How to get screen position of Solid Particle System Particle that is using billboard mode and a custom pivot

Questions
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1

As the title explains, how would I got around to get this coordinate in screen space? I’ve mostly issues with the fact that having the pivot offset messes up my calculations. I made a small example playground:
https://playground.babylonjs.com/#2HQNW6#3

2

You could use Vector3.Project on the particle’s position maybe? :smiley: Babylon.js Playground (babylonjs.com)

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3

Thanks! however the issue I’m running into is doing it without the use of picking, the end goal of why I need this is to get the screen coordinates of the bottom of the (now) disc particle. I just can’t seem to accurately get the correct location:

4

Oooh, I see, so you don’t want the screen coords of the center, but of another location on the particle, right? Well, in your case, since the particle is a disc, instead of projecting the particle position you could project position + radius and that should work.

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5

Even trying to use the current code you gave as an example I actually seem to be getting fluctuating results:
https://i.imgur.com/VGk5Vuu.png
https://i.imgur.com/4P0u7xl.png

I think the difference is created from the billboard/pivot that are applied?

My current playground:
https://playground.babylonjs.com/#2HQNW6#14

6

You’re right, billboard and pivot change the particle’s final position: Babylon.js/solidParticleSystem.ts at master · BabylonJS/Babylon.js (github.com), Babylon.js/solidParticleSystem.ts at master · BabylonJS/Babylon.js (github.com), so you’d have to do these same operations to find out the correct position to project :thinking:

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7

I wish my understanding of math / matrices / etc. was up to snuff, but I have to admit that I’m struggling to inverse/understand those calculations…
I think I got a semi accurate position for the center point, but I’m having issues getting any other point, like the bottom of the disc for example.

8

Could someone maybe give me a push in the right direction? I’m still struggling to figure this one out. Thanks in advance!

9

Going through the particles code again, I found out what might be a simpler way. Since the “updated” positions of the particles are considered to build the bounding box: Babylon.js/solidParticleSystem.ts at master · BabylonJS/Babylon.js (github.com), you could use the boundingInfo to get the position you want? Babylon.js Playground (babylonjs.com)