Newcomers to Google SketchUp's V-Ray may be tempted to use the built-in controls for adjusting translucent properties in a surface, but this can be tricky and ineffective. There's a trick you can use instead to bring together V-Ray standard materials to create the illusion of translucency; the only downside is the tendency toward unrealistic associated shadows. Discover the secrets of this method of creating translucent surfaces in this online video.
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Although the V-ray Standard Material does have its own translucency controls--ones that are designed to help us to create thin object translucency-- getting them to work and work well can take quite a bit of trial and error. In this video we're going to walk you through a very quick way of faking translucency using a couple of V-ray Standard Materials along with a V- Ray 2 Sided material that we'll wrap those inside of. To begin with, let's open up our V-Ray Material Editor by coming up to the V-Ray toolbar and clicking on the icon.
Now, what we want to do as a first step is essentially create two V-Ray Standard Materials that will serve as the front and the back of our tablecloth object. We're going to paint different colored materials onto each side of the tablecloth. Now we're just using straight colors; you could of course use bitmap files if that is what you want to do. So let's come to our Scene Materials label, right-click, come to Create Material, and create a new standard material. Straightaway of course, we're going to want to rename this, so let's right-click, go to Rename Material, and we'll call this first one TC_front. Once that updates, we can go and create another Standard Material. Of course, we need to be on our Scene Materials Label.
Create Material, Standard. And as you what expect, we will go and rename this one, so right-click, Rename Material, and we'll call this TC_Back. So now we have the two materials that we want to apply to either side of our tablecloth. We could think of it as inside and out materials. We're just calling them front and back because that essentially is how V-Ray will see things; it is applying these materials according to what it thinks is the front and back of the geometry.
Now we need to go and create our V-Ray Two Sided Material. So again, up to the Scene Materials Label, right-click, Create Material, and this time come down to the 2 Sided Option. Now I use the designation V-Ray 2 Sided Material for two reasons: one, because that is what it is called in all the applications that I've used V-Ray in, and secondly, to differentiate it from the SketchUp 2 Sided Material. So let's select that, and again, we want to go and rename it, so let's use the Rename Material Function, and I am just going to call this one Table Cloth.
Now as you can see, this material has a very simple control set. It has two slots named Front and Back, and as you would perhaps suspect, this is where we add our front and back materials. So let's go and select our TC_Front Material for the Front Slot, and let's go and select our TC_Back Material, naturally, for the Back slot. Next, we'll select our Table Cloth geometry and then right-click on our Table Cloth material and apply the material to the selection.
Now initially of course, nothing will change too much in the SketchUp viewport, simply because our two V-Ray Materials, the Front and Back Materials, just have a gray value added to them. So let's go and make a change in here. Let's go to our Front Material and let's set this to a nice obvious red color. That of course, we can see update in the SketchUp Viewport. And let's go to our Back Material and let's add a nice pale blue in there. Now you may wonder why I'm using a red and blue color. These are simply debug colors that I like to use.
They make it very obvious to me what is going on in a scene. You can of course assign finished colors if you want to, or as we mentioned, you can even use bitmap files. Now, if we were to take a render at this moment in time, we would not see any kind of a translucency effect, although it'd be good just to test now, to make sure that our materials are mapping on the front and back of our geometry as we would expect them to, so let's just click on this start render button. And our test render clearly shows that our two materials are mapping exactly as we wanted them to.
Of course, at this moment in time, we're not seeing any kind of a translucency effect. This is because there are still a couple of options that we need to work with. So again, back into our V-Ray Material Editor, we do want to do choose our Table Cloth, or V-Ray Two Sided Material. To get V-Ray to blend between our front and back materials, we need to work with this Color option; this essentially controls the blend between our front and back materials. The default value of black, which is what we have at this moment, doesn't allow any blending between these two materials; they are only allowed to sit on the respective side of the geometry to which they are assigned.
Either of their extreme values, black or white, would not allow any kind of a blend to take place. If we set a white value in our color swatch here, we would just essentially flip our two materials. As you would expect, if we set a mid-gray value in here, we would then get a 50-50 mix of the two materials. However, when it comes to creating the illusion of translucency, we generally want a fairly small amount of color to bleed through the material. So we just want to select our color swatch and in the Value Setting here, I'm going to set a relatively low value of something around about 14, and as you can see, that updates our R, G, and B channels.
With that option set, we can take another test render and see if that has improved our translucency effect. Now, whilst our render shows a definite shift in the colors assigned to our materials, we still couldn't honestly say that we've anything that looks like translucency. To understand why this is so, we need to take a look at the default settings of the V-Ray Standard Material. So let's just open up our Material Editor and select our TC_Front Material. And if we take a look inside the Options rollout, you can see one of the controls checked by default is this Double-Sided option.
This tells V-Ray that both sides of any polygons to which this material is assigned need to be rendered opaque, which of course isn't what we're trying do with our V-Ray Two Sided Material; we're trying to create a blend. So we can either disable the Double-Sided option in each of our V-Ray Standard Materials or we could instead come and select our V-Ray Two Sided Material, our Table Cloth Material, and put a check in these Force One-Sided option. This, as you can imagine, forces each of the V- Ray Standard Materials to act as a one-sided, not a double-sided, material.
Now of course, we should be able to see our translucency effect, so let's again take a test render and see if that is the case. What we get now of course does indeed resemble the passing of sunlight through a thin piece of fabric. We can even see where the folds in the geometry occur. The brilliant thing of course here is that we have two completely separate materials that can have different properties assigned to them. The downside of course is that this is just a material trick; we don't actually get any light passing through this material, so any shadows underneath this table would not be affected at all.
If we wanted to give the impression that the shadows were being lightened by sunlight passing through, we would need to use extra lights in the scene. So there we have it. We've seen how we can use our V-Ray Standard Materials to create thin object translucency. Of course, this doesn't just apply to fabric. We could think of items just as foliage, paper, indeed, any object that would allow direct light to pass through it to some degree. All we have to do is wrap our V-Ray Standard Materials in a Two Sided Material, tweak a couple of options, and we'll have a very nice effect for ourselves.
- Installing V-Ray
- Creating natural daylight with V-Ray Sun and Sky
- Bouncing light around with irradiance mapping and light caches
- Setting up a depth-of-field effect
- Creating diffuse and reflective surfaces
- Working with the Adaptive DMC engine
- Manipulating color mapping
- Adding caustic lighting and occlusion effects