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Without a doubt getting a believable exterior lighting solution in Twilight is a very achievable, dare I say even easy, task to accomplish, especially if we use the Physical Sun and Sky for our scene lighting and then just rendering over to one of Twilight's progressive render presets. The problem with rendering interiors, however, whether we're using the sun and sky or indeed any exterior light source, is that we are always going to struggle a little bit to pull enough light energy into our interior environment.
Anything then that we can do to squeeze a little bit more quality, a bit more light out of our render engine, that's at least going to be worth considering. What we want to do in this video is just show you how you can turn some simple SketchUp planes into Sky Portal objects. These can help our interior lighting solutions by really telling the render engine where to focus its global illumination sampling efforts. The first thing we need to do is take a look at how our Chapter 02 Portal scene is set up. So I am just going to middle-mouse- click in the viewport and then orbit around until we can just see the outside of our building.
Here, as you can see, we have two simple plane objects covering each of our window sets. You may wonder why we don't have a plane for each of the distinct window openings. Well, in SketchUp, as in all three applications, a plane is made up of two triangular faces. In Twilight, each triangle will represent a distinct light source once we add our Sky Portal material to this object. Each light source of course will mean more calculations; more calculations will naturally translate into slower renders.
With our current setup Twilight will read four extra light sources when it is rendering. If we added a plane at each distinct window opening, we would actually be adding 14 extra light sources. No prizes for guessing that that would of course add to our render times. Now again, if we just rotate around a little bit more in our scene, you can tell that these planes are facing outward. This is denoted by the white color. This geometry would currently fail if we tried to turn it into a sky portal, and of course as our windows are completely covered, all light into our interiors is being blocked.
This does actually raise a very vital point when it comes to setting up your Sky Portal planes. They have to be--how should we say?--watertight as it were. They really need to snap to each of the vertices around our window openings. We don't want any exterior light entering into our interior unless it is passed through our Sky Portal geometry. Reversing the phases on these plane objects is of course a very simple matter, so let's just double-click to make certain that we select everything in the geometry. Then we can just right-click and use the Reverse Faces function, and again let's do the same for our second object.
Now we can go back to our camera and our original composition. What we need now is a new SketchUp material that we can attach Twilight's Sky Portal definition to. So let's click on a paint bucket icon, make certain that we are looking at our In Model materials, which, as you can see, is just our default gray material, and I will come and create a new material. This we will just very humbly call Sky Portal. We can, if we want, give it a distinct color, just so that we can tell where it is in the scene. I am going to click OK.
And then finally, I can just dismiss the Browser dialog and just Ctrl+Click on each of our plane objects to make certain that I applied that Sky Portal material to all of the geometry. What we need now is the Twilight Material Editor, so let's come up to the Twilight toolbar, click on the icon; once that's open, we can just pull it off to one side. Using the From Scene dropdown, I'll just select our Sky Portal material and now rather than applying a template, we need to come into our Library tab. So as long as we are in the Architectural Twilight tab, you'll see the first definition is our Sky Portal or our Invisible Sky Portal option.
To attach these to our SketchUp material, all we need to do is double-click and that's it. We now have our Sky Portal material applied. Now of course taking a test render at this moment in time wouldn't really serve any purpose. To understand what is happening with our Sky Portals in place, we need to see a render of the scene with no Sky Portals. Well, if we jump into Adobe Photoshop, we can do just that, as we have a number of ready to be compared. What we have first of all, is, as the image title tell us, a no Sky Portals render.
This was taken using the Easy09_ preset and rendered for ten passes. As you can see, this took ten minutes to render. And what we have is a pretty reasonable lighting solution. It looks a little bit dark from my taste. You can tell that we're not getting quite as much light bounce or light penetration as we would perhaps like. So, what happens if we add Sky Portal objects? If we click on our next image, you can see that we do indeed get a considerable brightening. Keep in mind we're not changing camera exposure. We're not changing light intensity.
We are not even changing material reflectance. All we have done is added Sky Portals into our scene. Now, interestingly, you can see that the render times are not really that different. We have just added an extra minute with our Sky Portals added, which is pretty fair, considering the effect that we're getting so much more light into the environment. Clearly then, when using one of the progressive render presets, we get a fairly good result from adding Sky Portals into the mix. However, let's take a look at one of our photon map and final gather presets.
This render, again, no sky portals added. This was taken using the Easy03_renderingpreset. This took just 20 seconds to create. Clearly, our GI solution is looking a little bit ragged, and the light bounce, particularly at the far end of the room, doesn't look incredibly natural. So, what happens if we add Sky Portals into the mix? Well, as you can see, we get quite a considerable increase again in the level of illumination. We actually get a much cleaner global illumination solution as well. A lot of the noise smoothes out as we get extra light bouncing around inside our interior.
However, there is quite a shock when we compare the render times: 21 seconds for our no portals render, 54 minutes for our Sky Portals version, which is quite a considerable increase. Now, obviously Sky Portals can make quite a difference when it comes to pulling light into an interior space. We can see that with both of these sets of renders. We have seen that they are very easy to create, as really all we essential need to do is create a plane or two, add a Sky Portal library material, and we are good to go. We do have to keep you in mind, however, that if we are rendering with the photon and final gather presets, we probably will want to take that significant increase in render times into account.
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