Fire Simulator Tutorial: 20 Minutes to Masking Mastery


Learn how to create a masking effect in your fire simulations.


Welcome all, I’m Jonathan Kaye. This is 20 minutes to masking mastery. So, what is masking? I’m going to start out with the fundamental little story. We all have pictures, and let’s say that we need to make smoke and fire show up on the Charlie side, on the back side of the house. Now, we could just take smoke and fire with SimsUshare and kind of place it on the roof and sort of make the fire show up sort of over there, and you kind of get the idea. It’s not awful, it’s just not bad. You get the idea there’s smoke and fire coming off somewhere, but really you don’t know, like in this picture is it coming from the roof? Is it coming from the Bravo side? It’s really not that clear, and we really want to make it clear so that the first arriving officer is actually reporting it properly. 

Also, this obviously shows that the smoke and fire is kind of up high on the house. What if the smoke and fire were just somewhere maybe on the first floor or on the second floor? We don’t want to actually have it kind of there floating. We only see maybe the top of the smoke. Well of course, we could take the smoke and fire and then just push it down into the house, but now that’s really getting worse. We’re really trying to show it on the Charlie side, but now it’s pretty clearly the smoke and fire is on Bravo, and you will have a hard time explaining, “oh, just ignore that, try and think like it’s coming from Charlie.” No, that’s not going to do. So you’re going to reach a point when you’re creating these that you’re going to need to make your smoke and fire look like it’s coming from behind. So what we really want, also you’ll notice up in the front over here, we are putting some fire into this window and it’s sort of creeping into the edges. It’s okay, but in this situation let’s say we want fire inside the window. We don’t want it to be outside the window. We can not make it a little more transparent to show it’s in there, but it’s just a little bit sloppier. And with only a couple minutes of practice you can do a lot better. 

So what you can do, from the roof line here you can see, I can actually cut it off so now it really looks like the smoke and fire are coming from the back side, from the Charlie side of the house. Maybe a little harder to see here because we’ve started edging into the frame, but it is cut off much more neatly.

So really what masking is doing, is going to help us create this effect. You still have the smoke and fire there, but somehow we’re going to have to block out parts of the house or, in this case, block out around the window so that we contain our effect only to the things that are not blocked out. That really is the essence of masking.

So, to summarize this, imagine that you have this kind of invisible curtain that you could place over the picture that’s only going to block out the smoke or fire. And so that curtain is called the mask because it masks out the various effects. But now, instead of having this mask show like here, the mask is going to be invisible. So it’s going to still hide the smoke and fire, it’s just going to be invisible in itself which will then show the background picture, which is the building. So the mask is going to really only apply to the different effects that you have over here. 

So how do you get this sort of mask? When you’re in SimsUshare, you hit the plus key and then in the utility category you’ll see there is this entry called “Mask” and when you click on that, we’re going to see how you’re going to get a little shape. When you do your masking, what you want to do is you’re going to say, okay, I’m going to create some kind of shape. So the mask doesn’t have to be a rectangle or a square. It’s going to start as a square and you’re going to be able to adjust each of the points. Great, you can make the shape, but the two critical questions you have to answer when you’re masking is which effects do I want to mask? Because right here we want to mask the smoke and fire, but maybe we do have something on the Bravo side that we don’t want to mask. So just putting a mask down doesn’t automatically cover it. You have to say, which specific effects do I want the curtain to apply to? So you say which effects do I want it to apply to, and then the second thing is what’s the shape of that curtain? So when you create the shape, it starts as a square, just four points. You’re going to be able to, we’ll see, add points to make it more to kind of fit roof lines or any kind of obstructions. And you can actually even gently push the little points very finely or using your mouse click and drag them into place. And essentially the key thing about a mask is it’s going to hide what’s inside the shape, so in this situation it’s going to hide the base of the fire so only a little bit peeps out, it’s going to hide the base of the smoke so long as we say, apply this mask to those effects.

So, again, we’re going to be able to change the shape boundary because we may want to, like we saw, we may want to have some smoke show up from around the house. So we can see this boundary actually and you’ll see when we do the actual example, how closely it matches the side of the house. Change the shape, and then what you do as well, this is the part about choosing which effect gets masked. So you can selectively, with all your different smoke and fire you can say I want to I want the mass to apply to X, to Y, or whatever, but they don’t apply automatically. And so, once we’ve done that and we play the simulation, you’ll see we get a nice boundary here. We have a little bit of the fire and the smoke peeking out. This is much more clearly showing that it’s happening on the Charlie side. Now, this can happen anywhere on the house. So let’s take a look at what this is like in practice. 

Here is the house. So the first step I’m going to do is to go and put some smoke in. I’m going to go and let’s just say put turbulent smoke. I’m going to put it up here. Now, I don’t want to float. I’m going to push it down to where I want it to really be on the Charlie side, but I’m not going to worry about pushing into the house because I know I’m going to be blocking off this part of the house. So let’s say it’s going to be that. And now let me go and go get some fire. I’ll just use basic fire here and I’ll size this. And again, if the smoke is a little bit too thick and I need to see the house, I can always use the switch here. That always hides things that are not what I’m currently editing, so I can kind of fine-tune how I want this to be because I really am going to be watching it over the roof line. So I want to kind of think, ok if it’s in that back bedroom window, maybe this is a good representation. I might want to narrow it or do whatever to this. 

So when I’m done editing that, I’ve got those two shapes. Now is the time for the mask. I click on plus, I go to Utility, and I say “Mask.” So here, the mask shows up as a square. This big diamond is really just a way to grab it because you could grab it on the edges but especially on mobile devices, it’s hard to actually click on the edge. So this diamond just makes it easier to have something to click on. So when I click on it, now I’m editing the mask and I’m going to bring it over kind of to the area where I want to start. Now, this would only be a square. So what I need to do, remember the two steps are: what do I want a mask and which do I want to mask? So I’m going to go to the pencil tool, I’m going to say “Which to Mask,” so here is where I say okay, I want this turbulent smoke and I want the basic fire. And the second step is going to be the mask boundary. Click that again, “Mask Boundary,” and now here is where I get these points that I can move around. I can’t see the roofline so let’s use our tool here to hide that. So I’m going to go, I get that corner of the roof. So that’s not a bad start. I hit done and now if I hit play, you see, not bad but if you see here underneath the eaves, you can see we’ve got a little bit of leakage, it’s a little bit weird. We really should be able to see, if there’s smoke there, we should be able to see it and we’re not. And if you think about it, what’s happened, if I click on the mask as you’ll see, it’s masking everything from that edge of the roof downward. What I really want to do is push this mask inward a little bit. So what I do is I’ve clicked on the mask, I go to the mask boundary, and now, I can’t move this in without changing the line. So what I’m going to do is I’m going to hide the other elements, and now I’m going to use––notice over here Mask Boundary, I have plus to add points, minus to remove points that are selected, and then if things get all messed up I can always return to a square. Let’s say I have like 60 points and I wanted to say, I’m not getting it, let me just go back to the four points. So that’s what this four point thing is. But in this case I want to add points, so I’m going to click on plus and I’m going to click somewhere near, and it’s going to try and figure out what’s the closest two points and kind of add an edge in. And so what I’m going to do is I’m just going to go and move that in place, now what I mention with nudging on the keyboard, I can actually just gently nudge with up arrow, down arrow, left arrow, and you can see very carefully it moves the point over.

If you want big changes, just use your mouse. You can also do, a little more sort of advanced tip, if you hold down the shift key and then press the arrow, it moves in five pixel increments. So individual increments, just use the arrow keys. Now there’s my roofline. I hit done and now I hit play. And there. Now, I could tweak a little bit. Notice, if you look very carefully, I have a tiny bit of white space which could actually be a downspout, but it probably is me just not hugging the house close enough. So what I’ll do is I’ll go back in, click on editing that mask, choose Mask Boundary, and just nudge it over into the house a little bit. It’s always better from a visual point of view to be tighter on the house than being looser because you don’t want the sky to be showing through. And if it’s a little tighter, no one’s going to really know. So there, now we’re a little bit tighter, and that looks pretty good. 

Now if you notice over here, we are leaking a little bit. It’s very subtle, but we’re seeing some smoke come through the edge of the mask. We don’t want that to happen. So let’s go back. That’s because the last point there isn’t quite far enough over. So I’m going to click on this. And we’re going to say Mask Boundary and I’ll just stretch this up a little more. Now, you notice that one mask masks several items. So if we had some other things going on, we could just as easily mask the whole roof. I’m just going to go here and show you. Just keep adding points––nothing wrong with that. We can just keep adding points, nothing wrong with that. This can also be a very big mask. This might be useful, let’s say, just for convenience, if I have some other smoke and fire. So let’s say I’m going to have something else happen over in that part. I can hit plus, and I’ll just now get some other smoke, I’ll put that and make it a little bit darker so it stands out more. I’ll make it a little smaller, and I’ll just stick it up over here so it’s sort of just barely touching there. Now, just by virtue of having the mask here doesn’t mean that the mask is going to apply to that smoke. So if I hit play, you’ll see the smoke is still in front. I have to say which to mask. So what I do here is I go back to the mask, I click on the mask and I say pencil and then which to mask, and now Grey Laminar. Now, if I made a mistake because you can have more than one mask, I could also say oh, I didn’t mean to mask Grey Laminar, I wanted that somewhere else. I could just click “No” and then it gets released then another mask could be masking that smoke. But for now I’m going to say, “Yes.” Mask the Grey Laminar. Hit plus, and now we can see I didn’t do a great job on the roof. Let me go back. I click on the mask, I go to Mask Boundary. It’s a little hard to see. I hide the other elements, I sort of nudge that down a little bit to get tighter on the roof, and now it’s a little bit cleaner. So that’s terrific for let’s say blocking out stuff around here. 

Let’s go back to our example where we want some fire in the window. So if I go here and say plus and I say Fire, and I’ll just say let’s go and put some fire in this window here and I’m just going to go and reverse it like that, but now I really wanted to be inside the window. Let’s say that the window is intact. I could try and narrow it here and I could certainly go here, if I want it to be inside the window, I want to make it less opaque. That’s not bad. I mean, you get the point. And a lot of times, this masking is nice but if you want to just do something quick and dirty, then you may not need to use masking. So this is okay, but we can do a little better, especially with masking. 

So if we remember there, that actually looks pretty good, but then when I do the play, you’ll see we are kind of edging, we’re kind of coming out of the window which is not good. So now, with masks that we’ve learned, we could block off an area. So let me go here and I’ll get a mask, I’ll go “Utility Mask,” I’ll click on this and see, I can block off an edge pretty easily. Now, before I go and do this you might think to yourself, “I put the mask over here, I should be all done and I’m just going to block off this edge, so I should be ready to go.” 

But you realize if I hit play, it’s still leaking over here because I didn’t say which to mask. I sort of have a shape there but I didn’t say which to mask. So I have to click on the mask and then I say “Which to Mask” and now “Basic Fire.” And notice there’s no other elements here available because there’s another mask that we put them under. So if you have sort of a free agent affect, smoke that’s not claimed, all the smoke and fire that’s not claimed will be available to be claimed. But once you have a mask and say, let me mask this element, then other masks cannot actually apply to it. So this means that you can’t have an effect that is masked that subject to two separate masks. Each effect can only be masked by one thing. So you can have multiple things masked by one, like this house and the smoke. That’s the key thing to remember: you can have multiple smoke and fires that are all covered by the same mask.

So now if I’m over here and I now I’ve said, yes mask this, so I’m done with that, I hit done and play, and we can see is a very sharp line. So we’ve got that pretty well over here. And that’s really nice especially if I want to show it directionally. I can make the smoke here and I don’t have to worry about a fire here and it looks like it’s really coming in from that edge. 

So now, if I want to now, get to the other borders, I could start playing with the shape. I can say which to mask here and what I can do is I can start just adding points. This is one way of doing masking, but we’ll run into a problem in a moment. See what I could do is kind of make a really kind of odd looking, I can make a shape here because I also want the kind of want the bottom to become one of my masks here. So now the key thing is I’ve covered all the places that the fire would be bleeding onto the window frame. So I’ve got that and now it’ll be okay. It’s a little bit of a weird shape, but you notice it’s cut off on the right side and it’s cut off on the left, which is pretty good. It’s not cut off on the bottom, and let’s say that I want that window to have really a lot of fire. So I’m going to go and click on this and I’ll just all exaggerate this for right now so you can see it very clearly. 

Now, I want that whole window to be fire so you’ll see the problem that I’m going to run into: it’s cutting off the three sides but it’s not the fourth side. So we could try and do some more gymnastics, but there’s an easier way to do it, and maybe some careful viewers have noticed there was something I didn’t talk about in the menu. What we do right now, if I click on this mask, this is blocking out everything in this semi-transparent. So it blocks out what we can do instead of blocking out what’s inside, there’s a switch that will say, block out what’s outside. So we can flip this. So for example, let’s return this shape. I’ll go back here, Mask Boundary, and I’m going to return it to a square. Let’s say, we really want something where we just say, confine the effect (and it can be multiple effects) just to inside the shapes. If I do this right over here, this is going to confine, this is going to block out what’s inside the shape. So if you watch over here, you’ll see this and then we’re going to flip it. So you notice this is kind of what we want in the opposite. It’s blocking out everything inside the shape, which is kind of what we did over here––we blocked out everything inside the shape. But if you really want to do something in windows or confined to a space which have all these points, what you can do is you press this and there’s a third option––Mask Type. So Mask Type, by default, blocks out things that are inside, and we call that a mask. So we made up another thing called a Portal. A Portal is just the opposite––we’re going to block out with outside the shape. So now when we have this––and I can still adjust the points the same way, I can add points I can do everything I can do as I can with the other type––but it’s now going to show in the inside of a shape. So now when I do this, it makes it easier for contained spaces. I didn’t do a great job on the left there.

So that’s really the key. Remember Which to Mask and then what the shape of the mask is going to be, and using this you can get your three-dimensional feeling from the picture. You can really place the smoke and fire in the places that you want.

Now notice over here this lamp post. We could also mask the lamp post, but it’s going to be tricky. You see how tricky this is over here. So imagine we had some smoke, we could actually take a mask out and you’ll see here, I actually go and take a mask, I could set up a mask, let’s say we had some smoke and fire behind that. I could go here and then start with my work, let’s say you’ve got a utility pole or something, and so I could start masking this over here and start adding points. But this is really going to very likely drive you crazy. There’s just so many points on this thing. And particularly this happens with trees. Let’s say you have a tree, a lot of times you’ll take a picture and there will be a tree in the picture. You could try and mask it but first, the edges are sharp, and there are just so many points, it’s going to drive you crazy. So let’s say you had something like, I’m going to go here and show you, you have a tree over here. And let’s say I want to put this tree, though, into the picture what I can do is, when you have something like trees that are complex instead of trying to mask it to only have the background what you’d use is a tool whether Photoshop, or there’s a really good one called Clipping Magic. Let me show you, and that will be the topic for another time.

So what’s just as important to know is when not to mask. So when you have a complicated shape like this, it’ll kill you to do that masking. It’s easier to make PNG files which are files with transparency, and we recommend a tool called Clipping Magic, and basically what you do is you you cut out the object and you can have transparency as well, and you say which the transparent regions are. And so, this way, once you have your PNG file, you can go in here and let’s say I have some smoke and let’s say I have a tree in front, rather than trying to mask the tree, what I can do is go here with a PNG file, go and get a picture of a tree and just basically put the tree in the in the shot. This might be how you would actually put a tree that’s there instead of having to actually go and mask it. So again, when you’re trying to block things out of your scene, masking is really good for doing things like roofs, doing things that have maybe four, 10, even 15 points. Once you have more complicated stuff, you can see here it’s easier to make a PNG file and just stick it right on top of there, and then you won’t kill yourself with all the different masking and you can make it a little transparent there, it’ll look really good.

So now we’ve seen how to do the masking. We’ve seen how to mask it when it’s something that’s like a structure or something that has a fair, not too many points, and also said you know what, when it’s not right to mask and you have something more complex.

I appreciate your time. I’m ready now for any kinds of questions. I’ll see if anyone has some questions. You could type them in the chat panel. If you’d like to talk I can allow you to ask your question by voice. Anyone have any questions? 

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