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>

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. */
-export function colliderSize(props: PropertyBag): { w: number; h: number } {
+/** The size in the collider's own units, before any transform; a worn frame (#193) is its own size. */
+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());
   }
 }