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Using GridSquares to Create Running Circles

COW Library : Adobe After Effects Tutorials : Jim Tierney : Using GridSquares to Create Running Circles
Using GridSquares to Create Running Circles





A CreativeCOW.net After Effects Tutorial



Jim Tierney
Digital Anarchy, Palo Alto, California, USA

Article Focus:
Gridsquares is probably the best of the Geomancy filters to start off with. It's the most like a traditional particle system, and in fact, the only real difference is the use of the grid to control how the particles behave. In this tutorial, Jim Tierney explains the different parameters and helps take the 'fear' out of working with particle systems. You'll need Digital Anarchy's Geomancy filter for this. If you don't have it download the demo.

What's Up With This Grid Thing

The grid exists to help you wrangle those particles into going where you want them to. Normal particle systems (say something like Particle Systems II from Final Effects) are very good at letting you define the attributes and behavior of a particle at birth, but aren't so good about giving you control over that particle after it's been born. The grid gives you an extra level of control. Allowing you to set up a structure that the particles have to follow. Of course, you can spew out particles in all directions and ignore the grid almost completely if you want to use GridSquares as a normal particle system.

One thing that seems to overwhelm people is the sheer number of parameters. Keep in mind that a good many of those parameters are the Randomness parameters. These don't do anything by themselves. If you eliminate the Randomness parameters, Gridsquares doesn't have many more controls than something like Foam or other particle systems. The Randomness parameters are only there to help you vary the values of the parameter they are associated with. Let's take the LifeSpan parameter as an example. If it's set to 60, all particles created will exist on the screen for 60 frames, they'll be born and then die 60 frames later. If you set the LifeSpan Randomness to 50%, the particles will get a random LifeSpan between 30 and 90 frames (60 +/- (60 x 50%)). This is great for allowing you to easily adding a little chaos to your animation, without having to set keyframes and without giving up the control of the overall animation that the grid gives you.

So if we start off LifeSpan with an original value of 60, this is the chart we get:

LifeSpan Randomness Value Range of LifeSpan value
0 All particles have a value of 60
10 54 to 66
50 30 to 90
100 0 to 120


So, in this case, one particle would be born with a life span of 35, another with 78, another with 89, another with 47, etc., etc. Adjusting the Randomness up or down will give you exact control over how much variance you want to see. It's a essentially a built in Wiggler for every parameter. Convenient, but it does make the filter look a bit more daunting than it is.

 


 

How's This Here Grid Work Anyways?


Well, the first thing to know is that it's not really the grid we're working with, it's the empty spaces in the grid. If you look at the grid (Click the 'Show Grid' checkbox in the Grid Setup section), you'll see a bunch of red lines showing you the rows and columns. This is great, but the empty space between the rows and columns is what matters. This is where your particles will be created. This differs from the other two filters, which use where the red lines... but we don't care about that right now

By default, particles can only be created in the empty spaces between the lines (you can change that and we'll talk about how a bit later). Just look at the grid and everywhere you see an empty space, that's a potential location for a particle. If you change the rows to 3 notice how the empty spaces get bigger. That's great, but that means there's less places for particles to be created and making the empty spaces bigger will not increase the size of your particles. Particles have their own size control and the grid spacing won't affect them.

.

So, just remember that every where there's an empty space, that's a POTENTIAL location for a particle to be created. That doesn't mean a particle WILL be created there, just that it's possible. Whether a particle is created in any given location is a result of where the Producer Point is and we'll talk about that next. Also keep in mind that once a particle is created it can move all over the grid, unless you set it up so that it won't (set speed to 0, constrain it to the horizontal and vertical axis', etc).

 

 

The Director And The Producer Point


Let's get moving on this tutorial. We can talk about the producer point as we get things setup. Here's an example of what we're going to do. This is what you should have at the end of this. At the very end, we'll adjust a couple things and do some alternative endings, but basically, this is what we're shooting for.



Click on the image to see the movie (300K).

Jump back to the Grid section and let's set our foundation up. Set the Grid Height to 100, set the Grid Width to 640, set Rows to 3, and Columns to 20. As you'll notice from the movie above, we want the circles to go across the screen in a thin band. There's no need to have the grid bigger than the band, since the circles won't be moving around. So we've set the grid dimensions to the exact size we wanted the band. Since we wanted 3 rows of circles, we've set the grid to have 3 rows. As you'll see shortly, we could set the grid to have more rows and use the Producer Point to limit where the circles get created, but again, since the circles won't be moving around just making the grid have 3 rows is the easiest way to go about it.

The thing to keep in mind if the particles were moving, is that they are only visible on the grid. If the particles go off the edge of the grid they disappear. So there will be plenty of times where you'll want a grid with plenty of extra space around where the particles are being created. If the particles were moving we'd have a larger Grid Height and more rows, to let them have room to move around and remain visible.

The Producer Point controls where the particles get created. If it's really small, all the particles will be created in a single grid space (the empty space between the rows and columns) and will appear to come from a single point. The larger the producer point, the more grid spaces it'll cover, and the wider the area that particles will appear in.

In this case we want particles to be produced all across the height of the grid, but only in a very narrow section of the grid horizontally. Imagine a radar screen with the bright line revolving around it. We want the producer point to be that bright line. Leaving a trail of particles behind it, but only creating particles along the line.

Take a look at the difference between these two images, one with a thin producer point the other with a large one:

Producer Point = 30
Producer Point = 300



Twirl down the arrow for the Producer Point section and set the Height to 100 and the Width to 20. This gives us a tall, thin producer point. As the producer point moves across the screen it'll create particles. This way particles will slowly appear across the screen. Old ones will then slowly fade off.

If our grid was larger than 100 pixels in height, the particles would still only be created in the 3 rows that the producer point occupies as it crosses the screen. This is caused by the fact that the ppoint is still only 100 pixels high, even though the grid is larger. While this isn't important in this case, since the grid is going to remain 100 pixels high, it's still worth illustrating:

ppoint = 100, grid = 100 ppoint = 100, grid = 480


Ok, so now we have a grid that's 100 pixels high and a ppoint that is also 100 pixels high. Let's get particles going across the screen by animating the ppoint. At time 00:00 set the producer point value to 10,320. Move the time marker to 04:00 and set a value of 630, 320.

If you play the animation back now, you'll see that our particles are indeed created as the ppoint moves across the screen. Unfortunately, they don't stay put, and they're all sorts of different sizes.. They're flying around and flying off the edge of the grid. Now you can why you sometimes may want the grid larger than the ppoint.

Particles flying off the grid. Not what we want in this case.



However, in this case we don't want the particles flying around anywhere and we also don't want them all sorts of different sizes.. and we'll deal with that in a second. Before we deal with that, twirl down the Square Setup.

Square Setup is where you set what shape you want to use, where you set up the outlines, set the direction, and set up a few other things. One of those other things is the Grid Unit, which I'm not going to cover here, but make sure you read the manual before changing it.

In this case we want circles instead of squares, so set the Shape pop-up to 32-sided polygon. This creates circular shapes, which works really well for small to medium sized circles. If you want really large circles, go with the 64-sided polygons. While these will appear smoother at larger sizes, the 32-sided polys will render faster.

Since we don't want the outlines on, deselect the Outlines checkbox. That's all we need to do here, so close the Square Setup section.

At this point let's set up the colors that we want the circles to be. Go down to the Color section and twirl open that section.

Change the black color chip to match the blue color chip. Now turn off Colors 2 & 3. This will create a gradient that goes from red to blue. The circles will get their colors from this gradient.

Also, change the transfer mode to 'In Front'. This will cause any circle that gets created in the same grid space to be rendered on top of the one that's already there. If you just leave it at 'Normal' the circles will blend together and create other colors or add together to create white. 'In Front' is really cool and useful transfer mode. I mean, it's tough to get excited about a transfer mode, but this is pretty useful, so if you're going to get excited about a transfer mode, this is it.

Here's how the color parameters should look:



Open up the Square Attributes section (twirl down the arrow next to it).

We need to tell GridSquares what we want the particles to look like and how we want them to behave. For the most part, this is accomplished in the attributes section. Since we want them to stay still, set the Speed to 0.0. This will prevent the particles from moving once they're created. Speed controls how fast they move in a given direction once, they're created. Obviously, with a speed of zero, they're parked at home and ain't going nowhere.
Next, let's make sure all the particles have a nice uniform size. Set the Minimum and Maximum Width to 20 and do the same for Minimum and Maximum Height. What's up with the Min/Max controls? A little further down you'll notice the Horizontal and Vertical Growth Speed. If the Min and Max are different, the Growth Speed controls how fast they grow from the Min size to the Max. However, with Min and Max set to the same size, there's no room to grow, so the Growth Speed is ignored.

Usually, if the Min Width was set to something like 5, and the Max Width was set to 20, the particles would grow from 5 pixels wide to 20 pixels wide. With them both set to 20, all particles start off and end up at 20.

So, at this point, our parameters look like this:




The screen should look like this:



Now that we've got all that set up, let's do a few last tweaks.

If you play back the animation now, you'll notice that there are grid spaces that don't get filled up. We can usually solve that problem by cranking up the Birth Rate a little. Set Birth Rate to 3. This will cause 3 particles to be created every frame and should solve the problem. The more particles being created, the more likely one will be created in every grid space. Since the particles are random, there's no way to guarantee that they'll fill every space, unless you have enough of them being created.

The particles at the end of the stream (the ones that were created first) all seem to fade out evenly. This is ok, but we really want things to look a bit more 'organic' and have them fading out somewhat randomly. To get them to do this, set LifeSpan Randomness to 15. This will varying the LifeSpan just a little bit. For the most part, we want them living for 60 frames, but it'd be better if they randomly got a LifeSpan between say, 50 and 70. By changing the randomness parameter we allow that to happen automatically, without having to set any keyframes. There you have it... better living through plug-ins. ;-)

Now set Fade Out to 10 and Fade Out Randomness to 65. This will further vary the tail of particles. Fade Out is the number of frames that the particles fades out over when it dies off. By giving it a randomness of 65, we create a pretty wide range of possible values that each particle will get. Some will fade out over 3 frames, some over 16. Effectively causing much more randomness in how long each particle is on screen.

All this should give you an image that looks like this:



That finishes off this tutorial. I hope you have a better understanding of how this stuff works. If you have any questions feel free to email me at jim@digitalanarchy.com.


 



Jim Tierney is the creator of Digital Anarchy and has worked on some of the most widely known and respected After Effects plug-in packages out there. Starting at MetaCreations, with Final Effects, and moving on to Atomic Power and their Evolution and Psunami packages . He also worked for Cycore for awhile, but was primarily involved with their 3D software and only remotely involved with Cult Effects. You can visit Jim's website by clicking on his logo to the right.

Please feel free to come to the Adobe After Effects Cow to discuss this technique or others. Or drop into Jim's own Digital Anarchy Forum here at the COW. Jim Tierney is a frequent visitor and contributor.

If you've found this tutorial from a direct link outside our site, please drop by CreativeCOW for a visit. We hope you'll make it your new home.




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