Python - Callbacks help

[markinglevfx]

Hey Guys,

Still quite new to Python, hoping someone can help point me in the right direction on this that I've been grappling with for a while now.

I have a simple filecache .hda that I'd like to change color if it can/can't find the cache on disk. I've been able to use hou.ui.addEventLoopCallback() to continuously track and check the file parameter to see if the cache exists, and the color changing now works as expected. 

Where I'm having trouble is removing the event loop when the .hda is deleted from the node graph. An error pops up because Houdini is still trying to access the deleted node. I've been trying to look for a way to use the OnDeleted event handler, or hou.nodeEventType.BeingDeleted, but no luck yet and I feel out of my depth with my limited python experience.

The .hda is attached, and there's a preview of the code below. Any help would be appreciated!

custom_filecache.hda

####PythonModule####
import os
import hou
    
def nodeColor(kwargs):
    node = kwargs["node"]
    def colorCallback():
        filepath = node.evalParm("file")
        if(os.path.exists(filepath)):
            node.setColor(hou.Color((0.0, 0.8, 0.0)))
            node.setComment(filepath)
            node.setGenericFlag(hou.nodeFlag.DisplayComment,True)
        else:
            node.setColor(hou.Color((0.8, 0.0, 0.0)))
            node.setComment("File not found")
            node.setGenericFlag(hou.nodeFlag.DisplayComment,True)
    startCallback(colorCallback)
    #adding this code below crashes Houdini when hda is deleted
    #node.addEventCallback([hou.nodeEventType.BeingDeleted], endCallback(colorCallback))
    
def startCallback(callback):
    hou.ui.addEventLoopCallback(callback)

def endCallback(callback):
    hou.ui.removeEventLoopCallback(callback)


####OnCreated####
kwargs["node"].hdaModule().nodeColor(kwargs)

 

Edited August 28, 2020 by markinglevfx

[Stalkerx777]

Have you tried removing the callback in OnDeleted event handler instead of registering it in the nodeColor function?

On a side note, are you expecting your caches to pop up and go like every N milliseconds?  What you're trying to do looks redundant to me, and if you have a scene with a few dozens instances of you HDA , you'll likely experience a slowdown, because global event loop runs in the main Houdini thread. 

You could install your event on the node itself ( node.addEventCallback ) and see what nodeEventType works for you. Or install it on the parent container (say your hda is a SOP, install the event on your_node.parent()) so each time you dive into a geo container, it'll trigger the event. Anyway, there's a lot of options  

Edited August 28, 2020 by Stalkerx777

[markinglevfx]

Thanks Alex. I needed to look at node.addEventCallback further. I was able to have the node color update after any parameter changes, node name changes, or scene frame number changes.

####OnCreated####

import os
import hou

def nodeColor(node):
    filepath = node.evalParm("file")
    if(os.path.exists(filepath)):
        node.setColor(hou.Color((0.0, 0.8, 0.0)))
        node.setComment(filepath)
        node.setGenericFlag(hou.nodeFlag.DisplayComment,True)
    else:
        node.setColor(hou.Color((0.8, 0.0, 0.0)))
        node.setComment("File not found")
        node.setGenericFlag(hou.nodeFlag.DisplayComment,True)

def parmChanged(node, event_type, parm_tuple):
    nodeColor(node)
    
def nameChanged(node, event_type):
    nodeColor(node)
    
def frameChanged(event_type, frame):
    hda = kwargs['node']
    nodeColor(hda)

hda = kwargs['node']
nodeColor(hda)

hda.addEventCallback( (hou.nodeEventType.ParmTupleChanged, ), parmChanged)
hda.addEventCallback( (hou.nodeEventType.NameChanged, ), nameChanged)
hou.playbar.addEventCallback(frameChanged)