Orient Normals to View

[ShaunDon]

Howdy all --

We're doing a new tower visualization with VRay, however the client wants us to work with his team's CAD massing model for the first couple weeks of the project as they'll be drastically revising the design daily. The big problem though is flipped normals in his geometry, which I know will only get worse as they continue to define detail.

I'm told that Lightscape had the same backface rendering problems as VRay, and that it had an option to orient all normals to face the rendered viewpoint -- I've never seen or heard about something like this for max, but does anyone here know if it exists or if maybe someone's written a fancy script that might do the same? I've googled to no avail, so my hopes are fading...

Thanks everyone!

Shaun

[dennis]

is there a problem rendering backfacing ? i havent stumbled across one but would like to know if there is any.
Altough a pain to look at in viewport unless of course you toggle of culling.

i think Vray treats all polys as two-sided.

[ShaunDon]

It's more a problem with backfacing glass materials, I think... I'm hoping we don't encounter a problem, but if we do we'll need a quick-fix.

[natty]

Hi Shaun

yes vray sometimes does have problems with face's that are flipped .. the way to get round this is to select the mesh ... edit mesh and then Unify the normals and flip them .. could be tedious but thats the way i deal with it ..

[ShaunDon]

That's the way I deal with it too, when it's my model. The problem is we need to be re-imported an updated CAD massing from the client daily, so if two weeks of flipping faces every day is going to kill us, so we were hoping there was somewhere out there a better method.

Shaun

[natty]

yeah it would be nice to have a script to unify, flip and make sure all the normal are pointing towards the camera .. probably not to hard to macro it.

[mike.edel]

editable meshes have a "unify normals" switch
that might help

other than that it would be possible to script something like that

i already found something in the maxscript help that allows you to get the eye position and direction of the current viewport
from that it should be possible to calculate if a face normal is looking away from the viewer or towards it

i just dont have the time to put it all together...

might want to try a search (in the maxscript ref) for getViewDirectionRay

mike

[mike.edel]

ok, hacked something together...

found a QD (quick and dirty) solution:
it flips all faces of a selected editable mesh towards the camera/viewport

not failsave (it just checks if its a mesh and if it has faces to avoid the worst errors)
if you are looking from ortho side views, all faces get flipped down

you can expand it to work on selected faces if you want to - i already wasted too much time

hope that helps...

mike

fn getViewDirection =
(
-- The affine TM transforms from world coords to view coords 
-- so we need the inverse of this matrix 
local coordSysTM = Inverse(getViewTM()) 
-- The Z axis of this matrix is the view direction. 
local viewDir = -coordSysTM.row3
return (normalize viewDir)
)

--test02 mike
--get current viewports direction
viewDir = getViewDirection()
currentSel = selection
selCount = currentSel.count

--check if selection is empty
if &#40;selCount < 1&#41; 
then print "No object selected..."
--if not - go through selected objects
else for i=1 to selCount do
	&#40;
	currentObj = selection&#91;i&#93;
	--test if current object is of type editable mesh
	isMesh = isKindOf currentObj Editable_Mesh
	if not&#40;isMesh&#41;
	then print &#40;"Selected Object Nr. " + selection&#91;i&#93;.name as string + " is no Editable Mesh and is therefore ignored"&#41;
	else
		&#40;
		--get number of faces in object
		numFaces = getNumFaces &#40;currentObj&#41;
		
		--for each face of the current obj&#58; calculate angle between face the viewport ray 
		---> flip normal if facing away
		for n=1 to numFaces do
			&#40;
			--print &#40;n&#41;
			--get Face Nomal
			currentNormal = getFaceNormal currentObj n
			--print &#40;"Face Normal&#58; " + currentNormal as string&#41;
			
			--calculate dot product - if the face faces away from view it is positive, otherwise its negative
			local dotProduct = dot currentNormal viewDir
			--print &#40;"Product&#58; " + dotProduct as string&#41;
			
			--if dotProduct is positive, flip the normal
			--goto modify panel &#40;seems to be important for the meshop.flipnormals method&#41;
			max modify mode
			if dotProduct >0 then 
				&#40;
				--flip face
				meshop.flipNormals currentObj #&#123;n&#125;
				&#41;
			&#41;
		--update the mesh to save the changes
		update currentObj
		&#41;
	&#41;

[ShaunDon]

Thanks Mike! I'll give that a shot -- that sounds perfect.

[alkis]

shaun
we ve been having similar problems here all the time as well.
may i suggest a much simpler solution
since the main problem in vray and backfacing is when you have glass mats.
you can try and suggest a workflow to the team that is building the model. i found that by simply telling them to make layers by materials or at least put all the glass elements on a separate layer , then i could just select them in max and flip their faces or modify them very easily. depending on the software they use you can also try and work with them and fix the problem. instruct them to build the model in a particular way that eliminates the problems upon import. there are ways to do that in all the cad packages and get clean 3d data.
hope this helps
regards
alkis

[ShaunDon]

Thanks Alkis, I definitely agree with you. And we need those layer divisions anyway so we can apply basic materials to the progress model.

I've been getting much cleaner imports of geometry if I export a 3DS out of CAD first rather than import the DWG with max. Figured max would be able to do a good job by now of importing AutoCAD, but hey.

Thanks all for the help!

Shaun

[archcanvas]

Hi Mike, thank you very much. I tested the code for a while, it works perfectly by far.

[jaggos]

Hi
if you using Autocad, you should use the file ling manager to inport it to MAx, there you get the option to flipp normal and weld them also give smoothing angle, it works form me. its quite hard in the begining. with little efford youl get it. I hope this helps.