topic How to get vertex normal using python in 3ds Max Programming Forum

How to get vertex normal using python

Anonymous — Wed, 07 Mar 2018 03:33:24 GMT

I drag a box into an empty scene, then using the following python script to get vertex normal. However, the result is not what i expected.

From the output, we can see there are just two kind of normals, which is obviously wrong.

I know the face normal can be retrieved with Mesh.GetFaceNormal, but what I really want to get is the vertex normal taking smooth group into account(That means every vertex has three normals). I searched the python API docs, but can't find the right way to do that.

Can somebody help me?

python script:

n=list(MaxPlus.Core.GetRootNode().Children)[0]
obj=n.EvalWorldState(0).Getobj()
tri_obj = MaxPlus.TriObject._CastFrom(obj.ConvertToType(MaxPlus.ClassIds.TriMeshGeometry, 0))
mesh=tri_obj.GetMesh()
for i in xrange(mesh.GetNumVertices()): print mesh.GetRenderedVertexNormal(i)

output:

Point3(0, 0, -1.5708)
Point3(0, 0, -1.5708)
Point3(0, 0, -1.5708)
Point3(0, 0, -1.5708)
Point3(0, 0, 1.5708)
Point3(0, 0, 1.5708)
Point3(0, 0, 1.5708)
Point3(0, 0, 1.5708)

Re: How to get vertex normal using python

Anonymous — Wed, 07 Mar 2018 04:38:25 GMT

If i set three adjacent face have the same smooth group, then the shared vertex has only one normal.

In C++ SDK, I can get the right normal using RVertex. Is there something like that in Python.

Re: How to get vertex normal using python

Swordslayer — Wed, 07 Mar 2018 08:19:23 GMT

Looks like neither Face::getAllVerts nor Mesh::getRVert are exposed in python. As a workaround, you can find the smoothing group borders and for verts that share two or more calculate the normals separately.

Re: How to get vertex normal using python

Anonymous — Wed, 07 Mar 2018 09:58:03 GMT

Thanks for your reply.

Do you mean there is no way in python to get the internal rnormal of 3ds max, and we need to calculate the normals by ourselves?

Re: How to get vertex normal using python

Swordslayer — Wed, 07 Mar 2018 12:26:41 GMT

Definitely looks like that's the case, these methods are available in the .NET API but not in the python wrapper.

Re: How to get vertex normal using python

drew_avis — Wed, 07 Mar 2018 13:11:01 GMT

Hi there, here is an example of how to use this API:

'''
An example of how to populate RNormals and get them with GetRenderedVertexNormals()
'''
import MaxPlus

obj = MaxPlus.Factory.CreateGeomObject(MaxPlus.ClassIds.Box)
n = MaxPlus.Factory.CreateNode(obj, "myBox")

print "node name: %s" % n.Name
n.Convert(MaxPlus.ClassIds.TriMeshGeometry)
object_state = n.EvalWorldState()
obj_original = object_state.Getobj()
tri_obj = MaxPlus.TriObject._CastFrom(obj_original)
tri_mesh = tri_obj.GetMesh()
print "normals built? ", tri_mesh.GetNormalsBuilt() # will return 0 if normals are not yet built
tri_mesh.CheckNormals(True) # less expensive than BuildNormals(), because it will only build if normals
# do not yet exist
print "normals built? ", tri_mesh.GetNormalsBuilt() # will now return non-0 because CheckNormals() ensures
# we've built them
normal_count = tri_mesh.GetNormalCount()
vertex_count = tri_mesh.GetNumVertices()
print " normals: ", normal_count
print " verts: ", vertex_count

for i in range(0, vertex_count):
	print "vertex: " , tri_mesh.GetVertex(i)
	print "RNormal: ", tri_mesh.GetRenderedVertexNormal(i)

This is the script "demoGetRenderedNormals.py" under <3dsmax>\Scripts\Python\.

Drew

Re: How to get vertex normal using python

drew_avis — Wed, 07 Mar 2018 13:11:57 GMT

Hi there, here is an example of how to use this API:

'''
An example of how to populate RNormals and get them with GetRenderedVertexNormals()
'''
import MaxPlus

obj = MaxPlus.Factory.CreateGeomObject(MaxPlus.ClassIds.Box)
n = MaxPlus.Factory.CreateNode(obj, "myBox")

print "node name: %s" % n.Name
n.Convert(MaxPlus.ClassIds.TriMeshGeometry)
object_state = n.EvalWorldState()
obj_original = object_state.Getobj()
tri_obj = MaxPlus.TriObject._CastFrom(obj_original)
tri_mesh = tri_obj.GetMesh()
print "normals built? ", tri_mesh.GetNormalsBuilt() # will return 0 if normals are not yet built
tri_mesh.CheckNormals(True) # less expensive than BuildNormals(), because it will only build if normals
# do not yet exist
print "normals built? ", tri_mesh.GetNormalsBuilt() # will now return non-0 because CheckNormals() ensures
# we've built them
normal_count = tri_mesh.GetNormalCount()
vertex_count = tri_mesh.GetNumVertices()
print " normals: ", normal_count
print " verts: ", vertex_count

for i in range(0, vertex_count):
	print "vertex: " , tri_mesh.GetVertex(i)
	print "RNormal: ", tri_mesh.GetRenderedVertexNormal(i)

This is the script "demoGetRenderedNormals.py" under <3dsmax>\Scripts\Python\.

Hope that helps,

Drew

Re: How to get vertex normal using python

Anonymous — Wed, 07 Mar 2018 13:44:51 GMT

RNormal:  Point3(0, 0, -1.5708)
RNormal:  Point3(0, 0, -1.5708)
RNormal:  Point3(0, 0, -1.5708)
RNormal:  Point3(0, 0, -1.5708)
RNormal:  Point3(0, 0, 1.5708)
RNormal:  Point3(0, -0, 1.5708)
RNormal:  Point3(-0, 0, 1.5708)
RNormal:  Point3(0, 0, 1.5708)

Thanks for your reply:)

Following your code, I still get the same result as above:(

By the way, I use 3ds max 2017, there is no "demoGetRenderedNormals.py" in the demo script directory.

Re: How to get vertex normal using python

Anonymous — Wed, 07 Mar 2018 13:58:33 GMT

I guess you use 3ds max 2018, am I right?

Is your result correct? Can you post it here.

Thanks.

Re: How to get vertex normal using python

drew_avis — Wed, 07 Mar 2018 14:58:54 GMT

EDIT: Ok, I re-read your first post, you want to take the smoothing group into account - let me look at this again and get back to you.

I get the same results:

vertex:  Point3(-12.5, -12.5, 0)
RNormal:  Point3(0, 0, -1.5708)
vertex:  Point3(12.5, -12.5, 0)
RNormal:  Point3(0, 0, -1.5708)
vertex:  Point3(-12.5, 12.5, 0)
RNormal:  Point3(0, 0, -1.5708)
vertex:  Point3(12.5, 12.5, 0)
RNormal:  Point3(0, 0, -1.5708)
vertex:  Point3(-12.5, -12.5, 25)
RNormal:  Point3(0, 0, 1.5708)
vertex:  Point3(12.5, -12.5, 25)
RNormal:  Point3(0, -0, 1.5708)
vertex:  Point3(-12.5, 12.5, 25)
RNormal:  Point3(-0, 0, 1.5708)
vertex:  Point3(12.5, 12.5, 25)
RNormal:  Point3(0, 0, 1.5708)

Is this not what you're expecting?

I get the same thing in MAXScript:

b = box()
convertToMesh b
for v = 1 to b.numVerts do
(
	n = getNormal b v
	format "vertex: % normal: %\n" v n
)

-- result:
vertex: 1 normal: [0,0,-1.5708]
vertex: 2 normal: [0,0,-1.5708]
vertex: 3 normal: [0,0,-1.5708]
vertex: 4 normal: [0,0,-1.5708]
vertex: 5 normal: [0,0,1.5708]
vertex: 6 normal: [0,0,1.5708]
vertex: 7 normal: [0,0,1.5708]
vertex: 8 normal: [0,0,1.5708]

Re: How to get vertex normal using python

drew_avis — Wed, 07 Mar 2018 15:15:31 GMT

Ok, I just tested both the MAXScript and Python code on a box with all faces assigned to a smoothing group, and they appear to return the correct data.

mxs:

vertex: 1 normal: [0,-0.785398,-1.5708]
vertex: 2 normal: [0,-1.5708,-1.5708]
vertex: 3 normal: [0,1.5708,-1.5708]
vertex: 4 normal: [1.5708,0,-1.5708]
vertex: 5 normal: [0,-1.5708,1.5708]
vertex: 6 normal: [0,-0.785398,1.5708]
vertex: 7 normal: [0,0.785398,1.5708]
vertex: 8 normal: [0.785398,0,1.5708]

MaxPlus:

vertex:  Point3(-12.5, -12.5, 0)
RNormal:  Point3(0, -0.785398, -1.5708)
vertex:  Point3(12.5, -12.5, 0)
RNormal:  Point3(0, -1.5708, -1.5708)
vertex:  Point3(-12.5, 12.5, 0)
RNormal:  Point3(0, 1.5708, -1.5708)
vertex:  Point3(12.5, 12.5, 0)
RNormal:  Point3(1.5708, 0, -1.5708)
vertex:  Point3(-12.5, -12.5, 25)
RNormal:  Point3(0, -1.5708, 1.5708)
vertex:  Point3(12.5, -12.5, 25)
RNormal:  Point3(0, -0.785398, 1.5708)
vertex:  Point3(-12.5, 12.5, 25)
RNormal:  Point3(0, 0.785398, 1.5708)
vertex:  Point3(12.5, 12.5, 25)
RNormal:  Point3(0.785398, 0, 1.5708)

This is 2018.

Drew

Re: How to get vertex normal using python

Anonymous — Thu, 08 Mar 2018 01:36:29 GMT

That's not correct. There are just two different normal(positive z, negative z) for the 8 vertex.

RNormal:  Point3(0, 0, -1.5708)
RNormal:  Point3(0, 0, 1.5708)

Re: How to get vertex normal using python

drew_avis — Thu, 08 Mar 2018 13:36:49 GMT

EDIT: Ok, I think I understand now, sorry for the confusion - you want the 3 normals shown in your original diagram because the faces are not in the same smoothing group. It doesn't look like GetRenderedVertexNormals() returns more than the first vertex normal.

Drew

Re: How to get vertex normal using python

Anonymous — Fri, 09 Mar 2018 01:47:55 GMT

Yes. So do you think i have to calculate normals by ourselves in python? I am just wondering whether there is an API

can do that.

Re: How to get vertex normal using python

drew_avis — Fri, 09 Mar 2018 12:39:19 GMT

Right now you will need to calculate normals yourself, if there's more than 1 normal per vertex. Thank you for posting this - I've opened a defect on this lack of exposure, though if it does get fixed, it won't be until after the 2019 release.

Drew

Re: How to get vertex normal using python

Anonymous — Fri, 09 Mar 2018 13:10:55 GMT

Got it. Thanks

Re: How to get vertex normal using python

denisT.MaxDoctor — Fri, 09 Mar 2018 21:20:06 GMT

@drew_aviswrote:
Right now you will need to calculate normals yourself, if there's more than 1 normal per vertex.
Drew

what do mean by "calculate"? average? but it doesn't make sense. Every geometry vertex (by index) might have more than one corresponding RNormal. It's how it is. And you have to live with it...

i don't see any bug in code above. I just don't sure that

GetRenderedVertexNormal

does do everything right

Re: How to get vertex normal using python

Anonymous — Sat, 10 Mar 2018 11:18:27 GMT

Yeah, but the problem is that we can't access the rnormal with Python API (GetRenderedVertexNormal fails to do that).

With C++ API, we can.

Re: How to get vertex normal using python

denisT.MaxDoctor — Sat, 10 Mar 2018 18:32:06 GMT

GetRenderedVertexNormal

there is no this method in c++ api.

you can get pointer to the 'i-th' RVertex with mesh->getRVertPtr(int i)

after that you have access to RNormal(s). This is all that you need

Re: How to get vertex normal using python

Anonymous — Sun, 11 Mar 2018 07:01:02 GMT

I think you misunderstood me. Sorry for the confusion.

1. Of course I know there is no 'GetRenderedVertexNormal' in C++. The problem is that in Python, its result is wrong.

2. "With C++ API, we can", I mean in C++ we can get the right rnormal using RVertex like what you stated.