How to implement a gradient picker in Houdini

Introduction

I'll show you how to implement a gradient picker like Substance Designer in Houdini that Ando announced at the PySide Study Group the other day. Introduction of Ando's gradation picker, commentary article

When actually used, the gradation picked up by the picker is applied to the lamp parameters as shown in the figure below. In the figure below, the image is loaded into the network editor, but you can get the color anywhere on the screen.

Implementation method

1. Download the code from the URL below. https://snippets.cacher.io/snippet/2c7496d1dbbdc093033c
2. Move the downloaded ** gradationPicker.py ** to a folder where Houdini can read Python. If you don't know, copy it to % HOMEDRIVE %% HOMEPATH% \ Documents \ houdini version \ scripts \ python and it will be recognized automatically (create it if it doesn't exist).
3. From here, there is a slight difference between implementing in HDA and implementing in the parameters of an existing node.

-** When implementing on HDA ** Go to the HDA ** Type Properties **> ** Scripts tab ** and change the ** Event Handler ** to ** Python Module **. This will activate the Python code field on the right, where you can enter the code __ to apply the gradient to the __ramp parameters below.

-** When implementing in the parameter of the existing node ** Click ** Windows **> ** Python Source Editor ** in the Houdini menu to launch the Python Source Editor and enter the code ** to apply the gradient to the ** ramp parameters below in the code entry field.

Code that applies a gradient to the ramp parameters

# -*- coding: utf-8 -*-

import hou
from PySide2.QtCore import Qt

from gradationPicker import ColorPick

class _GCProtector(object):
    widgets = []

def rampColorPicker(parm, threshold=0.05):
    def setRampColor(colors):
        #The argument colors are[Gradient position,color]List containing
        curveKeys = []
        curveValues = []
        #Divide the two-dimensional list into two parts, curveKeys and curveValues.
        for pos, color in colors:
            curveKeys.append(pos)
            #2 because the color space of PySide is sRGB and Houdini is linear.Square and convert
            curveValues.append([(ch / 255.0) ** 2.2 for ch in color])
        linears = [hou.rampBasis.Linear] * len(colors)
        ramp = hou.Ramp(linears, curveKeys, curveValues)
        parm.set(ramp)

    picker = ColorPick()
    #Displayed in the foreground so that the focus does not shift
    picker.setWindowFlags(Qt.WindowStaysOnTopHint)
    #Set a threshold for how much color difference is identified
    picker.threshold = threshold
    #Make the picker's main window fill the screen
    picker.showFullScreen()
    #Execute a function when the mouse is released
    picker.getGradation.connect(setRampColor)
    #Processing to avoid freeing memory and disappearing immediately when displayed normally
    _GCProtector.widgets.append(picker)

4. Finally, create a button to execute this code.
5. Enter the following code in the Callback Script field of the created button.

-** For HDA ** hou.phm().rampColorPicker(kwargs['node'].parm('ramp'), threshold=0.05)

-** For nodes that already exist ** hou.session.rampColorPicker(kwargs['node'].parm('ramp'), threshold=0.05)

• Please change the part of parm ('ramp') to the name of the target lamp parameter. The lower the threshold value, the higher the accuracy, but the more keys there are.

If you want to set an icon for a button, enter BUTTONS_secondary_colors in the Button Icon field and an icon like that will be added.

Now when you press the button, you'll be in gradient picker mode, so drag and pick a color.

Finally

That's how to implement a gradient picker in Houdini. PySide can do many things and is fun. By the way, by modifying the gradation picker, you can also create a function to write the curve of the lamp parameter by hand as shown below.