()],
   params: [orderParam],
   hiddenParams: hiddenOrder,
 };

src/core/graph/nodes/events/OnCollisionExit.ts

@@ -1,14 +1,16 @@
 import type { NodeDef } from '../../NodeRegistry';
 import { hiddenOrder, orderParam } from '../../eventOrder';
-import { collisionOutputs } from '../shared';
+import { collisionOutputs, perCellPort, tileOutputs } from '../shared';
 
 export const OnCollisionExit: NodeDef = {
   type: 'OnCollisionExit',
   label: 'On collision exit',
   category: 'event',
-  description: 'Runs once when a collider of the owner stops overlapping another collider.',
-  inputs: [],
-  outputs: collisionOutputs(),
+  description:
+    'Runs once when a collider of the owner stops overlapping another collider – or leaves a trigger tile ' +
+    'of a tilemap: the whole stretch of touching cells of that tile, or with "per cell" each cell.',
+  inputs: [perCellPort()],
+  outputs: [...collisionOutputs(), ...tileOutputs()],
   params: [orderParam],
   hiddenParams: hiddenOrder,
 };

src/core/graph/nodes/events/OnCollisionStay.ts

@@ -1,6 +1,6 @@
 import type { NodeDef } from '../../NodeRegistry';
 import { hiddenOrder, orderParam } from '../../eventOrder';
-import { collisionOutputs, contactOutputs } from '../shared';
+import { collisionOutputs, contactOutputs, perCellPort, tileOutputs } from '../shared';
 
 export const OnCollisionStay: NodeDef = {
   type: 'OnCollisionStay',
@@ -9,9 +9,11 @@ export const OnCollisionStay: NodeDef = {
   description:
     'Runs while a collider of the owner overlaps another collider: every frame, or with an interval once ' +
     'each time that long has passed since they met. While playing, normal x/y, impulse and point x/y tell ' +
-    'how they touch right now (all 0 for a trigger and in the editor run).',
-  inputs: [],
-  outputs: [...collisionOutputs(), ...contactOutputs()],
+    'how they touch right now (all 0 for a trigger and in the editor run). On a trigger tile of a ' +
+    'tilemap, tile and cell x/y say which: the cell nearest to the own collider, or with "per cell" each ' +
+    'cell it lies on.',
+  inputs: [perCellPort()],
+  outputs: [...collisionOutputs(), ...contactOutputs(), ...tileOutputs()],
   params: [
     {
       key: 'interval',

src/core/graph/nodes/shared.ts

@@ -44,6 +44,34 @@ export const contactOutputs = (): PortDef[] => [
   num('pointY', 'point y'),
 ];
 
+/** A tile asset; unconnected as an input, it shows the tile picker. */
+export const tilePort = (key = 'tile', label = key): PortDef => ({
+  key,
+  label,
+  type: 'string',
+  field: { key, label: 'Tile', kind: 'asset', default: '', assetTypes: ['tile'] },
+});
+
+export const PER_CELL_INPUT = 'perCell';
+
+/**
+ * Which pairs a collision event hears of a map's trigger tiles (#160): off, one per area of a tile –
+ * a pond is entered once –, on, one per cell.
+ */
+export const perCellPort = (): PortDef => ({
+  key: PER_CELL_INPUT,
+  label: 'per cell',
+  type: 'boolean',
+  default: false,
+  field: { key: PER_CELL_INPUT, label: 'Per cell (trigger tiles)', kind: 'boolean', default: false },
+});
+
+/**
+ * The trigger tile a collider lies on (#160) and its cell in the map, which is then `other`. No
+ * tile and cell -1, -1 for anything else: another collider, or a map's solid cells.
+ */
+export const tileOutputs = (): PortDef[] => [tilePort(), num('cellX', 'cell x'), num('cellY', 'cell y')];
+
 export const keyParam: PropertyDef = { key: 'key', label: 'Key', kind: 'key', default: 'ArrowRight' };
 
 /** No `assetTypes`: any placeable asset is a valid answer here. */

src/core/model/tile.ts

@@ -21,6 +21,8 @@ export const TILE_FPS_KEY = 'fps';
 export const TILE_PLAYBACK_KEY = 'playback';
 /** Whether a cell of this tile blocks movement in the running game (#132). */
 export const TILE_SOLID_KEY = 'solid';
+/** Whether a cell of this tile reports what overlaps it instead of blocking it: water, lava, a goal (#160). */
+export const TILE_TRIGGER_KEY = 'trigger';
 /** Whether a solid tile only blocks from above, as a platform one jumps through from below (#155). */
 export const TILE_ONE_WAY_KEY = 'oneWay';
 /** How far a contact may lean from straight up and still land on a one-way tile, in degrees (#159). */
@@ -59,8 +61,13 @@ export function tilePlayback(asset: TileAsset): TilePlayback {
   return (TILE_PLAYBACKS as readonly string[]).includes(value) ? (value as TilePlayback) : 'loop';
 }
 
+/** A trigger never blocks, whatever Solid says: it is the collider's rule, where Trigger wins too. */
 export function isTileSolid(asset: TileAsset): boolean {
-  return asset.props[TILE_SOLID_KEY] === true;
+  return asset.props[TILE_SOLID_KEY] === true && !isTileTrigger(asset);
+}
+
+export function isTileTrigger(asset: TileAsset): boolean {
+  return asset.props[TILE_TRIGGER_KEY] === true;
 }
 
 export function isTileOneWay(asset: TileAsset): boolean {

src/core/model/tilemapCollision.ts

@@ -22,6 +22,9 @@
  * each function takes `oneWay` – so a platform never merges with a wall into one rectangle, nor with
  * a platform of another angle (#159). The same holds for a tile's surface (#193): with a `material`,
  * a function looks only at the tiles of that friction and bounciness.
+ *
+ * A trigger tile (#160) blocks nothing. Its cells are worked out by the same rules, apart from the
+ * solid ones, and handed on cell by cell: the collision events tell which one was walked into.
  */
 import type { TileAsset, TilemapAsset } from './Asset';
 import { tileQuadrants } from './autotile';
@@ -33,6 +36,7 @@ import { findFrame } from './texture';
 import {
   isTileOneWay,
   isTileSolid,
+  isTileTrigger,
   readTile,
   TILE_ONE_WAY_ANGLE_KEY,
   tileCollisionScale,
@@ -244,6 +248,17 @@ function passesFilter(tile: TileAsset, oneWay: OneWayFilter, material?: TileMate
   return oneWay === true || tileOneWayAngle(tile) === oneWay;
 }
 
+/**
+ * Whose cells a function works out: the solid tiles passing `oneWay` and `material`, or the trigger
+ * tiles (#160) – all of them, or the one named. A trigger tile is never among the solid ones.
+ */
+type TilePick = { oneWay: OneWayFilter; material?: TileMaterial } | { trigger: string | null };
+
+function picks(tile: TileAsset, pick: TilePick): boolean {
+  if ('trigger' in pick) return isTileTrigger(tile) && (pick.trigger === null || pick.trigger === tile.id);
+  return isTileSolid(tile) && passesFilter(tile, pick.oneWay, pick.material);
+}
+
 /** The solid tiles painted on the map, each once, in the order the layers first name them. */
 function solidTiles(project: Project, asset: TilemapAsset): TileAsset[] {
   const ids = new Set(asset.layers.flatMap((layer) => cellsTileIds(layer.cells)));
@@ -286,8 +301,7 @@ function blockingCells(
   project: Project,
   props: PropertyBag,
   asset: TilemapAsset,
-  oneWay: OneWayFilter,
-  material?: TileMaterial,
+  pick: TilePick,
 ): readonly CellBlock[] {
   const tiles = new Map<string, BlockingTile>();
   for (const layer of asset.layers)
@@ -296,7 +310,7 @@ function blockingCells(
       const tile = findAssetOf(project, id, 'tile');
       tiles.set(
         id,
-        tile && isTileSolid(tile) && passesFilter(tile, oneWay, material)
+        tile && picks(tile, pick)
           ? { scale: tileCollisionScale(tile), shape: tileShape(project, tile) }
           : null,
       );
@@ -304,8 +318,9 @@ function blockingCells(
   const key = [
     tilemapColumns(props),
     tilemapRows(props),
-    oneWay,
-    material ? `${material.friction}/${material.bounciness}` : '',
+    'trigger' in pick
+      ? `trigger:${pick.trigger ?? ''}`
+      : `${pick.oneWay}|${pick.material ? `${pick.material.friction}/${pick.material.bounciness}` : ''}`,
     asset.layers.map((layer) => cellsVersion(layer.cells)).join(','),
     [...tiles]
       .map(([id, t]) => (t ? `${id}:${t.scale}:${t.shape ? identityToken(t.shape) : 'box'}` : id))
@@ -373,7 +388,7 @@ export function solidCells(
   oneWay: OneWayFilter = false,
   material?: TileMaterial,
 ): Required<SolidCell>[] {
-  return boxCells(blockingCells(project, props, asset, oneWay, material));
+  return boxCells(blockingCells(project, props, asset, { oneWay, material }));
 }
 
 function boxCells(cells: readonly CellBlock[]): Required<SolidCell>[] {
@@ -393,7 +408,11 @@ export function solidPolygons(
   oneWay: OneWayFilter = false,
   material?: TileMaterial,
 ): readonly CellPolygon[] {
-  return derived(polygonsOf, blockingCells(project, props, asset, oneWay, material), (cells) => {
+  return polygonCells(blockingCells(project, props, asset, { oneWay, material }));
+}
+
+function polygonCells(blocks: readonly CellBlock[]): readonly CellPolygon[] {
+  return derived(polygonsOf, blocks, (cells) => {
     const polygons: CellPolygon[] = [];
     for (const cell of cells) {
       if (cell.box !== null) continue;
@@ -527,9 +546,126 @@ export function solidRects(
   oneWay: OneWayFilter = false,
   material?: TileMaterial,
 ): readonly CellRect[] {
-  return derived(rectsOf, blockingCells(project, props, asset, oneWay, material), (cells) =>
-    mergeCells(boxCells(cells)),
-  );
+  return rectCells(blockingCells(project, props, asset, { oneWay, material }));
+}
+
+function rectCells(blocks: readonly CellBlock[]): readonly CellRect[] {
+  return derived(rectsOf, blocks, (cells) => mergeCells(boxCells(cells)));
+}
+
+/** The trigger tiles painted on the map (#160), each once, in the order the layers first name them. */
+function triggerTiles(project: Project, asset: TilemapAsset): TileAsset[] {
+  const ids = new Set(asset.layers.flatMap((layer) => cellsTileIds(layer.cells)));
+  return [...ids].flatMap((id) => {
+    const tile = findAssetOf(project, id, 'tile');
+    return tile && isTileTrigger(tile) ? [tile] : [];
+  });
+}
+
+/**
+ * Where the map's trigger tiles lie (#160), as the scene view outlines it: merged into rectangles by
+ * the rules of the solid cells, but on their own – a pond never merges with its shore.
+ */
+export function triggerRects(project: Project, props: PropertyBag, asset: TilemapAsset): readonly CellRect[] {
+  return rectCells(blockingCells(project, props, asset, { trigger: null }));
+}
+
+/** The trigger cells that report with an outline, like `solidPolygons`. */
+export function triggerPolygons(
+  project: Project,
+  props: PropertyBag,
+  asset: TilemapAsset,
+): readonly CellPolygon[] {
+  return polygonCells(blockingCells(project, props, asset, { trigger: null }));
+}
+
+/**
+ * One cell of a trigger tile as the running game meets it (#160): what of the cell reports, in
+ * cells, and the area it is part of – the stretch of cells of the same tile touching side to side,
+ * named after its top-left one. Walking through a pond is one area, however many cells it crosses.
+ */
+export interface TriggerCell {
+  x: number;
+  y: number;
+  tileId: string;
+  area: string;
+  rects: readonly CellRect[];
+  polygons: readonly CellPolygon[];
+}
+
+const triggers = new KeyedMemo<ReadonlyMap<string, readonly TriggerCell[]>>();
+const NO_TRIGGERS: ReadonlyMap<string, readonly TriggerCell[]> = new Map();
+
+/**
+ * The trigger cells of a map by `x,y`. Each tile is worked out on its own, so a cell holding two
+ * trigger tiles on two layers reports both, and water next to lava is two areas.
+ */
+export function triggerCells(
+  project: Project,
+  props: PropertyBag,
+  asset: TilemapAsset,
+): ReadonlyMap<string, readonly TriggerCell[]> {
+  const tiles = triggerTiles(project, asset);
+  if (tiles.length === 0) return NO_TRIGGERS;
+  const blocks = tiles.map((tile) => blockingCells(project, props, asset, { trigger: tile.id }));
+  const key = tiles.map((tile, i) => `${tile.id}:${identityToken(blocks[i]!)}`).join(',');
+  return triggers.get(key, () => {
+    const byCell = new Map<string, TriggerCell[]>();
+    for (const [i, tile] of tiles.entries())
+      for (const cell of cellsOfTile(tile.id, blocks[i]!)) {
+        const at = `${cell.x},${cell.y}`;
+        const held = byCell.get(at);
+        if (held) held.push(cell);
+        else byCell.set(at, [cell]);
+      }
+    return byCell;
+  });
+}
+
+function cellsOfTile(tileId: string, blocks: readonly CellBlock[]): TriggerCell[] {
+  const boxes = new Map(boxCells(blocks).map((cell) => [`${cell.x},${cell.y}`, cell]));
+  const isBox = (x: number, y: number) => boxes.has(`${x},${y}`);
+  const areas = areasOf(blocks);
+  return blocks.map((block) => {
+    const at = `${block.x},${block.y}`;
+    const box = boxes.get(at);
+    return {
+      x: block.x,
+      y: block.y,
+      tileId,
+      area: areas.get(at)!,
+      rects: box
+        ? cellPieces(box, isBox).map((p) => ({ x: p.x0, y: p.y0, w: p.x1 - p.x0, h: p.y1 - p.y0 }))
+        : [],
+      polygons: box
+        ? []
+        : block.polygons.map(({ outline, pieces }) => ({ x: block.x, y: block.y, outline, pieces })),
+    };
+  });
+}
+
+/** Which area each cell is part of: cells joined side to side, the area named after its top-left cell. */
+function areasOf(cells: readonly { x: number; y: number }[]): Map<string, string> {
+  const open = new Set(cells.map((cell) => `${cell.x},${cell.y}`));
+  const areas = new Map<string, string>();
+  for (const first of [...cells].sort((a, b) => a.y - b.y || a.x - b.x)) {
+    const name = `${first.x},${first.y}`;
+    if (!open.delete(name)) continue;
+    const queue = [first];
+    for (let cell = queue.pop(); cell; cell = queue.pop()) {
+      areas.set(`${cell.x},${cell.y}`, name);
+      for (const [dx, dy] of [
+        [1, 0],
+        [-1, 0],
+        [0, 1],
+        [0, -1],
+      ] as const) {
+        const next = { x: cell.x + dx, y: cell.y + dy };
+        if (open.delete(`${next.x},${next.y}`)) queue.push(next);
+      }
+    }
+  }
+  return areas;
 }
 
 /**

src/core/properties/PropertySchema.ts

@@ -37,6 +37,7 @@ import {
   TILE_SORT_OFFSET_KEY,
   TILE_SORT_OFFSET_LIMIT,
   TILE_SOLID_KEY,
+  TILE_TRIGGER_KEY,
 } from '../model/tile';
 import { TILEMAP_COLUMNS_KEY, TILEMAP_MAX_CELLS, TILEMAP_ROWS_KEY, TILEMAP_TILE_KEY } from '../model/tilemap';
 import { PALETTE_KEY } from '../model/pixelart';
@@ -454,6 +455,8 @@ const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
     },
     // Solid is what the tile *is* – water, a wall – so it holds wherever the tile lies (#132).
     { key: TILE_SOLID_KEY, label: 'Solid', kind: 'boolean', default: false },
+    // A trigger tile blocks nothing and tells the collision events what lies on it (#160).
+    { key: TILE_TRIGGER_KEY, label: 'Trigger (reports, never blocks)', kind: 'boolean', default: false },
     // A solid tile that only blocks from above, like a platform one jumps through (#155).
     { key: TILE_ONE_WAY_KEY, label: 'One-way (from above)', kind: 'boolean', default: false },
     { ...ONE_WAY_ANGLE_ROW, key: TILE_ONE_WAY_ANGLE_KEY, shownWith: TILE_ONE_WAY_KEY },