Light do not go through glass material in Cycles

Dear Blender Guru,

I want to render simple window with glass material. I use Cycles render and material with Glass BSDF shader. It is strange for me that the glass material is transparent (I see an object behind window), but light do not got through this glass window.

What is the right way to fix this issue?

Sincerely,
Alex


Workaround 1: Avoid using glass at all and leave the hole
Workaround 2: If you need reflections from the window, instead of a glass shader, use a mix node with a transparent + glossy shaders
Workaround 3: If you really are set on glass, crank up the samples and add a slight roughness, say .005, which will take a long time to converge but give a little transmission.

Thank you! I will try.

Thank you, IkariShinji. It is really nice door glass window.

Instead of creating a new thread… Akalinin (if I may? Not to Hi Jack your Thread) I am dealing with the exact same thing… So to follow 360’s advice WA#2 and Ikari’s point of render, fireflies etc…via link. How would you cheat a fake scene, or glow in a window/glass? I was thinking maybe a screen grab of my interior scene and placing the image on a plane inside my hull?
I have a Hemi at 1.3 inside this ship and have no emission from it at all… What if Akalinin wants say a moon like I want ship glow and to interact with a camera pan?


Workaround 4, at least in some cases: Split the glass material in two components - one that deals with reflections and is affected only by camera rays (Light Path node: Is Camera Ray), and one fully transparent one for the rest.

Glass material: Could be standard glass or some custom one as mentioned above where you replace costly refractions by simple transparency, although I’ve previously found using fresnel to control transparency buggy. Don’t know if this still apply.

another thing to remember
it is hard to compare bl lamps and cycles lamps !

one of the Cycles dev told me that
All Bl lamps are fake and
Cycles lamps are real !

happy cl

And for that matter, who sez you have to do it all in Cycles? You’ve got a perfectly good compositor available to you, and two built-in render engines.

You’re entirely correct in saying that BI vs. Cycles handles light very differently. (That’s one of the reasons for having this totally-different algorithm in the first place: “great ‘soft-box’ light.”) But no rule in the book says that, in order to achieve a “realistic” effect, you ever have to “model reality.” (“This is CG … reality has nothing to do with it.”) If you can get the effect you want by sticking a billboard with a pretty interior scene on it … do that. Or, if you simply need a compositor-target with a certain object-ID# on it … do that. If there’s a certain (spot) lighting effect that Cycles isn’t doing well for you, but that BI can do easily … grab both tools. It isn’t hard. It just takes a wee bit of planning.

And it might also take a little bit of shot-cheating. Something might be technically-correct, e.g. some kind of “interaction with shot-panning,” but if anyone (other than “'round here” …) would actually notice the ‘omission,’ you don’t have to do it. Like I say, Star Wars Episode One shipped to theaters with a “crowd watching a podrace” that actually consisted of colored cotton-swabs. Millions of people never noticed. Today, we’d “CG” that crowd in there (and, for the DVD, they did …), probably spending a few million more on the effort, and they still wouldn’t notice they weren’t Q-Tips.

We really need a sticky for common questions like this.

My advice: Don’t use glass at all for thin panels. There’s no point since the refraction of light is nearly zero. Transparent + Glossy w/ Fresnel/facing do the trick just fine, and you don’t have to worry about light not passing through.

(BTW, light DOES pass through the glass material, but it’s ALL technically caustic lighting, which is why it takes forever to clear up.)

CarlG- I would need to see a node shot to get your WA#4 I understand the Light path, but am not getting your two components?

Secrop- Thanks for the link, great read or post from J

Sundials- you are correct, Power to the Q-tip whatever works. SO on that note, I asked and obvious took the advice of no glass but instead used it characteristics without paying for it in Samples or Render. I think that is what is being discussed here. Getting a look on the cheap.
That leaves me with the idea as stated 'Post a screen shot on a plane and if it looks like a duck, quacks like a duck…It could be a Chicken from Blender with some touch ups…

M910… So should i consider that hint to use Fresnal instead of Faces as I posted in my shot?

Love the discourse, great info in here. Thanks you guys
NC

That’s up to you. I personally use Facing for almost all cases, although Fresnel is technically more accurate. I just prefer the results with Facing.

My explanation sucked, as I mixed in some other things, see below. What I mean is mixing normal glass (slot #2) with transparency (slot #1) using LightPath in a Mix Shader. This because refraction (part of glass) doesn’t let any light through for shadow production unless you do caustics. So basically, the eye will see the glass, and anything else will just be transparent (allowing light through for shadow production). Using normal glass shader is preferred if you need frosted look on the transparent part, but you still need to combine with transparent shader for shadow production.

I believe the setup I use back when goes a bit beyond what you’re trying to achieve. I was trying to do more with it, and then I did need to use it. For reference:
Imgur

And I just tested with 2.72b. Fresnel (both using dedicated fresnel node and fresnel mode in layer weight node) is buggy as hell when dealing with transparency shader. Better off using facing mode in layer weight node instead, and save yourself the “wtf is going on here” :slight_smile:

Here’s how I would do it. Render the scene twice; once with a hole (no window pane), which will provide a quick clean render of the whole scene without the noise of all the tricks; then render a separate layer that has the window pane with glass or any shader combination you desire. Save render time by putting the glass on its own separate layer and mask out everything else, and be sure to save with Render->Film->Transparent checked and an image format with RGBA. Then composite the tiny window render on top of the whole scene.

Lots of times (and as I did a micro-tute a couple years ago now …) what you really want with “glass” is simply visual cues to the effect that “a piece of glass is there.” For instance, a slight change of hue/saturation for the area within the boundaries of (therefore, “behind”) the glass. Or maybe some apparent “reflections” from the glass surface. All of these are quite-easily achieved with compositing. You don’t actually need a piece of transparent material to be there … you don’t have to mimic reality. Simply look at whatever the effect looks like, never mind “how.” Achieve enough of a percentage of “what you see” to fool the (already fairly-disinterested passing-glance …) eye that “glass is there.” If possible, fuhgeddabout the hard(er) stuff: caustics, distortion, refraction, and such. 20% of the possible things that you might think of to do will carry 80% of the shot, and you can ignore the rest as “close enuf.”

Carl thanks for coming back and showing a grab, albeit not making 100% sense to me. Due to you know what you are wiring up and what the effects are…

See360- I think that is the next step for me in Blender is to get a ‘grip’ on compositing via passes. That really seems like the way to get away with a lot without paying for it. If you have happened to come across some good tuts on composting layers like you mentioned please share the link if you have em handy. That is a day long process in itself looking for decent tuts…I have a few subscriptions on Youtube from some good tut makers, but there is always someone who knows of a better one; I have found.

Which segways into Sundials cheat em if you can, which makes completes sense to me. Like a lens flare…