When working on particle and polytrail effects, it can be helpful to use the Preview desktop. Switch to the Preview desktop and then set the Particle Editor window to the left-hand side of the screen. Go to Particle System | Create and name it ShipExhaust. Click the Play button at the bottom of the Particle Editor window. The Scene Viewer window will appear as shown in the following screenshot:

You can see that the particle effects are displayed in the Scene Viewer window—if we make changes in the Particle Editor window, we'll immediately see the results. Start with the General tab and check the Use Object Transform option, as shown in the following screenshot:

Setting the Use Object Transform option ensures that the effects will move with the object that they are attached to—in this case it will be the ship. The Use Auto Start option indicates that the particle effects will start immediately in the scene rather than being triggered at some point. The Use Asynchronous Update option is used so that particle effects don't start at the same time. The collision options are pretty straightforward and are useful if you are creating effects that will interact with the terrain or with other colliders. If we set the Use Facing Up Particles option, the particle effects orient themselves to the xz plane, indicating that the effects can be seen from overhead, otherwise the texture of the particle effect is vertical and won't be viewable from above. Finally, the Use Velocity Oriented Particles option causes the particles to orient along their velocity.

Move to the Emitter tab and change the Type field to Cone and leave the angle at 0.00, as shown in the following screenshot:

The Angle modifier determines the direction in which the effects move. The Type field determines the general shape of the overall effect. The best way to see what the different types do is to experiment a bit. In fact, the best way to get the effect we are looking for is by the trial-and-error method. Once you experiment a bit, it is easier to get a feel for what the different options do.

The last tab is the Particles tab; there are quite a few options to set in this tab and each option can have a major impact on the way the particles behave. Rather than discuss what each option does, we will talk about what we are trying to achieve by adjusting the settings. The basis for the exhaust effect is that it should be a bright, fire-like effect with a fairly high velocity to suggest a great deal of thrust. We also want to flare out a bit just to add a bit more depth. With that in mind, let's take a look at the settings, as shown in the following screenshot:

To set the required settings in the Particles tab, you need to perform the following steps:

Our ship model has several engine exhaust ports, so we need to apply the exhaust effects to each one of them. In order to do this, we will need to rely on our handy helper objects again. We'll group the helper objects with the ship and make sure that the ship is the parent object, but there are two ways to do this. We could add the helper objects to the scene, position them, and then make sure they get grouped with the ship, but the easier way is to just open the ship model separately.

Before we open the model, let's make sure that the model is updated with any changes we may have made in the scene. Switch back to the General desktop, load the scene, right-click on the ship model, and select Model | Update Model from Instance. This takes all of the changes we have made to the ship, including any child objects, and copies it into the model file. Now, we can load the ship model and add our particle effects.

Double click on the ship model in the Data Explorer window. Once the ship is opened, we need to set up the other modules to which we need access. We'll need the Scene Viewer, Data Explorer, and Attribute Editor windows—the actual placement of the viewports is up to you.

In the previous screenshot, we are zoomed in on the back of one of the engines. To attach the particle effects, follow these steps:

To load the modified ship model back into the scene, load the scene and right-click on the ship and select Model | Update Instance from Model. This reloads the model and any attributes that have been changed. Run the game and see how it looks! Of course, it looks funny with only one engine running, as shown in the following screenshot:

It's pretty easy to get the other engines set up, so let's do that now. Reopen the ship model and select the helper object that has the particle effects attached. Now click the Z key to go into translate mode. Click on Edit | Duplicate to make a copy (the shortcut is Ctrl + D) of the object. Use the translation arrows to move the duplicate helper object to the back of another engine. It will look better if we ignore the smaller engine-type object between the first engine and the body of the ship—it's fairly small for an engine and the particle effects will be too overwhelming if there are six in a fairly small area. We'll put two on the main engine, stacked on top of each other, and one on each wing. Keep making duplicates and placing them behind the engines until all four are done. Save, load the scene again, and run the game. Now it looks much better, just see the following screenshot:

Now that we know how to do particle effects, it will be much easier to jump in and make a few more, especially considering that we will be using the same texture. Go back to the Preview desktop and open the Scene Viewer and Particle Editor windows. Create another new particle effect by clicking Particle System | Create and name it Explosion. The following are the suggested settings:

Now we have an explosion that we can use for collisions. But we need to have a way by which we can put them to use in our scene. Once again, helper objects are going to save the day. In the following steps, a helper object is created:

We have just about everything set up, but we need a way by which we can actually trigger the explosions. When the ship gets struck by an asteroid, we are going to make the ship invulnerable for three seconds and make it 50 percent transparent as a result. To make his happen, in ShipAI, add a new Boolean value called bInvulnerable and set the initial value to false. We'll set this flag when a collision occurs. Next, add a new function called CheckCollision that we will call in the onEnterFrame handler and then add the following code:

-- Get the last collision time so we can keep track of timers
local nLastCollisionTime = dynamics.getLastCollisionTime ( this.hShip ( ) )
-- Get number of collisions to see if a collision occurred
local nHitCount = dynamics.getLastCollisionContactCount ( this.hShip ( ) )

-- Number of collisions is > 0 then a hit has occurred
if(nHitCount > 0) then
    this.DoCollision()
end

-- Check if the ship is invulnerable and if it has been 3 seconds
if(this.bInvulnerable() and nLastCollisionTime > 3 ) then
    this.MakeInvulnerable ( false )
end

First, we check the elapsed time since the last collision and the number of collisions that have occurred in this frame. If there were any hits, then we make a call to the next function that we will create, that is, DoCollision.

Then, if the ship is currently invulnerable we'll see if the elapsed time has exceeded 3 seconds and if it has, then it is time to turn off invulnerability with a call to MakeInvulnerable, which we will define soon, and pass it false.

Since we are referencing the DoCollision function in the previous code, we better set one up. Create a new function called DoCollision and enter the following code:

this.DoExplosion ( )

this.ClearHorizontalMovement ( )
this.ClearVerticalMovement ( )
this.MakeInvulnerable( true )

Once again we make a call out to another function. DoExplosion will handle creating the actual explosion and the rest of this function sets up the ship properties. First, we clear out all the movement and then we have another reference to MakeInvulnerable, this time with true, which will change the opacity of the ship and turn off collisions. Since we have referred to it twice, let's create MakeInvulnerable before setting up the DoExplosion function. Create a new function called MakeInvulnerable, give it a parameter called bInvincible and then enter the following code:

-- The collisions are opposite the invincibility
dynamics.enableCollisions ( this.hShip ( ), not bInvincible )
-- Toggle the invulnerability
this.bInvulnerable ( bInvincible )

-- Set the opacity depending on the invulnerability
local nOpacity
if( bInvincible ) then
    nOpacity = 0.5
else
    nOpacity = 1
end

shape.setMeshOpacity ( this.hShip ( ), nOpacity )

First of all, we toggle the collisions by calling enableCollisions and pass in the opposite parameter of bInvincible, since when the ship is invincible the collisions are off and vice versa. Next, we set the invulnerability flag and then set the opacity of the ship. We are almost there; just create one more function called DoExplosion and enter the following code:

-- Get handles to scene and the explosion object.
local hScene = application.getCurrentUserScene ( )
local hExplosion = scene.getTaggedObject ( hScene, "explosion" )

-- Get the location of the collision
local nColX, nColY, nColZ = dynamics.getLastCollisionContactPositionAt ( this.hShip ( ), 0 )
-- Send the onExplosion event to the ExplosionAI
object.sendEvent ( hExplosion, "ExplosionAI", "onExplosion", nColX, nColY, nColZ )

We do the usual housekeeping of setting up local variables—we have one for a reference to the scene, one to reference the new explosion helper object that we created, and the last three will hold the location in which the collision occurred. Using this information, we then send the location of the collision to the explosion helper via the onExplosion event.

That's it! We can save and compile the code and run the game. Now when we click on the Play button, an explosion occurs when we get hit by asteroids and we are given a recovery time to get back in the game.