Catégorie : Tips

I’ve made one of my first HDK plugin. This was more a test in order to work with volumes in c++. You can find the code here.

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This node read one volume on input1 and advect the data with 3 volumes on input2. I’ve made a comparaison with Vex and Opencl with a volume of 100*100*100 and 3 substeps in advection :

• HDK advect : 1.813s
• Volumewrangle : 0.398s
• Opencl : 0.025s

I was surprised to get so much differences. My code in HDK is not threaded and I guess not optimized, I’ve made a test to thread my code with THREADED_METHOD2  but I didn’t get any improvement yet. My next step will be to try threads, opencl or cuda in HDK.

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The Opencl Code seems in this case much better, for those who want to have a look the otl is here and I have a hip file here. (made with indie licences)

I was curious to test flame fractal. I made a quick test : flame.hip

It is based from this paper :https://flam3.com/flame_draves.pdf

I always though you can only edit one data at a time with Sop Solvers but in fact you can output multiple datas from a Sop Solver. : sop_solver.hip

I’ve seen this with the vellum constraint and you need to use a compile block. In this example I just move some geometry from a data to an other but it can be very useful when you have many data to edit like a smoke object.

Here is a small experiment to learn the XOR function with a neuronal network in vex : neuronal_network.hip

Here is few links for people interested in Neuronal Network :

I’m curently doing a Mooc in French about Deep Learning : https://www.fun-mooc.fr/courses/course-v1:CNAM+01031+session01/about

A nice article with a python code that work inside Houdini :

A Step by Step Backpropagation Example

As the vdb_advect node was very slow, I decided to make my own advect node in Opencl : advect_opencl.hip

I’ve made a forward and backward advection. I’m uploading this node as it shows how to use atomic add with floats inside Houdini for the forward advection. It also use a bilinear interpolation to read or write into the voxels.

Here is a test to mix colors in different spaces like RGB RYB CMYK CIELab :

Hip File : color_mixing.hip

you will need this vex lib  : color.h

Below, from right to left : RGB mixing, RGB or CMYK in substractive mode, RYB with luminance based on RGB, and CIELAB.

Video : A test made with a color mixing in RYB space, I hope to upload soon the hip file for this effect.

Here is my Phd in French. It describes the procedural technics used in film production. I published it in 2013 : pdf