Hi all, I am a Houdini user dipping my toes into TD and loving it so far; I had a question as I’ve been messing with effects on top of footage, be it prerecorded or webcam-based. But doing something as basic as emitting particles from footage, I always run into the challenge where the particle system is square-based due to the UV space of the system, where my footage is 16*9 or of that 1.777 ratio. Is there any system or technique for having particles emit from a, say, 1280 x 720 grid that aligns to the footage easily?
Hi @timsep,
it depends a bit what particle system you are using and how it is implemented, but when dealing in SOPs use the Rectangle SOP with the Orientation parameter set to “Fill Camera View” and then specify your camera and camera aspect ratio.
This now can be used as the second input to a Transform SOP, which on its “Post” page has the options to scale the geometry (for example your emitter) to the “Reference Input” with the Post Scale parameters.
If you are in a TOP or glsl based particle system, the Point Transform TOP offers the same options as the Transform SOP.
Hope this helps
cheers
Markus
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Thank you, Markus, that is very informative! Im using TOPS and particlesGpu,
Here is a picture of what I’m doing. I got your method to work in Sops; my guess, though, is that in tops, the UV grid is ALWAYS 1:1, even if it’s rectangular. Meaning I’d have to do the effect on the squashed video then transform on “x” to the correct aspect ratio?
Hi @timsep,
yup, the resolution of the TOP has nothing to do with the data itself. The Ramps, if just using the default setting, will have a value range of 0-1 but in a Point Transform TOP, you could reference the aspect ration of the input to scale them properly:
If you are using the Point Transform TOP in this way, just be careful to pay also attention to the “Weights” page parameters as these control an offset per input pixel. You can switch this to “Alpha” if your reference image has a solid alpha channel.
cheers
Markus