Create Smoothing Groups from UV Islands

Note: A few people have reported that this script does not work with 3ds max 2016. I haven’t had a chance to investigate yet, so it might need a few modifications to work on the latest version of max.

It’s fairly common knowledge that when creating a model that will have a baked normal map, you want to have a split in your UV wherever you have a hard edge. Usually you’d have to make sure you keep in mind your UV layout when setting up your smoothing groups, or vice-versa. I’ve been meaning to get into learning Maxscript for awhile, so I figured I’d have a go at writing a script to make the process a bit easier and less prone to error.

What the script does, is put hard edges wherever there’s a seam on the UV. You could also think of it as assigning a single smoothing group to each UV island. I’m definitely not the first person to come up with this, but the scripts I’ve come across that do this tend to have some cases in which they don’t work, or produce incorrect results.

You can download it below, and be sure to check the header of the script for usage instructions!

Download – UVIslandsToSmoothingGroups.ms

------------------------------------- UV Islands To Smoothing Groups -------------------------------------
-- By Martin Palko 
-- www.martinpalko.com
--
--
-- Tested:	- Max 2014
-- 
-- Install:	- Drag script into max, then assign it to a hotkey or menu bar in "Customize -> User Interface"
--			- Can be found by setting the category to "MP_Tools" while in the "Main UI" group
--
-- Usage:	- Select any mesh object, and activate the script. Choose a UV channel and hit run.
--
-- Notes:	- This script will not affect your modifier stack, it will simply put an edit poly with the 
--				smoothing groups at the top.
--			- Undo is not currently supported, so save before, just in case. You can however, just delete 
--				the edit poly modifier to get your old smoothing groups back.
--			- Selecting any channel other than UV channel 1 will show a dialogue box asking if you want to 
--				reset UVs. You must hit yes for it to work based on the channel you've specified. This 
--				will NOT affect the model's existing UV set.

macroscript UVIslandsToSmoothing 
category:"MP_Tools"
buttontext:"UV 2 Smooth"
tooltip:"Convert UV islands to smoothing groups"
autoUndoEnabled:false
(	
	-- Helper function to get the index of the first true element in a bit array
	function getFirstActiveInBitarray aBitArray =
	(
		for i = 1 to aBitArray.count do
		(
			if aBitArray[i] == true do return i
		)
		-- return 0 if none are found active
		return 0
	)

	-- Actually performs the operation on the currently selected object
	function ConvertUVIslandsToSmoothingGroups aUVChannel =
	(
		if $ != undefined then
		(			
			modPanel.addModToSelection(Edit_Poly()) ui:on
			local editPoly = $.modifiers[#edit_poly]
			
			local facesDone = #{} -- empty bit array since no faces are done
			local allFaces = #{1.. polyop.getNumFaces $}
			local facesNotDone = allFaces
			
			-- Stick on a UVW modifier
			modPanel.addModToSelection (Unwrap_UVW ()) ui:on
			local uv_modifier = $.modifiers[#unwrap_uvw]				
			uv_modifier.unwrap2.setTVSubObjectMode 3 -- Use face selection
				
			if (aUVChannel != 1) then -- Only need to mess with this if it's not default
			(
				uv_modifier.unwrap.setMapChannel aUVChannel
				uv_modifier.unwrap.reset()
				forcecompleteredraw dodisabled:true -- Hacky fix for a bug, see http://www.polycount.com/forum/showthread.php?t=97059
			)
				
			local uv_islands = #() -- Empty array that will store bitarrays of all our UV islands
			local abort = false -- Abort boolean for breaking out of the loop and avoid the performance penalty of using break
			
			-- Build array of UV islands
			while (facesNotDone.isEmpty == false and abort == false) do
			(				
				nextFace = getFirstActiveInBitarray facesNotDone -- Get next face that hasn't been processed yet
				
				uv_modifier.unwrap2.selectFaces #{nextFace} -- Select that face
				uv_modifier.unwrap2.selectElement() -- Grow selection to element
				uv_island = uv_modifier.unwrap2.getSelectedFaces()	-- Get a bitaray of all those faces (representing a UV island)
				
				-- Update faces done/not done bit masks
				facesDone += uv_island
				facesNotDone -= uv_island
				
				insertItem uv_island uv_islands (uv_islands.count + 1) -- Add that bitarray to our array of UV islands
				
				if uv_islands.count > allFaces.count then -- this should never happen, if it does means we are in an infinite loop and will crash max, so bail
				(
					abort = true
					print ("Error, calculated too many islands, something went wrong")
				)
			)
			
			deletemodifier $ uv_modifier -- Don't need the UV modifier anymore
			
			editPoly.autoSmoothThreshold = 180.0 -- If we auto smooth, it should always be in the same smoothing group
			
			for island = 1 to uv_islands.count do -- Select and auto smooth each UV island
			(
				editPoly.SetSelection #Face uv_islands[island]
				editPoly.ButtonOp #Autosmooth
			)
		)
	)
	
	local isOpen = false -- Store if the rollout is open or closed
	
	rollout UV2SmoothRollout "UV_2_Smooth"
	(
		spinner UVChannelSpinner "UV Channel" range:[1,99,1] type:#integer
		button GoBtn "        Run        "
		
		on GoBtn pressed do
		(
			ConvertUVIslandsToSmoothingGroups (UVChannelSpinner.value)
			destroyDialog UV2SmoothRollout -- Close rollout after running
		)
		
		on UV2SmoothRollout close do
		(
			isOpen = false
			updateToolbarButtons() -- Update the toolbar icon when closing
		)
	)
	
	on execute do
	(
		if isOpen then --if open, close it
		(
			destroyDialog UV2SmoothRollout
		)
		
		else --if closed, open it
		(
			createDialog UV2SmoothRollout
			isOpen = true
		)
	)
  
	on isChecked return isOpen --return the flag
	
	on isEnabled do
	(
		-- Need an editable poly selected to work
		if $ == undefined then
		(
			-- Close the window if it's open and it shouldn't be
			if (isOpen) then
				destroyDialog UV2SmoothRollout
			
			return false
		)
		else
			return true
	)
)