Black render after adding material to object

fumoboy007

New member
Hi all, I am new to 3D modelling and Cheetah3D. I am playing with materials, but I can’t get the material to render.

I have attached my sample project. Here is what I did:
1. Add a ball.
2. Add a point light. Rendering at this step works; I see the ball and the light reflecting off of it.
3. Add a default Steel material to the ball. If I render at this step, I just get black.

What am I misunderstanding?
 

Attachments

  • Material Renders As Black.jas.zip
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Hi and Welcome.
What am I misunderstanding?
What you need to understand is that reflective and refractive materials like chrome and glass need an environment as a lighting source. Imagine you´re in a cellar with a chrome ball and a torch; what can you expect from that light source? At least just a tiny spot reflecting the torch on the surface of the ball.
Please have a look at Help: Cheetah3d samples->Rendering->Pig.jas and have a closer look at the light set up.
Reflective material.jpg


Cheers
Frank
 
Thanks for the reply, Frank!

Imagine you’re in a cellar with a chrome ball and a torch; what can you expect from that light source? At least just a tiny spot reflecting the torch on the surface of the ball.

That’s my intuition as well. However, I don’t get any reflected light off the ball when I use the material.
 

Attachments

  • Black Render.png
    Black Render.png
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An area light will reflect in the ball. I have no idea why the point light won't. Spot light or distant doesn't show either?????
You will Have to ask Martin the creator.
 
* Light (as in "light source") is a virtual invisible object unless it is defined as an area light (rectangle, discs or sphere) with visibility activated. In this case (area light) you will see both the object and its reflection in a render of a reflective metallic object.
* In all other cases (point, ..., camera light) you have a virtual-light-object of dimensions 0;0;0 and a solely reflective "real" object. As there is nothing to reflect you see nothing.
* If you were to set the background to white (or anything but jet black) you will - at least - see the outline of the object. It still cannot reflect anything, so it shows up as jet black.
 
* Light (as in "light source") is a virtual invisible object unless it is defined as an area light (rectangle, discs or sphere) with visibility activated. In this case (area light) you will see both the object and its reflection in a render of a reflective metallic object.
* In all other cases (point, ..., camera light) you have a virtual-light-object of dimensions 0;0;0 and a solely reflective "real" object. As there is nothing to reflect you see nothing.
* If you were to set the background to white (or anything but jet black) you will - at least - see the outline of the object. It still cannot reflect anything, so it shows up as jet black.

Thanks! So what is the point of a virtual light object if it doesn’t reflect off of objects?
 
Maybe this makes it a bit clearer for you:
pointlights.gif


Cheers
Frank

PS: This kind of query is one of the most common difficulty beginners have with 3d+lighting and this forum has more than 100 threads about this. So you´re not alone.#In case the next one is about chrome logos: https://www.cheetah3d.com/forum/index.php?threads/1935/#post-13327
And in general it might be useful to visit this thread: Master list of tutorials
To get an idea of virtual light set ups you can have a look here Light&Shadow table which might be outdated in some cases. ;)
 
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So what is the point of a virtual light object if it doesn’t reflect off of objects?
1. Faster rendering. Non-physical point lights are easier to calculate than area/mesh lights with triangulated geometry that has to be sampled correctly.
2. It does reflect off of diffuse and specular surfaces with at least a little roughness, only not of perfect mirrors.

Point and spot light are non-physical light sources (for the sake of easy rendering) and as such won't show physically correct results with physically based render engines such as Falcon.
For most consistent behavior in Falcon mesh lights (objects with emissive material) can be used, at the price of slow render times, especially because AFAIK direct light sampling is not yet implemented for them.
 
Maybe this makes it a bit clearer for you:

Cheers
Frank

PS: This kind of query is one of the most common difficulty beginners have with 3d+lighting and this forum has more than 100 threads about this. So you´re not alone.#In case the next one is about chrome logos: https://www.cheetah3d.com/forum/index.php?threads/1935/#post-13327
And in general it might be useful to visit this thread: Master list of tutorials
To get an idea of virtual light set ups you can have a look here Light&Shadow table which might be outdated in some cases. ;)

Thanks for the demonstration. It helped… a little 😅. And thanks for the tutorials!
 
1. Faster rendering. Non-physical point lights are easier to calculate than area/mesh lights with triangulated geometry that has to be sampled correctly.
2. It does reflect off of diffuse and specular surfaces with at least a little roughness, only not of perfect mirrors.

Point and spot light are non-physical light sources (for the sake of easy rendering) and as such won't show physically correct results with physically based render engines such as Falcon.
For most consistent behavior in Falcon mesh lights (objects with emissive material) can be used, at the price of slow render times, especially because AFAIK direct light sampling is not yet implemented for them.

I tried a mesh light, but it doesn’t look right. (See attached.) I’m so confused.
 

Attachments

  • Mesh Light.zip
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Maybe it would help if I give some context. I am trying to create an app icon and I am following the guidance here (see the “Design an icon with appropriate perspective and a realistic drop shadow.” section). How can I set up a scene in that way using metal and glass materials for the subject?
 
I tried a mesh light, but it doesn’t look right. (See attached.) I’m so confused.
The box gets reflected correctly now but otherwise your scene is empty with nothing other to reflect than the box so the result is again a black sphere.
You could add a HDRI object and choose an image that looks right for you, then disable "background" in the settings.

A very confusing quirk of Cheetah3D is that there is a camera background color that shows up in the render but not in reflections.
That's totally counterintuitive.
Other apps have a configurable background object that works with sky, HDRI, procedurals or plain color and works correctly in rendering (background emits light) but Cheetah has this annoying separation of HDRI object, sky light (those work correctly), background color (does not) and no way for procedurals.
That's why we nearly always end up with a HDRI because it is the only thing that works.
 
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Well, all has been said, but I will try with other words:

Think of Cheetah as the inside of a black box, like a room without windows and with black walls, yourself completely clad in black with a black mask. You have one flash light. Now if you put a reflective object in that room, like a silver ball, the only thing that will be visible would be the reflection of the light source. Everything else is reflected, too, but as it is black you only see black.

If you look closeley at a real life, high reflective metallic object (or a mirror), you will see the environment reflected. And this is what all the other answers in this thread mean: You need an environment. This can be something rather neutral like the environment in the product render studio or a hdri (actually jpegs work, too, only they don't give a very realistic light).

As soon as you set the hdri object in cheetah, a default one is already there (which does work now). Please do this, disable background in the setting and hit render. Et voilà, your object is seen.

If the default hdri isn't loaded or to get a better suited one, you'll find lots of high quality hdris in the net that can even be used for commercial purposes. One such site is https://hdrihaven.com. Once you understand the concept, you'll be able to find a suitable hdri for your scene. Probably, with a 100 % reflective material you'll want to change the material(s) of your mesh a bit, like a blur, maybe some diffuse or whatever (instead of a blurred reflection one can of course use a blurred hdri which would result in faster render times). Maybe you'd want to add a 'bloom effect' in post (in an app like photoshop).

Misoversaturated already highlighted Cheetah's (resp. Falcon's) shortcomings in this sector (no pun intended), at least most of them. The 'legacy' lights without light sources are indeed a bit hard to swallow, as are the backgrounds that don't contribute to the lighting. I myself don't care much for the emissive light here which isn't always strong enough to effectively light a scene (and it's a bit slow. But an easy way to implement softboxes and stuff). Environments like the mentioned product render studio are a bit dull by design. Actually this is intended. Look at any watch advertisement in any paper for example or visit the website of any of this firms with expensive watches. The reflections are always unrealistically blurred to make the product better visible (doesn't look too good in my opinion but I understand the reason behind it).

In the end, with Cheetah you really do need almost always a hdri to get a realistically lighted, photoreal scene (the other solution would be a very complex scene with enough objects that can be reflected and be it just images mapped to single polys). Even with materials that are not that reflective (in reality everything reflects light, of course), hdris give a more natural, realistic light than anything else.

This is somewhat of a downer, indeed, as photography – and therefore rendering – is all about light. In other apps you really have a pletora of possible lights to choose from that usually do work as expected in render (but even in the most expensive app, you still need an environment to get reflected on mirror objects). Already a neutral gradient works wonders for an image. So it is usually very easy to set a proper highlight on an object in another app. One of the big advantages of 3d vs Photography, at least in product rendering, that one has full control of the environment and what's reflected (one of the others is simple that the advertised product doesn't have any blemishes in 3d). With (almost) hdri-only we lose quiet a lot of this control in the Falcon renderer.

(Martin, the developper knows all this better than me. I'm sure he will address the lights sooner or later. Up to then we will have to use a lot of hdris. But please, be aware, even then in your exact situation, hdris will probably remain the best solution).
 
Needing an environment to reflect is also true in pre-computer vfx work. ET's spaceship was a metalic gold that reflected the stage walls, the camera, and everything else that ruined the illusion. The crew ended up surrounding the model with an igloo shaped structure that had a forest scene painted on the inside. You must give reflective objects something to be visible in the reflections.
 
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