Trigger colliders and Move and slide against solid colliders

- Collider property isTrigger (no blocking, still reports enter/stay/exit)
- Node 'Move and slide' with blocked x/y outputs, axis-wise resolution
- axisSeparation/axisCorrection geometry for box/box, circle/circle, box/circle
- Amber outline for trigger colliders in the viewport
- Demo mover uses Move and slide; E2E step 15b, 7 new unit tests

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/core/properties/PropertySchema.ts

@@ -44,6 +44,8 @@ export const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
     { key: 'width', label: 'Width', kind: 'number', default: 100, min: 1, step: 1 },
     { key: 'height', label: 'Height', kind: 'number', default: 100, min: 1, step: 1 },
     { key: 'radius', label: 'Radius', kind: 'number', default: 50, min: 1, step: 1 },
+    // Triggers report collisions but never block "Move and slide"; solid colliders do both.
+    { key: 'isTrigger', label: 'Trigger (no blocking)', kind: 'boolean', default: false },
   ],
 };
 

src/core/properties/collider.ts

@@ -16,6 +16,11 @@ export function colliderShape(props: PropertyBag, centre: Vec2): ColliderShape {
   return { kind: 'box', x: centre.x, y: centre.y, w: Math.max(0, Number(props.width ?? d.width)), h: Math.max(0, Number(props.height ?? d.height)) };
 }
 
+/** Whether the collider only reports overlaps (true) or also blocks movement (false). */
+export function isTrigger(props: PropertyBag): boolean {
+  return Boolean(props.isTrigger ?? defaultsFor('collider').isTrigger);
+}
+
 /** Footprint of a collider shape (used for culling and the selection gizmo). */
 export function colliderSize(props: PropertyBag): { w: number; h: number } {
   const shape = colliderShape(props, { x: 0, y: 0 });
@@ -38,3 +43,45 @@ export function shapesOverlap(a: ColliderShape, b: ColliderShape): boolean {
   const cy = Math.max(box.y - box.h / 2, Math.min(circle.y, box.y + box.h / 2));
   return (circle.x - cx) ** 2 + (circle.y - cy) ** 2 < circle.r * circle.r;
 }
+
+export type Axis = 'x' | 'y';
+
+/**
+ * The centre distance along `axis` at which the two shapes exactly touch, given their
+ * current offset on the other axis. Only meaningful when the shapes overlap on that other
+ * axis (otherwise they cannot collide by moving along `axis`); returns 0 when they do not.
+ */
+export function axisSeparation(a: ColliderShape, b: ColliderShape, axis: Axis): number {
+  const other: Axis = axis === 'x' ? 'y' : 'x';
+  const offset = Math.abs(a[other] - b[other]);
+  if (a.kind === 'box' && b.kind === 'box') {
+    return offset * 2 < extent(a, other) + extent(b, other) ? (extent(a, axis) + extent(b, axis)) / 2 : 0;
+  }
+  if (a.kind === 'circle' && b.kind === 'circle') {
+    const r = a.r + b.r;
+    return offset < r ? Math.sqrt(r * r - offset * offset) : 0;
+  }
+  const box = a.kind === 'box' ? a : (b as Extract<ColliderShape, { kind: 'box' }>);
+  const circle = a.kind === 'circle' ? a : (b as Extract<ColliderShape, { kind: 'circle' }>);
+  const halfOther = extent(box, other) / 2;
+  const halfAxis = extent(box, axis) / 2;
+  // Circle centre within the box's span on the other axis: the flat side is hit.
+  if (offset <= halfOther) return halfAxis + circle.r;
+  // Otherwise the corner is the closest point: a circle-vs-point solution.
+  const corner = offset - halfOther;
+  return corner < circle.r ? halfAxis + Math.sqrt(circle.r * circle.r - corner * corner) : 0;
+}
+
+/**
+ * How far `mover` has to be pushed back against its travel direction `dir` (±1) along
+ * `axis` so it just touches `obstacle` (0 when they do not overlap). Only valid when
+ * `mover` approached from the far side, i.e. it did not overlap before its move.
+ */
+export function axisCorrection(mover: ColliderShape, obstacle: ColliderShape, axis: Axis, dir: 1 | -1): number {
+  if (!shapesOverlap(mover, obstacle)) return 0;
+  return Math.max(0, dir * (mover[axis] - obstacle[axis]) + axisSeparation(mover, obstacle, axis));
+}
+
+function extent(box: Extract<ColliderShape, { kind: 'box' }>, axis: Axis): number {
+  return axis === 'x' ? box.w : box.h;
+}