vray rendering glass

Rendering Glass and Liquidauthor:

Wouter Wynen

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Rendering Glass and Liquidby:

Wouter Wynen

June 2006

Rendering Glass and Liquid

This tutorial assumes you already completed the other V-Ray tutorials before this one in the list.

You will learn how to model and render a glass filled with liquid, in our studio lighting setup (previous tutorial).

INTRODUCTION

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1. Continue with the end result of the studio lighting tutorial

Delete or hide the 3 spheres, we don’t need them any-more.

Set the render properties like this:

- output size to 400x480px- global switches: turn off default lights- image sampler to adaptive QMC- antialiasing filter “mitchell-netravali”- indirect illumination ON- Secondary bounces: QMC GI and multiplier to 0.8- refractive GI caustics ON- Irradiance map settings: - custom min/max=-4/-3 - HSph subdivs = 20 = interp samples - clr=nrm=0.4 - dist=0.1- environment: - skylight pure white color, 0.1 multiplier - reflection/refraction pure black, 1.0 multiplier- QMC sampler: noise threshold = 0.005- system: - render region division 50x50px - frame stamp: delete all except render time part.

The V-Ray lights should have the ‘store with IR map’ op-tion turned ON to start with. The left light has a value of 3, the right one is set to 5. Position them like in my screenshot.

Also adjust the camera position like I did, set the lens length to 85mm.

Your scene should have both system and display units set to metric mm.

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2. Import my glass model

Glass is a material that everyone tries to render while learning or testing a new renderer. V-Ray is capable of rendering very realistic glass in a very short amount of time.

I already explained a lot about creating glass in the basic materials tutorial. A lot of it will be repeated here, but this time we will render a real object instead of some weird blob like thing.

Download my glass model here (it’s zipped!). Use the import function to bring it into the scene (turn off ‘convert units’ in the import options). The glass should be sized like in my screenshot. If not, simply resize it :-) (probably your units are set wrong or convert units was still on if the glass imports too big/small)

3. Move it up a little bitAny renderer will always have problems with overlap-ping faces. Especially with transparent materials this can cause visible problems. The glass bottom faces lie exactly on the faces of the ground plane, they are in the exact same location. Although it will not be very visible here, it’s a good rule to remember, avoid coinci-dent faces! Moving the glass up by 0.2 mm is already more than enough.

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Create a new V-Ray material. We will first make clear high reflec-tive glass. To do that, first set the diffuse color to pure black. Then set refraction color to pure white. Pure white means 100% refractive, resulting in the diffuse component having no effect at all anymore.

Make reflection color almost pure white and check fresnel reflections.

4. Create the basic glass material

5. Reflect on backside

Notice the dark border on the inside glass surface? To get rid of this, we will turn on the ‘reflect on backside’ option in the options rollout of the glass material.

Render again to see the difference.

This option creates internal reflections, an effect that happens in real life too.

This is the base of our glass material. It is 100% clear, very reflective glass.

Assign to the glass object and render. It should look like my example.

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These options control the number of times a ray can reflect/refract before it is removed from further calculations. Lower numbers will cause faster render times, but go too low and parts or the whole object will turn black.

Increase them both to 10 and render again. The difference is huge on the foot of the glass and in the middle part (because in these parts, internal reflections will happen a lot, exceeding the max depth quickly).

Values of 10 are okay, don’t go too high because rendertimes will increase a lot!

6. Reflection/refraction depth

7. Adjust the studio setup

Our studio setup is a bit ‘too much’ for this scene. We will adjust it by turning off the left light. To compensate for the light decrease, turn the environment skylight multiplier to 0.4.

Render the scene, it should look more or less like my example:

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8. Filling a glass with water

To fill a glass with water, you should model the water. This isn’t as easy as it sounds. First of all, the surface of the water will bend up where it touches the glass because of adhesion forces. We call this curved top surface the meniscus. This effect has to be modeled or your water will not look very realistic.

Then there’s the problem of coincident faces. If you model the liquid exactly as large as the inner surface of the glass, the rendering will look weird because of these coincident faces (right glass). The best way is to model the water a bit larger than the inner glass surface (middle glass). If you model it slightly smaller, it’s not realistic either (left glass).

Click on the image to see examples of all three. I modeled the glass in rhino, it’s a revolved curve. I show you these curves also to see how the glass vs water is mod-eled.

9. Import the water

Download the water model here and im-port it in max (turn off ‘convert units’). The water should be positioned perfectly into the glass.

Create a new V-Ray material, name it water and give it a pure white diffuse color.

Render the scene.

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Go to your water material and change the settings according to the image on the right. In fact, these are the same settings as the clear glass, only the IOR is different.

Also go to the options rollout and turn on reflect on backside like we did for the glass material.

10. Water material

Now we have a nice wineglass filled with water :-)

As you can see, it’s pretty easy to get a decent result for glass/wa-ter in V-Ray. Already our first render looked pretty good. But to fine tune it, you need to know some tricks. Questions regarding glass pop up a lot in the V-Ray forum, so I hope this tutorial will clear things up a bit :-)

11. Render again

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12. Red wine

To give the scene a more interesting look, we will copy the glass and put it on the floor like as if it was tipped over.

So select the glass model and copy it, ro-tate it and position it like I did.

Change the output render size to 430x480px.

13. Expand the scene

Copy the water material and name it ‘red wine’. Change the fog color to a saturated red, and turn down the multiplier to 0.05. This will tint refractions red. Apply the wine material to the water. Render to see the effect.

Experiment with different colors and multi-pliers to create other liquids too.

Of course you can do the same thing with the glass material, to create a colored glass.

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With the rotate tool, roll the camera -8 degrees. Also move it to create a better composition. Render the scene, it should look like this.

15. Smaller V-Ray light

The shadows are very dim because our area light is so big. We will adjust the V-Ray light, make it smaller and reposition it. You can see in the screenshot how I placed it. It’s not only smaller but also placed further away.

U-size= 250mm and V-size=300Light multiplier is set to 22. It’s much higher because the area of the light is smaller.

Also change the sky multiplier (V-Ray environment settings) to 0.15 instead of 0.4. This way, the environ-ment lighting will not brighten up the shadow regions as much as before.

14. Roll the cameramap

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16. Nice caustics

This smaller light will also result in more noticeable caustics.

Remember my rambling about GI caustics on page 2 of the materials settings tutorial? Well, here we will use them again.

First render the scene with the new light settings. It should look like my example. Notice the shadows that are much more visible now. The smaller the light source, the sharper the shadows.

17. No GI caustics

In the GI settings, turn off refractive GI caustics. You will clearly see that shadows get darker. No light is able to pass trough the transparent materials.

This is just a reminder to show you the effect of GI caustics.

Turn the refractive GI caustics back on.

I usually don’t use reflective GI caustics, because they do more bad than good in most cases. Refractive ones are way more im-portant as you can see from this example.

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18. Sharper caustics

Because the shadow and caustics quality is controlled completely by the IR map set-tings, we will fine tune them.

Note that shadows are created by the IR map because we have ‘store with IR map’ in the V-Ray light turned on. So our V-Ray light doesn’t cast direct light but GI light for the moment.

Open the Irradiance map rollout and make the following changes:Min/max=-4/-1HSph subdivs= 35

There will be less undersampling, and sample quality is increased because of more HSph subdivs.

Turn on ‘show calc fase’ so you can watch the progress of the IR map calculation. This will speed up the rendering psycho-logically :-)

As you can see, the caustics are already sharper.

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19. High quality GI settings

If you want a better GI solutions to increase caustics and shadow quality even more, you have a few options.

First is to increase min/max settings, to for example -2/1. For low resolutions like this, -2/1 is really high quality, don’t go higher or you will loose the benefit of the undersampling.

You can also increase the HSph subdivs. This will calcu-late each taken sample better.

The clr threshold is also important, going from 0.4 to 0.3 will have a huge effect, but also on render times... The dist threshold can be useful here too (more sam-ples where objects are close to each other, important for region under the foot of the glass)

So what settings are the best? A bit of everything :-)

The min/max settings have the biggest impact. For this rendering I used the following IR map settings:- min/max=-3/1- HSph subdivs= 40- clr=0.35- nrm=0.4- dist=0.25

The caustics (especially these under the glass that lies down, look at the foot area) are much better now. But render time increased a lot... Usually you don’t need this high settings, because no client will ever see the differ-ence...

Note that the max setting of +1 is only used as long as the resolution stays at 430x480.

For resolutions from 640 to 800px, use -3/0 as the high-est settings (-4/-1 for 1280 to 1600 etc...). I will explain the irradiance map behavior in another tutorial.

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20. Store with IR map option

As you can see, we need very high IR map settings to make sure shadows and caustics will be calculated ac-curately.

As I said before, the shadow quality depends on IR map settings because of the ‘store with IR map’ option in the V-Ray light, treating the light as GI light instead of direct light.

By turning this option off, shadows will be raytraced, which results in very high quality. Rendertimes will be higher, but since quality now almost completely depend on the subdivs of the light, we can use lower IR map settings! So IR map calculation will speed up, and the actual rendering pass will slow down, resulting in +- the same overall render time, but better shadow detail.

When you use raytraced area shadows, note that the GI caustics will still be calculated by the IR map settings (the V-Ray light is the only light being able to produce direct light AND GI caustics at the same time, making it an ideal light for product renderings). So we can’t go too low on these settings or else the caustics will loose too much of their quality.

Turn off the ‘store with IR map’ option in the V-Ray light, and set the subdivs to 30.

Go to the IR map settings and change min/max to -4/-1, and HSph subdivs to 35.

Render the image, look at the process. Note that dur-ing IR map calculation, everything looks darker, because the V-Ray light doesn’t cast GI light anymore. This IR map pass will go pretty fast, but the actual rendering pass will go slow because the direct light (and area shad-ows) need to be computed now also...

The result is very pleasing. Caustics are a bit less detailed, but this is compensated by the raytraced area shadows.

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21. Final imageWe will now render the image at a higher resolution.

Set the render output to 717x800px.

We want the same GI quality as in the pre-vious image, but since the IR map settings are resolution dependant, we will need to make a small change. We nearly doubled the render resolution, so in order to have the same GI quality, you only need to lower both the min and max setting by 1. So set these at -5/-2. The tresholds and HS ph subdivs are not resolution dependant so leave them at their current values.

To get rid of the last noise in the shadows and anti aliasing, go to the QMC sampler rollout and change the noise threshold to 0.002.

Render the image!

Click the image on the right to see the high resolution version.

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About the author

Wouter Wynen has studied product development for 5 years at the university in Antwerp, Belgium. During these years, his interest in 3D modeling and visualization grew more and more. In the end, it even overpowered the interest in product design.

After graduation, he founded the company Aversis, offer-ing 3D viz & webdesign services.

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