Converting an emitter into an "explosion" emitter. 25 Jul 00
(Note: an Illusion project file containing all of the emitters used here
can be found at the end of the tutorial, and CAN be loaded by the demo version of Illusion.)
One of the things I like to do most with Illusion is "blow stuff up". Well, I don't actually use
any 3D scenes or anything -- I just create explosions and envision the other stuff. (I don't have
the patience for that 3D stuff any more.) Here's how you can turn any "regular" emitter into an
"explosion" or "burst" emitter.
First, we need an emitter to start with. I'll choose the "shoot smoke" emitter (I want something relatively simple
to start with).
I want the explosion to be omnidirectional (particles fly out in all directions) so I need to change the Emission Range to
360, and I know I'll need more particles so I'll change the particle type number property to Max.
Now we're ready to start making it into an explosion (it will be an explosion of smoke).
There are three basic features that all explosion emitters have. They are:
1) A large number of particles being emitted for a very short time
2) The particles move very quickly at first
3) Variation in particle size, life, and velocity.
There are other features that many explosion emitters have in common, but they aren't universal.
For instance, you could say that #4 should be "a bright central flash". That's true for "pyro"
explosions, but what about for a dust explosion, or a burst of steam? We'll stick to the very
general features here.
The "Shoot Smoke" emitter already has #2 -- the particles start out fast and slow down over time.
(Some of you are probably thinking "the particles wouldn't slow down if the explosion were in space".
Yes, that may be true, but to make the emitter LOOK like a good explosion, I've found that the particles
should slow down to some extent over time.) Here's what the "velocity over life" graph looks like:
The emitter already has feature #3 as well -- variation. Its Size Variation, Life Variation, and
Velocity Variation graphs are shown here:
These may need some adjusting later, but we'll leave them for now (or for good -- depends on what things look
like later).
Now we just need to take care of #1 -- large number of particles for a short time. We'll tackle the
"short time" part first. It's simple -- just change the emitter Number graph so it steps down to 0
at frame 10.
The emitter now creates a short burst of particles, but it's not really enough of them to look good, at
least in this case.
We need MORE PARTICLES! This will usually be the case when the emitter is "on" for only a short time -- there
are not enough particles generated. So we'll adjust the emitter Number graph to create more particles.
Select the emitter Number property, then r-click in the graph window and select "Scale". Leave "scale values (y)"
selected, and enter "400" in the value box and click OK.
The number graph should now be at 600 (150 x 400%) at frame 1. How does that look?
Well, that looks good -- except for the big hole in the center! We'll take care of that hole
in a second, but first we need to understand why the hole is there. The reason is: the
particles all have non-zero velocities. Actually, we can say that none of the particles have velocities
that are very small either. Therefore when the emitter Number property goes to 0 to "shut off" the creation of particles,
the particles that were created last keep moving, which creates this "hole". Make sense?
Okay, so how do we fix it? The solution is to make sure that some of the particles that are created last (just
before the emitter "shuts off") are moving very slowly, or not moving at all. Then these particles
will fill in the hole. Great, so how do we do that? I usually do it by decreasing the emitter Velocity
graph as the number value goes to 0. Here's what the graph looks like:
That filled the hole nicely. (You may have to tweak it a little to get it the way you want it.)
Well, that is the basic procedure for making an emitter into an explosion. True, this example is
not too interesting...
Let's make it cooler (hopefully)!
Start by opening the properties dialog for the emitter, then select the "plumes" particle type (there
is only one particle type) in the hierarchy. Now click the "New Particle Type" button below the
hierarchy. This will create a new particle type called "Copy of plumes" which is a copy of the smoke
puff particle type. We'll start with this and just modify it a little.
(Remember to rename your particle types, or you'll end up with names like "plume" that don't make any sense.)
An explosion without some intensity just isn't an explosion, so select the "Copy of plumes" particle
type (it should be selected after the copy) then make it "intense".
That's too intense, so let's do a few things. First decrease the visibility of the "Copy of plumes" particle type
to about 50%. Then decrease the size to a little less than half scale. Finally, change the initial color
from white to orange and uncheck the "choose random color but do not cycle" option. Here's the particle type
alone, and the entire emitter:
I don't really like it -- too many "puffs". Let's try a different shape. Click the "change shape" tab (for the "Copy of plume" particle
type -- we're not going to change the "plume" particle type at all) and select "diamond star" if it's
available. If not, just select some sort of appropriate "sparkle" shape image. Then click the "Behavior"
tab and set the Particle Angle to "specify" -- we want all of the sparkles to be aligned the same. You'll have to
set the "spin variation" to Min as well to stop them from spinning.
That's the final emitter -- pretty decent explosion for only a small amount of work. You should be able to
repeat the procedure of copying a particle type and modifying it to create sparks, streaks, chunks of debris, etc. to make
your explosion even more interesting. Give it a shot and see what you can come up with!
A final note: After watching this emitter explode for a while, I realized that I might want it to explode faster, that is
increase the initial velocity of the particles. I would do this (but won't) by increasing the emitter velocity graph values, then
adjusting the velocity over life graphs so they slow down sooner. An exercise for the reader... =)
The project file: 
(32 KB)
(This project file CAN be loaded by the demo version of Illusion.)
Alan Lorence 25 Jul 00