Create and delete entities

The "Window Scene" window shows the entities in a game scene. We remind you that a scene corresponds to the environment (2D or 3D) in which the objects that make up our game are rendered.
How entities are managed by the DreamIn Engine editor engine ?
In this window, the entities are displayed one after the other in relation to their identifier.
To create a "OneMoreEntity" entity, simply click on the "ADD ENTITY" button and a menu opens. In this menu, we identify:

• The name
• The position on the X axis
• The position on the Y

Note: The 3D version is still in development and only two dimensions are shown in this article. Finally, click on the "ADD" button to add a "OneMoreEntity" entity to the[250;250] coordinates in the scene. We see a second container on the right-hand side of the image that shows the newly created entity in the image below:

Only the entities created do not have much value. Let's add some components to them !

Attach components to entities

How to attach components to entities ?
To attach components to entities, use the window on the right side of the editor.

This window first shows the characteristics of the selected entity (e.g. "OneMoreEntity (id: 3, mask: 5)).
We can see that this entity already has basic components:

• SpriteComponent. This component allows the entity to be rendered with a Sprite (a Sprite is a component that has an image as well as a position in a 2D space)
• InputComponent. This component allows to control an entity with the computer keyboard when a simulation is in progress

Thanks to these two components, it is possible to control the entity with the computer keyboard and follow the rendering on the screen. To do this, you must be in "simulation mode".

Start/Stop a simulation

At the top left of the editor, we see an action bar, like this:

It groups all the actions to modify the state of a scene:

• Run simulation corresponds to the first action button and starts a simulation
• Stop simulation corresponds to the second action button and stops a running simulation

Note that the buttons are greyed out when they have been clicked:

• When a simulation is running, the start button of the simulation is grayed out
• When no simulation is running, the simulation stop button cannot be clicked

What happens if you want to change the information of a component such as its position, size, color? Do we need to stop the simulation to make these changes?
No, it is quite possible to modify the parameters of the components at the "runtime", i. e. when a simulation is running.

View and modify component information

Regardless of whether a game simulation is on or off, it is always possible to view and modify the component information in the "DETAIL COMPONENTS" window located at the bottom right of the editor.
For this example, the "Sprite" component has been selected, which contains the following information:

• Position
• Size
• Rotation
• Color
• Texture

Note: a texture variable is integration, so that it is possible to modify the texture of a component associated with an entity.

Manage textures

DreamIn Engine has its own texture manager and the textures that can be used for the project are displayed in the resource explorer (e.g. "Resource Explorer"):

Let's take the scene of the editor as a whole:

It is possible to modify the texture of a selected entity, simply by clicking on the texture to be used from the resource explorer. In the example below, we have replaced the texture of the "container" with the texture "button_open" from the resource explorer.
Note: a Drag'N'Drop function is present and allows you to drag a texture from the resource explorer to the texture present in the Sprite component information.
When changes have been made to a project, you may want to save the changes.

Save a project

A bar at the top of the window compiles all the possible shortcuts offered by the editor and groups them into clickable tabs in a drop-down list:

The "Project" tab concerns the functionalities related to the opened project. It has several features:

• " New project " creates a new project
• " Open project " opens a window that allows you to load an existing project
• " Save " saves a project and saves-sub if the project is new
• " Save as " saves the project as whatever happens
• " Quit", or the shortcut "Alt+F4" close the application

This action bar allows you to manage a project as in the example shown below where you try to save a project.

Note: this application is under development and needs to be improved for the moment.

View the project architecture and file content

At any time, you can step back and visualize the architecture of the current project. It can be easily viewed using the project explorer (e.g. window with the "Project Explorer" tab).
This menu scrolls through the project files and displays them. By clicking on a folder, the menu scrolls and displays what it contains.
By clicking on a file, it is possible to see its contents from the file explorer tab (e.g. window with the "File Explorer" tab) at the bottom left of the application.

Entity

The entities are the "new GameObjects".
They are often represented as a simple identifier (ID) and have a data association role.
In practice, entities are very light in a scene unlike GameObjects which have a lot of information. Moreover, entities are not "physically" present in a scene because of their simple identifier character.

Component

The components contain absolutely all the data (e.g. a "Transform" component could contain position, rotation and scale data of an entity).
Components do not contain any logic.

System

The systems manage all the logic at once for all the entities associated with them.

What makes ECS better?

• The entity concept saves memory. We have more control over data and logic. Moreover, we know how components are stored and managed in memory
• This model avoids expensive GameObjects creations (more data and logic) in favor of Component creation (less data and no logic)
• Making the code parallel becomes easier to achieve. The separation of data and logic in an ECS makes it possible to parallelize the execution of systems and within a system
• The code can be easily optimized to be "cache-friendly". As the components only contain data, they can be stored contiguously in memory

What are the limits of the ECS?

• It is difficult to debug entities
• It is sometimes necessary to write more code for the same functionality
• It is not really taught to video game programmers
• ECS is based on a Data Oriented Design (DOD) whose concept may be difficult to understand

Using Data Oriented Design (DOD)

We have seen the characteristics, advantages and limitations of an ECS, but what does the DoD concept refer to in an architectural pattern?
Unlike OOP where everything is solved around objects, DoD concerns exactly all data. Instead of structuring the code as we imagine it, it is preferable to structure it by taking into account the data flow that we need to handle.