Maya API, getting UV border vertices struggle

[Benjam901]

Hello all,

So here is my struggle at the moment.

I am trying to guesstimate the "actual" in-engine vert count for a given object in Maya so we can validate the LOD steps per object before we export.

Proposed solution:

The way I am trying to do this is by checking that a vertex is on a UV border edge and adding this to the total vert count.

So for example an object with 500 verts which has a UV border straight through the middle will end up with 1000 verts in-engine because of the UV split.

The problem I am having is wrapping my head around the underlying data models for verts, faces, edges and uvs.

Solution 1:

I have a sort of working solution that does not use the API but instead relies on the mel command: polySelectBorderShell 1

import pymel.core as pm

import maya.mel as mel

sel = pm.ls(sl=True)[0] # Get object selection

# Edges must be selected here

mel.eval("polySelectBorderShell 1")

uvs = pm.polyListComponentConversion(fe=True, tuv=True)

uvList = pm.ls(uvs, flatten=True)

uvDict = {}

for i in uvList:

   print i

   uvNum = int(i.split('[')[-1].split(']')[0])

   uvDict.update({uvNum:i})

vertBorders = {} # e.g. {'map1':[1, 2, 3, 5, 71]}

uvSets = pm.polyUVSet(sel, query=True, allUVSets=True)

for uvSet in uvSets:

   vertBorders.update({uvSet:[]})

   uvs = pm.polyEvaluate(sel, uvs=uvSet, uv=True)

   for uvNum in range(uvs):

       if uvNum in uvDict:

           vert = pm.polyListComponentConversion(uvDict[uvNum], fuv=True, tv=True)[0]

           vertBorders[uvSet].append(vert)

count = 0

multiList = vertBorders.values()

result = set(multiList[0]).intersection(*multiList[:1])

count += len(result)

newMultiList = []

for L in multiList:

   newList = [i for i in L if i not in result]

   count += len(newList)

print count

The above solution kinda gets me there and I need to make sure its legit and patch it up but for the most part it works.

Problem is that it is SLOW hence trying to use the API.

Solution 2:

For the API I am following along with this mode of thinking here: http://forums.cgsociety.org/archive/index.php?t-729364.html

Mu current solution and where I am stuck is here. I know I need to run some comparisons but how and on what I am deadlocked at.

def getVertFromId(dagPath, vertID):
    vertIt = OM.MItMeshVertex(dagPath)
    vtxIdUtil = OM.MScriptUtil()
    vtxIdUtil.createFromInt(0)
    vtxIdPtr = vtxIdUtil.asIntPtr()
    vertIt.setIndex(vertID, vtxIdPtr)
    return vertIt

def getFaceFromId(dagPath, faceId):
    faceIt = OM.MItMeshPolygon(dagPath)
    faceIdUtil = OM.MScriptUtil()
    faceIdUtil.createFromInt(0)
    faceIdPtr = faceIdUtil.asIntPtr()
    faceIt.setIndex(faceId, faceIdPtr)
    return faceIt

def getVertUVInfo(vertIn):
    uArr = OM.MFloatArray()
    vArr = OM.MFloatArray()
    fIDs = OM.MIntArray()
    uvIndices = OM.MIntArray()
    uvSet = 'map1'
    vertIn.getUVs(uArr, vArr, fIDs, uvSet)
    vertIn.getUVIndices(uvIndices, uvSet)

    print uArr, vArr, fIDs, uvIndices
    return fIDs, uvIndices

def stripUnecessaryFaces(currentEdgeFaces, faceIDs1, faceIDs2):
    fID1 = []
    fID2 = []
    for fID in faceIDs1:
        if fID in currentEdgeFaces:
            fID1.append(fID)

    for fID in faceIDs2:
        if fID in currentEdgeFaces:
            fID2.append(fID)

    return fID1, fID2

def main():
    mSelList = OM.MSelectionList()
    OM.MGlobal.getActiveSelectionList(mSelList)
    sel = OM.MItSelectionList(mSelList)

    dagPath = OM.MDagPath()
    sel.getDagPath(dagPath)
    dagPath.extendToShape()
    connFaces = OM.MIntArray()

    edgeIter = OM.MItMeshEdge(dagPath)
    while not edgeIter.isDone():
        f1 = None
        f2 = None
        edgeIter.getConnectedFaces(connFaces)
        if len(connFaces) == 1:
            # open edge
            print 'Open edge'

        f1 = connFaces[0] # face 1
        try:
            f2 = connFaces[1] # face 2
        except:
            pass

        vert1Index = edgeIter.index(0)
        vert2Index = edgeIter.index(1)

        MfVert1 = getVertFromId(dagPath, vert1Index)
        MfVert2 = getVertFromId(dagPath, vert2Index)

        fIdsvert1, uvIndicesVert1 = getVertUVInfo(MfVert1)
        fIdsvert2, uvIndicesVert2 = getVertUVInfo(MfVert2)

        edgeIter.next()

Any suggestions on where to go from here or how to solve this is very much appreciated!

// Ben

[damon shelton]

Would just retrieving the number of uvs in a given uvset give you the count you are looking for?

I created a sphere, then started creating uv shells out of part of the mesh.

len(cmds.ls('pSphere1.map[*]', fl=True))

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[Michael Boon]

For speed, you definitely want to use OpenMaya, but more importantly, avoid creating new Python objects every time you loop over a vert. Try to create some lists of regular Python ints upfront, then just count them.

Once you have a MFnMesh, you can get a list of the UV IDs used at each corner of each face using MFnMesh.getVertices() and MFnMesh.getAssignedUVs().

polyVertices = fnMesh.getVertices()

polyUVIDs = fnMesh.getAssignedUVs() # with optional UV set name

Both those functions return two lists. The first list in each is the list of vertex counts in each polygon, which we don't care about. The second lists are the vert IDs, and the corresponding UV IDs. It's significant that these are corresponding lists, since we're going to zip them together.

Create a list with an entry for each vert in the mesh, then you can put the UV IDs each vert uses into its entry in the list. You know the number of verts, so you can create the main list in one hit, for speed. By using sets, you only record the unique IDs used at each vert.

vertUVIDs = [set() for _ in range(fnMesh.numVertices)]

Then go through the getAssignedUVs result in a loop and record which UV IDs are used at each vert:

(Note: itertools.izip will be much faster than regular zip here because it doesn't create a new list)

for vID, uvID in izip(polyVertices[1], polyUVIDs[1]):

    vertUVIDs[vID].add(uvID)

Once you have the UV IDs at each vert, you just sum the lengths of the sets:

totalVertCount = sum(len(s) for s in vertUVIDs)

Note that verts with no UVs will not be counted at all this way. You might want to add a check that every set has at least one element in it.

I can count ~20k verts in ~30ms that way, which is certainly good enough for games work :)

[Benjam901]

Hey Michael,

Thank you for the tips on the API and techniques to use for speed. 

I was testing out your code and it works great. I am a bit confused though (I have not managed to wrap my head around how each return list corresponds to each other yet).

I need border edges for the UV shells. This way I can iterate each uv set, get the border uvs, check that this particular UVs vertex has not already been counted and add this to the total vert count rather than each UV.

- Ben

[Michael and Amanda]

Hey Ben, 

I have to admit I can't follow the UV shell technique you described. I would expect a 500 vert object with a seam up the middle to have 500 + (number of verts in the seam) verts in the game. The technique I described does that, by counting verts twice if they are on UV seams (or more than twice if they are on more than one seam).

I'll try to describe that technique a little better. 

Actually it might help to describe how a mesh is put together first. There is a list of vertex positions (which are points in space), and a list of faces (each face is just a list of IDs into the vertex list). However for efficiency, all the faces are run together into a single list, and there's a second list that tells how many verts are in each face so you can count through them to get to whichever face you want. Get your head around that, then consider UVs are exactly the same. First there's a list of UVs (points in 2D space), then there's a list of faces where each face is a list of IDs into the UV list, and the list of faces is all run together just like it is for vertices.

getVertices and getAssignedUVs each return two lists. The first list for each is the number of verts in each face (which we don't care about in this case). For getVertices, the second list is a list of vertex IDs. For getAssignedUVs, the second list is a list of UV IDs. Those two lists are in the same order, so we can zip them together to see which vertex corresponds to which UV. Remember these lists are for every vertex on every face, so each vertex ID will come up multiple times. If a vertex is not on a seam, every time that vertex ID comes up, the corresponding UV ID will be the same. If a vertex is on a seam, there will be two different UV IDs corresponding to that vertex ID. My technique just counts how many different UV IDs each vertex has, then adds then all together.

Now, if that's not what you need, to get UV shell information, you could use MFnMesh.getUvShellsIds. To get border edges, you will have to use an iterator. I might be able to take a look at that tomorrow, though no guarantees :)

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[Ben Hearn]

Hello Michael,

You explained it precisely how I needed it explained thank you! I was very confused about the return values for vertex IDs and UV UDs and how they tied together.

I am going to expand further and iterate each map and check that each vertex has already been split or not. Am I correct in thinking that if a vertex already belongs to a seam it would not split it again if it was on another map?

- Ben

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[Benjam901]

Hey Michael,

I copied some UVs into a new UV map and tried the same method and to highlight what was happening I am selecting the UVs.

For the 2nd UV set however the method looks like it fails, when I select the UVs it selects almost all the verts in the map.

I amended the code to give me the additional vert count i.e. verts only on seams adn the output for the 2nd map is 166 which is not correct.

Can you replicate this error also?

Code and screenshot is below:

import pymel.core as pm

import maya.OpenMaya as OM

from itertools import izip

sel = pm.ls(sl=True)[0]

selName = str(sel.nodeName())

mSelList = OM.MSelectionList()

OM.MGlobal.getActiveSelectionList(mSelList)

sel = OM.MItSelectionList(mSelList)

path = OM.MDagPath()

sel.getDagPath(path)

fnMesh = OM.MFnMesh(path)

vertCount = OM.MIntArray()

vertList = OM.MIntArray()

uvCounts = OM.MIntArray()

uvIDs = OM.MIntArray() 

#uvSet='map1'

set2 = 'uvSet'

tempSets = ['map1', 'uvSet']

additional = 0

#for uvSet in tempSets:

fnMesh.getVertices(vertCount, vertList)

#fnMesh.getAssignedUVs(uvCounts, uvIDs, uvSet)

fnMesh.getAssignedUVs(uvCounts, uvIDs, set2)

vertUVIDs = [set() for _ in range(fnMesh.numVertices())]

for vID, uvID in izip(vertList, uvIDs):

    vertUVIDs[vID].add(uvID)

totalVertCount = sum(len(s) for s in vertUVIDs if len(s)>1)

additional += totalVertCount

print additional

totes = [i for i in vertUVIDs if len(i) > 1]

for i in totes:

    for j in i:

        pm.select('{0}.map[{1}]'.format(selName, j), add=True)

[Michael Boon]

Hi Ben,

I can't see your image, but I can run your code on a mesh of my own. In really basic tests it seems to work correctly.

It's a bit tricky to read through. There's a fair bit of temp code in there, and things that are assigned and not used. Also, why are you using Python API 1.0? It's more difficult to use than 2.0 (unless you're more familiar with C++, I guess).

There are a few ways it could go wrong. 

• The most likely problem, I think, is that the code I gave you assumes that every face has UVs. I said "Note that verts with no UVs will not be counted at all this way. You might want to add a check that every set has at least one element in it," and that the two face lists (from getVertices and getAssignedUVs) will be identical. That was incorrect. If any faces have no UVs, they will get a 0 in the face list from getAssignedUVs and your vertex ID and UV ID lists will no longer correspond.
  
• There's also the problem that selecting '{0}.map[{1}]' will select UVs in the currently active UV set, which may or may not be 'uvSet'. You can set the currently active UV set in script, or in the UV Editor.
  
• The basic idea of doing "totalVertCount = sum(len(s) for s in vertUVIDs if len(s)>1)" seems flawed to me. You're only counting verts that are on seams. How are you going to use that number?

If you can get your image attached properly (I think the problem is at your end...), and confirm that your mesh has UVs for all faces in 'uvSet', we can build up from there.

[Ben Hearn]

Hello Michael,

Thanks for the support on this it is much appreciated.

I was not aware that I was using API 1.0, I have been reading the C++ docs for my reference so I assumed it was the correct API. I will make the switch to 2.0.

The selection of the UVs is just a visual test to check that I am getting the correct number of borders so we can ignore that issue (I switch UV sets to make sure in my tests)

The reason I am only counting UVs on seams is those are the only ones that split the vertex when we use them in the engine. We are trying to "guess-timate" the total vert count before we jump into the engine so the artist can be as efficient as possible with their source maya files and using the UVs for the time being can get us as close as possible.

Not all faces have UVs in uvSet that I can confirm for sure so the lists are out of sync. What if I iterated the face vertices and checked each vertex has UVs first and then cross referenced each list?

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[Michael Boon]

Hey, in case you haven't figured this out yourself by now, here's how I'd do it. This is very similar to the approach from my first post, but it grabs UVs from the first two channels, allows for faces with no UVs, and also allows for easy extension to handle vertex colors or normals (as I expect your engine splits on normals as well as UVs).

I've put a bunch of comments inline. With all the lists of vertex IDs it gets very hard to name variables so they make sense. I create a bunch of generators that compartmentalize the code more, but whether that would actually make it clearer is debatable.

A couple of essential concepts:

• zip, (and izip, izip_longest)
  zip takes two or more lists, and returns the first element of all of them, then the second, then the third, etc. izip does the same but is more memory efficient and hence faster. izip_longest is only different when the lists have different lengths. zip and izip will stop when they reach the end of the shortest list. izip_longest will keep returning values until it reaches the end of the longest list, and you can supply a "fillvalue" that it returns for the shorter lists.
• vertex splitting
  I'm assuming your engine works like the others I've seen. This means that each vertex has a position, one UV for each channel, and probably one normal too. One way to go from Maya verts to engine verts, is to split the Maya mesh along UV seams (and probably along hard edges). The way I do that is by actually creating those engine-style vertices (a position and 1 or 2 UVs) for every corner of every face, and then counting how many unique vertices I get. It's simpler to do that than to chase edges looking for UV seams or UV shells.

Anyhow, hopefully this code works for you, and makes sense!

import maya.api.OpenMaya as om

from itertools import izip, izip_longest

# Get the currently selected mesh.

mSelList = om.MGlobal.getActiveSelectionList()

path = mSelList.getDagPath(0)

fnMesh = om.MFnMesh(path)

# So the engine splits vertices if their UVs are different.

# Another way of looking at it, is that the engine stores each vertex like this:

# (position, uv0, uv1)

# So that's what we're going to do. We'll collect the position and the uvs of each 

# corner of each face, then put each of those corners into a set to find out how many 

# unique corners there are. That should tell us exactly how many vertices the engine 

# will count.

# Note that we are actually storing IDs rather than real values, just because it's 

# easier.

allFacesVertCounts = []

allFacesVertIDs = []

counter = []

# The first "channel" of face-vertex properties we want is the regular vertex positions.

polyVertices = fnMesh.getVertices()

allFacesVertCounts.append(polyVertices[0])

allFacesVertIDs.append(polyVertices[1])

counter.append(0)

# The next 2 channels are the UVs. This collects the first 2 UV channels but you could 

# change that to whatever you want.
numUVChannelsUsed = 2

uvSets = fnMesh.getUVSetNames()

for uvSet in uvSets[:numUVChannelsUsed]:

    f, ids = fnMesh.getAssignedUVs(uvSet)

    allFacesVertCounts.append(f)

    allFacesVertIDs.append(ids)

    counter.append(0)

    

# If you wanted to, you could also add normals, tangents, binormals and/or colors here.

numVertProperties = len(counter)

print 'Counting {} properties for {} vertex-faces...'.format(

    numVertProperties, len(allFacesVertIDs[0]))

    

uniqueVerts = set()

assert [len(c) == len(allFacesVertCounts[0]) for c in allFacesVertCounts]

for vertCounts in izip(*allFacesVertCounts):

    # Inside this loop, we're looking at one face at a time.

    # vertCounts contains the number of verts this face has in each channel.

    # vertCounts[0] will be the number of actual verts.

    # The other channels will either have the same number (if the face is mapped) 

    # or 0 (if the face is not mapped in this channel).

    assert len(vertCounts) == numVertProperties, (len(vertCounts), numVertProperties)

    faceVertIds = [None] * numVertProperties

    for i in range(numVertProperties):

        # Some faces don't have UVs in some channels, so they will have 0 verts in 

        # that channel. We need to count through the UV id lists by the correct 

        # amount for each channel.

        assert isinstance(vertCounts[i], int), type(vertCounts[i])

        assert (vertCounts[i] == 0 or vertCounts[i] == vertCounts[0]), (vertCounts[i], vertCounts[0])

        faceVertIds[i] = allFacesVertIDs[i][counter[i]:counter[i]+vertCounts[i]]

        counter[i] += vertCounts[i]

    # izip_longest lets us fill any empty faces with a default value (None in this case)

    for vertParams in izip_longest(*faceVertIds, fillvalue=None):

        # vertParams is a list of ids for this corner of the face. 

        # The first id is the vertex id. The second is the uv id in the first uv set.

        # We store all these ids because if any of them are different, the game engine 

        # will create a new vert, so we want to count it as a new vert.

        uniqueVerts.add(vertParams)

for i in range(numVertProperties):

    assert counter[i] == len(allFacesVertIDs[i]), (i, counter[i], len(allFacesVertIDs[i]))
print 'Done.'

print 'Number of Maya verts:', fnMesh.numVertices

print 'Number of face-verts:', len(allFacesVertIDs[0])

print 'Number of engine verts:', len(uniqueVerts)

[Ben Hearn]

Hey Michael,

Thank you for the help on this I have learned a ton of good knowledge on how engines store and process vertices from a mesh.

It took me a while to dig through your code and understand the relationship between vert counts, ids and uv ids and how you have assembled the data but I think I got it :D

Thanks again!

Ben

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