Game Development Reference
In-Depth Information
Chapter 23
Pairing the Penguins
23.1 Introduction
In this chapter, we will program the main gameplay for the
Penguin Pairs
game. We
will discuss how to move penguins around on the board, and what to do when a
penguin collides with another game object such as a shark or another penguin.
23.2 Penguin Selection
Before we can move penguins around, we need to be able to
select
a penguin. When
we click on an animal such as a penguin or a seal, four arrows should appear that
allow us to control in which direction the animal should move. In order to display
these arrows and handle the input, we will add a class called
AnimalSelector
that will
deal with this. Since the animal selector contains four arrows, it will inherit from
the
GameObjectList
class. Furthermore, we want to achieve a nice visual effect that
when the player moves the mouse over one of the arrows, it becomes darker. We
can achieve this effect by adding a class
Arrow
that contains two sprites: one for
the 'regular' arrow, and one for the arrow image when we hover over it. Further-
more, the
Arrow
class should be able to show an arrow in any of the four possible
directions.
23.2.1 The
Arrow
Class
Although we could have a single arrow image and rotate it depending on the desired
direction, we have chosen to keep things simple by having an image that contains
the arrow pointing in all four directions (see Fig.
23.1
). Therefore, when we load the
sprite, the
sheet index
indicates which arrow we should show. For the hover status,
we load another sprite containing the same arrow images, in the same order, but
