Tuto tiny-ecs demo Part 9 Player Shoots Enemies Die

In this chapter we will make the player1 able to "shoot" and "hurt" enemies.

This will be done in two parts: first enabling the player1 "shoot" action, then hurting the enemies with some fx and make them "die".

Player1 can Shoot

We implement player1 can shoot in the SDynamicBodies system.

Please go to the "sDynamicBodies.lua" file to add some code.

SDynamicBodies = Core.class()

function SDynamicBodies:init(xtiny, xnmes) -- tiny function
	self.tiny = xtiny -- ref so we can remove entities from tiny system
	self.tiny.processingSystem(self) -- called once on init and every update
	self.nmes = xnmes -- a list of nmes we can hurt
end
-- ...

In the init function we add the list of enemies to the function signature and we make that list available to the other functions.

Then in the process function, we check if the player presses the action1 button (the spacebar) and we set a random enemy in the nmes list to be hurt.

function SDynamicBodies:process(ent, dt) -- tiny function
	-- ...
	-- actions (player1)
	if ent.isplayer1 and ent.isaction1 then
		ent.isaction1 = false
		if #self.nmes > 0 then -- check nmes list is not empty
			self.nmes[math.random(#self.nmes)].isdirty = true
		else -- nmes list is empty
			print("you killed everybody!")
		end
	end
	-- move
	ent.x += ent.body.vx * dt
	ent.sprite:setPosition(ent.x, ent.y)
end

I set the hurt behavior as being the flag isdirty (some of my Box2D leftovers).

So every time the player presses the spacebar, a random enemy from the nmes list will get hurt.

Enemies can die

In order to hurt an enemy we need to add a new System. The system will decrease an enemy health which will eventually "die".

In the systems folder "_S", create a file called "sNme1.lua" for example, and copy the following code:

SNme1 = Core.class()

function SNme1:init(xtiny, xnmes) -- tiny function
	self.tiny = xtiny -- ref so we can remove entities from tiny system
	self.tiny.processingSystem(self) -- called once on init and every update
	self.nmes = xnmes
end

function SNme1:filter(ent) -- tiny function
	return ent.isnme
end

function SNme1:onAdd(ent) -- tiny function
end

function SNme1:onRemove(ent) -- tiny function
	print("SNme1:onRemove")
end

function SNme1:process(ent, dt) -- tiny function
	for i = #self.nmes, 1, -1 do -- scan in reverse
		if self.nmes[i].isdirty then -- hit
			self.nmes[i].health -= 1
			self.nmes[i].washurt = 5 -- timer for a flash effect
			self.nmes[i].sprite:setColorTransform(2, 0, 0, 3) -- the flash effect (a bright red color)
			self.nmes[i].isdirty = false
			if self.nmes[i].health <= 0 then -- dead :-(
				self.tiny.world:removeEntity(self.nmes[i]) -- sprite removed from sprite layer in SDrawable
				self.nmes[i] = nil -- remove from table
				table.remove(self.nmes, i) -- remove from table
			end
		end
	end
end

In this system, when an entity is dirty (hurt), we decrease its health, set a timer for a flashing effect and if it dies, we remove it from tiny-ecs world and the nmes list.

Please note the sprite is removed from the sprite layer in the SDrawable system:

function SDrawable:onRemove(ent) -- tiny function
	ent.spritelayer:removeChild(ent.sprite)
end

Let's add the flashing effect to the SDynamicBodies system like so:

function SDynamicBodies:process(ent, dt) -- tiny function
	-- hurt fx
	if ent.washurt and ent.washurt > 0 then
		ent.washurt -= 1
		if ent.washurt <= 0 then
			ent.sprite:setColorTransform(1, 1, 1, 1)
		end
	end
	-- movement
	if ent.isleft and not ent.isright then -- LEFT
		ent.body.vx = -ent.body.speed
	elseif ent.isright and not ent.isleft then -- RIGHT
		ent.body.vx = ent.body.speed
	-- ...

If an entity counter washurt is greater than 0, we decrease it. When the counter reaches zero we set the entity sprite color back to normal.

Action

To see the result of our work, we need to add the SNme1 system to tiny-ecs world.

In the "levelX.lua" file add the SNme1 system:

	-- ...
	-- add systems to tiny-ecs
	self.tiny.world:add(
		SDrawable.new(self.tiny),
		SDynamicBodies.new(self.tiny, nmes), -- add the nmes list here too!
		SPlayer1Control.new(self.tiny),
		SAI.new(self.tiny),
		SNme1.new(self.tiny, nmes)
	)
	-- ...

Remember we changed the SDynamicBodies init function signature, so you need to add the new paramters to the System here too!

That's it!

You can run the demo and press the spacebar. A random enemy should get hit and eventually die.

Next?

In the next part, we ...

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