Game Objects in a Structure - Learning C# by Programming Games - page 213

this .position = new Vector2(

−

10, grid.CellHeight

∗

selectedRow

−

10);

We place the row selection object 10 pixels to the left and to the top to account for
the space between the jewels and the row selection object.
If the player presses the left or right arrow key, we call the ShiftRowLeft or
ShiftRowRight method, and we pass along the currently selected row to these methods
so that they know which row to shift. These instructions are rather straightforward:

if (inputHelper.KeyPressed(Keys.Left))
grid.ShiftRowLeft(selectedRow);
else if (inputHelper.KeyPressed(Keys.Right))
grid.ShiftRowRight(selectedRow);

14.5 Creating the Game Objects

Now that we have shown how different game object classes can be constructed,
the only thing left to do is create these objects, and the rest will be dealt with by the
objects themselves. First we create the gameWorld object, and we add the background
image at layer 0 (which is the default layer value). Then we create the playingField
object and add it to the gameWorld object as well. For this object, we set the layer
index to 1, to ensure that it is drawn on top of the background:

gameWorld = new GameObjectList();

Texture2D background = Content.Load<Texture2D>("spr_background");
gameWorld.Add( new SpriteGameObject(background));

GameObjectList playingField = new GameObjectList(1);
playingField.Position = new Vector2(85, 150);
gameWorld.Add(playingField);

Then, we create the grid and the row selection object. Both of these objects are
added to the playingField object:

JewelGrid grid = new JewelGrid(10, 5);
playingField.Add(grid);

Texture2D selectorFrame = Content.Load<Texture2D>("spr_selector_frame");
RowSelectGameObject rowSelector = new RowSelectGameObject(grid,
selectorFrame, 1);

playingField.Add(rowSelector);

Finally, we create all the Jewel instances that need to be added to the grid. Every
time we create an instance, we randomly select between three different sprites, in