feat: add ShapeTypeStaticChainLoop and ShapeTypeEdge collider shapes

pkg/plugin/physics2d/component/collider.go

@@ -20,9 +20,17 @@ const (
 	ShapeTypeBox
 	// ShapeTypeConvexPolygon uses Vertices as a convex polygon in the shape's local frame.
 	ShapeTypeConvexPolygon
-	// ShapeTypeStaticChain uses ChainPoints for open chain segments (static/terrain-style
-	// geometry only; not for moving dynamic shapes).
+	// ShapeTypeStaticChain uses ChainPoints for open chain segments (static or kinematic
+	// bodies only; not for dynamic bodies which require mass).
 	ShapeTypeStaticChain
+	// ShapeTypeStaticChainLoop uses ChainPoints for closed chain loops (static or kinematic
+	// bodies only; not for dynamic bodies). Unlike ShapeTypeStaticChain, the last vertex
+	// automatically connects back to the first, creating a sealed boundary.
+	ShapeTypeStaticChainLoop
+	// ShapeTypeEdge uses EdgeVertices (exactly 2 points) for a single line segment
+	// (static or kinematic bodies only). Lighter than a 2-point chain for isolated barriers
+	// or triggers.
+	ShapeTypeEdge
 )
 
 // ColliderShape is one child shape inside a compound Collider2D.
@@ -33,17 +41,20 @@ const (
 //   - ShapeTypeBox → HalfExtents (half-width on X, half-height on Y, axis-aligned before LocalOffset/LocalRotation)
 //   - ShapeTypeConvexPolygon → Vertices (convex polygon, respect backend limits)
 //   - ShapeTypeStaticChain → ChainPoints (open polyline in local space)
+//   - ShapeTypeStaticChainLoop → ChainPoints (closed loop in local space)
+//   - ShapeTypeEdge → EdgeVertices (exactly 2 points in local space)
 type ColliderShape struct {
 	ShapeType     ShapeType `json:"shape_type"`
 	LocalOffset   Vec2      `json:"local_offset"`
 	LocalRotation float64   `json:"local_rotation"`
 	IsSensor      bool      `json:"is_sensor"`
 
 	// Geometry (use fields matching ShapeType).
-	Radius      float64 `json:"radius,omitempty"`
-	HalfExtents Vec2    `json:"half_extents,omitempty"`
-	Vertices    []Vec2  `json:"vertices,omitempty"`
-	ChainPoints []Vec2  `json:"chain_points,omitempty"`
+	Radius       float64 `json:"radius,omitempty"`
+	HalfExtents  Vec2    `json:"half_extents,omitempty"`
+	Vertices     []Vec2  `json:"vertices,omitempty"`
+	ChainPoints  []Vec2  `json:"chain_points,omitempty"`
+	EdgeVertices [2]Vec2 `json:"edge_vertices,omitempty"`
 
 	// Material and per-shape collision filtering (fixture-level in Box2D).
 	Friction     float64 `json:"friction"`
@@ -117,9 +128,15 @@ func (s ColliderShape) Validate() error {
 			return err
 		}
 	}
+	for i, v := range s.EdgeVertices {
+		if err := validateVec2(fmt.Sprintf("edge_vertices[%d]", i), v); err != nil {
+			return err
+		}
+	}
 
 	switch s.ShapeType {
-	case ShapeTypeCircle, ShapeTypeBox, ShapeTypeConvexPolygon, ShapeTypeStaticChain:
+	case ShapeTypeCircle, ShapeTypeBox, ShapeTypeConvexPolygon, ShapeTypeStaticChain,
+		ShapeTypeStaticChainLoop, ShapeTypeEdge:
 	default:
 		return fmt.Errorf("shape_type: unknown value %d", s.ShapeType)
 	}

pkg/plugin/physics2d/internal/create.go

@@ -121,8 +121,12 @@ func attachFixture(
 	sh component.ColliderShape,
 	bodyType uint8,
 ) error {
-	if sh.ShapeType == component.ShapeTypeStaticChain && bodyType != box2d.B2BodyType.B2_staticBody {
-		return errors.New("static chain colliders require a static body")
+	//nolint:exhaustive // We only care about static chain, static chain loop, and edge shapes
+	switch sh.ShapeType {
+	case component.ShapeTypeStaticChain, component.ShapeTypeStaticChainLoop, component.ShapeTypeEdge:
+		if bodyType == box2d.B2BodyType.B2_dynamicBody {
+			return fmt.Errorf("%d shape type cannot be used on dynamic bodies (zero mass)", sh.ShapeType)
+		}
 	}
 
 	shape, err := buildShape(sh)
@@ -155,6 +159,10 @@ func buildShape(sh component.ColliderShape) (box2d.B2ShapeInterface, error) {
 		return buildPolygonShape(sh)
 	case component.ShapeTypeStaticChain:
 		return buildChainShape(sh)
+	case component.ShapeTypeStaticChainLoop:
+		return buildChainLoopShape(sh)
+	case component.ShapeTypeEdge:
+		return buildEdgeShape(sh)
 	default:
 		return nil, fmt.Errorf("unknown shape_type %d", sh.ShapeType)
 	}
@@ -194,6 +202,24 @@ func buildChainShape(sh component.ColliderShape) (box2d.B2ShapeInterface, error)
 	return &chain, nil
 }
 
+func buildChainLoopShape(sh component.ColliderShape) (box2d.B2ShapeInterface, error) {
+	pts := make([]box2d.B2Vec2, len(sh.ChainPoints))
+	for i := range sh.ChainPoints {
+		pts[i] = shapePointToBodySpace(sh.ChainPoints[i], sh.LocalOffset, sh.LocalRotation)
+	}
+	chain := box2d.MakeB2ChainShape()
+	chain.CreateLoop(pts, len(sh.ChainPoints))
+	return &chain, nil
+}
+
+func buildEdgeShape(sh component.ColliderShape) (box2d.B2ShapeInterface, error) {
+	v1 := shapePointToBodySpace(sh.EdgeVertices[0], sh.LocalOffset, sh.LocalRotation)
+	v2 := shapePointToBodySpace(sh.EdgeVertices[1], sh.LocalOffset, sh.LocalRotation)
+	edge := box2d.MakeB2EdgeShape()
+	edge.Set(v1, v2)
+	return &edge, nil
+}
+
 // shapePointToBodySpace maps a point from shape-local space into body-local space using
 // LocalOffset and LocalRotation (radians, CCW +Y up) on the ColliderShape.
 func shapePointToBodySpace(p, offset component.Vec2, localRot float64) box2d.B2Vec2 {

pkg/plugin/physics2d/internal/shadow.go

@@ -49,6 +49,7 @@ func deepCopyColliderShape(s component.ColliderShape) component.ColliderShape {
 		HalfExtents:   s.HalfExtents,
 		Vertices:      cloneVec2Slice(s.Vertices),
 		ChainPoints:   cloneVec2Slice(s.ChainPoints),
+		EdgeVertices:  s.EdgeVertices,
 		Friction:      s.Friction,
 		Restitution:   s.Restitution,
 		Density:       s.Density,
@@ -140,7 +141,9 @@ func colliderShapeDeepEqual(a, b component.ColliderShape) bool {
 		a.GroupIndex != b.GroupIndex {
 		return false
 	}
-	return vec2SliceEqual(a.Vertices, b.Vertices) && vec2SliceEqual(a.ChainPoints, b.ChainPoints)
+	return vec2SliceEqual(a.Vertices, b.Vertices) &&
+		vec2SliceEqual(a.ChainPoints, b.ChainPoints) &&
+		a.EdgeVertices == b.EdgeVertices
 }
 
 // Collider2DStructuralEqual reports whether two colliders match for Box2D fixture shape
@@ -166,7 +169,8 @@ func colliderShapeStructuralEqual(a, b component.ColliderShape) bool {
 		a.Radius == b.Radius &&
 		vec2Equal(a.HalfExtents, b.HalfExtents) &&
 		vec2SliceEqual(a.Vertices, b.Vertices) &&
-		vec2SliceEqual(a.ChainPoints, b.ChainPoints)
+		vec2SliceEqual(a.ChainPoints, b.ChainPoints) &&
+		a.EdgeVertices == b.EdgeVertices
 }
 
 // ColliderShapeMutableFieldsEqual compares per-shape fields that Box2D can update without

pkg/plugin/physics2d/plugin.go

@@ -50,10 +50,12 @@ const (
 
 // Collider shape kinds (ColliderShape).
 const (
-	ShapeTypeCircle        = component.ShapeTypeCircle
-	ShapeTypeBox           = component.ShapeTypeBox
-	ShapeTypeConvexPolygon = component.ShapeTypeConvexPolygon
-	ShapeTypeStaticChain   = component.ShapeTypeStaticChain
+	ShapeTypeCircle          = component.ShapeTypeCircle
+	ShapeTypeBox             = component.ShapeTypeBox
+	ShapeTypeConvexPolygon   = component.ShapeTypeConvexPolygon
+	ShapeTypeStaticChain     = component.ShapeTypeStaticChain
+	ShapeTypeStaticChainLoop = component.ShapeTypeStaticChainLoop
+	ShapeTypeEdge            = component.ShapeTypeEdge
 )
 
 // Contact / trigger system events (implement ecs.SystemEvent; register with WithSystemEventEmitter).