» A TOPS recipe for creating wedges for simulations and other purposes. «
I never really get used to the TOP’s context (PDG). I mostly wrote Python scripts tailored to my needs. However, I wanted to streamline my caching and wedging workflow. This is especially important when working to a deadline. The LAB’s caching node incorporates some TOP mechanics, but I don’t like the way it’s implemented. Here is a simple approach that I used in this demo with the AXIOM solver. I used this ‘module’ as a recipe, which also works pretty well for other caching tasks.
Simulating things on the GPU requires some attention. You often need to set the work order of the work items to ‘All Frames in One Batch’ to avoid losing performance or simulating the same frames repeatedly. Debugging is important here.
Houdini comes with its own useful Deadline scheduler. However, as always, there are some issues that you should be aware of.
The great thing is that you can instantly deploy the TOP network on Deadline and let the ‘farm’ do its thing. This is really useful if you have a large farm with computing power and lots of licences available. Deadline starts a Hython instance per job, so you need an Engine/Indie/FX licence. Organising the jobs is pretty straightforward.
My goal was to automate the caching process and obtain a preview of the different versions with an overlay of the wedge attribute(s), as well as a nice capture/render.
Cache -> Flipbook(OpenGL/Vulkan/Karma) -> Flipbooks_overlay (COP) -> Montage (ImageMagick) -> FFmpeg (.mp4) -> Delete_tmp_files
I have provided the .hip file below, but I will highlight some steps here and there.
You can capture your wedges using OpenGL/Vulkan or Karma. I set up the whole caching process first, and after all the wedges, the TOP network compute the flipbook preview work items (therefore the ‘caching_on_deadline_feedback’ file reader). This is because the simulations run on the GPU, and this method produced the best performance outcome in my tests. I’m not 100% convinced it’s the smartest way, but it works in this case.
Please note that you should not close the current Houdini session. You can view updates to the computed work items in real time. If you close it, the Deadline jobs will fail. If you want the cache task to be a persistent Deadline job, you can submit it here.
I like the separation with the different deadline schedulers. It creates separate Deadline jobs, which makes it easier to debug and follow. Of course, you can just use one Deadline scheduler.
Walk Through the TOP Network:
This could be optimised and automated further. But here just chaining wedge nodes and linking the wedge attributes to the AXIOM solver.
It is important to set the ‘All Frames in One Batch’ flag to generate one Deadline job for every wedge sequence. The output paths are assembled with and against the ‘@wedgeindex’ attribute.
The settings are the same here, and I set the ‘Generation When’ flag to ‘All Upstream Items are Generated’, so the node is waiting for the work items in the CACHE TOP node to finish.
Here comes the capturing/rendering, checkerboard and overlay text together.
I`m really confused sometimes with the color outputs and OCIO in Houdini. This is a bit of flaw right know and have to investigate more about my the color management. It`s relly messy sometimes.
I render out .exr files (AcesCG) because .png gives wrong results with the Alpha channel.
I only get the right colors (which I set up in the 3D editor) when the ‘None’ option is selected in the ‘Color Correction’ menu under ‘OpenGL/Flipbook ROP’. The Karma ROP i set the Image Filter and the C plane to “Gamma 2.2 Rec.709” and the input space to AcesCG.
The File loader in the COP network i had to set “Raw” at the ‘Incoming Colors’ space menu. The output is set to ‘Un-tone-mapped’.
In COPs, it’s not easy to translate text, for example, because you don’t really have a pixel space. You always have to calculate the conversion from picture ratio to pixel space. As well as drawing a simple yellow border for each montage tile, I had to use a wrangle like this:
You have to install ImageMagick manually, SideFX dont ship it in there package!
‘Partion by attribute ‘, here by ‘frame’ generate work items where the frame number is matching in every wedge flipbook+overlay sequence. Here i had to deselect ‘All Frames in One Batch’. The CMD output string whould be to long for Deadline. Funny.
Rendering a final .mp4 via ffmpeg and delete tmp files/folders with a Python TOP node.
