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Python module HOM

Python HOM

General explanation

Python Scripting | SideFX

Write attributes from python to geo1

When creating attributes from python into the geometry the attribute MUST be created first:

python
geo.addAttrib(hou.attribType.Global, "parents", {})
geo.setGlobalAttribValue("parents", parent_dict)

Get a channel or parameter

python
evalParm("../CTRL_comb_version/comb_version")
## is the same as ch('node/channel')

When to use python expression in channels

For easy connections is better to use hscript, for more advanced and verbose stuff use python.

A good comparison here

hscript
bbox(0, D_YMAX)
python
hou.pwd().inputs()[0].geometry().boundingBox().maxvec()[1]

So, try to use hscript for simple stuff, even if SideFx says hscript is being deprecated

Create Parameters in Houdini with Python

Python Get node

python
#get node (find the path in your node's info panel)
n = hou.node("/path/to/node")


# get the max x value of a bounding box for the SOP box
node('../Body/box').geometry().boundingBox().maxvec().x()

Get bounding box max Y

python
hou.node("../hemitrans").geometry().boundingBox().maxvec().y()

Bounding box size

python
node("../source").geometry().boundingBox().sizevec().x()

Write a dictionary to detail

In houdini ALL the keys of a dictionary must be converted to strings, the values can be of any type

python
for tile_index in set_c:
    rotations_dict[str(tile_index)] = 0
    parent_dict["{}".format(tile_index)] = tile_index


# using python in hou, the parameter is created
# then it can be modified
geo.addAttrib(hou.attribType.Global, "parents", {})
geo.setGlobalAttribValue("parents", parent_dict)

Basic python json exporter

Reference tutorial: Houdini 18 - Python Projects - Creating a Generic Json Exporter - YouTube

WFC JSON exporter

python
import json
import hou


data = []
components = ["x", "y", "z", "w"]


def export(kwargs):
    node = kwargs["node"]
    geo: hou.Geometry = node.node("export_node").geometry()
    generate_name: int = node.parm("generatename").evalAsInt()




    attribs = []


    if node.parm("filtered").evalAsInt() == 1:
        attribs = [node.parm("attribute_{}".format(x+1)).evalAsString() for x in range(node.parm("entries").evalAsInt()) ]
        print(attribs)
    else:
        attribs = [x.name() for x in geo.pointAttribs()]


    for point in geo.points():
        entry = {}


        if generate_name == 1:
            entry["Name"] = "Tile_{}".format(point.number())


        for attrib in attribs:
            if geo.findPointAttrib(attrib) is not None:
                point_attr = geo.findPointAttrib(attrib)
                size = point_attr.size()
                val = point.attribValue(attrib)
                array = point_attr.isArrayType()


                out = val


                if array:
                    if size > 1 and size <= 4:
                        out = []
                        for i in range(0, len(val), size):
                            vals = val[i:i+size]
                            out.append(dict(zip(components, vals)))


                        out = val


                elif size == 1:
                    out = val


                elif size > 1 and size <= 4:
                    out = {}
                    for i in range(size):
                        out[components[i]] = val[i]


                """ else:
                    raise hou.NodeError("Attribute {} not supported!".format(attrib)) """


                entry[attrib] = out
        data.append(entry)


    path = node.parm("json_path").evalAsString()




    # num_rows = geo.attribValue("rows")
    # detail = {"numrow" : num_rows}


    # https://docs.python.org/3.8/library/json.html#py-to-json-table
    # dict is mapped as an object


    dict_obj: dict = {"tiles" : data}
    # dict_obj["detail"] = detail




    with open(path, 'w') as f:
        # json.dump(dict_obj, f, indent=4)
        json.dump(dict_obj, f, indent=4)

Reload or cook a node using a callback

Using a button in a parameter interface editor, select the button, find the callback script field and add the following

python
hou.node(".").cook(force=True)

Python states

https://aaronsmith.tv/Case-Studies

A live session on building a tool with Python States in Houdini 18