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/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
-        ? {
-            rects: solidRects(project, props, asset),
-            polygons: solidPolygons(project, props, asset),
-            oneWay: oneWayAngles(project, asset).map((angle) => ({
-              angle,
-              rects: solidRects(project, props, asset, angle),
-              polygons: solidPolygons(project, props, asset, angle),
-            })),
-          }
-        : { rects: [], polygons: [], oneWay: [] };
+      // One group per side and surface, so cells only merge with cells that block alike (#159, #193).
+      const groups = (angle: number | null) =>
+        tileMaterials(project, asset!, angle ?? false).map((material) => ({
+          angle,
+          material,
+          rects: solidRects(project, props, asset!, angle ?? false, material),
+          polygons: solidPolygons(project, props, asset!, angle ?? false, material),
+        }));
+      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) }];
-    const { rects, polygons, oneWay } = this.blocksOf(world, body);
+      return [
+        { 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) => [
-      ...cells
-        .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),
-      ...oneWay.flatMap((group) =>
-        shapes(group.rects, group.polygons, up && { ...up, cone: oneWayCone(group.angle) }),
-      ),
-    ];
+    return this.blocksOf(world, body).flatMap(({ angle, material: surface, rects, polygons }) => {
+      const facing = angle === null ? null : up && { ...up, cone: oneWayCone(angle) };
+      return [
+        ...rects
+          .filter((rect) => near(rect.x, rect.y, rect.w, rect.h))
+          .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
- * own and has what a new collider starts with.
+ * object moved by the graph slides as far as one the engine moves. A tile brings its own (#193).
  */
-function frictionBetween(own: Entity, obstacle: Entity): number {
-  const of = (e: Entity) => colliderMaterial(e.type === 'collider' ? e.props : {}).friction;
-  return (of(own) + of(obstacle)) / 2;
+function frictionBetween(own: Entity, obstacle: Entity, surface?: TileMaterial): number {
+  return (surfaceOf(own).friction + surfaceOf(obstacle, surface).friction) / 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. */