Controlling secondary light bounces - Unreal Engine Tutorial

- [Instructor] Although we typically have global illumination set up by default in a new project or level whenever we create them from an Unreal template, we're probably going to want to know how to fine tune the amount of light that we have bouncing around an environment, so that we can tweak and direct the lighting in our level so as to suit the needs of the project that we're working on. Coming to the World Outliner then, and searching for the word light, we can see that in this particular version of our scene, we're using just a directional light. Let's see what kind of global illumination solution we can get out of this as we move forward then, focusing particularly on the GI quality that we're able to produce. As we come to the Lightmass rollout then, the second option that we see lets us control the number of indirect light bounces that are allowed inside our environment. With this set to zero, and rebuilding, we see only the effects of direct lighting in the scene as this essentially turns off our bounced light calculation. Setting the value to one, and rebuilding again, gives us just a single bounce of light in the level, although we can see how even that small change is able to drastically improve the lighting solution that we have. Five bounces will give us this result, which again gives a big boost to the illumination levels. And then finally, if we set the number of bounces to 10, this is what we get, which in this particular scene now starts to produce diminishing returns as the build here took longer to calculate than the bounce value of five, but is only improved the overall look of the solution by a very small amount. Naturally then, it will be up to us as the controlling artist to gradually increase the number of bounces that are being used until we have things looking just right for our particular scene, hopefully striking a nice balance between quality and performance. In my personal experience, I would say that bounce values above 10 do start to become a little bit of a waste of computing resources given the diminishing returns that we see. And we also have to remember that final GI quality can be improved by the use of other controls in the engine as well. For instance, just below the Indirect Bounces control, assuming that we are using version 4.18 of the engine or later, we now have a Skylight Bounce control as well. To test this, let's load the 03_01b version of our level, which in this instance is being lit by just a skylight, as opposed to the directional light. This being created by simply dragging one out from the light section of the Modes tab. Now a skylight, by default is set up to capture the most distant parts of a level and then use that information to light the scene. And so, to give the skylight something to capture, let's come to the World Settings tab and from inside the Lightmass controls, make sure that Environment Intensity is set to a value of one. After which, we can click the color swatch and set the Environment Color to RGB values of 0.7, 0.9, and one. If we then set our Skylight Bounces to zero, and again build the lighting, the result that we see is coming now from just a single default bounce of the skylight. Let's see how much light we can actually move around the environment then by moving up to a value of one, which as we can see after rebuilding, does give us better light levels. And if we try out a value of five and rebuild, we get to see even more of the environment. Of course, we aren't going to achieve believable levels of light here by increasing just the Skylight Bounces value alone. If we want to add more ambient light to this scene then, what we really need to do is increase the intensity of the light as well. Only, as our skylight is currently set to capture the environment, we can't specifically use it's Intensity control. And so, let's come instead to the Lightmass Settings and change the Environment Intensity to a value of 10. After which, we can rebake our lighting solution. Now that we're clearly adding more light to this scene, let's again bump the Skylight Bounces up to 10 just as we did with the Directional Light, build our lighting, and note that even after increasing the Environment Intensity, we are still only seeing a minimal change between the five and 10 bounce versions. The point here being that, although it is good practice to work with or set up the direct and the skylight bounces in isolation so that we can see clearly what each are doing, what we ultimately need to do is blend them together. And so let's open up the 03_01c version of the level, which has both directional and skylights in the scene. We can set the intensity of the directional light to five and then come to the Lightmass rollout in the World Settings tab and use an Environment Intensity value of five for the skylight as well. Whilst in the Lightmass rollout, let's also set an Indirect Bounces value of seven with Skylight Bounces of four. After which, we can rebake our lighting. And by using both lights and their controls together now, we can easily see the lighting improvements that we're getting by essentially using our indirect bounces to illuminate most of the room and the skylight bounces to fill in the illumination gaps. Of course, we would probably want to revisit any intensity settings used here once we tweak the GI using the controls that we're going to be looking at in the remainder of the course.