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Traces & Raycasting

How to use Traces & Raycasting to gather world information in runtime.

Traces offer a method for reaching out in your maps and getting feedback on what is present along a line segment. You use them by providing two end points (a start and end location) and the physics system “traces” a line segment between those points, reporting any Actors that it hits. Traces are essentially the same as Raycasts or Raytraces in other software packages.

The following example will show you how to get what and where the player is looking at.

-- Traces at each 100ms
-- Gets the middle of the screen
local viewport_2D_center = Viewport.GetViewportSize() / 2

-- Deprojects to get the 3D Location for the middle of the screen
local viewport_3D = Viewport.DeprojectScreenToWorld(viewport_2D_center)

-- Makes a trace with the 3D Location and it's direction multiplied by 5000
-- Meaning it will trace 5000 units in that direction
local trace_max_distance = 5000

local start_location = viewport_3D.Position
local end_location = viewport_3D.Position + viewport_3D.Direction * trace_max_distance

-- Determine at which object we will be tracing for (WorldStatic - StaticMeshes - and PhysicsBody - Props)
local collision_trace = CollisionChannel.WorldStatic | CollisionChannel.PhysicsBody

-- Sets the trace modes (we want it to return Entity and Draws a Debug line)
local trace_mode = TraceMode.ReturnEntity | TraceMode.DrawDebug

-- Last parameter as true means it will draw a Debug Line in the traced segment
local trace_result = Trace.LineSingle(start_location, end_location, collision_trace, trace_mode)

-- If hit something draws a Debug Point at the location
if (trace_result.Success) then

-- Makes the point Red or Green if hit an Actor
local color = Color(1, 0, 0) -- Red

if (trace_result.Entity) then
color = Color(0, 1, 0) -- Green

-- Here you can check which actor you hit like
-- if (trace_result.Entity:GetType() == "Character") then ...

-- Draws a Debug Point at the Hit location for 5 seconds with size 10
Debug.DrawPoint(trace_result.Location, color, 5, 10)
end, 100)

As you could see, we can pass bit-wise operators to Trace for more than one CollisionChannel at once! Use | between the CollisionChannels to achieve that.