Particle Sprite with Karma?

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Hi

I recently started using the Karma renderer, is it possible to render Particle Sprite with the Karma renderer?
I tried rendering a Particle set up in Sprite SOP with Karma, but the Sprite was not rendered...

If you know of any documentation, etc., I would appreciate it if you could let me know.
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Hi Uryu,

you can use "Render Geomtry Settings" LOP and switch between different render options for points. Parameter calls "Render Points As". Points can be rendered as camera oriented discs, spheres or discs oriented to the normal attribute.

However, I don't think disks have any UV or "st" coordinates what can be useful for shading... I've tried to access with materialx and vex shaders but both with no luck. Is there any ways how I can access it?
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I don't think there's any built in sprite mojo, but you could use a point instancer with a rectangle mesh as the prototype prim, and set the orient attribute to face the camera.
tamte
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looks like a big oversight, particles should definitely have a sprite rendering mode

you can't fake it with lookat constraint, not only it is tedious workaround
it also doesnt behave like sprites

the main advantage of sprites (at least to my understanding) is that they face all the rays that evaluate them (like for shadow cating etc...), unlike oriented rectangles
Tomas Slancik
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tamte
looks like a big oversight, particles should definitely have a sprite rendering mode

you can't fake it with lookat constraint, not only it is tedious workaround
it also doesnt behave like sprites

the main advantage of sprites (at least to my understanding) is that they face all the rays that evaluate them (like for shadow cating etc...), unlike oriented rectangles

a renderer would have to support sprites though, and I think modern renderers are essentially triangle tracers now, so geometry that looks different from different angles won't work.

Sure, there could be a spriteAPI at the USD level to make it more portable or easy to author, but it's probably not something Pixar needs.
tamte
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jsmack
so geometry that looks different from different angles won't work.
what about rendering curves as ribbons? isn't that the same principle?
Karma supports those, so why wouldn't sprites

EDIT: or even rendering particles as discs should be rendered based on ray direction, are you saying it's not the case with Karma?

EDIT2: just checked, it renders discs properly based on ray direction, so no excuse for not having proper sprite type
Edited by tamte - Aug. 3, 2022 22:25:39
Tomas Slancik
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Thank you all...!
I'll either render it as a short ribbon, or if that doesn't work
I will render only the Sprite elements in Mantra (as long as Sidefx supports it...)

Hopefully, the Karma renderer will have the ability to texture and render Particles as easily as Sprite...
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