Transform System

Myriad includes an optional system for updating hierarchical transforms. This system will automatically calculate the world transform (and store it into a component) from a local transform and a parent reference.

System Setup

Create a new system derived from BaseUpdateTransformHierarchySystem<TData, TTransform, TLocalTransform, TWorldTransform, TTransformParent>.

• TData: The normal system data parameter.
• TTransform : ITransform: The types of the transform (e.g. a matrix).
• TLocalTransform : ILocalTransform: A component which represents the local transform of an entity, relative to it's parent.
• TWorldTransform : IWorldTransform: A component which represents the world transform of an entity. Automatically calculated by this system.
• TTransformParent : ITransformParent: A component which specifies the parent of an entity in the transform hierarchy.
  • Myriad.ECS.Components.TransformParent component is provided as a ready made implementation.

Edge Cases

Roots

The local transform of root entities is copied directly to the world transform, with no other changes.

Reference Loops

It's possible to create a set of entities which reference each other in a loop (e.g. A parent of B parent of C parent of A). When a loop is detected the LoopDetected(Entity entity) method will be called with an arbitrary entity in the loop. Override LoopDetected to handle this error. While there is a loop an arbitrary entity in the loop will be used as the root.

Invalid parents

Any entity may be referenced as a parent. However, some entites are invalid as transform parents, for example a dead/phantom entity or one without a world transform. In this case the reference will be ignored, i.e. the "child" entity will act as the root.

ITransform

Transforms are represented by ITransform. This interface has a Compose method, which composes together a parent and child transform:

struct OffsetTransform
    : ITransform<OffsetTransform>
{
    public Vector3 Offset;

    OffsetTransform Compose(OffsetTransform child)
    {
        return new()
        {
            Offset = Offset + child.Offset;
        };
    }
}