Transforming Robot Production Pipeline Volume 10: Compositing

In this lesson we're going to learn how we define the particle's look by taking a look at the noise and the 2D nodes we used to create the particle. And the particle curves node which we used to adjust the particle over time. So here's where we left off in Truck Particles Five, and let's begin by taking a look at this particle at the top. Just began with a normal constant, sort of a dark brown, to get the base color of the particle. And then to that we added on some noise. Now I gave the noise a separate color, gave it a nice, warm, bright color here. Now at this point we really don't have much of an alpha channel at all, so we used a roto shape to create a nice soft fall-off on our particle. See here, we've got a little bit of a feather and we've modified the fall-off a bit. Next, we've graded this down a little bit and we actually graded this down to remove some of the background. And to be honest, I think that this gave us some color problems later down the pipeline. So I would be hesitant to do this again, because as you can see we ran into a lot of negative values here. And wherever we black clamped, you can see the colors are becoming a little bit strange there. So we'll probably avoid doing that in the future. But I wanted to show you exactly how things went down during the production process so that you could see that even those who make great work sometimes make mistakes. Now the last thing that's very important with these particles is the BlendMat node. And this is important if you ever want to control your particle's opacity with time in the particle curves node, or if you want to change how these particles interact with each other. So in this case we took the blend Mat and set the surface blend to modulate, which meant we could control the opacity. And we set the operation to plus so that we could have these particles interact with each other and add to each other, as opposed to just covering each other up. So I'm going to just pause the video while this processes, and so we can see the scan line render result of this. And I'll switch the operation back to its normal over so we can see what that looks like as well. So here are the particles. And I've just turned on proxy mode and turned off our display out of bounds values. So now we can see here are the particles. And you can see wherever they are overlapping, they add up with each other creating an overblown value or an ultra white value. If we had this set to the default of over, what would happen is instead of adding to each other, these particles would simply cover each other. And we'll take a look at that here in one second. So here we are with that. Now this is useful for some particle effects. But again, I wanted those ultra-bright values because dust gets hit by light and then the light begins diffracting through the dust. And so it becomes much, much brighter the denser it is. And with a plus operation, this allows us to have values that are over-bright, depending on the density of the particles. So let's jump up here and take a look at the emitter. Just give this a second to process. So we talked about a lot of these values in the last lesson. The only other one is since we want to start this at frame one but we want the dust to have been generated before that, we had to start at a negative 40. Which is why you see we reprocess the frame every time we change the time and that's why the time starts at around negative 40. We have the lifetime of around 40 frames converted into seconds. So that's about, I'd say, 1.6 seconds and we're giving it a third range. So we'll probably get between one and two seconds lifetime for these particles. Now it's important to set the lifetime correctly, because a lot of the later corrections and the later changes we're going to make are going to be based off of this lifetime. Now as you can see, the velocity is very high. Again, fast moving object, fast moving particles, especially dust particles being picked up by a rotating tire, happen to move very fast. So we needed to capture that with a velocity. Size really doesn't matter. We overwrite this in the particle curve, which we'll look at here in a second. This is not going to have a change at all, although changing this may cause you to resimulate your particle. So as always, be careful changing values on any of these particle nodes. As a single change could, again, take a look and freeze comp for about 20 to 30 seconds or more, depending on the complexity and the amount of particles you have. Now, we have a cancel button, but I've seen it backfire before. However, in this case it did pause our viewer, so we can move on. So now let's take a look at our particle curve node that we have after our turbulence. And the order of this is sort of arbitrary. We could have the curve node above our turbulence. And we have control over quite a few things here, but we have to make sure we check on to apply the curve to whichever of these attributes we want to modify. Now in this case, I've got a nice curve on the RGBA slots which start bright. So they start at a value of one, which is the original color of the particle we're piping in. But as time goes on, we're setting this down to point two and we've got sort of a linear key frame at the end here and a horizontal key frame at the beginning. So the change accelerates as it grows older and older. And what this is doing is it is making our particles darker and darker as time goes on. Now size also has a key or a curve on this. We start at a size of around 300 at the beginning. Thought process is these particles or these dust clouds are going to start small and grow larger over time. So we just have a nice soft curve here from 300 to 500 at the end of their life span. And again, scene size and the particles you're trying to create are going to very drastically, potentially, change these values. So I found these work well for dust clouds in our scene, but as always this is just a tool. So you can modify the particles in your own scene and after that we're essentially done. We set up all of our forces and the last thing we have here is our ground material which is doing the very important job of cutting out our particles wherever it intersects with the ground. So if we jump back to our render node here, as you can see, the particles are getting cut-off by the ground wherever they intersect that. And this is really simple-- black constant into a fill material so that it fills both the RGB components and the alpha components of this. And then we just read in our ground geo connected to the scene and we are good to go for cutting off our particles underneath the ground. Typical scan line render node, I believe we do bump up the samples to include a little bit of motion blur. But again, we have to be careful with this. And I actually don't believe we are motion blurring this in our scan line render node-- well, I guess we are. So we have eight samples which explain to you why the render is taking so long. It's taking essentially eight samples per frame and we're doing six resimulations per frame, so the render time on this can actually creep up pretty high. But the great thing about this system is once we've got the render out, we can of course come in and make tweaks and then continue to modify this inside of our main NUKE script. So this was just a quick look at how we affected the color of these particles, the shading, as well as how we changed them over time using the particle's curve node. So in the next lesson, let's take a look at some of the post-processing we did to these particles before we rendered them to try to match them more closely to the background scene we were targeting.