Adding game functionality
If each event is described in as much detail as before, it's going to be quite a long tutorial. Let's make the description a little briefer for the next events. Remember, the steps to add a condition or action are:
1. Double-click to insert a new event, or click an Add action link to add an action.
2. Double-click the object the condition/action is in.
3. Double-click the condition/action you want.
4. Enter parameters, if any are needed.
From now on, events will be described as the object, followed by the condition/action, followed by any parameters. For example, the event we have just inserted could be written:
Add condition System -> Every tick
Add action Player -> Set angle towards position -> X: Mouse.X, Y: Mouse.Y
Get the player to shoot
When the player clicks, they should shoot a bullet. This can be done with the Spawn an object action in Player, which creates a new instance of an object at the same position and angle. The Bullet movement we added earlier will then make it fly out forwards. Make the following event:
Condition: Mouse -> On click -> Left clicked (the default)
Action: Player -> Spawn another object -> For Object, choose the Bullet object. For Layer, put 1 (the "Main" layer is layer 1 - remember Construct 2 counts from zero). Leave Image point as 0.
Your event should now look like this:
If you run the game, you'll notice the bullets shoot from the middle of the player, rather than from the end of the gun. Let's fix that by placing an image point at the end of the gun. (An image point is just a position on an image that you can spawn objects from.)
Right-click the player in the project or object bar and select Edit animations.
The image editor for the player reappears. Click the origin and image points tool:
...and the image points dialog opens up:
Notice the object origin appears as a red spot. That's the "hotspot" or "pivot point" of the object. If you rotate the object, it spins around the origin. We want to add another image point to represent the gun, so click the green add button. A blue point appears - that's our new image point. Left-click at the end of the player's gun to place the image point there:
Close the image editor. Double-click the Spawn an object action we added earlier, and change the Image point to 1. (The origin is always the first image point, and remember Construct 2 counts from zero.) The event should now look like below - note it says Image point 1 now:
Run the game. The bullets now shoot from the end of your gun! The bullets don't do anything yet, though. Hopefully, however, you'll start to realise that once you get to grips with the event system, you can put functionality together very quickly.
Let's make the bullets kill monsters. Add the following event:
Condition: Bullet -> On collision with another object -> pick Monster.
Action: Monster -> Destroy
Action: Bullet -> Spawn another object -> Explosion, layer 1
Action: Bullet -> Destroy
The explosion effect
Run the game, and try shooting a monster. Oops, the explosion has that big black border!
You might have predicted it'd look like that from the start, and wondered if our game was really going to end up like that! Don't worry, it won't. Click the Explosion object in either the Object bar in the bottom right, or the Project bar (which was tabbed with the layers bar). Its properties appear in the properties bar on the left. At the bottom, set its Blend mode property to Additive. Now try the game again.
Why does this work? Without going in to the nuts and bolts, ordinary images are pasted on top of the screen. With the additive effect, each pixel is instead added (as in, summed) with the background pixel behind it. Black is a zero pixel value, so nothing gets added - you don't see the black background. Brighter colors add more, so appear more strongly. It's great for explosions and lighting effects.
Making monsters a little smarter
Right now the monsters just wander off the layout to the right. Let's make them a bit more interesting. First of all, let's start them at a random angle.
Condition: System -> On start of Layout
Action: Monster -> Set angle -> random(360)
They will still wander off forever when they leave the layout, never to be seen again. Let's keep them inside. What we'll do is point them back at the player when they leave the layout. This does two things: they always stay within the layout, and if the player stands still, monsters come right for them!
Condition: Monster -> Is outside layout
Action: Monster -> Set angle toward position -> For X, Player.X - for Y, Player.Y.
Run the game. If you hang around for a while, you'll notice the monsters stay around the layout too, and they're going in all kinds of directions. It's hardly AI, but it'll do!
Now, suppose we want to have to shoot a monster five times before it dies, rather than instant death like it is at the moment. How do we do that? If we only store one "Health" counter, then once we've hit a monster five times, all the monsters will die. Instead, we need each monster to remember its own health. We can do that with instance variables.