Crash Course 2: Invaders - Part 12
by Hectate (Updated on 2015-05-02)
Part 12: Destroying the Enemy Ships
Now we put those bullets to use! We want to give the enemy some health so it can take a few hits, and then destroy it once it takes too much damage.
Step 83: While still in the Bullet's events we should be looking at the Actor - Type collision event. We're going to use the same collision to also tell the Enemy Ship that it was hit by a bullet.
From the palette, find the Trigger Event [text] in all behaviors for [Actor] block (found in Behavior > Triggers) and snap it above the Kill Self block (we want it to be triggered first).
Type "Hit" into the text field, and then grab the blue Actor Of Type block from the collision event wrapper above and insert it into the Actor spot. The event should look like the image below.
Step 84: Switch to the Enemy Ship actor and access the Events tab for it. Click Add Event and select Advanced > Custom Event.
Step 85: The event wrapper will appear, in the blank field type "Hit". This will cause the previous "tell" block we added (to the bullet) to trigger any code that we put in this event when triggered.
Now, if the enemy was just going to take one hit and be destroyed we could put a kill self block in here and be done with it. However, we actually want the enemy ship to take multiple hits. To track how many hits it can take, we're going to need an attribute to store a "Health" value.
Step 86: Create a new Attribute, select Number for its type, and name it Health Points (click the Attributes button on the Palette, then the Create an Attribute button).
Step 87: Add another event to the Enemy Ship. Create a When Creating Event (click + Add Event, then mouse over Basics, then click When Creating).
Step 88: Now lets actually set the initial Health value. Click on Attributes -> Setters in the Palette and drag over the Set Health Points to [ ] block, snap it inside the When Created Event, and type 3 into the empty field.
Step 89: Now that each Enemy Ship will have 3 health points when they're created, lets do some damage to them when they're hit.
Switch back to the Enemy Ship's Custom Event, and then grab the Increment Number By [ ] block (found in Numbers & Text > Math in the pallete) and put it inside the custom event. Switch the "increment" field to "decrement", and select "Health Points" in the number field (if not there already). Finally, in empty field type "1".
Step 90: Finally, we need to add an Event that checks the number of Health Points the Enemy Ship has left and destroys it if it has 0 (or fewer, in case it gets hit more than once very quickly).
To start, click the + Add Event button, mouse over Basics again, and select When Updating. Next, drag an if block inside the Always block (in Flow -> Conditions in the Palette).
Step 91: Now we add a "Less Than Or Equal To" block (under Flow -> Conditions again, it looks contains a "<=" between two numbers) to the empty field in the if block and then check whether Health Points (found in Attributes > Getters) is less than or equal to 0 or not.
Step 92: Here's where we put the Kill Self block (under Actor > Properties, if you recall).
Now our enemy ships will be killed if they are hit by three or more bullets! Feel free to test this out now. That said, its not very fun for them to just disappear; let's fix that!
Step 92: We want to use our Explosion sound effect we uploaded earlier. If we add a [Play] [Sound] block (found in Sound & Images > Sound) and select our Explosion sound effect from the dropdown menu (click the block and then select the Explosion sound we uploaded earlier), that sound will play right as our Actor is removed from the Scene.
Step 93: Now we need to add an effect to our Enemy Ship Actor Type so the player can tell when it’s hit. Switch back to the Custom Event. We’re going to use blocks under Actor -> Effects in the Palette
For the effects, grab these three blocks:
- Apply Effect [ ] to [Actor]
- Make Negative
- Remove All Effects From [Actor]
We also need to have a Do After timer block (Flow > Time in the palette).
Put the Make Negative block inside the Apply Effect block's blank space. Snap the Do After block in just below this and type ".1" into the blank for the time. Finally, put the Remove All Effects block inside the timer.
With all this in place, test the game. If everything is working, it’s time to create a way for our player to win the game.
To anyone having the problem where the Math/Increment [Number] by [whatever] block won't let you pick your Health Points attribute from the dropdown list: make sure you've set Health Points as an Attribute and not a Game Attribute. You want a blue box and not a purple one.
For everyone who has the problem that the bullets just go through the enemy ships and nothing happens, try to put the If-Block that makes the sound and kills the enemy ship in the CUSTOM-Event INSTEAD and deactivate the "When Updading" Event. It worked for me.
For all those who can't HIT or KILL enemies here is what you have to do :
Go to the Events tab of your Bullet actor.
Drag the 'trigger event' block to put it BEFORE the 'kill self' block.
So, to everyone hing the problem where the enemies explode when you test the game, instead of subtracting hit points, add them.
-when created, set hit points to 0 instead of 3
-In the the Hit function, instead of using decrement, use increment.
-Instead of using: "if hit points <= 0", use: "hit points >=3"
I was having the same problems. What I did was instead of adding a new event for step 92, I added those conditions to the custom event. It is working perfectly for me now.
I shoot the alienacji grabber 3 times... BUT ALL THE ALIENS DIED! I dodaje everything right, can some1 help Please?
So when I shoot the enemies they do not die. I think I know why I just don't know how to fix it.
When I created a new event and put my cursor over "Basic" and added "when updating" it did not start with an "always" block instead it is a "when Updating".
It must be something that got updated. But I don't know what to do. I'll try and figure my own way to do it if I do ill post another comment.
No matter how many times you shoot the Space Grabber thingies they don't die no matter how many times you shoot them. Can u help? thx. ;)
I can't select "Health Points" in the number field, it only allow me to select "Number" in this part of the excercise:
Switch back to the Enemy Ship's Custom Event, and then grab the Increment Number By [ ] block (found in Numbers
I have triple checked the steps and seem to have done it right but my enemy does not lose health/ die no matter how many times i shoot it.
It seems like my decrement function is not working?
Any ideas on what could be wrong?