How to Make a Game Like Jetpack Joyride in Unity 2D – Part 3

Killing the Mouse

Right now the mouse can easily pass through the enabled laser without so much as a bent whisker. Better get to fixing that.

Open the MouseController script and add an isDead instance variable.

private bool isDead = false;

This instance variable will indicate the player has died. When this variable is true, you will not be able to activate the jetpack, move forward, or do anything else that you’d expect from a live mouse.

Now add the following two methods somewhere within the MouseController class:

void OnTriggerEnter2D(Collider2D collider)
{
    HitByLaser(collider);
}

void HitByLaser(Collider2D laserCollider)
{
    isDead = true;
}

The OnTriggerEnter2D method is called whe then mouse collides with any laser. Currently, it simply marks the mouse as dead.

Now, when the mouse is dead it shouldn’t move forward or fly using the jetpack. Make the following changes in the FixedUpdate method to make sure this doesn’t happen:

bool jetpackActive = Input.GetButton("Fire1");
jetpackActive = jetpackActive && !isDead;

if (jetpackActive)
{
    playerRigidbody.AddForce(new Vector2(0, jetpackForce));
}

if (!isDead)
{
    Vector2 newVelocity = playerRigidbody.velocity;
    newVelocity.x = forwardMovementSpeed;
    playerRigidbody.velocity = newVelocity;
}

UpdateGroundedStatus();
AdjustJetpack(jetpackActive);

Note that jetpackActive is now always false when the mouse is dead. This means that no upward force will be applied to the mouse and also, since jetpackActive is passed to AdjustJetpack, the particle system will be disabled.

In addition, you don’t set the mouse’s velocity if it's dead, which also makes a lot of sense. Unless they’re zombie mice. Switch back to Unity and run the scene. Make the mouse fly into the laser.

Hmm... it looks like you can no longer use the jetpack and the mouse doesn’t move forward, but the mouse seems rather OK with that. Perhaps you do have zombie mice about, after all!

The reason for this strange behavior is that you have two states for the mouse: run and fly. When the mouse falls down on the floor, it becomes grounded, so the run animation is activated. Since the game cannot end like this, you need to add a few more states to show that the mouse is dead.

Adding the Fall and Die Mouse Animations

Select the mouse GameObject in the Hierarchy and open the Animation view. Create a new clip called die. Save the new animation to the Animations folder.

After that, follow these steps to complete the animation:

1. Open the Sprites folder in the Project view.
2. Select and drag the mouse_die_0 and mouse_die_1 sprites to the Animation view's timeline.
3. Set Samples to 8 to make the animation slower.

That was easy. In fact I think you can create the fall animation yourself. This time, simply use the mouse_fall sprite as a single frame. However, if you get stuck feel free to expand the section below for detailed instructions.

[spoiler title="Need help creating the fall animation?"]

1. Select the mouse in the Hierachy.
2. In the Animation view, select the animation clips dropdown on the top left and select Create New Clip...
3. Create a new animation named fall and save it in the Animations folder.
4. Make sure the Sprites folder is open in the Project view and drag mouse_fall from the mouse_sprite_sheet into the Animation view timeline.

[/spoiler]

Transitioning to Fall and Die Animations

After creating the animations, you need to make the Animator switch to the corresponding animation at the right time. To do this, you’re going to transition from a special state called Any State, since it doesn’t matter what state the mouse is currently in when it hits the laser.

Since you created two animations (fall and die), you’ll need to handle things differently depending on whether the mouse hits the laser in the air or while running on the ground. In the first case, the mouse should switch to the fall animation state and, only after hitting the ground, should you play the die animation.

However, in both cases you need one new parameter (as you don't yet have a parameter to handle the mouse's death by laser!) Open the Animator view and create a new Bool parameter called isDead.

Next, create a new Transition from Any State to fall.

Select this transition and in the Conditions, set isDead to true. Add isGrounded as a second parameter by clicking the + button and set its value to false.

Next, create a new transition from Any State to die. Select this transition and in Conditions set both isDead and isGrounded parameters to true.

This way there are two possible combinations:

1. Dead but not grounded.
2. Dead and grounded.

This way, if the mouse is dead, but still in the air (not grounded) the state is switched to fall. However, if the mouse is dead and grounded, or was dead and becomes grounded after falling to the ground, the state is switched to die

The only thing left to do is update the isDead parameter from the MouseController script. Open the MouseController script and add the following line to the end of the HitByLaser method:

mouseAnimator.SetBool("isDead", true);

This will set the isDead parameter of the Animator component to true. Run the scene and fly into the laser.

When the mouse hits the laser, the script sets the isDead parameter to true and the mouse switches to the fall state (since isGrounded is still false). However, when the mouse reaches the floor, the script sets the isGrounded parameter to true. Now, all conditions are met to switch to the die state.

Once again, there is something not quite right. Your poor mouse is not resting in peace. Honestly, now is not the time to pull out the dance moves and break into “The Worm”!

Using a Trigger to Make the Mouse Die Once

During play mode, click on the Animator view after the mouse dies and you will see the die animation is being played on repeat. Oh, the brutality!

This happens because you transition from Any State to die repeatedly, forever. The grounded and dead parameters are always true, which triggers the animator to transition from Any State.

To fix this, you can use a special parameter type called a Trigger. Trigger parameters are very similar to Bools, with the exception that they are automatically reset after use.

Open the Animator view and add a new Trigger parameter called dieOnceTrigger. Set its state to On, by selecting the radio button next to it.

Next, select the transition from Any State to die, and add dieOnceTrigger in the Conditions section.

Next, open the Animations folder in the RW directory in the Project view and select die. In the Inspector, uncheck Loop Time. This will stop the animation from looping.

Run the scene and collide with a laser.

This time the mouse looks far more peaceful!