Fake caustics guides

[tricky]

Somebody might have a method for this already, but here goes in any case:-

Occasionally, we will want to try and add some caustics effects to our images. We don't really need the hassle of trying to get perfectly rendered caustics directly from VRay (as more than likely, the client will want us to lose them anyway!), so we'd like the ability to add these in post as harshly or subtly as we think we can get away with.

Here's a quick iPhone snap I took yesterday showing real life caustics behaviour:-


So, what would be handy would be some way of rendering some sort of 'projection' from the primary light source (the VRay sun in many cases) and bounce it off selected geometry (glass windows in many cases) and have it render a rectangle on the floor/wall surfaces where caustics would likely happen. It doesn't need to have any special warping or anything like that: just a basic black and white matte would suffice.

Is this possible?

[Dave_Wortley]

This still works really well....

http://www.3dtotal.com/tutorial/3d_s...austics_01.php

[tricky]

This still works really well....

http://www.3dtotal.com/tutorial/3d_s...austics_01.php

Let me take a look. I recall seeing some tutorial some years ago about creating a light specifically for caustics: not sure if this is the same thing.

[Pixelcon]

Try finding some examples on a blank surface online and just photoshop it. Will be 100x faster and you're not baking in something that the client might hate...

[tricky]

Try finding some examples on a blank surface online and just photoshop it. Will be 100x faster and you're not baking in something that the client might hate...

Exactly what we are doing, but I wanted to know if we could have some sort of 'ray guidance' for positioning and working out bounced light is tricky.

[super gnu]

any kind of "ray guidance" would be actual caustics. so just use caustics at whatever crappy setting gives some kind of result, and use that as your guide.

[tricky]

any kind of "ray guidance" would be actual caustics. so just use caustics at whatever crappy setting gives some kind of result, and use that as your guide.

Crappy caustics yield a blurry mess that doesn't help. Plus, even crappy caustics takes a while to calculate. What I want is this:-

Give it to me

[Morne]

What I want is this:-
[ATTACH=CONFIG]28200[/ATTACH]
Give it to me

Like so?
Or is that still too crappy?
(this is real)



This is with GI off and a grey override (excluding my "windows" which has a shiny white material on it)
Use the VRayCaustics element and just comp over the render.
Right click the sun > VRay properties > Caustics subdivs > make it low for FAST tests - defaults are fine
For final, up the caustics subdivs to what you need. In this example mine was 40000 and it still calculated fast

[Joelaff]

How about using a cutout of the windows as a shadow caster for a separate light which is rotated 180 deg across the plane of the glass? In other words, you use another light to create just the reflection effect, but it's not really a reflection, but a light shining through a standin cutout object with holes in it where the windows go.

[tricky]

Like so?
Or is that still too crappy?
(this is real)

[ATTACH=CONFIG]28213[/ATTACH]

This is with GI off and a grey override (excluding my "windows" which has a shiny white material on it)
Use the VRayCaustics element and just comp over the render.
Right click the sun > VRay properties > Caustics subdivs > make it low for FAST tests - defaults are fine
For final, up the caustics subdivs to what you need. In this example mine was 40000 and it still calculated fast

Looking good Morné...

[tricky]

How about using a cutout of the windows as a shadow caster for a separate light which is rotated 180 deg across the plane of the glass? In other words, you use another light to create just the reflection effect, but it's not really a reflection, but a light shining through a standin cutout object with holes in it where the windows go.

I wondered about something like that myself. I guess with windows in a simple wall it would work fine, but with more complex scenes with composite walls etc it could be tricky to isolate just the wall with its openings. Not impossible, just a faff.

[Morne]

VRay 3 has that render "selected" mask, which could work great. Select your wall(s) to receive the "light" and render. It will calculate and render just the wall then. Together with the render selected, you can even enable the region either from max or from the VFB, that way you should get lightning fast renders which you can then comp over your main render.