Terrible Graphics

local Players = game:GetService("Players")
local AssetService = game:GetService("AssetService")
local RunService = game:GetService("RunService")
local UserInputService = game:GetService("UserInputService")
local Workspace = game:GetService("Workspace")

local W, H = 160, 120
local MAX_DIST = 1000

local camera = Workspace.CurrentCamera

local playerGui = Players.LocalPlayer:WaitForChild("PlayerGui")

local existing = playerGui:FindFirstChild("RaytracerGui")
if existing then existing:Destroy() end

local sg = Instance.new("ScreenGui")
sg.Name = "RaytracerGui"
sg.ResetOnSpawn = false
sg.IgnoreGuiInset = true
sg.Parent = playerGui

local img = Instance.new("ImageLabel")
img.Size = UDim2.fromScale(1, 1)
img.ScaleType = Enum.ScaleType.Stretch
img.BackgroundColor3 = Color3.new(0, 0, 0)
img.Parent = sg

local editable = AssetService:CreateEditableImage({ Size = Vector2.new(W, H) })
img.ImageContent = Content.fromObject(editable)

local pixbuf = buffer.create(W * H * 4)

local rayParams = RaycastParams.new()
rayParams.FilterType = Enum.RaycastFilterType.Exclude
local function refreshFilter()
	local char = Players.LocalPlayer.Character
	rayParams.FilterDescendantsInstances = char and { char } or {}
end
refreshFilter()
Players.LocalPlayer.CharacterAdded:Connect(refreshFilter)

local function vlerp(a, b, f)
	return a + (b - a) * f
end

local WHITE = Vector3.new(1, 1, 1)
local SKY = Vector3.new(0.5, 0.7, 1.0)
local lightDir = Vector3.new(-0.4, 1, 0.3).Unit

local function skyColor(rd)
	local t = 0.5 * (rd.Y + 1)
	return vlerp(WHITE, SKY, t)
end

local connections = {}
local function shutdown()
	for _, conn in connections do
		if conn.Connected then conn:Disconnect() end
	end
	table.clear(connections)
	if sg then sg:Destroy() end
	print("raytracer killed")
end

local function render()
	local cf = camera.CFrame
	local origin = cf.Position

	local fovRad = math.rad(camera.FieldOfView)
	local halfH = math.tan(fovRad * 0.5)
	local halfW = halfH * (W / H)
	local right = cf.RightVector
	local up = cf.UpVector
	local forward = cf.LookVector

	local offset = 0
	for y = 0, H - 1 do
		local ndcY = (1 - (y + 0.5) / H * 2) * halfH
		for x = 0, W - 1 do
			local ndcX = ((x + 0.5) / W * 2 - 1) * halfW
			local dir = (forward + right * ndcX + up * ndcY).Unit

			local result = Workspace:Raycast(origin, dir * MAX_DIST, rayParams)

			local r, g, b
			if result then
				local base = result.Instance.Color -- Color3
				local n = result.Normal
				local diff = math.max(n:Dot(lightDir), 0)
				local shade = 0.25 + diff * 0.75 -- ambient + lambert
				r = base.R * shade
				g = base.G * shade
				b = base.B * shade
			else
				local c = skyColor(dir)
				r, g, b = c.X, c.Y, c.Z
			end

			buffer.writeu8(pixbuf, offset,     math.clamp(r, 0, 1) * 255)
			buffer.writeu8(pixbuf, offset + 1, math.clamp(g, 0, 1) * 255)
			buffer.writeu8(pixbuf, offset + 2, math.clamp(b, 0, 1) * 255)
			buffer.writeu8(pixbuf, offset + 3, 255)
			offset += 4
		end
	end

	editable:WritePixelsBuffer(Vector2.zero, Vector2.new(W, H), pixbuf)
end

table.insert(connections, UserInputService.InputBegan:Connect(function(input, gpe)
	if gpe then return end
	if input.KeyCode == Enum.KeyCode.X then
		shutdown()
	end
end))

table.insert(connections, RunService.Heartbeat:Connect(render))

print("live raytracer running - press X to kill")