shapes

Working with Shapes in FlatRedBall2

All shape types and TileShapes are in the FlatRedBall2.Collision namespace — add using FlatRedBall2.Collision; in any file that uses them.

FlatRedBall2 has three built-in shape types: AARect, Circle, and Polygon. All shapes implement both IRenderable and ICollidable, so they handle both drawing and collision.

Shape Types

Type	Key Properties	Notes
AARect	Width, Height	Cannot rotate
Circle	Radius
Polygon	Points, Rotation	Use factory methods to create

Exposing a shape from an Entity: make the field a public auto-property (public Circle Circle { get; private set; }) and let callers write entity.Circle.Color = ... directly. Do not wrap it in a forwarding property like FillColor — that pattern silently fails when assigned after CustomInitialize. See entities-and-factories → references/reactive-properties.md.

Step 1: Create a Shape

var rect = new AARect { X = 0, Y = 0, Width = 64, Height = 64 };
var circle = new Circle { X = 100, Y = 0, Radius = 32 };

// Polygon factory methods:
var poly = Polygon.CreateRectangle(64, 64);         // rotatable rectangle
var custom = Polygon.FromPoints(new[] {
    new Vector2(0, 0), new Vector2(50, 0), new Vector2(25, 40),
});
// Concave polygons are fully supported for both rendering and collision.
// FromPoints automatically decomposes concave shapes into convex parts (Hertel-Mehlhorn)
// for correct collision — no manual decomposition needed.

Step 2: Make the Shape Visible

Shapes default to IsVisible = false. Always set IsVisible = true or the shape won't render.

Step 3: Add to the Render Pipeline

Option A — Directly on the Screen: Call Add in CustomInitialize:

Add(rect);

Option B — Attached to an Entity: entity.Add(shape) auto-adds to the render pipeline (as long as Engine is set).

Note: entity.Add(child) only auto-registers if the entity already has an Engine reference (via Factory or Screen.Register).