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I want to progressively weed out the particles in a particle system using a texture. Here I slowly reduce the surface occupied by the particles by keyframing the siders on the color ramp that is linked to the texture so that progressively more of the particles are removed in an animation.

This all works well apart from this: at every frame, all of the particles are repositioned, creating chaos in the animation. Indeed the surface of the particles is reduced, but it looks like total chaos. I would like the particles to remain in the same spot until they are removed.

I use a vertex group to position the particles (mussels) on bumps in the landscapes, and a cloud texture to make them patchy. This works fine when there is no animation.

I have already tried to provide a fixed particle seeding value, but this didn’t help.

See here an animation, chaos starts at about 5 seconds. https://youtu.be/cvPsl97V3C0

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try this setting in shader: the "particle info node > index" in shader helps you to control a single particle (use a math operation to filter which particles to hide).

Please note:

  1. animate the value inside the MATH -> GREATER THAN (from 0 to the number of hairs)
  2. you need alpha = 100% to hide the objects

enter image description here

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  • $\begingroup$ This would make all the particles gradually transparent. That would work, but is not want I want. I want empty patches to develop within the particles that expand. That is why I wanted to use the texture to influence placement in the particle system. Thanks for the suggestion though! $\endgroup$ Mar 16, 2020 at 22:57
  • $\begingroup$ the particles are rearranged every time the weight map changes because blender tries to distribute the same amount of hairs into a different area. I'm afraid you should try to find another solution, for example: apply the particle modifier and control the size / visibility of every single hair with a driver that is animated with a keyframe. What's the final effect you are looking for? have you got a reference? $\endgroup$
    – Sanbaldo
    Mar 17, 2020 at 9:17
  • $\begingroup$ I will give it a try and see how it looks! ;-) $\endgroup$ Mar 17, 2020 at 14:47
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    $\begingroup$ In the end, I followed the suggestion above, although the transparency was linked to a combination of topography (Z value of the geometry node) and a cloud noise texture. See the result here: youtu.be/tNdjw744Tyk $\endgroup$ Mar 24, 2020 at 22:01

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