Physics

PixelStorm exposes AABB physics, gravity, and triggers. The system is deliberately simple, but it is enough to support movement, obstacle blocking, and scene interaction for a 2D game.

Collision

Collision works on axis-aligned boxes.

Method	Use
CreateAABB(transform, collider)	builds the world-space box
Overlaps(a, b)	checks overlap
CheckAABB(a, b)	returns a collision manifold

CollisionManifold

Field	Meaning
IsColliding	whether the boxes overlap
Normal	separation direction
PenetrationDepth	minimum distance needed to separate the boxes

Important

CreateAABB() uses:

• Transform::Position
• Collider::Offset
• Collider::Size

It does not use rotation or scale from the transform.

warning

This means the engine's public physics is deliberately simple and axis-aligned. If you rotate a sprite, the collider remains an AABB.

Physics

Physics applies integration and collision resolution.

Method	What it does
Integrate(transform, rigidbody, deltaTime)	applies velocity to position
ResolveAABB(dynamic, static, ...)	resolves a dynamic body against a static body
ResolveAABB(first, second, ...)	resolves two dynamic bodies

Rules

• static bodies are not integrated
• triggers do not block movement
• resolution separates bodies along the axis of smallest penetration
• velocity is cleared on the collision axis

PhysicsSystem

PhysicsSystem is the system that Application::Run() updates automatically.

Public API

Method	Use
PhysicsSystem()	creates the system with default gravity
Update(registry, deltaTime)	integrates, resolves, and gathers triggers
SetGravity() / GetGravity()	controls global gravity
GetTriggerEvents()	returns the events from the last frame
GetTriggerEventsFor(entity)	filters trigger events for one entity

Default Gravity

PhysicsSystem starts with:

Vec2(0.0f, 980.0f)

That gives the engine a platformer-like gravity feel by default.

Trigger Events

TriggerEventType can be:

• Enter
• Stay
• Exit

TriggerEvent exposes:

• Type
• First
• Second
• Involves(entity)
• Other(entity)

Example

for (const TriggerEvent &event : GetPhysicsSystem().GetTriggerEventsFor(player))
{
    if (event.Type == TriggerEventType::Enter)
    {
        Log::Debug("entered trigger");
    }
}

Triggers

To use a trigger in practice:

1. create an entity with CreateStaticBox(..., true)
2. register callbacks with Entity::Trigger()
3. or read events from GetTriggerEventsFor()

Callback Example

zone.Trigger().SetOnEnter([&](Entity other)
{
    if (other.GetId() == player.GetId())
    {
        Log::Debug("player entered zone");
    }
});

tip

Trigger callbacks receive the other entity involved in the overlap. That makes it easy to filter by ID or by component presence.