Environment

The Environment object contains the definition of how the game will be controlled by the player, the conditions underwhich the game ends, and the levels that are contained in the game.

Step 1 - Player Configuration

The Player configuration

Player:
  AvatarObject: avatar

Step 2 - Termination Conditions

Termination conditions are the rules which decide when the game episodes are complete, and whether the agent wins or loses.

Rules can be defined seperately for Win and Lose. In Sokoban, we just have a win condition where the player wins if all of the boxes have fallen into the holes. This is how it is defined in GDY.

Termination:
    Win:
      - eq: [box:count, 0]

We define here that the agent wins in the case that the number of box objects in the environment reaches 0. The :count option can be appended to any object name to return the number of any of the objects.

Step 3 - Levels

In our Sokoban game we are going to define two levels. The layout of each level is defined by a level string which is made up of the MapCharacter characters that were defined in the Objects section of this tutorial.

the dot . character means that the space in the map in unoccupied.

Levels:
    - |
      wwwwwww
      w..hA.w
      w.whw.w
      w...b.w
      whbb.ww
      w..wwww
      wwwwwww
    - |
      wwwwwwwww
      ww.h....w
      ww...bA.w
      w....w..w
      wwwbw...w
      www...w.w
      wwwh....w
      wwwwwwwww

the two defined levels will look like this when rendered:

Step 4 - Name, TileSize and Background Image

– code-block:: YAML

Name: sokoban TileSize: 24 BackgroundTile: images/gvgai/newset/floor2.png

Here we specify the size of the tiles in pixels TileSize. Also if we want to use an image for the background when there are no objects present we can supply a BackgroundTile image. The BackgroundTile is ignored any Observers except from Sprite2D.

Additionally every environment must have a unique Name to differentiate it from other environments.

Putting it all together

The environment definition with all the parts described looks like this:

Environment:
   Name: sokoban
   TileSize: 24
   BackgroundTile: images/gvgai/newset/floor2.png
   Player:
     AvatarObject: avatar
   Termination:
     Win:
       - eq: [box:count, 0] # If there are no boxes left
   Levels:
     - |
       wwwwwww
       w..hA.w
       w.whw.w
       w...b.w
       whbb.ww
       w..wwww
       wwwwwww
     - |
       wwwwwwwww
       ww.h....w
       ww...bA.w
       w....w..w
       wwwbw...w
       www...w.w
       wwwh....w
       wwwwwwwww