Killer Game Programming in Java

Managing WorldItems

WorldItems maintains an ArrayList of TileOccupier objects (called items) ordered by increasing tile row. Figure 13-10 shows that row 0 is the row furthest back in the game, and the last row is nearest the front. When the ArrayList objects are drawn, the ones in the rows further back will be drawn first, matching the intended z-ordering of the rows.

Tip

A TileOccupier object can represent a block, pickup, or sprite.

The ArrayList changes over time. The most frequent change is to add sprites temporarily, so they can be drawn in their correct positions relative to the blocks and pickups. Pickups are deleted as they are collected by the player.

The WorldItems constructor stores floor information. This is used to translate the tile coordinates of the TileOccupiers into pixel locations on the floor:

    // max pixel width/height of a tile
    private int tileWidth, tileHeight;

    // 'start of first even row' coordinate
    private int evenRowX, evenRowY;


    // 'start of first odd row' coordinate
    private int oddRowX, oddRowY;

    private ArrayList items;
           // a row-ordered list of TileOccupier objects


    public WorldItems(int w, int h, int erX, int erY, int orX, int orY)
    { tileWidth = w; tileHeight = h;
      evenRowX = erX; evenRowY = erY;
      oddRowX = orX; oddRowY = orY;
      items = new ArrayList();
    }

Adding an Entity

Adding an entity (a pickup or a block) requires the creation of a TileOccupier object and its placement in the items ArrayList sorted by its row/column position:

 public void addItem(String name, ...