Making Games Like StickMasterLuke's "Draw It"?

I just wanted to try and attempt recreating his game from scratch. (I wanted to do it in SurfaceGui, instead of ScreenGui) But I ran into a problem.

So currently, I use Localscript for this. Localscript is in StarterPack, chalkboard is the part name (in Workspace), inside chalkboard part, there is a SurfaceGui, and inside the SurfaceGui, there is a Frame.

chalkboard = workspace.chalkboard
frame = chalkboard.SurfaceGui.Frame
local player = game.Players.LocalPlayer
local mouse = player:GetMouse()

function draw()
	if mouse.Target == chalkboard then 
		while true do 
			wait()
			local mark = Instance.new("Frame", frame)
			mark.Size = UDim2.new(0,1,0,1)
			mark.Position = UDim2.new(0,mouse.X, 0, mouse.Y)
			mark.BackgroundColor3 = Color3.fromRGB(0,0,0)
		end
	end
	
end

mouse.Button1Down:connect(draw)

When I execute, it does draw, but how do you get it so that when player clicks on the SurfaceGui, it draws in that spot of the Frame, instead of Mouse position??? Thanks.

You could try getting the difference between the mouse position and the frame, and then offsetting the mark by that difference.

local mousePos = Vector2.new(mouse.X,mouse.Y)
local offset = mousePos - frame.AbsolutePosition
mark.Position = UDim2.new(0,offset.X,0,offset.Y)