Detecting Hits

Detecting hits is the process of identifying when blasts collide with players, then reducing their health accordingly. At a high-level, you can think of this work as either:

1. A physically simulated check of whether a projectile struck the target.
2. An instantaneous check of whether the blaster was aimed at the target.

The type of hit detection you use depends on the gameplay requirements of your experience. For example, a physically simulated check is appropriate for a dodgeball experience where balls need to leave the hand at a certain velocity, drop as they move through the air, or change direction from weather conditions. However, an instantaneous check is a better match for a laser tag experience where beams must have a near-infinite velocity and ignore environmental factors like gravity and wind speed.

Using the sample laser tag experience as a reference, this section of the tutorial teaches you about the scripts behind hit detection in the 3D space, including guidance on:

• Getting the blast direction from the current camera values and the player's blaster type.
• Casting rays in a straight path from the blaster as it blasts.
• Validating the blast to prevent exploitation of blaster data.
• Reducing player health according to the blast damage from each type of blaster and how many rays hit the player.

After you complete this section, you can explore additional development topics to enhance your gameplay, such as audio, lighting, and special effects.

Get Blast Direction

After a player blasts their blaster, ReplicatedStorage > Blaster > attemptBlastClient > blastClient > generateBlastData calls two functions to start the hit detection process: rayDirections() and rayResults().

generateBlastData
local rayDirections = getDirectionsForBlast(currentCamera.CFrame, blasterConfig)
local rayResults = castLaserRay(localPlayer, currentCamera.CFrame.Position, rayDirections)

The inputs for rayDirections are straightforward: the current camera position and rotation values, and the player's blaster type. If the sample laser tag experience only gave players blasters that produce a single laser beam, ReplicatedStorage > LaserRay > getDirectionsForBlast would be unnecessary because you could use currentCamera.CFrame.LookVector to calculate the direction for the blast.

However, because the sample provides an additional blaster type that produces several laser beams with a wide, horizontal spread, getDirectionsForBlast must calculate the direction for each laser beam of the spread according to their angles within the blaster configuration:

getDirectionsForBlast
if numLasers == 1 then
	-- For single lasers, they aim straight
	table.insert(directions, originCFrame.LookVector)
elseif numLasers > 1 then
	-- For multiple lasers, spread them out evenly horizontally
	-- over an interval laserSpreadDegrees around the center
	local leftAngleBound = laserSpreadDegrees / 2
	local rightAngleBound = -leftAngleBound
	local degreeInterval = laserSpreadDegrees / (numLasers - 1)

	for angle = rightAngleBound, leftAngleBound, degreeInterval do
		local direction = (originCFrame * CFrame.Angles(0, math.rad(angle), 0)).LookVector
		table.insert(directions, direction)
	end
end

To demonstrate this concept further, if you were to include a third blaster type with a wide, vertical spread, you could create a new blaster attribute, such as spreadDirection, then adjust the CFrame calculation to use a different axis. For example, note the difference in the direction calculations in the following script below for this hypothetical third blaster type.

if numLasers == 1 then
	table.insert(directions, originCFrame.LookVector)
elseif numLasers > 1 then
	local leftAngleBound = laserSpreadDegrees / 2
	local rightAngleBound = -leftAngleBound
	local degreeInterval = laserSpreadDegrees / (numLasers - 1)
	for angle = rightAngleBound, leftAngleBound, degreeInterval do
		local direction
		if spreadDirection == "vertical" then
			direction = (originCFrame * CFrame.Angles(math.rad(angle), 0, 0)).LookVector
		else
			direction = (originCFrame * CFrame.Angles(0, math.rad(angle), 0)).LookVector
		end
		table.insert(directions, direction)
	end
end
return directions

Ultimately, the rayDirections() function returns a table of Vectors that represent the direction of each laser beam. If it's helpful, you can add some logging to get a sense of what this data looks like.

generateBlastData
local rayDirections = getDirectionsForBlast(currentCamera.CFrame, blasterConfig)
for _, direction in rayDirections do  -- new line
    print(direction)                  -- new line
end                                   -- new line
local rayResults = castLaserRay(localPlayer, currentCamera.CFrame.Position, rayDirections)

Cast Rays

castLaserRay(), the second function in ReplicatedStorage > Blaster > attemptBlastClient > blastClient > generateBlastData, performs the more complex operations within the script. It begins by specifying parameters so that it can make Workspace:Raycast() calls for raycasting purposes. Raycasting is the process of sending out an invisible ray from a Vector3 point in a specific direction with a defined length, then checking its path to see where it intersects with other objects.

This information is particularly useful for first-person shooter experiences because it allows you to see when and where blasts intersect with players or the environment. For example, the following image demonstrates two rays that are casting parallel to each other. According to their point of origin and direction, Ray A misses the wall and continues until it meets its maximum distance, while Ray B collides with the wall. For more information on this process, see Raycasting.

The castLaserRay() parameters specify that Raycast() calls must consider every part in the workspace except the character who blasted. The script then casts a ray for each direction in the directions table. If a ray hits something, it generates a RaycastResult, which has five properties:

• Distance – The distance between the ray origin and the intersection point.
• Instance – The BasePart or Terrain cell that the ray intersects.
• Material – The Enum.Material at the intersection point.
• Position – The Vector3 position of the intersection between the ray and the Instance.
• Normal – The Vector3 of the normal vector of the face the ray intersects with.

The Instance value is the most critical of these properties for the sample laser tag experience's gameplay because it communicates when rays collide with other players. To retrieve this information, the experience uses the ReplicatedStorage > LaserRay > castLaserRay > getPlayerFromDescendant helper function. If it returns nil, the instance isn't part of a player, meaning the ray hit an inanimate object within the environment.

castLaserRay() then uses Position and Normal to create a new CFrame that it calls the ray's destination. Every ray has a destination, and it's either where the ray hit in the 3D space, or the point at the end of its maximum distance. Depending on how well your players aim, many or most taggedPlayer values are nil.

castLaserRay
if result then
	-- The blast hit something, check if it was a player.
    destination = CFrame.lookAt(result.Position, result.Position + result.Normal)
    taggedPlayer = getPlayerFromDescendant(result.Instance)
else
	-- The blast didn't hit anything, so its destination is
	-- the point at its maximum distance.
	local distantPosition = origin + rayDirection * MAX_DISTANCE
	destination = CFrame.lookAt(distantPosition, distantPosition - rayDirection)
	taggedPlayer = nil
end

Validate the Blast

To prevent cheating, the previous chapter Implementing Blasters explains how blastClient notifies the server of the blast using a RemoteEvent so that it can verify all data that each client sends, such as whether or not they truly tagged another player with their blaster. This ray validation process occurs in ServerScriptService > LaserBlastHandler > getValidatedBlastData > getValidatedRayResults, and each check correlates to a nested module script:

1. First, getValidatedRayResults calls validateRayResult to check that each entry in the rayResults table from the client is a CFrame and a Player (or nil).

2. Next, it calls isRayAngleFromOriginValid to compare the expected angles of the laser spread to the ones from the client. This code in particular shows the advantage of using ReplicatedStorage because the server can call getDirectionsForBlast itself, store the return as the "expected" data, and then compare it against the data from the client.

   Just like blaster validation from the previous chapter, isRayAngleFromOriginValid relies on a tolerance value to determine what constitutes an "excessive" difference in angles:

   isRayAngleFromOriginValid
   local claimedDirection = (rayResult.destination.Position - originCFrame.Position).Unit
   local directionErrorDegrees = getAngleBetweenDirections(claimedDirection, expectedDirection)
   
   return directionErrorDegrees <= ToleranceValues.BLAST_ANGLE_SANITY_CHECK_TOLERANCE_DEGREES

   Roblox abstracts away the most involved bits of math, so the result is a short, highly reusable helper function with applicability across a range of experiences:

   getAngleBetweenDirections
   local function getAngleBetweenDirections(directionA: Vector3, directionB: Vector3)
       local dotProduct = directionA:Dot(directionB)
       local cosAngle = math.clamp(dotProduct, -1, 1)
       local angle = math.acos(cosAngle)
       return math.deg(angle)
   end

3. The next check is the most intuitive. Whereas getValidatedBlastData uses DISTANCE_SANITY_CHECK_TOLERANCE_STUDS to verify that the player who blasted was near the beam's point of origin, isPlayerNearPosition uses identical logic to check if the tagged player was near the beam's destination:

   isPlayerNearPosition
   local distanceFromCharacterToPosition = position - character:GetPivot().Position
   if distanceFromCharacterToPosition.Magnitude > ToleranceValues.DISTANCE_SANITY_CHECK_TOLERANCE_STUDS then
       return false
   end

4. The final check isRayPathObstructed uses a variation of the ray cast operation to check if the ray's destination is behind a wall or other obstruction from the client's position. For example, if a malicious player were to systematically remove all walls from the experience to tag other players, the server would check and confirm that the rays are invalid because it knows every object position within the environment.

   isRayPathObstructed
   local scaledDirection = (rayResult.destination.Position - blastData.originCFrame.Position)
   scaledDirection *= (scaledDirection.Magnitude - 1) / scaledDirection.Magnitude

No anti-exploit strategy is comprehensive, but it's important to consider how malicious players may approach your experience so that you can put checks in place that the server can run to flag suspicious behavior.

Reduce Player Health

After verifying that a player tagged another player, the final steps in completing the main gameplay loop in the sample laser tag experience are to reduce the tagged player's health, increment the leaderboard, and respawn the player back into the round.

Starting with reducing the tagged player's health, Spawning and Respawning covers the distinction between Player and Player.Character, specifically that a character is a Humanoid model. Humanoid models have a Health property with a default value of 100. Rather than implementing its own system, the sample laser tag experience uses this built-in property to keep track of how much damage a player needs before they are tagged out of the round.

The experience stores damage values in the damagePerHit attribute of each blaster. For example, the blaster that blasts a single laser beam inflicts 10 points of damage, so it takes ten blasts with this blaster to tag out another player. To start the process of tagging a player out, LaserBlastHandler calls ServerScriptService > LaserBlastHandler > processTaggedPlayers, which checks the now-validated rayResults table for players and passes damagePerHit to onPlayerTagged.

Health doesn't accept negative values, so onPlayerTagged has some logic to keep player health at or above zero. After verifying that player health is above zero, it compares health to damagePerHit and uses the smaller of the two values. For example, if a player has 10 health and is hit by a 15 damage laser beam, the laser only inflicts 10 points of damage.

This way of approaching the problem might seem a bit convoluted. For example, why not just set player health to zero if it would be negative? The reason is because setting health values circumvents the force field. Using the Humanoid:TakeDamage() method ensures that players don't take damage while their force fields are active.

onPlayerTagged
local function onPlayerTagged(playerBlasted: Player, playerTagged: Player, damageAmount: number)
	local character = playerTagged.Character
	local isFriendly = playerBlasted.Team == playerTagged.Team

	-- Disallow friendly fire
	if isFriendly then
		return
	end

	local humanoid = character and character:FindFirstChild("Humanoid")
	if humanoid and humanoid.Health > 0 then
		-- Avoid negative health
		local damage = math.min(damageAmount, humanoid.Health)

		-- TakeDamage ensures health is not lowered if ForceField is active
		humanoid:TakeDamage(damage)
		if humanoid.Health <= 0 then
			-- Award playerBlasted a point for tagging playerTagged
			Scoring.incrementScore(playerBlasted, 1)
		end
	end
end

The next step is to increment the leaderboard. It might have seemed unnecessary for LaserBlastHandler to include the player who blasted alongside the blast data, but without that information, the experience can't credit the player with tagging someone out. Finally, the tagged out player respawns back into the round, which you can review in Spawning and Respawning.

The five chapters in this curriculum cover the experience's core gameplay loop, but there are still plenty of areas to explore, such as:

• Blaster visuals: See ReplicatedStorage > FirstPersonBlasterVisuals and ServerScriptService > ThirdPersonBlasterVisuals.
• Audio: See ReplicatedStorage > SoundHandler.
• Custom Modes: How could you modify this experience to introduce new types of objectives, such as scoring the most points before the time runs out?

For extended gameplay logic for the laser tag experience, as well as reusable, high-quality environmental assets, review the Laser Tag template.