PyQt Agnostic Launcher II

As part of the improvements i have been carrying on to the VFX pipeline we are developing i wanted to dig deeper into the problem of executing a PySide Maya tool outside the DCC, this is, as standalone, as well as being able to execute it inside Maya without doing any changes to the code. I already came out with a first version of the launcher which you can see in http://jiceq.blogspot.com.es/2016/08/pyqt-agnostic-tool-launcher.html  . This basically detects whether there isn´t a Qt host application running and if not, we assume it is Maya running.

 @contextlib.contextmanager  
 def application():    
   if not QtGui.qApp:  
     app = QtGui.QApplication(sys.argv)  
     parent = None  
     yield parent  
     app.exec_()  
   else:  
     parent = get_maya_main_window()  
     yield parent  

This works fine for the beginnings of a VFX pipeline, mostly based in Maya. But as soon as you face the need to integrate other heterogeneous packages (that ship with any version of Python and PyQt, which is becoming a standard in the industry. see: http://www.vfxplatform.com/  ) you will probably want to be able to, at least, run the same GUI embedded in different packages as well as standalone. So the need to distinguish between host apps arises and this first solution falls short.

One poor solution is to query the Operating System whether the maya.exe/maya.bin or nuke.exe/nuke.bin processes were running. In the following fashion, for example:

  
def tdfx_is_maya_process_running():    
   return tdfx_is_process_running('maya')
def tdfx_is_nuke_process_running():    
   return tdfx_is_process_running('nuke')
def tdfx_is_process_running(process_name):
   if os.platform() == 'windows':
      ''' specific os code here '''
      return is_running    
   elif os.platform() == 'linux':
      ''' specific os code here '''
      return is_running
   return False

And use this instead in the previous if-statement to retrieve the corresponding QApplication main window instance.

This is a very poor solution, if we can call it a solution. It doesnt work well: you may have an instance of Maya or Nuke running, but you may want to run in standalone mode your custom script from your preferred IDE. The above functions will both return True, first problem. Second, it will depend on order of evaluation, so if you are testing first "tdfx_is_maya_process_running()" then your launcher will attempt to get the Maya main window instance. And third and most important, your launcher wont work because internally it is detecting Maya, so it is reporting the presence of a QApplication.qApp pointer, when you are in standalone mode and there is no qApp pointer actually!

So basically, this approach is not valid. What we really want to query is not the processes running, but more specifically if my current script is running embedded in a qt host application or not, and if so, i want to be able to know which one is.

I googled a little bit and was surprised that some people had faced this problem and meanly resolved it their own -not so great and elegant- way. I just thought there must be some way in Qt to query the host application. I just cant acknowledge something so basic wasnt taken into account in the framework. After some looking into the documentation..eureka, i found this line:

QtWidgets.QApplication.applicationName()

which returns the name of the host application. In standalone Qt apps, it is a parameter that must be set by the programmer.

def tdfx_qthostapp_is_maya():
    return tdfx_qthostapp_is('Maya-2017')

def tdfx_qthostapp_is_nuke():
    return tdfx_qthostapp_is('Nuke')

def tdfx_qthostapp_is(dcc_name):
    from PySide2 import QtWidgets
    hostappname = QtWidgets.QApplication.applicationName()
    if hostappname == dcc_name:
        return True
    return False

Consequently my new contextmanager version takes the following form:

 @contextlib.contextmanager  
 def application():    
   if tdfx_qthostapp_is_none():  
     app = QtGui.QApplication(sys.argv)  
     parent = None  
     yield parent  
     app.exec_()  
   elif tdfx_qthostapp_is_maya():  
     parent = get_maya_main_window()  
     yield parent
   elif tdfx_qthostapp_is_nuke():
     parent = get_nuke_main_window()
     yield parent  

This is a step improvement towards easing the integration of other PyQt-API-based DCCs in a VFX pipeline and easing the task of the programmer, thus avoiding to produce GUI application-specific code. Nonetheless, there is still some work to do that i will deal with when i have more time. This is, making the GUI code fully portable between PySide2 and PySide (or Qt4 and Qt5). There are already some solutions out there like the "Qt.py module" that intends to abstract the GUI from the Qt4 to Qt5 big jump in recent Maya 2017 Python API.

PyQt Agnostic Tool Launcher

After some weeks of resting and a new challenge at Drakhar Studio where i am developing the nuts & bolts of a pipeline software that communicates with TACTIC, i have now some spare time to talk about one of my recent discoveries concerning Python programming.

I'm always looking on how to improve my code (in general, no matter what the programming language is), although it's certainly true Python is one in a million because of many reasons, one of them being that a bunch of design patterns are an intrinsic part of the language, such as decorators and context managers.

More specifically, i was looking for a way to run my tools regardless or whether it was standalone (this is, running its own QtApplication, or embedded into Maya's). In the past, i didnt have much time to dig into this and consequently, i used two separate launchers.

Last week this was solved by the use of a context manager. I realised i could make good use of it, since in both cases (running standalone or in a host app) i had to make the same two calls:

 tool_window = Gui_class(parent)  
 tool_window.show()  

Where Gui_class() is the main GUI PyQt Class. The difference is the parent argument where in one case it must be None and in the other it must be a pointer to the Maya GUI Main Window.

This difference in the parent argument could be handled just the same way as for example the open() context manager works:

 with open(filepath, 'wb') as f:  
    src_lines = f.readlines()  

In this case, the advantage is the user doesnt have to remember to close the file stream and the open() method yields the stream as 'f'.


LAUNCHER IMPLEMENTATION

 @contextlib.contextmanager  
 def application():    
   if not QtGui.qApp:  
     app = QtGui.QApplication(sys.argv)  
     parent = None  
     yield parent  
     app.exec_()  
   else:  
     parent = get_maya_main_window()  
     yield parent  

This is my implementation of my custom context manager, it is basically an if statement that checks whether the tool is being lauched from a host application or in his own QApplication. This function could be already the main launcher, the only need is to put the previous two lines showed where the yield statement goes. But this goes against one of the OOP principles, Dont Repeat Yourself (DRY).

So if we push a little bit further we end up with:

 def launcher(cls):      
   with application() as e:  
     window = cls(parent=e)  
     window.show()  

Where cls is the name of the main GUI class. This way, we have an agnostic launcher prepared to work as standalone and within a host app like maya.

Needless to say that some pieces of the tool only will work inside Maya but this way at least we can launch the tool for GUI refinement and development.

No more separate launchers with duplicate parts of the code!!

Plugin Loading And Threads

Back to coding: TTL_Cameratronic

 

After some time solving issues regarding the publishing process of the shots i m finally back to coding. This time it's a tool whose purpose is to be able to ease the task of the crowd department. They need to work faster and cook simulations faster so the way the tool will work is: they will load the layout of a sequence of shots, with the corresponding cameras obviously, perform the cache of all the sequence and then cut where necessary.

This will require the tool first to iterate through the file system searching for camera files which come as alembics, read from the last published version the duration of the shot and then reference all the cameras setting them with the corresponding frame offset.

Ideally, the tool should also create a master camera which will switch between all the cameras referenced thus composing the sequence's final camera behaviour. I will do this by "parentconstraining" the master camera to all the shot cameras and then keyframing the weights to 0 or 1. Seems easy to do this way.

The tool also will show list of the camera names (which will have to be renamed after the shot number they represent), the start and end frames and finally the alembic file to be loaded (since there may be several different versions we will take always by default the last one).

Those are images of the look & feel of the tool still in development but so far functional: with splash screen and the final result in a list. It needs some tweaks more like a "delete cameras button" for example and offsetting the start frame. Also it lacks the master camera functionality. But i think all left to do won't be much problematic.

GUI & Threads

Since the search process in the filesystem can take a while i will have to deal with threads. Recall that the main thread is responsible for all the GUI painting so any process i want to do has to be pushed into the background in a secondary thread.

Also there is a progress bar which means in this case  a third thread responsible for actually referencing all the camera.

Both secondary threads are used sequentially, so there is no harm and trouble in things like data sharing or concurrency.

The bigger problem I faced, so to speak, and the reason of this post is that loading the alembic plugin caused me some pain at first. The tool has to check whether the plugin is loaded, and if not, proceed to the load.

Now, in the beginning i tried to do this in the same thread responsible for the alembics referencing just before. The result was Maya crashing....

Then, intuitively ( i hadnt read the documentation at that moment) i decided to move that method to the main thread. Now it wasnt crashing but the cameras werent loaded. But i noticed something: loading a maya plugin seems to take some time, a time where Maya is busy presumably registering all the plugins and furthermore seemingly also updates the GUI. This made me think of the "evalDeferred()" method and its updated, non-deprecated equivalent "executeDeferred()" which according to documentation:

maya.utils

The maya.utils package is where utility routines that are not specific to either the API or Commands are stored. This module will likely expand in future versions.

Currently, the maya.utils package contains three routines relevant to threading (see the previous section for details on executeInMainThreadWithResult).

There are two other routines in maya.utils:

• maya.utils.processIdleEvents(). It is mostly useful for testing: it forces the processing of any queued up idle events.
• maya.utils.executeDeferred().
  (Similar to maya.utils.executeInMainThreadWithResult() except that it does not wait for the return value.) It delays the execution of the given script or function until Maya is idle. This function runs code using the idle event loop. This means that the main thread must become idle before this Python code is executed.
  There are two different ways to call this function. The first is to supply a single string argument which contains the Python code to execute. In that case the code is interpreted. The second way to call this routine is to pass it a callable object. When that is the case, then the remaining regular arguments and keyword arguments are passed to the callable object.

 As said "It delays the execution of the given script or function until Maya is idle."

All i had to do is put the plugin loading method in the main thread and execute the code inside my thread with Maya.utils.executeDeferred().

Additional Comment

Another solution which havent been tested but i believe should work according to the documentation is if you really want the code of loading the plugin in the thread you should use executeInMainThreadWithResult().

Despite restrictions, there are many potential uses for threading in Python within the context of Maya; for example, spawning a thread to watch a socket for input. To make the use of Python threads more practical, we have provided a way for other threads to execute code in the main thread and wait upon the result.

The maya.utils.executeInMainThreadWithResult() function takes either a string containing Python code or a Python callable object such as a function. In the latter case, executeInMainThreadWithResult() also accepts both regular and keyword arguments that are passed on to the callable object when it is run.

 

 
 

Python Idiosyncrasies (I)

I want to post here some Python language characteristics i find different and interesting for anyone coming from more traditional ones such as C. So far i've used them every once and a while in the time i've been coding tools here in Madrid and i intend to do several related posts in the future as i learn new features.

I have to say that this only relates to Python 2.7 which is the version Mayapy 2015 comes with.

Composite conditions

Here we find the two key words: "any" and "all"

Both can receive as input a list of expressions that return a boolean and in turn the result is a boolean

"any" equivalent: "if sentence1 or sentence2 or sentence3.... or sentenceN"

"all" equivalent: "if sentence1 and sentence2 and sentence3... and sentenceN"

This way those complex expressions in the conditional can be reduced in combination with a list comprehension. For example this snippet of code shows how to check if some letters appear in a string:

1:  if any(letter in "somestring" for letter in ['a','b','c','s']):  

would return True whereas:

1:  if all(letter in "somestring" for letter in ['a','b','c','s'])  

would return False. 

Iterating multiple lists (I)

Use here the zip() command as stated here:

1:  for elementA, elementB in zip(listA,listB):  

It is worth noting that the zip command iterates until the last element of the shortest of the lists. Though many times both lists have same length, it might not always be the case. Furthermore, you might encounter the need to iterate until the longest list, returning a predefined value for empty element. There is another command for this from the itertools module:

1:  import itertools  
2:  list1 = ['a1','b1']  
3:  list2 = ['a2','b2','c2']  
4:  for element1, elemen2 in itertools.izip_longest(list1,list2)   

By default empty indices' value are set to 'None'.

What happpens if you want this behaviour but also be able to use the element's index?

There is the "enumerate" command that returns a list's current index and element.

1:  for index,element in enumerate(list1):  

And even more: we can combine iterating through multiple lists with the index of the element. In this case we will have one index and two variables holding each current element like so:

 for same_index, elementA, elementB in enumerate(zip(listA,listB)):  

 

 Iterating multiple lists (II)

What we have seen previously is okay, but there is a better way to do the same things in terms of execution time and memory consumption and it relies again on the itertools module.

Using a context manager i have measured the execution time of both functions hereby:

 def slow():  
          for i, (x,y) in enumerate(zip(range(10000000),range(10000000))):  
              pass  
 def quick():  
          for i, x,y in itertools.izip(itertools.count(), range(10000000),range(10000000)):  
              pass  
 measure(slow)  
 measure(quick)  

 Slow() function took 3.32 seconds whereas quick() took 1.30!! A good reason to take into account the itertools module.

Joining strings

Difference between os.path.join() and str.join() both are similar in behaviour.

os.path.join('path','to','directory')

takes a variable number of string arguments to assemble them all into a string with os.sep (operating system path separator). Note that it won't put an os.sep character at the beginning of the string neither at the end. But, if it's an absolute path you can always set as first argument the os.sep character.

if you have the arguments in a list instead of comma separated you can expand the list into it using the * operator thus this would also work:

os.path.join(*['path','to','directory'] 


 Now the str.join method does take a tuple or list as argument and the 'str' string or character will be the separator thus this:

'-'.join(['a','b','c'])

yields the following string : 'a-b-c'. Note again that there is no '-' at the beginining nor at the end.   

Overriding Python str class setter.. How?

Coding another tool in python as usual i was getting tired of printing several debug messages. The script performs some calls to multiple main methods that in turn call other secondary  methods. I wanted to track the final status of each call so i thought that it would be a good idea to print a message each time a "msg" object changes its value. Thus recurring to the 'set value triggers function call' paradigm.

One solution i found was to create a new class that inherits from "object" and use @property and @<member>.setter with an intermediate string object to store the text.

But i wasn't satisfied enough and coming from C++ i was wondering if it was possible to inherit directly from "str" class and just override its setter.

Since i found no info on the web, i resorted to write to a tech forum. 

Here is my post:


I'm coding a script that performs different complex tasks and i want to output status messages regarding the execution of the script.
Rather than doing a "print" statement after each main function call i 've thought it would be nicer to have a string object that automatically prints something each time the variable's value changes.
So this lead me to write a custom class with a variable and a setter to it like the following:

Code:

class Msg(object):
    def __init__(self):
        self._s = None
    
    @property
    def status(self):
        return self._s
    @status.setter
    def status(self, value):
        self._s = value
        call_custom_function()

Now the question: I've come to the above solution but i'm wondering if it's possible to inherit directly from str class and just override the setter... thus not needing an intermediate variable like _s and be able to do something like

Code:

msg = Msg()
msg = "hello"

instead of the current:

Code:

msg = Msg()
msg.status = "hello"

I've searched the web and i haven't found how the str class works besides the fact that it's a "sequencer" type just like a list...

The same day i received several answers that despite interesting were missing the point of my question, until i got finally the explanation.

Here is the final reply that enlighted me:

Code:

msg = Msg()
msg = "hello"

to anyone who write python code, these lines mean this:

1. Create an instance of the class Msg and assign it to msg
2. msg is now the string "hello"

Your instance of the Msg class has been overwritten. Thats why it makes no sense. Why create an isntance of a class just to over-write it with a string.

Ahhhh this is what i was getting wrong!!! In a language like C++ one can overload the "=" operator and hence the second line would call the overloaded method from the "=" operator from the msg instance of Msg() Class. The type of "msg" doesnt change!!!!

But in Python we dont have such behaviour, so when we assign "hello" we are just changing the type of the variable to be a string!! 

How To Get Rid of PyQt Widgets Correctly

Introduction. The Tool.

In recent weeks i was told it would be nice to have some kind of reference editor outside Maya. Something simple that allowed animators to chose which references they wanted to load in the scene and which ones they didn't want.

What are the advantages for this requirement? The main reason is although we have at the studio powerful workstations in terms of Ram, CPU and Graphics processor some assets like set, props etc are really big, one single prop can take 3 GB!! and depending on the scene you can have almost 400 references. If each prop took that much space.. you can do the math.. it's simply unmanageable. It's not that huge in reality but it remains a big problem also if you take into account the amount of time it takes to load them all and finally open the scene. An animator would normally only want to load the character he/she is about to work with leaving aside all the props and set elements that don't interact with the character. This enables everyone to work faster.

Obviously the external reference editor must be "non-destructive". What i mean for this is it should not delete the reference node in Maya. Why? Obviously this external reference editor is useful for opening a scene file for the first time. Once the scene is loaded in Maya the animator must use the Maya reference editor to load/unload assets. In this case, to load all the necessary assets once the animation is finished, so that everything is in place when the playblast is published. So we need to let the animator the chance to load in Maya the rest of the assets and for this, he needs the reference node of the asset to be present in the scene.

After analyzing the Maya ASCII scene file it was clear what changes to do to the file to unload a specific asset.

Design. The problem.

Here is what i thought it would be a good design: i would use a dynamic list of widgets where each line would be composed of a QCheckBox showing the current state of the reference and the reference node of the asset.

I used the same approach as other times when i needed to code a dynamic list of widgets which consisted mainly in two steps:

A) we have a widget that triggers the fullfillment of the dynamic list. It can be something like a QComboBox to select the file's work area.

B) each time the dynamic list is filled we need to create a "line widget" with its proper layout which contains the QCheckbox and the QLineEdit. Those widgets are created each time which also means they need to be properly deleted, otherwise we will run into memory problems. And that was the origin of the bug i had.

When i first coded a dynamic list like this and wasn't that much versed into python i googled to look for the proper way to delete a widget, and i found this site in stackoverflow to be very useful although somewhat confusing. So many ways to apparently delete QWidgets!!

Digging into the proper solution.

There were three methods that apparently reached the same result:

1) the close() method in the QWidget class

2) the setParent() to None method also in the QWidget class also

3) the deleteLater() also in the QWidget class

I always thought the setParent() to None in each parent widget worked well. So in the method before filling the list i called a cleanup_scrollArea() method which was coded like this:

for i in reversed(range(layout.count())): 
        layout.itemAt(i).widget().setParent(None)

Relying on the fact that in the documentation they say: "the new widget is deleted when its parent is deleted".

I wont explain much. Only tell that this apparently works. Setting the the parent of a widget to None breaks the connection of the PyQt tree and causes all the children to not show anymore.

But there was a big bug. Whenever i tried repeatidly to test the tool with different files the tool crashed within the third or fourth iteration. The dynamic list's behaviour was apparently correct and working well, everything looked alright and i had no error message to give a hint of the problem.

I had the suspicion it had to do with a problem in the deletion of the widgets because the memory increased in each iteration even if the file had less refereneces to show than the previous one!. And obviously it was crashing when you tried to repeatidly use it. It must be a problem in the dynamic list!!

The Solution.

It  took me a short but intense moment  to figure out what was happening. And here my experience with a language such as C/C++ that deals with memory management helped me a lot since PyQt is a bind for Nokia's Qt written in C++.

What was happening?

Setting the  widget's parent to None only breaks the connection in the Qt widgets tree and causes the python reference to be deleted by the garbage collector. But what about the C++ QWidget Object that python was referencing? C++ does not have a garbage collector, so the C++ object's memory has to be deleted manually.

Here is why we have to use deleteLater() 's QWidget method. That's what it does, it frees the memory the C++ object is using..That's what we were missing! Furthermore deleting the C++ object makes the python references invalid therefore we don't need to set anymore to None the parent's widget,

The cleanup_scrollArea() method became:

while aLayout.count() > 0:

    item = aLayout.takeAt(0)

    widget = item.widget()

    if not widget:

        continue

    widget.deleteLater()

Design Improvement Quick Note

Creating and deleting widgets is expensive. It's a very stressful task even for a language like C++ with it's new and delete methods. So it may look like this behaviour for a dynamic list is not the best fit.

In the PyQt documentation they say that for this it may be better to use a QStackedWidget and play with the show() / hide() methods of the widgets which i believe reserves memory for a set of widgets and in the next iteration it reuses the same widgets changing their properties, hiding and adding new widgets on demand as needed. Might want to try this sometime!

My first Maya Python/PyQt plugin

THE PLUGIN

What i'm gonna show in the next video is the first plugin for Maya i've coded. I wanted to do something with GUI so i forced myself to use PyQt and the QTDesigner to get familiar with it. The idea of this plugin came up during one of the sessions of the Máster in audiovisual production with Autodesk Maya that i'm following at CICE here in Madrid.

I recalled that 3ds max has a very complete tool for pivot alignment and orientation. One can do the practically the same with Maya but the local axis alignment. This comes handy when we cannot do a snap to the grid or geometric vertex to position the object's pivot.

Modifying the object's pivot position is a very usual operation when we find ourselves modeling stuff. It allows for example to rotate an object's duplicate around a geometric center that can be found through the bounding box of the proper object itself.

ABOUT MY INTEREST IN MAYA TOOLS DEVELOPMENT

The course is mainly focused on 3d concepts such as NURBS & polygon modeling, lighting, texturing, rendering, dynamics etc, all from a Maya artist point of view so no coding at all taught. I felt very disappointed when the other Master i was about to do was cancelled, this one oriented exclusively to Maya tools development and API understanding. The reason was that there wasnt people enough interested in the course. Truth is we were at first 10 people (enough for it) but 5 of them were being sent by the same company as an education at work thing and this company backed off at the last moment. So there we were only 5 people, which the school though was not a proper amount to dedicate a room during five and a half months, in other words, it wasn't profitable.

'Okay, then i'll try in April 2015 while im working' (the schedule allowed me to balance it with work) but then new surprise "the teacher is leaving to work for MPC in Canada, the course will not be released anymore".

Well then find another teacher!!! Apparently this is such a "high profile" that there is little demand for this kind of education (usually 3d artist dont wanna know anything about coding) and at the same time it's difficult to find a teacher. Is this caused by the fact that there are few Technical Directors or Tech Artists out there? is it a "niche" job?

All this said, that's why im trying to make it up and start learning tools development on my own since there is no place else where to study this here in Spain. It will require more effort and the steps will be smaller but with help from other technical directors in a facebook group and mainly my will power  (yes! i can !) i hope to get enough understanding and experience to land a job as CG Generalist/TD.

Ohhhh excuse me, this post is about the plugin. I 'll let the video do the talking!!