Moving a light around an object to simulate a time lapse

Hi all,

I am trying to get a light to rotate around an object, and to cast a shadow, to simulate a sort of time lapse.
I am particularly interested to get an accurate shadow, so that at “midday” the shadow is closer to the object, and at “sunset” the shadow is elongated. I would love to be able to control the light source to cast a realistic shadow.

To be precise I would like to achieve this effect for a transparent object like a drinking glass, but solid object would do to for now because I am completely lost and very new when it gets to geometry, SOPs, FBX, PBR…

I was wondering if someone could point me in the right direction?

Hey @FaustoB - give this a look:

base_timelapse_shadow.tox (2.7 KB)

Translucence is a much harder question that’s a bit too big to dig into here. However, paths and shadows we can certainly get to right away. Here’s the simple set-up:

image

So big pieces here are shadows and path for your light. I’d recommend reading the shadows article to get a sense of how these work in touch:

https://docs.derivative.ca/Rendering_Shadows

The important switches will be to make sure you turn on shadows, and set your shadow casting objects on your lights:

You can also use a depth TOP to help you visualize what your light is actually seeing - which can be an important part of getting nice shadow details:

This example has both look-ats to make aiming the camera and light easier, and a path for the light to follow:

Hopefully this is enough to get you started. :slight_smile:

Thank you so much Matthew, this is plenty to get me started!

The Look At and Path are very powerful tools, I wasn’t aware of them. And setting the correct geo in the Shadow Casters in the Light COMP was the other big piece I was missing.

Today I was able to have a go at this and came out with a look that is very close to what i am trying to achieve.

I managed to achieve a sort of translucent look on the glasses, via trial and error using composite and edge TOPs.
I am sort of ok with the way the glasses look, but the light obviously still cast a shadow for the solid objects (because I have used a cheap workaround to achieve that translucent effect), not to mention that the glasses sort of disappear when I move the camera around! :slight_smile:

Here below the file I am working on.
Geometry Shadow Time Lapse.toe (10.5 KB)

What are the implications and which techniques should I be looking at to achieve a realistic shadow for translucent objects, like a glass of water for example?

One way to get there will be to dig into writing a custom glsl material.

There’s a step through in this PDF about translucent shadows:

And some other ideas about that process here:

I’d also give the wiki page about custom materials with glsl and shadow mappging a good read:
https://docs.derivative.ca/Write_a_GLSL_Material#Projection_and_Shadow_Mapping

Thinking out loud - you might be able to cheat a bit here using another light as a projector and projection an approximation of the effect back onto the floor - then comping that in with another render pass.

This is very good advice Matthew, thank you so much for providing these links & tips and for your time !

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