How to sort vertices in posX and negX coordinates using MEL?

[aishwarya]

Hi friends,
               Just wanted to know how one can sort vertices of any polygon geometry.I mean for eg. if i selected all +x verts and want a program to automatically select the corresonding -x verts what would be the code.Pls help.Thanks.

[joojaa]

Mel is not a programming language so it doesn't need very deeply complex algorithmic facilities (that is what the API is for, no need to do same thing 2 times). So in essence you dont really use mel to do this kind of sorting, its totally outside of mels scope. Mel is just  a scripting interface just like a unix shell would be, but rather specialized. Trying to think like a computer scientist does not help you here. So in essence if youd designing something taht loops over big amounts of things and needsw to do complex computation that is outside the realm of mel. So the minute yu go need to use a structure... your not thinking mel, and thereby not using your resources the best way. You can brute force but thats it.

You can not sort anything more complex than strings and vectors and flat onedimesnional arrays with mel. So the real answer is you dont. You use facilities provided to you to solve the problem indirectly, mel is not a tool for extending maya its a tool for using what you have more efficiently to build a solution. Tough if you really wanted to make a correspondence list you COULD use string sorting for this.

Theres a few ways to do thsi partially effectively by using a closest point node but its far more efficient to do this in the api if the direct querry is needed. Thing is tough you can for MOST tasks you can trick maya around so you dont need to mirror at all.

[aishwarya]

Hi,
    Thanks Jooja for clarification,actually i was using a mel script named "abSymMesh" this script is basically used for mirroring blend shape etc.,I was trying to understand the script,all parts are pretty clear except the one in which he used some kind of sorting between -x and +x verts so wanted to know if there is any clear explanation for that.

Yes you are right that MEL is incapable of that but API is.I think the script i was talking about is written in C++ API with MEL GUI.

If you select any vert and goto component editor under polygons you will find its no. and x,y and z coordinates and their values.I went through several MEL prog books and they all have given access to those values by using vector array which i understood and can do but none of them has mentioned how to access a vert on the basis of its corresponding neg or pos vert but i know its possible because "abSymMesh" does exactly that.

Please help to clarify this doubt of mine.Thanks for reading and replying.

[joojaa]

Its possible but its slow. Becsue its slow you dont want to use it.

n+x verts so wanted to know if there is any clear explanation for that.

well yes its just stupid to use mel for this but yes its very soimple to do. Just sort the vertices by absolute value, if you remove things thet dont have a corresponding pair then the paidr of every odd number is the the next even number and every even numbers pair is every odd number. Uts just thet the sorting is convoluted because MEL is specifically designed NOT to do this. So the fact that it was hard was a CLUE for not useing mel for it.

basically used for mirroring blend shape

Yes except offcourse maya knows how to mirror a blendshape without you needing to know the corresponding point. This is one of those things where its clear that mel is not a programming language.

What you can do is model the blend on one side of a symmetrical model then make a blendshape Retaining toe original shapes. Then you copy the base shape scale the object by -1 along the symmetry axis take the mesh shape erap the target shape and run the blend target to 1 and bam youve done a mirror on the shape.  YOu didnt program any loop at all you were using nodes which is what mel is supposed to do. nSo i can mirror the mesh in 7 or 8 lines of mel if i needed to, and using no loops.

So yes you can do this like they do in "abSymMesh", but it is NOT a very good example on what you should use mel for! Its a 1000 line script for something i can ultimately do in less than 100 lines with far better efficency. See just because somebody did something does not mean it was a sane thing to do.

went through several MEL prog books

Well good luck with that. i have yet to see a single book on maya programming that does even a remotely good job at explaining the idea.

[aishwarya]

yes you are right it might be a little bit slow,although i never noiced it,to be true,anyways my point is by knowing this method you can not only do simple mirroring of BS but also flip the vertices or exchange their values in any way you want them not only modelling parameters but also paint weight values, UV values which can give you tremendous control and ability to manipulate data on these verts and can help you create some efficient plugins.

Thats why i was seeking advice,I had been thinking, everything else seems clear except this sorting.

Thank you.

[aishwarya]

If not Mel then please tell how i can do this with C++ API?

[joojaa]

Well yes EXCEPT the same trick that was used for mirroring the blendshape can be used for transfeering any data! BEcause maya has a tool for mesh to mesh data transferal. So you dont need to know or loop the items over.

The direct guideline is that:

IF you do something on a vertex to vertex level looping. then your NOT supposed to use maya scripting interface. Its fine for small diirty things but ultimataly you get a 100 times performance boost out of the api and for stuff like this its MUCH EASIER.

The ultimate probelm is that youll be calling a lot fo settattributes that need to be pushed and updated in the stack and thats not the menaing, So when you deal with massed component lelvl stuff ist mostly not mel anymore

[aishwarya]

*Just sort the vertices by absolute value, if you remove things thet dont have a corresponding pair

how will i find that a vertex has a corresponding pair or not?

all i know is :-

for ex. if i have an array by the name say vector geo1[];

if i=1 increment the pointer by three for ex. i+3 i access all the verts in the geo.

if i=0 do i+1 i access x cord of vertx 1 i+2 y cord and i+3 z cord and so on

with this above data how i am going to find that which vert has a corresponding pair and which not?

[joojaa]

Well i dont have maya at hand but thing is c has a HUGE overhed on your skill. Theres a few months of training to get your first thing to compile, i suggets you use python instead!

[joojaa]

You modify the list, since python is a general purpose language its much easier to prototype this in python:

Pseudocode in python script environ looks as follows (port it to api calls yourself):

 
#concrete
class pointToBeSorted(object):
    I = -1
    posX = 0
    posY = 0
    posZ = 0
    def __init__(self,index, posX, posY, posZ):
        self.I = id
        self.X = abs(posX)
        self.Y = abs(posY)
        self.Z = abs(posZ)
    def __cmp__(self,other):
        return cmp(self.X,other.X) or cmp(self.Y,other.y) or cmp(self.Z,other.Z)
 
# following is pseudocode it does NOT work but it depicts the idea
#
# thats what pseudocode is for:
 
pointArray =[]
for index in vertexIdNumber:
    pos=pointPosition("object.vtx["+str(index)+"]")
    pointArray.append(pointToBeSorted(index,*pos))
pointArray.sort()
corespndenceDict={}
for i in range(len(pointArray)):
    try:
        if cmp(pointArray[i],pointArray[i+1])==0:
            corespndenceDict[pointArray[i].I]=pointArray[i+1].I
            corespndenceDict[pointArray[i+1].I]=pointArray[i].I

done now all you need to do is do corespndenceDict[yourindex] and your get the mirrored index. Offcoyrsethets pseudocode in real code you need to handle stuff like what if 2 points overlap etc... but thats a dufferent story.

[aishwarya]

Thanks a lot,thats what i was looking for

[joojaa]

Had a slight omission. Anyway like i said you dont really want to do stuff like thsi with teh scriptin interface, Its not productive, YOu can mirror any stuff in maya with 8 lines and then use the trasfer tools to do the bulk of the job. This si just a execice in rpogramming.

BUT SCRIPTING IN MAYA IS NOT ABOUT PROGRAMMING SKILL!

[aishwarya]

actually i wanted to use this method for making paint weight task a bit easier,if you have used exporting paint weight maps in alpha images and re imported them it takes a while and in that moment you will see maya reordering all vertices according to the alpha image so i was wondering if i save small templates of alpha images made in PS then use some script or api tool which automatically assign that image as weight values to coresponding joint it will automate the process and will help you skip the blocking process of weight painting,you can straight away then go and smooth or tweak weight according to your need.

the code i was thinking in general was:-

select the joint(s)
select the image and hit apply.
tweak.
Done.

[joojaa]

Yes that is what the artisan is all about.

[aishwarya]

but with artisan tool you have to paint evry time from scratch whereas with this method you will get that particular part painted instantly,say for ex. you have multiple biped characters with different vert counts when you skin them according to the options selected in smooth skin option box Maya assign each vert with a joint(s) so instead of going and painting each character from scratch if you have a tool which takes an alpha image takes a joint as input takes +y or -y orientation from user calculate the falloff based on the vertices associated with that joint or instead take no. of edgerings to paint from user and assigns that alpha image as weights then you wont have to use artisan and paint from scartch?

[joojaa]

No you dont artisan has a import map functionality. So everything you can set with a brush based toolset you can map with a texture.