Ask the Server

Lesson 6 of 25 in Coddy's Roblox Game: Battlegrounds course.

Abilities start on the player's device. BattleClient is a LocalScript in the HUD. ContextActionService ties an action to keys, and with true as the third argument it also puts a button for it on a phone screen:

ContextActionService:BindAction("Wave", use, true, Enum.KeyCode.T)

The function gets the action's name and the input's state, Begin when the key goes down. The server owns the rules, so the client only asks, through the RemoteEvent Remotes.Ability. On the server, OnServerEvent hears it, and Roblox passes the player who fired it first:

remotes.Ability.OnServerEvent:Connect(function(player, name)
	print(name .. " from " .. player.Name)
end)

Challenge

Medium

Make Q ask the server for a dash.

In BattleClient, write use(name, state): on Enum.UserInputState.Begin, call remotes.Ability:FireServer(name).
Bind it: ContextActionService:BindAction("Dash", use, true, Enum.KeyCode.Q).
In BattleServer, connect remotes.Ability.OnServerEvent to print(player.Name .. " asked for " .. name).

Press Play and press Q: the Output reads Player1 asked for Dash. Then Check.

Try it yourself

local Players = game:GetService("Players")
local ServerStorage = game:GetService("ServerStorage")
local Settings = require(game.ReplicatedStorage.Settings)

local lastSwing = {} -- player -> when they last swung

-- Roblox's own sword animations
local slash = Instance.new("Animation")
slash.AnimationId = "rbxassetid://522635514"

print("Swords deal " .. Settings.SwordDamage .. " damage")

-- A swing: the animation, then everyone in the box in front of you is hit
local function swing(player)
	local character = player.Character
	local root = character and character:FindFirstChild("HumanoidRootPart")
	if not root or character.Humanoid.Health <= 0 then
		return
	end
	local now = time()
	if lastSwing[player] and now - lastSwing[player] < Settings.SwingCooldown then
		return
	end
	lastSwing[player] = now
	character.Humanoid.Animator:LoadAnimation(slash):Play()
	-- the box in front of you, never your own body
	local params = OverlapParams.new()
	params.FilterDescendantsInstances = { character }
	local box = root.CFrame * CFrame.new(0, 0, -3)
	local hit = {} -- each humanoid once per swing
	for _, part in workspace:GetPartBoundsInBox(box, Settings.HitboxSize, params) do
		local humanoid = part.Parent:FindFirstChildOfClass("Humanoid")
		if humanoid and not hit[humanoid] then
			hit[humanoid] = true
			humanoid:TakeDamage(Settings.SwordDamage)
			print(humanoid.Parent.Name .. " is at " .. humanoid.Health)
		end
	end
end

-- Every player gets a sword every life
Players.PlayerAdded:Connect(function(player)
	player.CharacterAdded:Connect(function()
		local sword = ServerStorage.Sword:Clone()
		sword.Parent = player.Backpack
		sword.Activated:Connect(function()
			swing(player)
		end)
	end)
end)

-- The training dummy: its health bar follows its health, and a beaten
-- dummy comes back after a moment, a fresh copy in the same place
local function setupDummy(dummy)
	local humanoid = dummy.Humanoid
	humanoid.HealthChanged:Connect(function(health)
		dummy.HealthBar.Back.Fill.Size = UDim2.fromScale(health / humanoid.MaxHealth, 1)
	end)
	humanoid.Died:Connect(function()
		local spot = dummy:GetPivot()
		task.wait(0.5)
		dummy:Destroy()
		task.wait(Settings.DummyRespawn)
		local fresh = ServerStorage.Dummy:Clone()
		fresh:PivotTo(spot)
		fresh.Parent = workspace
		setupDummy(fresh)
	end)
end
setupDummy(workspace.Dummy)