0.11 Slick0210: collision detection and sound  (Page 2/8)

Figure 1 . Graphic output near the beginning of the simulation.

A fat and happy predator beetle

Figure 2 shows the situation some time later when all but 173 of the green beetles had been eaten. Note that the process of eatingthose nutritious beetles has caused the red beetle to gain some weight in Figure 2 .

Figure 2 . Graphic output near the middle of the simulation.

Cleaning up the scraps

Figure 3 shows the situation with only 36 green beetles remaining. Collisions between the beetles is rare at this point, so quite a bit more time willprobably be required before the red beetle can collide with and eat the remaining green beetles.

Figure 3 . Graphic output near the end of the simulation.

What you have learned

In the previous module, you learned how to develop a sprite class from which you can instantiate and animate swarms of sprite objects.

What you will learn

In this module, you will learn how to use the Sprite01 class developed in the earlier module to write a predator/prey simulation program involving thousands of sprites, collision detection, and sound effects.

General background information

Actually, it may have been more appropriate to describe this program in terms of jellyfish, (which eat on the basis of opportunity) instead of beetles, (which are more deliberate in their actions) .

In this program, the red sprite consumes a green sprite only when the two happen to collide by chance. The sprites are notattracted to one another. (That would be a good exercise for a student project - attraction plus collision.)

Two scenarios

A baseball coach is attacked by a swarm of fierce green flying sprites. Fortunately, a red predator sprite comesalong and attacks the green sprites just in time to save the coach.

There are two scenarios that can be simulated by setting the variable named dieOnCollision (see Listing 1 ) to either true or false .

Harmless blue sprites

In one scenario ( dieOnCollision = false) , the vicious green sprites become harmless blue sprites when theycollide with the red sprite. A screen shot of this scenario is shown in Figure 4 .

Figure 4 . Output for the harmless blue sprite scenario.

Green sprites get consumed

In the other scenario ( dieOnCollision = true) , the green sprites are consumed by the red sprite upon contact and are removed fromthe population. This is the scenario shown in Figure 3 .

Get fat and happy

In both scenarios, contact between a green sprite and the red sprite causes the red sprite to increase in size.

If you allow the program to run long enough, the probability is high that all of the green sprites willhave collided with the red sprite and will either have turned blue or will have been consumed.

Discussion and sample code

The class named Sprite01

The class named Sprite01 is shown in Listing 12 . I will explain only those portions of that class that I use in this program thatweren't explained in the earlier module.

The class named Slick0210

Will explain in fragments

A complete listing of the class named Slick0210 is provided in Listing 11 . I will break the code down and explain it in fragments.