Storing and Recalling Game Data - Building JavaScript Games for Phones, Tablets, and Desktop - page 276

of instructions, as you did in the example with cases 3 and 4. The syntax of the switch instruction is
part of the instruction syntax diagram. Figure 21-1 shows the part of that diagram belonging to the
switch instruction.

switch instruction

switch ( expression ) {

default

declaration

case expression : }

instruction

Figure 21-1. Syntax diagram for the switch instruction

Loading Different Kinds of Tiles
You can use the switch instruction to load all the different tiles and game objects. For each
character in the levelData.tiles variable, you need to perform a different task. For example, when
the character “.” is read, you need to create a normal playing-field tile. The following instructions
do that:

t = new Tile(sprites.field, ID.layer_objects);
t.sheetIndex = row + col % 2;
tileField.addAt(t, col, row);
break;

The sprite used for the tile is a strip consisting of two different sprites. By switching the sheet index
using the formula row + col % 2 , you get an alternating checkerboard pattern, as you can see by
running the example program belonging to this chapter. Another example is adding a transparent
background tile:

t = new Tile(sprites.wall, ID.layer_objects);
t.type = TileType.background;
tileField.addAt(t, col, row);
break;

Although the background sprite is invisible, you still load a sprite belonging to this tile. Why is that?
Because the Tile class inherits from the SpriteGameObject class, which requires a sprite. Of course,
another option would be to modify the SpriteGameObject class so that it can deal with a sprite that is
null . However, in this case, you follow the simple solution of providing a sprite, even if the player will
never see it. When you have to place a penguin, two things need to be done:

 Place a normal tile.

 Place a penguin.