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I'm making an indoor scene with a storm outside. I want the windows in my scene to have rain just bucketing over them. Ideally I would like some animated effect that can be composited over the background, which might be something like a bokeh image. How can I achieve this?

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A polygon-rich approach

I gave it a go with a shower of particles. This may be a little bit too resource-intense for just a background feature though.

The setup

I created a simple "room" with

  • a double-layered window (two plane meshes);

  • a plane out in the sky, almost vertical, with a particle system;

  • two strong wind force fields that push the particles toward the window;

  • a simple icosphere as a dupliobject.

enter image description here

The building and the inner window layer are set as Collision objects with "Kill particles" activated.

The outer window is a Collision object with very high stickiness (no kill), and high damping/friction on particles.

The particle system has strong Normal velocity and low Gravity field weight, so that the rain drops don't fall off screen too quickly; "Object" > "Icosphere" is selected as "Render" option, with "Emitter" un-checked.

enter image description here

(this preview is from an earlier version, with less particles and less friction on the surface)

The render

By giving the icospheres and window layers a Principled shader with very high transmission; adding some orange streetlamps and violet "dusk" sun (and a sad Suzanne in the storm); with some DOF and motion blur: this is a very rough result:

enter image description here

     (Only 7 frames)

Using nodes and a "Geometry" input, I made the raindrop's shader completely transparent (shadeless) when the "y" coordinate is less than y0 (the position of the window) to cut away the part of the sphere that "permeates" the first layer.

This answer's blend file



Even heavier for a close up shot (with metaballs)

If you want a close-up shot as in here, an additional Particle System with similar physics, but from a nearer plane (just near the camera) and with big meta-balls as DupliObjects, can help:

enter image description here

Result:

enter image description here

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  • $\begingroup$ This is certainly an approach I can take, so I'll try it. Thank you! What bothers me about simulation approaches is that they work up from the ground rather than down from the impression you want. For example, unless you have an extreme close-up shot of the window, the individual drops are invisible: youtube.com/watch?v=3J40T2-lWZQ $\endgroup$ – dixiepig Mar 28 '18 at 8:52
  • $\begingroup$ Yes, I realize that obtaining a particular result with a simulation approach would require some intense trial and error. However, I'm uploading an updated version of my file and render $\endgroup$ – Nicola Sap Mar 28 '18 at 8:57
  • $\begingroup$ Anyway, given this footage, I would have two different particle systems for such a close up shot: one for the background with spheres and one for the window (particles falling almost vertically from very close) with metaballs $\endgroup$ – Nicola Sap Mar 28 '18 at 9:10
  • $\begingroup$ @dixiepig updated with an additional particle system, just for close ups $\endgroup$ – Nicola Sap Mar 28 '18 at 10:21
  • $\begingroup$ @dixiepig I was looking at my file and I can say that the wind is really too strong in my file, and it's also too parallel to the window; also, the friction on the glass' surface should really be high! My simulation looks a lot like a moving train $\endgroup$ – Nicola Sap Mar 28 '18 at 17:09

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