Colliders take a frame's outline and tiles have their own surface (#193)

Issue #193 asked where friction, bounciness and density of a tile
live. Tiles had a fixed surface (friction 0.5, bounciness 0) and a
collider could not use the outline drawn on a texture frame (#141).
Both gaps are closed here.

- A collider has a fifth shape "Frame collision" with a Frame row.
  The frame is picked like a sprite's texture and stored as the
  value 'frame'.
- The shape is linked, not copied. Redrawing the outline in the
  texture tab changes every collider using that frame, in the editor
  and on the next play.
- The frame centre sits on the collider origin, one image pixel is
  one unit. The shape turns, scales and mirrors like any other.
- Every outline ring blocks. Each ring is split into convex parts the
  same way a polygon is.
- Without a frame, with a whole texture or with a frame that has no
  outline, the collider is drawn red as a box and blocks nothing.
- Move, Rapier, raycast, detection, hit test, drawing and footprint
  all resolve the frame. At runtime an entity looks the frame up
  live in the current project.
- A tile has Friction and Bounciness next to Solid and One-way. The
  rows only show when Solid is on. Defaults and mixing rules match
  the collider. Density is left out because a tilemap never moves.
- Tilemap cells are grouped by surface as well as by one-way angle.
  Ice and stone never merge into one rectangle, and every cell brings
  its surface to Move and Rapier.

Findings:

- A tile with a collision scale below 1 is no longer flush with a
  neighbour of another surface. It is inset there like at an open
  side, the same as next to one-way tiles today.
- A bounce test first measured 0.84. The ball had landed on the hero
  at the origin, not on the tile. On the tile it measures 0.993.

Tests:

- ./check.sh: 130 files, 1931 tests, exit 0 (was 129 / 1917).
- 14 new unit tests in tests/core/surface.test.ts. The Move tests run
  against the editor run and the physics system.
- 3 new e2e checks: 40l (surface rows follow Solid), 42e (collider
  has frame size, a walker climbs the slope in the frame).
- GM_STEPS=1-8,39-43 freshly seeded: ALL PASSED, 376 checks.
- Three counter-probes bite: Move ignores the tile surface (2 fail),
  Rapier ignores it (1 fails), frame shape falls back to a box
  (5 fail).
- Check sum 1198 is computed (1195 + 3), the full run belongs to CI.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -43,7 +43,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1195 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1198 checks (GM_STEPS=20 for one step)
                                                    #   every tool signs in first – see the Accounts page
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs

src/core/model/frameOutline.ts

@@ -0,0 +1,46 @@
+/**
+ * A frame's collision outlines (#141) as a collider wears them (#193): centred on the collider's
+ * origin, one image pixel to one unit – the size a sprite of that frame is placed with.
+ */
+import type { TextureFrame } from './Asset';
+import { convexPieces } from './polygon';
+import type { Project } from './Project';
+import type { Vec2 } from './Properties';
+import { findFrame } from './texture';
+
+export interface FrameOutline {
+  /** The frame's size in pixels, which is the collider's footprint. */
+  w: number;
+  h: number;
+  /** Every outline the frame has, in the collider's own units. */
+  rings: Vec2[][];
+  /** What collides: the convex pieces of every ring that is a polygon. */
+  pieces: Vec2[][];
+}
+
+/** One per drawn outline list, so a frame is cut into pieces once and not on every test. */
+const cache = new WeakMap<TextureFrame, { from: TextureFrame['collision']; outline: FrameOutline }>();
+
+function isCurrent(
+  known: { from: TextureFrame['collision']; outline: FrameOutline },
+  frame: TextureFrame,
+): boolean {
+  return known.from === frame.collision && known.outline.w === frame.w && known.outline.h === frame.h;
+}
+
+/**
+ * What the frame with that id blocks with, or null when the id names no frame. A frame without a
+ * drawn outline has no rings: the collider then collides with nothing, like a broken polygon.
+ */
+export function frameOutline(project: Project | null, frameId: string): FrameOutline | null {
+  const found = project ? findFrame(project, frameId) : null;
+  if (!found) return null;
+  const { frame } = found;
+  const known = cache.get(frame);
+  if (known && isCurrent(known, frame)) return known.outline;
+  const centre = (p: Vec2): Vec2 => ({ x: p.x - frame.w / 2, y: p.y - frame.h / 2 });
+  const rings = (frame.collision ?? []).map((ring) => ring.map(centre));
+  const outline = { w: frame.w, h: frame.h, rings, pieces: rings.flatMap((ring) => convexPieces(ring)) };
+  cache.set(frame, { from: frame.collision, outline });
+  return outline;
+}

src/core/model/tile.ts

@@ -26,6 +26,9 @@ export const TILE_ONE_WAY_KEY = 'oneWay';
 export const TILE_ONE_WAY_ANGLE_KEY = 'oneWayAngle';
 /** How big the blocking box of a cell is against the cell, 1 = the whole cell (#140). */
 export const TILE_COLLISION_SCALE_KEY = 'collisionScale';
+/** The surface of a solid tile (#193): the same rows, and the same defaults, as a collider's material. */
+export const TILE_FRICTION_KEY = 'friction';
+export const TILE_BOUNCINESS_KEY = 'bounciness';
 export const TILE_COLLISION_SCALE_MIN = 0.1;
 export const TILE_COLLISION_SCALE_MAX = 2;
 

src/core/model/tilemapCollision.ts

@@ -20,7 +20,8 @@
  *
  * One-way tiles (#155) block only from above. They are worked out on their own, by the same rules –
  * each function takes `oneWay` – so a platform never merges with a wall into one rectangle, nor with
- * a platform of another angle (#159).
+ * 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.
  */
 import type { TileAsset, TilemapAsset } from './Asset';
 import { tileQuadrants } from './autotile';
@@ -40,6 +41,7 @@ import {
 } from './tile';
 import { cellOrigin, inGrid, neighboursOf, parseCellKey, tilemapSize, tilemapTileSize } from './tilemap';
 import { type ColliderShape, oneWayAngle, type ShapeBounds } from '../properties/collider';
+import { colliderMaterial } from '../properties/rigidbody';
 
 /** A rectangle in cells: top-left corner and size. Whole cells at collision scale 1, parts of one otherwise. */
 export interface CellRect {
@@ -192,11 +194,51 @@ function tileOneWayAngle(tile: TileAsset): number {
   return oneWayAngle(tile.props[TILE_ONE_WAY_ANGLE_KEY]);
 }
 
-function passesFilter(tile: TileAsset, oneWay: OneWayFilter): boolean {
+/** The surface of a solid tile (#193), read like a collider's. A map never moves, so no density. */
+export interface TileMaterial {
+  friction: number;
+  bounciness: number;
+}
+
+export function tileMaterial(tile: TileAsset): TileMaterial {
+  const { friction, bounciness } = colliderMaterial(tile.props);
+  return { friction, bounciness };
+}
+
+function sameMaterial(a: TileMaterial, b: TileMaterial): boolean {
+  return a.friction === b.friction && a.bounciness === b.bounciness;
+}
+
+/**
+ * Which solid tiles a function looks at: those passing `oneWay`, and with a `material` only the
+ * tiles of that surface – so ice and rubber never merge into one rectangle (#193).
+ */
+function passesFilter(tile: TileAsset, oneWay: OneWayFilter, material?: TileMaterial): boolean {
+  if (material && !sameMaterial(tileMaterial(tile), material)) return false;
   if (!isTileOneWay(tile)) return oneWay === false;
   return oneWay === true || tileOneWayAngle(tile) === oneWay;
 }
 
+/** The surfaces of the solid tiles painted on the map that pass `oneWay`, each once. */
+export function tileMaterials(
+  project: Project,
+  asset: TilemapAsset,
+  oneWay: OneWayFilter = false,
+): TileMaterial[] {
+  const materials: TileMaterial[] = [];
+  const seen = new Set<string>();
+  for (const layer of asset.layers)
+    for (const tileId of Object.values(layer.cells)) {
+      if (!tileId || seen.has(tileId)) continue;
+      seen.add(tileId);
+      const tile = findAssetOf(project, tileId, 'tile');
+      if (!tile || !isTileSolid(tile) || !passesFilter(tile, oneWay)) continue;
+      const material = tileMaterial(tile);
+      if (!materials.some((known) => sameMaterial(known, material))) materials.push(material);
+    }
+  return materials.sort((a, b) => a.friction - b.friction || a.bounciness - b.bounciness);
+}
+
 /** The angles of the solid one-way tiles painted on the map, each once, smallest first. */
 export function oneWayAngles(project: Project, asset: TilemapAsset): number[] {
   const angles = new Set<number>();
@@ -216,13 +258,14 @@ function blockingCells(
   props: PropertyBag,
   asset: TilemapAsset,
   oneWay: OneWayFilter,
+  material?: TileMaterial,
 ): CellBlock[] {
   const tiles = new Map<string, { scale: number; shape: TileShape | null } | null>();
   const tileOf = (id: string) => {
     if (tiles.has(id)) return tiles.get(id)!;
     const tile = findAssetOf(project, id, 'tile');
     const value =
-      tile && isTileSolid(tile) && passesFilter(tile, oneWay)
+      tile && isTileSolid(tile) && passesFilter(tile, oneWay, material)
         ? { scale: tileCollisionScale(tile), shape: tileShape(project, tile) }
         : null;
     tiles.set(id, value);
@@ -279,8 +322,9 @@ export function solidCells(
   props: PropertyBag,
   asset: TilemapAsset,
   oneWay: OneWayFilter = false,
+  material?: TileMaterial,
 ): Required<SolidCell>[] {
-  return blockingCells(project, props, asset, oneWay)
+  return blockingCells(project, props, asset, oneWay, material)
     .filter((cell) => cell.box !== null)
     .map(({ x, y, box }) => ({ x, y, scale: box! }));
 }
@@ -296,9 +340,10 @@ export function solidPolygons(
   props: PropertyBag,
   asset: TilemapAsset,
   oneWay: OneWayFilter = false,
+  material?: TileMaterial,
 ): CellPolygon[] {
   const polygons: CellPolygon[] = [];
-  for (const cell of blockingCells(project, props, asset, oneWay)) {
+  for (const cell of blockingCells(project, props, asset, oneWay, material)) {
     if (cell.box !== null) continue;
     for (const { outline, pieces } of cell.polygons) polygons.push({ x: cell.x, y: cell.y, outline, pieces });
   }
@@ -410,8 +455,9 @@ export function solidRects(
   props: PropertyBag,
   asset: TilemapAsset,
   oneWay: OneWayFilter = false,
+  material?: TileMaterial,
 ): CellRect[] {
-  return mergeCells(solidCells(project, props, asset, oneWay));
+  return mergeCells(solidCells(project, props, asset, oneWay, material));
 }
 
 /**

src/core/properties/PropertySchema.ts

@@ -22,10 +22,12 @@ import {
 import { findAssetOf, type Project } from '../model/Project';
 import { ALL_LAYERS, COLLIDES_WITH_KEY, COLLISION_LAYER_KEY } from '../model/collisionLayers';
 import {
+  TILE_BOUNCINESS_KEY,
   TILE_COLLISION_SCALE_KEY,
   TILE_COLLISION_SCALE_MAX,
   TILE_COLLISION_SCALE_MIN,
   TILE_FPS_KEY,
+  TILE_FRICTION_KEY,
   TILE_KIND_KEY,
   TILE_ONE_WAY_ANGLE_KEY,
   TILE_ONE_WAY_KEY,
@@ -105,6 +107,25 @@ const ONE_WAY_ANGLE_ROW: FlatDef<'number'> = {
   shownWith: 'oneWay',
 };
 
+/** The surface a collider or a solid tile (#193) offers, read by the physics engine and by `Move` (#146, #150). */
+const FRICTION_ROW: FlatDef<'number'> = {
+  key: 'friction',
+  label: 'Friction',
+  kind: 'number',
+  default: 0.5,
+  min: 0,
+  step: 0.05,
+};
+const BOUNCINESS_ROW: FlatDef<'number'> = {
+  key: 'bounciness',
+  label: 'Bounciness',
+  kind: 'number',
+  default: 0,
+  min: 0,
+  max: 1,
+  step: 0.05,
+};
+
 /**
  * Which colliders may meet (#152). Both rows sit on colliders and on tilemaps, so a map can be
  * ground that only some things walk on. The defaults are layer 0 against every layer, which is
@@ -343,6 +364,9 @@ const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
     // 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 },
+    // No density: a map never moves, so what its cells would weigh counts for nothing.
+    { ...FRICTION_ROW, key: TILE_FRICTION_KEY, shownWith: TILE_SOLID_KEY },
+    { ...BOUNCINESS_ROW, key: TILE_BOUNCINESS_KEY, shownWith: TILE_SOLID_KEY },
     // Below 1 a cell blocks less than its square, above 1 more – but only on the sides without a
     // blocking neighbour, so a wall of such cells stays closed (#140).
     {
@@ -433,6 +457,7 @@ const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
         { value: 'circle', label: 'Circle' },
         { value: 'capsule', label: 'Capsule' },
         { value: 'polygon', label: 'Polygon' },
+        { value: 'frame', label: 'Frame collision' },
       ],
     },
     // A box and a capsule fill width × height; the capsule is rounded along the longer side.
@@ -450,10 +475,12 @@ const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
         { x: -50, y: 50 },
       ],
     },
+    // The frame whose collision outlines (#141) the "Frame collision" shape wears, kept linked (#193).
+    { key: 'frame', label: 'Frame', kind: 'texture', default: '' },
     { key: 'isTrigger', label: 'Trigger (no blocking)', kind: 'boolean', default: false },
     // The material, read by the physics engine where a rigidbody takes part (#146).
-    { key: 'friction', label: 'Friction', kind: 'number', default: 0.5, min: 0, step: 0.05 },
+    FRICTION_ROW,
-    { key: 'bounciness', label: 'Bounciness', kind: 'number', default: 0, min: 0, max: 1, step: 0.05 },
+    BOUNCINESS_ROW,
     { key: 'density', label: 'Density', kind: 'number', default: 1, min: 0, step: 0.1 },
     // Blocks only what comes from that side, turned with the object; the rest passes through (#155).
     { key: 'oneWay', label: 'One-way', kind: 'boolean', default: false },

src/core/properties/bounds.ts

@@ -4,6 +4,7 @@
  * where its corners are.
  */
 import { type AssetType, hasSceneIcon } from '../model/AssetTypes';
+import type { FrameOutline } from '../model/frameOutline';
 import {
   apply,
   boxCorners,
@@ -49,15 +50,22 @@ export function textAnchor(props: PropertyBag): number {
   return align === 'left' ? 0 : align === 'right' ? 1 : 0.5;
 }
 
-/** Centred on the object's position; text is anchored instead (see `textAnchor`). */
+/**
-export function footprintOf(type: AssetType, props: PropertyBag): { w: number; h: number } {
+ * Centred on the object's position; text is anchored instead (see `textAnchor`). A collider that
+ * wears a frame (#193) is that frame's size, which only the caller can look up.
+ */
+export function footprintOf(
+  type: AssetType,
+  props: PropertyBag,
+  frame?: FrameOutline | null,
+): { w: number; h: number } {
   switch (type) {
     case 'sprite':
       return { w: Number(props.width ?? 1), h: Number(props.height ?? 1) };
     case 'text':
       return textSize(props);
     case 'collider':
-      return colliderSize(props);
+      return colliderSize(props, frame);
     case 'behavior':
       return { w: BEHAVIOR_SYMBOL, h: BEHAVIOR_SYMBOL };
     case 'container':
@@ -93,16 +101,27 @@ function anchorOffset(type: AssetType, props: PropertyBag, w: number): number {
 }
 
 /** The footprint's corners in world units, grown by `pad` world units on every side. */
-export function footprintCorners(type: AssetType, props: PropertyBag, m: Mat, pad = 0): Vec2[] {
+export function footprintCorners(
+  type: AssetType,
+  props: PropertyBag,
+  m: Mat,
+  pad = 0,
+  frame?: FrameOutline | null,
+): Vec2[] {
   const placed = placementOf(type, m);
-  const { w, h } = footprintOf(type, props);
+  const { w, h } = footprintOf(type, props, frame);
   const local = pad / (scaleOf(placed) || 1);
   return boxCorners(placed, w + 2 * local, h + 2 * local, anchorOffset(type, props, w), 0);
 }
 
 /** The world rectangle around the drawn footprint – what culling, framing and labels need. */
-export function footprintExtent(type: AssetType, props: PropertyBag, m: Mat): Extent {
+export function footprintExtent(
-  return extentOfPoints(footprintCorners(type, props, m));
+  type: AssetType,
+  props: PropertyBag,
+  m: Mat,
+  frame?: FrameOutline | null,
+): Extent {
+  return extentOfPoints(footprintCorners(type, props, m, 0, frame));
 }
 
 export function footprintContains(type: AssetType, props: PropertyBag, m: Mat, point: Vec2): boolean {

src/core/properties/collider.ts

@@ -3,8 +3,10 @@
  * "overlaps" means. A box is oriented: it turns and grows with the body it sits on. A capsule and a
  * polygon (#151) carry their points in the world already, and a polygon its convex pieces.
  */
+import { type FrameOutline, frameOutline } from '../model/frameOutline';
 import { angleOf, apply, type Mat, scaleOf } from '../model/matrix';
 import { convexPieces, pointsOf, signedArea } from '../model/polygon';
+import type { Project } from '../model/Project';
 import { type PropertyBag, type PropertyValue, textOf, type Vec2 } from '../model/Properties';
 import { dot } from '../util/vec';
 import {
@@ -28,15 +30,55 @@ export type ColliderShape =
   | { kind: 'circle'; x: number; y: number; r: number }
   /** The segment `a`–`b` grown by `r`. */
   | { kind: 'capsule'; x: number; y: number; angle: number; a: Vec2; b: Vec2; r: number }
-  /** `outline` as drawn; `pieces` what collides – none when the outline is no polygon (see `polygonProblem`). */
+  /**
-  | { kind: 'polygon'; x: number; y: number; angle: number; outline: Vec2[]; pieces: Vec2[][] };
+   * `outline` as drawn; `pieces` what collides – none when the outline is no polygon (see
+   * `polygonProblem`). A frame's outline (#193) may be several rings: then `rings` holds them all,
+   * `outline` the first. Read them through `outlinesOf`.
+   */
+  | {
+      kind: 'polygon';
+      x: number;
+      y: number;
+      angle: number;
+      outline: Vec2[];
+      rings?: Vec2[][];
+      pieces: Vec2[][];
+    };
 
 type Box = Extract<ColliderShape, { kind: 'box' }>;
 type Circle = Extract<ColliderShape, { kind: 'circle' }>;
+type Polygon = Extract<ColliderShape, { kind: 'polygon' }>;
 type Classic = Box | Circle;
 
+/** Every outline a polygon is drawn with – one, or a frame's several (#193). */
+export function outlinesOf(shape: Polygon): Vec2[][] {
+  return shape.rings ?? [shape.outline];
+}
+
 /** Where a polygon collider keeps its corners (#151). */
 export const COLLIDER_POINTS_KEY = 'points';
+/** Which frame a collider of the shape "Frame collision" wears (#193): a frame id, as a sprite's texture holds it. */
+export const COLLIDER_FRAME_KEY = 'frame';
+
+/** Whether the collider wears a frame's outline (#193), which only the project can resolve. */
+export function wearsFrame(props: PropertyBag): boolean {
+  return props.shape === 'frame';
+}
+
+/** The frame a collider names, looked up in `project` – null for another shape or a dangling id. */
+export function colliderFrame(project: Project | null, props: PropertyBag): FrameOutline | null {
+  return wearsFrame(props) ? frameOutline(project, textOf(props[COLLIDER_FRAME_KEY] ?? '')) : null;
+}
+
+/** The four corners of a centred `w` × `h` box, clockwise on screen. */
+function boxRing(w: number, h: number): Vec2[] {
+  return [
+    { x: -w / 2, y: -h / 2 },
+    { x: w / 2, y: -h / 2 },
+    { x: w / 2, y: h / 2 },
+    { x: -w / 2, y: h / 2 },
+  ];
+}
 
 /** A polygon's pieces in its own units, cut once per stored list rather than on every test. */
 const piecesCache = new WeakMap<object, Vec2[][]>();
@@ -61,8 +103,12 @@ function capsuleCore(w: number, h: number): { a: Vec2; b: Vec2; r: number } {
   return { a: { x: -(w - h) / 2, y: 0 }, b: { x: (w - h) / 2, y: 0 }, r: h / 2 };
 }
 
-/** The shape as it sits in the world: sized by the transform's scale, turned (and mirrored) with it. */
+/**
-export function colliderShape(props: PropertyBag, m: Mat): ColliderShape {
+ * The shape as it sits in the world: sized by the transform's scale, turned (and mirrored) with it.
+ * A collider of the shape "Frame collision" (#193) needs its frame from `colliderFrame`. Without one it is drawn
+ * as the frame's box, or its own width × height, and collides with nothing.
+ */
+export function colliderShape(props: PropertyBag, m: Mat, frame?: FrameOutline | null): ColliderShape {
   const scale = scaleOf(m);
   if (props.shape === 'circle')
     return {
@@ -96,6 +142,20 @@ export function colliderShape(props: PropertyBag, m: Mat): ColliderShape {
       pieces: localPieces(value).map((piece) => piece.map((p) => apply(m, p))),
     };
   }
+  if (wearsFrame(props)) {
+    const worn = frame && frame.pieces.length > 0;
+    const rings = worn ? frame.rings : [frame ? boxRing(frame.w, frame.h) : boxRing(w, h)];
+    const placed = rings.map((ring) => ring.map((p) => apply(m, p)));
+    return {
+      kind: 'polygon',
+      x: m.tx,
+      y: m.ty,
+      angle: angleOf(m),
+      outline: placed[0] ?? [],
+      rings: placed,
+      pieces: worn ? frame.pieces.map((piece) => piece.map((p) => apply(m, p))) : [],
+    };
+  }
   return { kind: 'box', x: m.tx, y: m.ty, w: w * scale, h: h * scale, angle: angleOf(m) };
 }
 
@@ -167,13 +227,15 @@ export function movedShape(shape: ColliderShape, move: (p: Vec2) => Vec2, turn:
         ...centre,
         angle: shape.angle + turn,
         outline: shape.outline.map(move),
+        ...(shape.rings && { rings: shape.rings.map((ring) => ring.map(move)) }),
         pieces: shape.pieces.map((piece) => piece.map(move)),
       };
   }
 }
 
-/** The size in the collider's own units, before any transform. */
+/** The size in the collider's own units, before any transform; a worn frame (#193) is its own size. */
-export function colliderSize(props: PropertyBag): { w: number; h: number } {
+export function colliderSize(props: PropertyBag, frame?: FrameOutline | null): { w: number; h: number } {
+  if (wearsFrame(props) && frame) return { w: frame.w, h: frame.h };
   // Centred like every footprint, so it reaches as far as the farthest corner on each axis.
   if (props.shape === 'polygon') {
     const points = colliderPoints(props);
@@ -407,7 +469,7 @@ export function shapeBounds(shape: ColliderShape): ShapeBounds {
         bottom: Math.max(shape.a.y, shape.b.y) + shape.r,
       };
     case 'polygon':
-      return boundsOfPoints(shape.outline);
+      return boundsOfPoints(outlinesOf(shape).flat());
   }
 }
 

src/editor/viewport/FreeViewport.ts

@@ -34,7 +34,7 @@ export abstract class FreeViewport extends WorldViewport {
   fit(): void {
     const { items } = this.collectFrame();
     const boxes = items.map((item) => {
-      const e = footprintExtent(item.type, item.props, item.m);
+      const e = footprintExtent(item.type, item.props, item.m, item.frame);
       return { id: item.id, x: e.left, y: e.top, w: e.right - e.left, h: e.bottom - e.top };
     });
     const { minX, minY, maxX, maxY } = boundsOf(boxes, { minX: 0, minY: 0, maxX: 0, maxY: 0 })!;

src/editor/viewport/SceneViewport.ts

@@ -1094,7 +1094,7 @@ export class SceneViewport extends FreeViewport {
         if (!item) continue;
         // Two screen pixels outside the footprint, whichever way it is turned.
         const corners = this.screenCorners(
-          footprintCorners(item.type, item.props, item.m, 2 / view.scale),
+          footprintCorners(item.type, item.props, item.m, 2 / view.scale, item.frame),
           view,
         );
         // A switched-off object draws nothing, so its outline is the only way to see where it

src/editor/viewport/WorldViewport.ts

@@ -191,7 +191,7 @@ export abstract class WorldViewport extends Widget {
     const view = this.currentView();
     const item = this.lastItems.find((i) => i.id === objectId);
     if (!item || !view) return null;
-    const extent = footprintExtent(item.type, item.props, item.m);
+    const extent = footprintExtent(item.type, item.props, item.m, item.frame);
     const local = worldToScreen(view, (extent.left + extent.right) / 2, (extent.top + extent.bottom) / 2);
     const origin = this.getGlobalPosition();
     return {
@@ -229,8 +229,8 @@ export abstract class WorldViewport extends Widget {
     const seen = new Set<string>();
     for (const item of items) {
       seen.add(item.id);
-      const size = footprintOf(item.type, item.props);
+      const size = footprintOf(item.type, item.props, item.frame);
-      const extent = footprintExtent(item.type, item.props, item.m);
+      const extent = footprintExtent(item.type, item.props, item.m, item.frame);
       // A switched-off object is not drawn at all, in the scene view as in the game; it is
       // selected and switched back on from the hierarchy panel. A source is never culled by its
       // own little square: its particles may be anywhere on screen while it is not.

src/runtime/Entity.ts

@@ -1,6 +1,7 @@
 import type { ENTITY_HANDLE } from '../core/graph/NodeContext';
 import type { AnimationPlayer } from '../core/model/animation';
 import type { AssetType } from '../core/model/AssetTypes';
+import type { FrameOutline } from '../core/model/frameOutline';
 import type { PropertyBag } from '../core/model/Properties';
 
 /** A live instance of a scene object; its resolved props are mutable runtime state the world mirrors back. */
@@ -26,4 +27,9 @@ export interface Entity {
   animations?: AnimationPlayer[];
   /** How often an `Emit` node has restarted this particle source; out of `props` for the same reason. */
   emits?: number;
+  /**
+   * The frame a collider of the shape "Frame collision" wears (#193), looked up in the world's project on every
+   * call, so a changed `frame` prop or a redrawn outline counts at once. Absent outside a world.
+   */
+  wornFrame?: () => FrameOutline | null;
 }

src/runtime/World.ts

@@ -9,7 +9,7 @@ import { descendantsBelow } from '../core/model/walk';
 import { findAsset, findScene, type Project } from '../core/model/Project';
 import { createSceneObject, type SceneObject } from '../core/model/SceneObject';
 import { footprintContains } from '../core/properties/bounds';
-import { colliderShape, shapeContains } from '../core/properties/collider';
+import { colliderFrame, colliderShape, shapeContains } from '../core/properties/collider';
 import { resolveSceneObjectProps } from '../core/properties/resolve';
 import type { Entity } from './Entity';
 import type { System } from './systems/System';
@@ -176,6 +176,10 @@ export class World {
         props: {},
         parent: null,
       };
+      if (asset.type === 'collider') {
+        const collider = entity;
+        collider.wornFrame = () => colliderFrame(this.project, collider.props);
+      }
       this.entities.push(entity);
     }
     entity.assetId = asset.id;
@@ -309,7 +313,9 @@ export class World {
     const parts = [entity, ...this.descendantsOf(entity)].filter((e) => isHandleEnabled(e));
     const colliders = parts.filter((e) => e.type === 'collider');
     if (colliders.length > 0)
-      return colliders.some((c) => shapeContains(colliderShape(c.props, worldMatrixOf(c)), point));
+      return colliders.some((c) =>
+        shapeContains(colliderShape(c.props, worldMatrixOf(c), c.wornFrame?.()), point),
+      );
     return parts.some(
       (e) =>
         (e.type === 'sprite' || e.type === 'text') &&

src/runtime/physics/PhysicsSystem.ts

@@ -12,6 +12,7 @@ import type { Vec2 } from '../../core/model/Properties';
 import { signedArea } from '../../core/model/polygon';
 import { parentChain } from '../../core/model/walk';
 import { collisionFilterOf, interactionGroups } from '../../core/model/collisionLayers';
+import type { TileMaterial } from '../../core/model/tilemapCollision';
 import {
   type ColliderShape,
   contactBetween,
@@ -47,6 +48,7 @@ import {
   shapeOf,
   type SolidShape,
   Solids,
+  surfaceOf,
 } from '../systems/solids';
 import type { System } from '../systems/System';
 import { type Rapier, toMetres, toPixels } from './engine';
@@ -507,10 +509,11 @@ export class PhysicsSystem implements System, CollisionSource {
     const local = shapes.map((solid) => ({ ...solid, pieces: piecesInBody(origin, solid.shape) }));
     const shapeKey =
       JSON.stringify(
-        local.map(({ entity, pieces, facing }) => [
+        local.map(({ entity, pieces, facing, surface }) => [
           entity.id,
           pieces.map(pieceKey),
           facing && [round(facing.x), round(facing.y), facing.cone],
+          surface ?? 0,
           entity.type === 'collider' ? [isTrigger(entity.props), colliderMaterial(entity.props)] : 0,
           // The layers sit on the engine collider, so changing one has to rebuild it (#152).
           interactionGroups(collisionFilterOf(entity.props)),
@@ -530,10 +533,10 @@ export class PhysicsSystem implements System, CollisionSource {
         (sum, { entity, shape }) => sum + (isSolid(entity) ? shapeArea(shape) : 0),
         0,
       );
-      for (const { entity, shape, facing, pieces } of local)
+      for (const { entity, shape, facing, surface, pieces } of local)
         for (const piece of pieces) {
           const share = mass > 0 && area > 0 ? (mass * pieceArea(piece)) / area : 0;
-          const desc = this.colliderDesc(entity, piece, share, facing !== null);
+          const desc = this.colliderDesc(entity, piece, share, facing !== null, surface);
           if (!desc) continue;
           const collider = this.engine!.createCollider(desc, body.body);
           body.colliders.push(collider);
@@ -574,7 +577,13 @@ export class PhysicsSystem implements System, CollisionSource {
   }
 
   /** The engine collider of one piece; null for a piece of no size, which the engine would refuse. */
-  private colliderDesc(entity: Entity, piece: Piece, mass: number, oneWay: boolean): ColliderDesc | null {
+  private colliderDesc(
+    entity: Entity,
+    piece: Piece,
+    mass: number,
+    oneWay: boolean,
+    surface?: TileMaterial,
+  ): ColliderDesc | null {
     const R = this.rapier;
     if (pieceArea(piece) <= 0) return null;
     let desc: ColliderDesc | null;
@@ -597,9 +606,10 @@ export class PhysicsSystem implements System, CollisionSource {
     if (!desc) return null;
     if (piece.kind !== 'convex')
       desc.setTranslation(toMetres(piece.x), toMetres(piece.y)).setRotation(piece.angle);
-    // A tile has no material of its own; it gets what a new collider starts with.
+    // A tile's cell brings its tile's surface (#193); a density it does not need, a map never moves.
     const material = colliderMaterial(entity.type === 'collider' ? entity.props : {});
-    desc.setFriction(material.friction).setRestitution(material.bounciness);
+    const { friction, bounciness } = surfaceOf(entity, surface);
+    desc.setFriction(friction).setRestitution(bounciness);
     // The livelier side wins, as in Box2D: a ball that should bounce does so on plain ground too.
     desc.setRestitutionCombineRule(R.CoefficientCombineRule.Max);
     if (!isSolid(entity)) desc.setSensor(true).setDensity(0);

src/runtime/systems/solids.ts

@@ -13,6 +13,8 @@ import {
   oneWayAngles,
   solidPolygons,
   solidRects,
+  type TileMaterial,
+  tileMaterials,
 } from '../../core/model/tilemapCollision';
 import { parentChain } from '../../core/model/walk';
 import {
@@ -106,6 +108,8 @@ export const NOT_BLOCKED: MoveResult = Object.freeze({
 export interface SolidShape {
   shape: ColliderShape;
   facing: OneWaySide | null;
+  /** A tilemap cell's surface (#193); a collider's is read off its own props (see `surfaceOf`). */
+  surface?: TileMaterial;
 }
 
 /** A shape in the mover's way and the collider or tilemap it belongs to. */
@@ -143,6 +147,8 @@ export interface RayFilter {
 /** Where a sweep stopped: what it met, with which own collider, the normal, and the move left over. */
 interface SweepContact {
   by: Entity;
+  /** The surface of the shape met when it is a tile's (#193). */
+  surface?: TileMaterial;
   own: Entity;
   normal: Vec2;
   left: Vec2;
@@ -203,17 +209,15 @@ export class Solids {
       const asset = findAssetOf(world.project, tilemap.assetId, 'tilemap');
       const { project } = world;
       const { props } = tilemap;
-      blocks = asset
+      // One group per side and surface, so cells only merge with cells that block alike (#159, #193).
-        ? {
+      const groups = (angle: number | null) =>
-            rects: solidRects(project, props, asset),
+        tileMaterials(project, asset!, angle ?? false).map((material) => ({
-            polygons: solidPolygons(project, props, asset),
-            oneWay: oneWayAngles(project, asset).map((angle) => ({
           angle,
-              rects: solidRects(project, props, asset, angle),
+          material,
-              polygons: solidPolygons(project, props, asset, angle),
+          rects: solidRects(project, props, asset!, angle ?? false, material),
-            })),
+          polygons: solidPolygons(project, props, asset!, angle ?? false, material),
-          }
+        }));
-        : { rects: [], polygons: [], oneWay: [] };
+      blocks = asset ? [...groups(null), ...oneWayAngles(project, asset).flatMap(groups)] : [];
       this.blocks.set(tilemap, blocks);
     }
     return blocks;
@@ -228,27 +232,25 @@ export class Solids {
   solidShapesOf(world: World, body: Entity, within?: ShapeBounds): SolidShape[] {
     const m = worldMatrixOf(body);
     if (body.type !== 'tilemap')
-      return [{ shape: colliderShape(body.props, m), facing: oneWayFacing(body.props, m) }];
+      return [
-    const { rects, polygons, oneWay } = this.blocksOf(world, body);
+        { shape: colliderShape(body.props, m, body.wornFrame?.()), facing: oneWayFacing(body.props, m) },
+      ];
     const up = oneWayFacing({ oneWay: true }, m);
     // A map is many solids under one entity, so the cells out of reach are dropped before any of
     // them is worked out in world units at all (#184).
     const range = within ? cellsWithin(body.props, m, within) : null;
     const near = (x: number, y: number, w?: number, h?: number) => !range || cellsMeet(range, x, y, w, h);
-    const shapes = (cells: CellRect[], outlines: CellPolygon[], facing: OneWaySide | null) => [
+    return this.blocksOf(world, body).flatMap(({ angle, material: surface, rects, polygons }) => {
-      ...cells
+      const facing = angle === null ? null : up && { ...up, cone: oneWayCone(angle) };
-        .filter((rect) => near(rect.x, rect.y, rect.w, rect.h))
-        .map((rect) => ({ shape: cellRectShape(body.props, rect, m), facing })),
-      ...outlines
-        .filter((polygon) => near(polygon.x, polygon.y))
-        .map((polygon) => ({ shape: cellPolygonShape(body.props, polygon, m), facing })),
-    ];
       return [
-      ...shapes(rects, polygons, null),
+        ...rects
-      ...oneWay.flatMap((group) =>
+          .filter((rect) => near(rect.x, rect.y, rect.w, rect.h))
-        shapes(group.rects, group.polygons, up && { ...up, cone: oneWayCone(group.angle) }),
+          .map((rect) => ({ shape: cellRectShape(body.props, rect, m), facing, surface })),
-      ),
+        ...polygons
+          .filter((polygon) => near(polygon.x, polygon.y))
+          .map((polygon) => ({ shape: cellPolygonShape(body.props, polygon, m), facing, surface })),
       ];
+    });
   }
 
   shapesOf(world: World, body: Entity, within?: ShapeBounds): ColliderShape[] {
@@ -391,7 +393,11 @@ export class Solids {
       const contact = sweep(entity, frame, own, obstacles, passing, rest);
       if (!contact) break;
       contacts.push(contact);
-      rest = slideAlong(contact.left, contact.normal, frictionBetween(contact.own, contact.by));
+      rest = slideAlong(
+        contact.left,
+        contact.normal,
+        frictionBetween(contact.own, contact.by, contact.surface),
+      );
     }
     if (contacts.length === 0) return NOT_BLOCKED;
     const pushed = new Set<Entity>();
@@ -486,6 +492,7 @@ function sweep(
     const left = distance - i * step - (step - correction);
     return {
       by: obstacle.body,
+      surface: obstacle.surface,
       own: collider,
       normal: contactBetween(shapeOf(collider), obstacle.shape, forward).normal,
       left: { x: forward.x * left, y: forward.y * left },
@@ -510,12 +517,15 @@ function slideAlong(move: Vec2, normal: Vec2, friction: number): Vec2 {
 
 /**
  * The friction of a pair, as the physics engine combines it for its bodies (the average), so an
- * object moved by the graph slides as far as one the engine moves. A tile has no material of its
+ * object moved by the graph slides as far as one the engine moves. A tile brings its own (#193).
- * own and has what a new collider starts with.
  */
-function frictionBetween(own: Entity, obstacle: Entity): number {
+function frictionBetween(own: Entity, obstacle: Entity, surface?: TileMaterial): number {
-  const of = (e: Entity) => colliderMaterial(e.type === 'collider' ? e.props : {}).friction;
+  return (surfaceOf(own).friction + surfaceOf(obstacle, surface).friction) / 2;
-  return (of(own) + of(obstacle)) / 2;
+}
+
+/** What a shape of `body` offers to what meets it: a tile's own surface, else the collider's material. */
+export function surfaceOf(body: Entity, surface?: TileMaterial): TileMaterial {
+  return surface ?? colliderMaterial(body.type === 'collider' ? body.props : {});
 }
 
 /** The rectangle around every shape, or null without one – nothing to narrow anything down with. */
@@ -552,15 +562,19 @@ function unitOf(v: Vec2): Vec2 {
   return length > 0 ? { x: v.x / length, y: v.y / length } : v;
 }
 
-interface TilemapBlocks {
+/**
+ * A map's blocking cells, one group per surface (#193) and side: `angle` null for the cells that
+ * block from everywhere, else the angle one-way cells land things within (#159).
+ */
+type TilemapBlocks = {
+  angle: number | null;
+  material: TileMaterial;
   rects: CellRect[];
   polygons: CellPolygon[];
-  /** The one-way cells, one group per angle their tiles land things within. */
+}[];
-  oneWay: { angle: number; rects: CellRect[]; polygons: CellPolygon[] }[];
-}
 
 export function shapeOf(collider: Entity): ColliderShape {
-  return colliderShape(collider.props, worldMatrixOf(collider));
+  return colliderShape(collider.props, worldMatrixOf(collider), collider.wornFrame?.());
 }
 
 /** What of an entity stops at walls when it moves: its solid colliders that are switched on. */

src/viewport/items.ts

@@ -17,6 +17,8 @@ import {
 import { findAsset, findAssetOf, type ObjectHolder, type Project } from '../core/model/Project';
 import { fontFileOf } from '../core/model/font';
 import { resolveTexture, type TextureRef } from '../core/model/texture';
+import type { FrameOutline } from '../core/model/frameOutline';
+import { colliderFrame } from '../core/properties/collider';
 import { enabledAlongChain } from '../core/properties/enabled';
 import { fontOf } from '../core/properties/fonts';
 import { resolveSceneObjectProps } from '../core/properties/resolve';
@@ -49,6 +51,8 @@ export interface DrawItem {
   tilemap: TilemapDraw | null;
   /** How often an `Emit` node has restarted this source; a change is what makes it start over. */
   emits: number;
+  /** The frame a collider of the shape "Frame collision" wears (#193), resolved here like a sprite's picture. */
+  frame: FrameOutline | null;
 }
 
 interface DrawList {
@@ -167,6 +171,7 @@ export function collectHolderItems(
       particles: asset.type === 'particles' ? asset : null,
       tilemap: asset.type === 'tilemap' ? resolveTilemap(project, asset.id, props) : null,
       emits: 0,
+      frame: asset.type === 'collider' ? colliderFrame(project, props) : null,
     });
   }
   const byId = new Map(items.map((i) => [i.id, i]));
@@ -204,6 +209,7 @@ export function collectWorldItems(world: World): DrawList {
       particles: e.type === 'particles' ? (findAssetOf(world.project, e.assetId, 'particles') ?? null) : null,
       tilemap: e.type === 'tilemap' ? resolveTilemap(world.project, e.assetId, e.props) : null,
       emits: e.emits ?? 0,
+      frame: e.wornFrame?.() ?? null,
     }));
   return { items, background: world.backgroundColor };
 }

src/viewport/symbols.ts

@@ -8,6 +8,7 @@ import {
   isTrigger,
   oneWayAngle,
   oneWayFacing,
+  outlinesOf,
 } from '../core/properties/collider';
 import { SHEET_EDGE } from '../core/shader/nodes';
 import type { NineSlice } from '../core/model/texture';
@@ -150,9 +151,10 @@ export function drawItem(
     case 'collider': {
       // Only the outline band is hit-testable, so clicks inside still reach the sprite that the
       // collider sits on.
-      const shape = colliderShape(item.props, IDENTITY);
+      const shape = colliderShape(item.props, IDENTITY, item.frame);
       traceShape(node, shape);
-      // A polygon that crosses itself collides with nothing, and says so in red.
+      // A polygon that crosses itself collides with nothing, and says so in red – as does a frame
+      // outline without a frame or without a drawn outline (#193).
       const color =
         shape.kind === 'polygon' && shape.pieces.length === 0
           ? Theme.colors.danger
@@ -201,7 +203,7 @@ function shapeBounds(shape: ColliderShape): Bounds {
               { x: p.x - shape.r, y: p.y - shape.r },
               { x: p.x + shape.r, y: p.y + shape.r },
             ])
-          : shape.outline;
+          : outlinesOf(shape).flat();
   return {
     left: Math.min(...points.map((p) => p.x)),
     top: Math.min(...points.map((p) => p.y)),
@@ -280,7 +282,7 @@ function traceShape(node: Graphics, shape: ColliderShape): void {
       return;
     }
     case 'polygon':
-      if (shape.outline.length >= 2) node.poly(shape.outline, true);
+      for (const ring of outlinesOf(shape)) if (ring.length >= 2) node.poly(ring, true);
       return;
   }
 }
@@ -299,10 +301,12 @@ function colliderOutlineHitArea(
   if (shape.kind === 'capsule')
     return { contains: (x, y) => Math.abs(distanceToSegment({ x, y }, shape.a, shape.b) - shape.r) <= band };
   if (shape.kind === 'polygon') {
-    const ring = shape.outline;
+    const rings = outlinesOf(shape);
     return {
       contains: (x, y) =>
+        rings.some((ring) =>
           ring.some((a, i) => distanceToSegment({ x, y }, a, ring[(i + 1) % ring.length]!) <= band),
+        ),
     };
   }
   const hw = shape.w / 2;

tests/core/one-way-angle.test.ts

@@ -105,8 +105,12 @@ describe('the one-way angle (#159)', () => {
     const angleRow = tile.find((d) => d.key === TILE_ONE_WAY_ANGLE_KEY)!;
     expect(isRowShown(angleRow, { [TILE_ONE_WAY_KEY]: false })).toBe(false);
     expect(isRowShown(angleRow, { [TILE_ONE_WAY_KEY]: true })).toBe(true);
-    // Rows without a switch are always there.
+    // Rows without a switch are always there; the surface waits for Solid (#193).
-    expect(tile.filter((d) => !isRowShown(d, {})).map((d) => d.key)).toEqual([TILE_ONE_WAY_ANGLE_KEY]);
+    expect(tile.filter((d) => !isRowShown(d, {})).map((d) => d.key)).toEqual([
+      TILE_ONE_WAY_ANGLE_KEY,
+      'friction',
+      'bounciness',
+    ]);
   });
 });
 

tests/core/surface.test.ts

@@ -0,0 +1,316 @@
+import { beforeAll, describe, expect, it } from 'vitest';
+import { CreateAssetCommand, SetAssetPropertyCommand } from '../../src/core/commands/assetCommands';
+import { AddColliderCommand, AddRigidbodyCommand } from '../../src/core/commands/colliderCommands';
+import { AddFrameCommand, SetFrameCollisionCommand } from '../../src/core/commands/frameCommands';
+import { SetOverrideCommand } from '../../src/core/commands/sceneObjectCommands';
+import { PaintTilesCommand } from '../../src/core/commands/tilemapCommands';
+import type { TextureAsset, TilemapAsset, TileAsset } from '../../src/core/model/Asset';
+import { translation } from '../../src/core/model/matrix';
+import type { PropertyValue, Vec2 } from '../../src/core/model/Properties';
+import { findAsset } from '../../src/core/model/Project';
+import { TILE_BOUNCINESS_KEY, TILE_FRICTION_KEY, TILE_SOLID_KEY } from '../../src/core/model/tile';
+import { TILEMAP_COLUMNS_KEY, TILEMAP_ROWS_KEY } from '../../src/core/model/tilemap';
+import { solidRects, tileMaterial, tileMaterials } from '../../src/core/model/tilemapCollision';
+import {
+  colliderFrame,
+  colliderShape,
+  colliderSize,
+  outlinesOf,
+  shapeContains,
+} from '../../src/core/properties/collider';
+import { isRowShown, schemaFor } from '../../src/core/properties/PropertySchema';
+import { loadPhysics } from '../../src/runtime/physics/engine';
+import { COLLISION_SYSTEMS, makeSpriteScene, place, roundTrip, startWorld } from '../helpers';
+
+beforeAll(async () => {
+  await loadPhysics();
+});
+
+const P = (...xy: number[]) =>
+  Array.from({ length: xy.length / 2 }, (_, i) => ({ x: xy[2 * i]!, y: xy[2 * i + 1]! }));
+
+/**
+ * A scene with a texture of one 40 × 40 frame, and `add`, which places an object with a collider
+ * (and maybe a rigidbody) and sets the collider's properties.
+ */
+function frameScene() {
+  const f = makeSpriteScene('Thing');
+  const texture = new CreateAssetCommand('texture', 'Sheet');
+  f.stack.execute(texture);
+  const sheet = findAsset(f.project, texture.asset.id) as TextureAsset;
+  sheet.file = `${'a'.repeat(64)}.png`;
+  sheet.width = 64;
+  sheet.height = 64;
+  const frame = new AddFrameCommand(texture.asset.id, { x: 0, y: 0, w: 40, h: 40 });
+  f.stack.execute(frame);
+  const outline = (...outlines: Vec2[][]) =>
+    f.stack.execute(new SetFrameCollisionCommand(texture.asset.id, frame.frameId, outlines));
+  const add = (at: Vec2, collider: Record<string, PropertyValue>, body?: Record<string, PropertyValue>) => {
+    const id = place(f, f.spriteId, at);
+    const command = new AddColliderCommand(f.sceneId, id);
+    f.stack.execute(command);
+    for (const [key, value] of Object.entries(collider))
+      f.stack.execute(new SetOverrideCommand(f.sceneId, command.objectId, key, value));
+    if (body) f.stack.execute(new AddRigidbodyCommand(f.sceneId, id));
+    return id;
+  };
+  return { ...f, textureId: texture.asset.id, frameId: frame.frameId, outline, add };
+}
+
+/** The right half of the 40 × 40 frame: in the collider's units x runs 0 … 20, y −20 … 20. */
+const RIGHT_HALF = P(20, 0, 40, 0, 40, 40, 20, 40);
+/** A triangle in the top left corner and a square in the bottom right: two rings. */
+const TRIANGLE = P(0, 0, 16, 0, 0, 16);
+const SQUARE = P(24, 24, 36, 24, 36, 36, 24, 36);
+
+describe('a collider wearing a frame outline (#193)', () => {
+  it('is a shape of its own with a frame row, the frame picked like a texture', () => {
+    const schema = schemaFor('collider');
+    const shape = schema.find((d) => d.key === 'shape')!;
+    expect(shape.kind === 'enum' && shape.options.map((o) => o.value)).toContain('frame');
+    expect(schema.find((d) => d.key === 'frame')).toMatchObject({ kind: 'texture', default: '' });
+  });
+
+  it('takes every ring of the frame, centred on its origin, a pixel to a unit, and the frame size', () => {
+    const s = frameScene();
+    s.outline(TRIANGLE, SQUARE);
+    const props = { shape: 'frame', frame: s.frameId };
+    const frame = colliderFrame(s.project, props);
+    expect(frame).toMatchObject({ w: 40, h: 40 });
+    expect(colliderSize(props, frame)).toEqual({ w: 40, h: 40 });
+    const shape = colliderShape(props, translation(100, 50), frame);
+    if (shape.kind !== 'polygon') throw new Error(shape.kind);
+    expect(outlinesOf(shape)).toEqual([P(80, 30, 96, 30, 80, 46), P(104, 54, 116, 54, 116, 66, 104, 66)]);
+    // Inside a ring collides, the gap between them does not.
+    expect(shapeContains(shape, { x: 83, y: 33 })).toBe(true);
+    expect(shapeContains(shape, { x: 110, y: 60 })).toBe(true);
+    expect(shapeContains(shape, { x: 100, y: 50 })).toBe(false);
+  });
+
+  it('stays linked: a redrawn outline is what the collider wears next, and undo brings the old one back', () => {
+    const s = frameScene();
+    s.outline(TRIANGLE);
+    const props = { shape: 'frame', frame: s.frameId };
+    const ringsNow = () => colliderFrame(s.project, props)!.rings;
+    expect(ringsNow()).toHaveLength(1);
+    s.outline(TRIANGLE, SQUARE);
+    expect(ringsNow()).toHaveLength(2);
+    s.stack.undo();
+    expect(ringsNow()).toEqual([P(-20, -20, -4, -20, -20, -4)]);
+  });
+
+  it('without a frame, with a whole texture or with nothing drawn it is a box that collides with nothing', () => {
+    const s = frameScene();
+    const shapeOf = (frame: string) => {
+      const props = { shape: 'frame', frame, width: 30, height: 10 };
+      return colliderShape(props, translation(0, 0), colliderFrame(s.project, props));
+    };
+    // No frame, or an id that is no frame: the collider's own width × height.
+    for (const id of ['', s.textureId, 'gone'])
+      expect(shapeOf(id), id).toMatchObject({
+        kind: 'polygon',
+        outline: P(-15, -5, 15, -5, 15, 5, -15, 5),
+        pieces: [],
+      });
+    // A frame nobody drew an outline on: the frame's box.
+    expect(shapeOf(s.frameId)).toMatchObject({ outline: P(-20, -20, 20, -20, 20, 20, -20, 20), pieces: [] });
+  });
+
+  it('keeps shape and frame through a round trip', () => {
+    const s = frameScene();
+    s.outline(RIGHT_HALF);
+    s.add({ x: 0, y: 0 }, { shape: 'frame', frame: s.frameId });
+    const collider = roundTrip(s.project).assets.find((a) => a.type === 'collider')!;
+    const object = roundTrip(s.project)
+      .assets.flatMap((a) => (a.type === 'scene' ? a.objects : []))
+      .find((o) => o.assetId === collider.id)!;
+    expect(object.overrides).toMatchObject({ shape: 'frame', frame: s.frameId });
+  });
+});
+
+describe.each(COLLISION_SYSTEMS)(
+  '$system: a frame outline blocks where it is drawn (#193)',
+  ({ physics }) => {
+    it('Move stops at the outline, not at the frame box, and a click hits only the outline', () => {
+      const s = frameScene();
+      s.outline(RIGHT_HALF);
+      const wall = s.add({ x: 100, y: 0 }, { shape: 'frame', frame: s.frameId });
+      const hero = s.add({ x: 0, y: 0 }, { width: 20, height: 20 });
+      const { world, collisions } = startWorld(s, { physics, collisions: true });
+      const mover = world.findByObjectId(hero)!;
+      expect(collisions.moveAndSlide(world, mover, 200, 0)).toMatchObject({ blockedX: true, hit: true });
+      // The outline's left face is at 100 (the frame's would be at 80): the hero's right side stops there.
+      expect(mover.x).toBeCloseTo(90, 6);
+      const target = world.findByObjectId(wall)!;
+      expect(world.hitTest(target, 110, 0)).toBe(true);
+      expect(world.hitTest(target, 90, 0)).toBe(false);
+    });
+  },
+);
+
+describe('physics: a body lands on a frame outline (#193)', () => {
+  it('a dropped box comes to rest on the drawn top, not on the frame box', () => {
+    const s = frameScene();
+    // The lower half of the frame: its top face lies at the collider's origin.
+    s.outline(P(0, 20, 40, 20, 40, 40, 0, 40));
+    s.add({ x: 0, y: 200 }, { shape: 'frame', frame: s.frameId });
+    const box = s.add({ x: 0, y: 100 }, { width: 10, height: 10 }, {});
+    const started = startWorld(s, { physics: true, collisions: true });
+    for (let i = 0; i < 120; i++) started.frame(1 / 60);
+    // Resting on y = 200, half its 10 up; the frame box would hold it at 175.
+    expect(started.world.findByObjectId(box)!.y).toBeCloseTo(195, 0);
+  });
+});
+
+/**
+ * A scene with a 10 × 10 map of 48 px cells at the origin – cell (x, y) spans x·48 − 240 … – a
+ * solid Wall and a solid Ice tile, and a 40 × 40 hero with a collider at the origin.
+ */
+function tileScene() {
+  const f = makeSpriteScene('Hero');
+  f.stack.execute(new SetAssetPropertyCommand(f.spriteId, 'width', 40));
+  f.stack.execute(new SetAssetPropertyCommand(f.spriteId, 'height', 40));
+  const wall = new CreateAssetCommand('tile', 'Wall');
+  const ice = new CreateAssetCommand('tile', 'Ice');
+  const map = new CreateAssetCommand('tilemap', 'Ground');
+  for (const command of [wall, ice, map]) f.stack.execute(command);
+  for (const tile of [wall, ice])
+    f.stack.execute(new SetAssetPropertyCommand(tile.asset.id, TILE_SOLID_KEY, true));
+  f.stack.execute(new SetAssetPropertyCommand(ice.asset.id, TILE_FRICTION_KEY, 0));
+  f.stack.execute(new SetAssetPropertyCommand(map.asset.id, TILEMAP_COLUMNS_KEY, 10));
+  f.stack.execute(new SetAssetPropertyCommand(map.asset.id, TILEMAP_ROWS_KEY, 10));
+  place(f, map.asset.id, { x: 0, y: 0 });
+  const hero = place(f, f.spriteId, { x: 0, y: 0 });
+  f.stack.execute(new AddColliderCommand(f.sceneId, hero));
+  const mapAsset = () => findAsset(f.project, map.asset.id) as TilemapAsset;
+  const paint = (at: [number, number][], tileId: string) =>
+    f.stack.execute(
+      new PaintTilesCommand(
+        map.asset.id,
+        mapAsset().layers[0]!.id,
+        at.map(([x, y]) => ({ x, y, tileId })),
+      ),
+    );
+  const tile = (id: string) => findAsset(f.project, id) as TileAsset;
+  return { ...f, wallId: wall.asset.id, iceId: ice.asset.id, mapAsset, paint, hero, tile };
+}
+
+const COLUMN_SIX = Array.from({ length: 10 }, (_, y) => [6, y] as [number, number]);
+
+describe('the surface of a solid tile (#193)', () => {
+  it('has the rows and defaults of a collider, no density, shown only while the tile is solid', () => {
+    const tile = schemaFor('tile');
+    expect(tile.find((d) => d.key === TILE_FRICTION_KEY)).toMatchObject({
+      kind: 'number',
+      default: 0.5,
+      min: 0,
+    });
+    expect(tile.find((d) => d.key === TILE_BOUNCINESS_KEY)).toMatchObject({ default: 0, min: 0, max: 1 });
+    expect(tile.some((d) => d.key === 'density')).toBe(false);
+    const row = tile.find((d) => d.key === TILE_FRICTION_KEY)!;
+    expect(isRowShown(row, { [TILE_SOLID_KEY]: false })).toBe(false);
+    expect(isRowShown(row, { [TILE_SOLID_KEY]: true })).toBe(true);
+  });
+
+  it('is read like a collider material and survives a round trip', () => {
+    const s = tileScene();
+    expect(tileMaterial(s.tile(s.wallId))).toEqual({ friction: 0.5, bounciness: 0 });
+    s.stack.execute(new SetAssetPropertyCommand(s.iceId, TILE_BOUNCINESS_KEY, 0.8));
+    const ice = findAsset(roundTrip(s.project), s.iceId) as TileAsset;
+    expect(tileMaterial(ice)).toEqual({ friction: 0, bounciness: 0.8 });
+    // Out of range or unreadable, held like a collider's.
+    s.tile(s.iceId).props[TILE_BOUNCINESS_KEY] = 7;
+    s.tile(s.iceId).props[TILE_FRICTION_KEY] = 'x';
+    expect(tileMaterial(s.tile(s.iceId))).toEqual({ friction: 0.5, bounciness: 1 });
+  });
+
+  it('ice and wall never merge into one rectangle; each surface is its own group', () => {
+    const s = tileScene();
+    s.paint(
+      [
+        [0, 0],
+        [1, 0],
+      ],
+      s.wallId,
+    );
+    s.paint(
+      [
+        [2, 0],
+        [3, 0],
+      ],
+      s.iceId,
+    );
+    const asset = s.mapAsset();
+    // Drawn, the row is one rectangle; for collision, one per surface.
+    expect(solidRects(s.project, asset.props, asset)).toEqual([{ x: 0, y: 0, w: 4, h: 1 }]);
+    const materials = tileMaterials(s.project, asset);
+    expect(materials).toEqual([
+      { friction: 0, bounciness: 0 },
+      { friction: 0.5, bounciness: 0 },
+    ]);
+    expect(solidRects(s.project, asset.props, asset, false, materials[0])).toEqual([
+      { x: 2, y: 0, w: 2, h: 1 },
+    ]);
+    expect(solidRects(s.project, asset.props, asset, false, materials[1])).toEqual([
+      { x: 0, y: 0, w: 2, h: 1 },
+    ]);
+  });
+});
+
+describe.each(COLLISION_SYSTEMS)('$system: Move slides by the tile surface (#193)', ({ physics }) => {
+  /** The hero pressed against column six while walking down it, 60 times: how far down it got. */
+  function slideDown(tileId: 'wall' | 'ice'): number {
+    const s = tileScene();
+    s.paint(COLUMN_SIX, tileId === 'wall' ? s.wallId : s.iceId);
+    const { world, collisions } = startWorld(s, { physics, collisions: true });
+    const hero = world.findByObjectId(s.hero)!;
+    hero.y = -200;
+    collisions.moveAndSlide(world, hero, 97.3, 0);
+    for (let i = 0; i < 60; i++) collisions.moveAndSlide(world, hero, 3.1, 6.7);
+    expect(hero.x).toBeCloseTo(28, 6);
+    return hero.y + 200;
+  }
+
+  it('the pair averages the hero’s 0.5 with the tile’s own friction', () => {
+    expect(slideDown('wall')).toBeCloseTo(60 * (6.7 - 0.5 * 3.1), 6);
+    expect(slideDown('ice')).toBeCloseTo(60 * (6.7 - 0.25 * 3.1), 6);
+  });
+});
+
+describe('physics: a ball bounces by the tile it lands on (#193)', () => {
+  /** How high a ball dropped onto the bottom row climbs again after its first bounce. */
+  function rebound(bounciness: number): number {
+    const s = tileScene();
+    s.stack.execute(new SetAssetPropertyCommand(s.iceId, TILE_BOUNCINESS_KEY, bounciness));
+    s.paint(
+      Array.from({ length: 10 }, (_, x) => [x, 9] as [number, number]),
+      s.iceId,
+    ); // top face at y = 192
+    // Clear of the hero, who stands on the origin with a collider of its own.
+    const ball = place(s, s.spriteId, { x: 120, y: 0 });
+    const collider = new AddColliderCommand(s.sceneId, ball);
+    s.stack.execute(collider);
+    for (const [key, value] of Object.entries({ shape: 'circle', radius: 16 }))
+      s.stack.execute(new SetOverrideCommand(s.sceneId, collider.objectId, key, value));
+    s.stack.execute(new AddRigidbodyCommand(s.sceneId, ball));
+    const started = startWorld(s, { physics: true, collisions: true });
+    const y = () => started.world.findByObjectId(ball)!.y;
+    let landed = false;
+    let highest = Infinity;
+    for (let i = 0; i < 240; i++) {
+      started.frame(1 / 60);
+      if (y() > 192 - 16 - 1) landed = true;
+      else if (landed) highest = Math.min(highest, y());
+    }
+    return Number.isFinite(highest) ? 192 - 16 - highest : 0;
+  }
+
+  it('a dead tile keeps it down, 0.5 sends it back a quarter of the drop, 1 nearly all of it', () => {
+    const drop = 192 - 16;
+    expect(rebound(0)).toBeLessThan(1);
+    const half = rebound(0.5) / drop;
+    expect(half).toBeGreaterThan(0.2);
+    expect(half).toBeLessThan(0.3);
+    expect(rebound(1) / drop).toBeGreaterThan(0.9);
+  });
+});

tools/e2e/40-tilemap.mjs

@@ -715,6 +715,9 @@ export async function tilemap(t) {
   await openTab(t, 'scene');
   await select({ kind: 'asset', assetId: 'at-grass' });
   const solidRow = await json("__gm.inspectorField('Solid')");
+  const surfaceRows = () =>
+    json("[__gm.inspectorField('Friction'), __gm.inspectorField('Bounciness')].map(Boolean)");
+  const surfaceBefore = await surfaceRows();
   if (solidRow) await click(solidRow.x, solidRow.y);
   await settle();
   check(
@@ -722,6 +725,13 @@ export async function tilemap(t) {
     Boolean(solidRow) && (await t.asset('at-grass'))?.props.solid === true,
     JSON.stringify({ solidRow, props: (await t.asset('at-grass'))?.props }),
   );
+  // Its surface (#193) is a solid tile's business: the rows come with the switch.
+  const surfaceAfter = await surfaceRows();
+  check(
+    'Friction and Bounciness show on a tile only once it is solid',
+    JSON.stringify(surfaceBefore) === '[false,false]' && JSON.stringify(surfaceAfter) === '[true,true]',
+    JSON.stringify({ surfaceBefore, surfaceAfter }),
+  );
   await mutate(`__gm.lookAt(0, ${LANE})`);
   await settle();
   const outlined = await json(`__gm.tilemap.solids(${JSON.stringify(MAP_OBJECT)})`);

tools/e2e/42-shapes.mjs

@@ -5,7 +5,8 @@ import { LANES, MAKE_OBJECT } from './lib/scaffold.mjs';
  * Capsules and polygons (#151), and the collision outline of a frame that a tile blocks with
  * (#141). What only a running editor can show: the corners of a polygon collider are edited on
  * its outline in the scene, the engine lets a capsule slide down a polygon ramp, the Texture tab
- * draws a frame's outline with clicks, and a painted map blocks with that outline in the game.
+ * draws a frame's outline with clicks, and a painted map blocks with that outline in the game – as
+ * does a collider that wears the frame's outline (#193).
  */
 
 /** A 32 × 32 picture, pasted like a file: the texture the outline is drawn on. */
@@ -354,4 +355,70 @@ export async function shapes(t) {
     JSON.stringify({ frames: climb.length, highest, top: MAP_Y - 10, last: climb.at(-1) }),
   );
   await clearShapes();
+
+  // 42e. A collider wears the same frame's outline (#193), linked: shape "Frame collision", the frame
+  //      picked like a texture. It is the frame's size in the scene, and a walker climbs its slope –
+  //      a box of that size would have stopped it at its side.
+  const F = Y; // the floor's top face; the wedge stands on it, its slope rising to x = 16
+  await mutate(`
+    const scene = __gm.state.activeScene;
+    const assets = __gm.state.project.assets;
+    const texture = assets.find((a) => a.id === ${JSON.stringify(texture?.id)});
+    texture.frames.find((f) => f.id === 'sh-frame').collision = [[{ x: 0, y: 32 }, { x: 32, y: 0 }, { x: 32, y: 32 }]];
+    ${MAKE_OBJECT}
+    ${put}
+    const behavior = structuredClone(assets.find((a) => a.id === 'mover'));
+    Object.assign(behavior, { id: 'sh-climb', name: 'Climb', props: { enabled: true, runInEditor: false }, variables: [], graph: ${JSON.stringify(climbGraph)} });
+    assets.push(behavior);
+    assets.push({ id: 'sh-col-wedge', type: 'collider', name: 'sh-col-wedge',
+      props: { shape: 'frame', frame: 'sh-frame', isTrigger: false } });
+    assets.push({ id: 'sh-col-floor', type: 'collider', name: 'sh-col-floor',
+      props: { shape: 'box', width: 400, height: 32, isTrigger: false } });
+    assets.push({ id: 'sh-col-walker', type: 'collider', name: 'sh-col-walker',
+      props: { shape: 'box', width: 20, height: 20, friction: 0, isTrigger: false } });
+    put('sh-floor', 'crate', '', 0, ${F + 16}, 'Floor', { width: 20, height: 20 });
+    put('sh-floor-col', 'sh-col-floor', 'sh-floor', 0, 0);
+    put('sh-wedge', 'crate', '', 0, ${F - 16}, 'Wedge', { width: 20, height: 20 });
+    put('sh-wedge-col', 'sh-col-wedge', 'sh-wedge', 0, 0);
+    put('sh-walker', 'crate', '', -100, ${F - 10}, 'Walker', { width: 20, height: 20 });
+    put('sh-walker-col', 'sh-col-walker', 'sh-walker', 0, 0);
+    put('sh-walker-climb', 'sh-climb', 'sh-walker', 0, 0, 'Climb');
+    __gm.state.select(null)`);
+  await evaluate(`__gm.lookAt(0, ${F})`);
+  await settle();
+  const wedgeRect = await json(`__gm.objectRect('sh-wedge-col')`);
+  const floorRect = await json(`__gm.objectRect('sh-floor-col')`);
+  check(
+    'a collider wearing a frame outline is the size of the frame in the scene, not its own width',
+    wedgeRect &&
+      floorRect &&
+      Math.abs(wedgeRect.w - wedgeRect.h) < 1 &&
+      Math.abs(floorRect.w / wedgeRect.w - 400 / 32) < 0.2,
+    JSON.stringify({ wedgeRect, floorRect }),
+  );
+  await shot('42-frame-collider');
+  await play();
+  await evaluate(`(() => {
+    const out = (window.__frameClimb = []);
+    const begin = performance.now();
+    const sample = () => {
+      const w = __gm.world();
+      if (!w) return;
+      const e = w.entities.find((x) => x.objectId === 'sh-walker');
+      out.push({ x: e?.worldX, y: e?.worldY });
+      if (performance.now() - begin < 3000) requestAnimationFrame(sample);
+    };
+    requestAnimationFrame(sample);
+  })()`);
+  await sleep(3300);
+  const frameClimb = await json('window.__frameClimb');
+  await stop();
+  // Over the wedge's top corner (16, F − 32) the walker's centre stands 10 higher.
+  const peak = Math.min(...frameClimb.map((s) => s.y));
+  check(
+    "a walker whose Move collides climbs the slope drawn in the collider's frame and goes on past it",
+    frameClimb.length > 100 && peak < F - 42 + 1 && peak > F - 42 - 3 && frameClimb.at(-1).x > 45,
+    JSON.stringify({ frames: frameClimb.length, peak, top: F - 42, last: frameClimb.at(-1) }),
+  );
+  await clearShapes();
 }