Components

Overview

Components are what allow Entities to be different from one another. They store the data associated with each entity, and grant them properties by making them visible to families (see Systems).

Components should normally be fine grained. For example, if you want a moving sprite on the screen, consider having three components representing that: a PositionComponent, a VelocityComponent, and a SpriteComponent.

Declaring Components

Syntax

Components are code generated (see ECS Overview). They follow the following format:

component:
  name: TextLabel
  members:
    - text: 'Halley::TextRenderer'
    - layer: int
    - mask: int

At top level, the YAML document should contain an entry called component. It should have two keys inside it, name, specifying a unique name for the component (NB: the actual class generated will have Component appended to it, so in the example above it would generate a class called TextLabelComponent), and members, which is a list containing all members in the component.

Each member is specified by a name, followed by its C++ type. Note that it's necessary to use the full namespace for Halley classes, as the components will be compiled in translation units that don't invoke using namespace Halley;

At this time, it's not possible to specify default values, and all component members must be explicitly initialised in the generated constructor.

Custom types

If any of your members uses a type that your game declares, you need to help the codegen find the appropriate header to include. You can do this by using a declaration in this format:

type:
  name: CurveType
  include: "src/config/art/curve_type.h"

Note that the name must match exactly. e.g. if your component needs a std::vector<CurveType>, you'd need to declare a type for name: 'std::vector<CurveType>'.