I am making a build tool for my game and i want to know how to calculate the offset, I thought the easiest way to do it was to detect intersecting hitboxes,create a ray, then move in the opposite direction based on its magnitude.
So i want to detect when this happens:
try
local pos = --raycastResult.Position
local norm = -- raycastResult.Normal
local item = -- block or item or whatever you are trying to place
local endPos = pos + (norm * (item.PrimaryPart.Size*.5))
item:SetPrimaryPartCFrame(CFrame.new(endPos))
What does raycast result.Normal mean? Correct me if im wrong but wasn’t it the orientation of the side it hit?
yes the surface normal is the orientation of the surface from raycast.Instance.
did you try what I sent?
Wow thats very useful!, im trying it right now
Welp its not working lemme try using screenpoint to ray
oof then I’m not sure what you are trying to do, I thought you wanted the placing part offset from the part it was touching so that this wouldnt happen
I found the method I showed from a post by StickMasterLuke
with an example file DragModelExample.rbxl (23.4 KB)
Ok it works, the problem is with the ray´s filtering behaving weirdly, thank you! 
Wait no now its lagging badly for some reason
It could something is creating RenderStepped events recursively. Can I see the run.RenderStepped function with the raycast?
while true do
Buildmode = Player:GetAttribute("Buildmode")
if Buildmode == true then
block = game.ReplicatedStorage.SelectBox:Clone()
block.Parent = workspace.Ignore
Mouse.TargetFilter = workspace.Ignore
raycastparams = RaycastParams.new()
raycastparams.FilterType = Enum.RaycastFilterType.Blacklist
raycastparams.FilterDescendantsInstances = {Player.Character}
elseif workspace.Ignore:FindFirstChild("SelectBox") then
workspace.Ignore.SelectBox:Destroy()
end
while Buildmode == true do
ray = workspace:Raycast(Player.Character.Head.Position ,Mouse.Hit.Position , raycastparams )
if ray ~= nil then
local pos = ray.Position
local norm = ray.Normal
local item = block
local endPos = pos + (norm * (item.Size*.5))
print("script run once")
item.CFrame = CFrame.new(endPos)
end
game:GetService("RunService").RenderStepped:Wait()
end
wait(0.5)
end
I did not think about using that xd wouldn’t it lag the game a lot?
ok it still runs super slow like once every minute.
firstly while loops are less efficient
you should use
game:GetService("RunService").RenderStepped:Connect(function()
-- render stepped fires before the next frame is rendered
-- cast a ray
-- position the block based on the raycast result
end)
p.s. that code is formatted poorly it’s hard to see what is going on
it’s very hard to tell what your code is supposed to do
your RenderStepped function should look like this
game:GetService("RunService").RenderStepped:connect(function()
local mouseRay = mouse.UnitRay
local rayCastParams = RaycastParams.new()
rayCastParams.FilterDescendantsInstances = {item,player.Character}
rayCastParams.FilterType = Enum.RaycastFilterType.Blacklist
local raycastResult = game.Workspace:Raycast(mouseRay.Origin,mouseRay.Direction.unit * MAX_PLACEMENT_DISTANCE,rayCastParams)
if raycastResult then
target = raycastResult.Instance:GetFullName()
pos = raycastResult.Position
norm = raycastResult.Normal
local endPos = pos + (norm * (item.PrimaryPart.Size*.5))
item:SetPrimaryPartCFrame(CFrame.new(endPos))
end
end)
don’t put any while loops
Ok, i m gonna test that, in the meantime, can you explain what makes code easier to read? Or how can I make it less messy?
yes, the code you posted above was not indented correctly.
Anytime you have a condition statement or a function you indented the code
for example in your code you had
while true do
while true do
end
end
making it a lot harder to read, instead of
while true do
while true do
end
end
Roblox Studio automatically indents lines for you if you press enter
Ok it worked, youre right it IS much easier to understand, thank you 
No problem, glad I can help! 
small nitpick but i think it’s better to define the rayCastParams variable outside the runservice function