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Particular - Frequently Asked Effects

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Particular - Frequently Asked Effects
A CreativeCOW.net Adobe After Effects Tutorial


Trapcode Particular: Frequently Asked Effects

Mylenium
Mylenium
http://www.mylenium.de
Germany

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Article Focus:
Ever since Particular was released one year ago, many people have developed a keen interest in this tool. However, even after this time many people find themselves confronted with problems. Regular questions on the Trapcode forum here at the COW clearly prove this. This tutorial is meant to explain some of the commonly asked questions and make your life easier by giving a few tips and tricks as well as some simple expressions.

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Example 1: Sky Type

Most people seem to have no idea how this is created. Most often they are looking for a way to change the text and are assuming it is created using a normal font. This is not the case. Create a layer with Particular and apply the t_skytype preset that comes with the plugin install. The simply hit U. All animated parameters for the layer will now be revealed and you will see that everything is just a clever combination of animating the emitter position and emission rate. Isn't it amazing? So you see how useful the U shortcut can be. Perhaps time to memorize it for future work? Still, the process can be made easier which is especially useful if you are intending to write a lot of text this way.

A simple expression

Yes, you guessed it, it's expression time again. But don't worry. This one is super simple but also super useful. Let's first dig into the theoretical side of things a bit.

What is it that we want to do? Our goal is to tie the particle birth rate (Particles/ sec) to how fast our emitter is moving. On the assumption that between strokes our emitter will move very fast because it needs to "jump" to the start of the next stroke, we want no particles being born during that short period of time. For this we need to find out the absolute velocity. Lucky for us, After Effects provides an easy way for this since it will give us the velocity as two separate vector components. All we need to do is create a formula to calculate their combined value. So lets get to work.

Create your layer with Particular and load the t_skytype preset as described above. Delete all keyframes on the Particles/ sec parameter and disable the stopwatch. Now create another layer, which we simply are calling Controller again. Make it a helper layer so it won't render or simply make it invisible by disabling the eye icon. Add two slider expression controls to it and name them Emission Rate and Velocity Cutoff. Now go back to your Particular layer and Alt+click on the stopwatch on the Particles/ sec parameter. This will enable the use of expressions for this parameter. Now add the following lines of code:
cutoff=thisComp.layer("Controller").effect("Velocity Cutoff")("Slider");
rate=thisComp.layer("Controller").effect("Emission Rate")("Slider");
velocity_X=effect("Particular")("Postition XY").velocity[0];
velocity_Y=effect("Particular")("Postition XY").velocity[1];

cutoff_velocity=Math.sqrt(Math.pow(velocity_X,2)+Math.pow(velocity_Y,2));
if(cutoff_velocity <= cutoff && cutoff_velocity > 5)
{rate = rate}
else if( cutoff_velocity <= 5)
{rate = 0}
else (rate = 0);

[rate]
Let me explain what we are doing. The first two lines simply link variables to the two sliders on our Controller layer. The next two lines will create variables for the two velocity components. Next we are calculating the combined velocity by once again using Pythagorean formula. Math.pow(X,2) is the same as X*X and Math.sqrt will take the square root from a value. The last bit is a conditional statement telling After Effects to do the following: If the velocity is lower than our cutoff velocity and larger than 5, emit particles with the rate we have defined by our slider. Is the velocity smaller than 5 (the emitter does not move enough), no particles shall be emitted as well as in all other possible situations (i.e. if the emitter moves too fast). Look at the picture to get some idea what I'm talking about. The red arrow is a velocity that's too high, the yellow arrow is a usable value below our cutoff threshold.



Now play back you animation again. You will see that your emitter will emit smoke, but it looks absolutely screwed and not what we wanted. Even if we tweak our value for Velocity Cutoff it's nowhere near to something usable. We are going to fix this.

We cannot manipulate velocity directly - it's a calculated value already based on the animation we create and After Effects will calculate it for us. So what can we change? We can change our formula. That's not very practical. We could create code to cover a lot of options, but it may still not look right. We can adjust our animation timing without too much trouble, though, and that is the road we take. For this we need some help. Just like the internal velocity values, our calculated value is nowhere readable. In order to still be able to see it, we are building another helper layer for it. This is a simple text layer that we place in our comp (we call it Velocity Info). Add the following expression to the Source text property:
velocity_X=effect("Particular")("Postition XY").velocity[0];
velocity_Y=effect("Particular")("Postition XY").velocity[1];

cutoff_velocity=Math.sqrt(Math.pow(velocity_X,2)+Math.pow(velocity_Y,2));

[Math.round(cutoff_velocity)]
Basically we are just again calculating the velocity again so it can be displayed. The Math.round() will round off our values, otherwise they would be displayed with many digits after the period which is not relevant for our purposes. With that info in place, we are able to easily adjust our keyframes. Move them around in the timeline and see how our values adjust accordingly. Remember: Values below the cutoff velocity will draw a stroke, higher values should only occur between strokes where no particles are required. After a while of experimentation your Type should look OK again, but this time without having to set any keyframe on the emission rate! Now go ahead and paint other words!


Example 2: Fairy Dust

This is another thing that is a bummer for some people. The main problems are as follows:

- How do I tie my emitter position to the position of my talent/ actor/ model?
- How do I manage obscuration?


I'm not going to lay out all the specifics of the project I created and will focus on the above key points. You may dissect and analyze it yourself if you want to explore some of the specific techniques involved. Take a look at the image to get some idea how it is constructed. I used some little plush figure called Rudolfo as a stand-in to avoid any problems with other photos snatched from the web.



Linking the Emitter Position

Theoretically this is very simple, practically it is not. The simple solution is to use the pickwhip and connect both the Position XY and Position Z to the corresponding 3D layer that your talent is. This may work in some situations, but in general it will not yield the result you may be looking for. Why? First, depending on how you have placed your 3D layer, the Anchor Point may not be in the right place. As in our example, where we are working with a Floor layer, the emitter would be placed at the feet. Secondly, all particles would appear as though they are emitted from inside our person. This works quite well if you use your model as the emitter in Layer or Layer Grid mode, but e.g. with a Point emitter it looks funny. In case you are using a Layer emitter type, you also have the disadvantage that your emitter is directly dependent on all the animation of your emitter. Though that can be alleviated by cloning your layer and manipulating it separately, it means yet one more layer to fiddle around with.

The better, and in our case preferred solution, is to create a largely independent emitter that refers to the object's position via some expressions. In our example we wanted to create a spiraling motion that creates some kind of cylindrical veil around our talent. This way the sparkles can appear before our object and since they are around it, it will help to further propagate the illusion of 3D since it will allow you to work with obscuration properly. First off, let me throw the code at you:

Position XY
talent_position=thisComp.layer("Rudolfo a").position;

fairy_radius=effect("Fairy Dust Radius")("Slider");
fairy_speed=effect("Fairy Dust Speed")("Slider");
fairy_rise=effect("Fairy Dust Rising Speed")("Slider");

X=talent_position[0]+Math.sin(time*fairy_speed)*fairy_radius;
Y=talent_position[1]-time*fairy_rise;

[X,Y]
Position Z
talent_position=thisComp.layer("Rudolfo a").position;

fairy_radius=effect("Fairy Dust Radius")("Slider");
fairy_speed=effect("Fairy Dust Speed")("Slider");
fairy_rise=effect("Fairy Dust Rising Speed")("Slider");

Z=talent_position[2]+Math.cos(time*fairy_speed)*fairy_radius;

[Z]
The sliders this time can be found on the Particular layer itself. The math is pretty simple. All we are doing is calculating a circular trajectory in the XZ plane which we incrementally shift upwards so it creates a spiral. For reasons of efficiency we are working with rather few and large particles, but if you decrease their size and increase their number, you can create something like a fairy dust curtain. One thing you will also notice is that we need a separate layer for each instance of Particular. This is not by choice, it's a requirement imposed by the plugin. Unfortunately you cannot use multiple instances of it on the same layer - one overwrites the data of the other so never more than one particle system is visible on any given layer.

Obscure Obscuration

This is the tricky part since it requires some thinking ahead. Basically this option does nothing more than calculate a Alpha mask or stencil based on your scene's 3D layers but it will take into account the distance of the particle from the camera. If you are clever, you can easily circumvent some limitations by memorizing this fact. There are two options for obscuration provided in the plugin interface:

Obscuration Layer

This is a layer freely selectable by you i.e. any 3D layer you want.

Also Obscure with...

Here you can choose additional layers, but they have to be used somewhere in the plugin already. You can use Layer emitters, Floor and Wall layers (in Bounce mode).

In order to avoid certain problems, try to follow those simple rules and keep in mind a few tips and tricks:

As stated in the online help files for Particular, make sure all layers that are referenced by the plugin are below the Particular layer and ideally even below the scene camera. This will help avoid rendering glitches.

Name your layers properly and adjust their label colors. This will greatly improve workflow and help you keep track of what you are trying to achieve. Some parameters will also by default look for certain named items such as a light named Shadow for the Cloudlet/ Smokelet particle types.

Try to build your particle effects around the origin (0,0,0) of your virtual world. Yes, sometimes it will be necessary to move the emitter and animate the camera as well, but move within a limited area. This will help with problems explained later on.
Do not use excessive scene sizes. In theory you can have things infinitely far away, but it may not look that great. You may have to scale objects and increase particle sizes for them to show up at all. In all my time I have rarely needed to go beyond 5000 pixels in all dimensions let alone 10000.

Obscuration does not work with the continuous rasterize/ collapse transformations layer switch. If you e.g. try to build a cube inside a sub-composition and want to use it in your other comp, you have to find ways to turn it into a "flat" 3D layer. This can be achieved by copying all layers into a separate comp (lights, camera) and linking them via simple pickwhip expressions to the motion and parameters of the originals in the main composition. If you have successfully done so, it is easy to place this sub-composition as a 3D layer in the main composition, but leave the little sun switch off.

Similarly, if your scene is rather large and your need to particles encompass a lot of different objects, it may be necessary to use multiple compositions with identical Particular layers, but different obscuration settings. You can always mask out unwanted parts and then later re-assemble everything in another comp. Just make sure you stack your layers in a consistent manner to maintain the illusion of depth. This means that layers farther away should be below the ones that are closer to the camera. Also beware of Alpha issues.


The tips above should take care of most situations. However, sometimes this still is not enough. In such rare cases use duplicates of your 3D compositions in Stencil Alpha (Background) mode or Silhouette Alpha (Foreground) and sandwich your particles between them or use those copies as mattes. Also consider using other masking techniques.


Example 3: Logo Assembly

While it may seem straightforward enough, many people still can't figure out how to approach this type of project. There are a few common traps that people fall for. Here's my take on how to overcome certain problems. As you will see, I have approached things a bit differently from the Belief logo everyone tries to re-create (watch the animation in the gallery at www.trapcode.com).

Some volume, please!

The first thing we need is some thickness to our logo. In this process the Physics Time Factor (PTF) is of key importance. What does it do? Inside the computer there is no such thing as time by default (well, technically even in real life time as we perceive it does not exist, but let's not get philosophical). Time is just another variable or function which is somehow calculated. This means it can be manipulated and tweaked. If it is now a global variable that is referred to by any other function, it is easy to manipulate those functions just as easily. PTF does just that. Think of it as some form of time remapping but working at the root of everything instead of working after all the other functions. So how can we put this to our advantage? Let's create our basic setup.

Create your logo or import whatever file you need for that. On top of that create a layer with an instance of Particular. Set the emitter mode to Layer and crank up the number of particles a bit. Use the Cloudlet or Smokelet particle type. Adjust other parameters as you see fit. Scrub you timeline or create a preview and you will see particles emanating from your layer. We now have some volume, but it does not look like a massive logo because everything moves all the time. Worry not, PTF comes to the rescue! Create a keyframe for this parameter at the start of your animation with the default value of 1. Now move to a point where enough particles are already emitted and your logo looks like it's made up of little smoke puffs. At this point set PTF to zero. This now means that from this point on all particles stop their motion, won't change their Color over Life and Opacity over Life and so on because time has stopped until we tell the clock to tick again by setting another keyframe with a non-zero value. Your composition should look something like that:




Everybody spread out!

If you remember the animation from the Belief logo, you will see that it starts out as a field of clouds. How can we achieve that? The easiest, but also least controllable way is let our particle simulation run again by turning on time again. So just create keyframes for the PTF. The result may look rather wild, so here is a counter-proposal: Don't use any Velocity on the emitter and instead let forces do their thing! You can choose between quite a few, ranging from Wind for directional motion to Gravity to Turbulence in two flavors. For our purposes the Spin Amplitude that can be found under the Air physics model is most suitable. It will take our particles and move them in a swirling fashion. In order to be able to fly through our field of clouds, the particles should be apart quite a bit, so use large values. Once you have found suitable values and a frame, where everything looks nice, use PTF again to freeze you particles in space. You should now have a frozen spread of Cloudlets which you can fly around with your camera.



Basically you are now set to create your animation - you have some mysterious clouds that once were a logo. All that is left to refine everything by tweaking a few other parameters. But wait - aren't we missing something? Yes! Time to...

...flip-reverse it!

Exactly! Take your composition and drop it into another composition. Choose Layer -> Time stretch and set it to -100%. This will play your entire layer in reverse. But hey "Mum, I'm lost.". Yes, you will feel some disorientation. How good, After Effects has a marker system that will help us keep track of time. Go back to your original comp and add some timeline markers by dragging the little symbol (yellow circle) to the proper position (red circle).



Now delete your time-reversed instance of the composition or replace it with itself by Alt-dragging it onto the timeline. Just like magic our timeline markers have turned into layer markers.



This will greatly help you to adjust the timing. In most instances you will only need two markers at the start and end of your particle animation, but you can use more if you need them.

Polishing the chrome

With everything in place, you can now focus on integrating everything with the rest of your design. Normally this means animating the camera and applying other effects. When you use motion, keep in mind that everything you do in your composition with the Particular logo must be reflected time-reversed in your other composition(s). This can be automated using expressions, but to keep things simple, you should resort to the Time-Reverse Keyframes keyframe assistant. Other things I did include the following:

- I used two layers of Particular - one for the logo, another for the clouds. I wanted larger clouds than the logo puffs allowed for. I combined them by manipulating Opacity over Life and applying a Box Blur with animated parameters.

- I used an animated Hue/ Saturation effect to get rid of too intensive colors in the clouds.

- I added a normal instance of the logo as a 3D layer which I then faded in using animated Opacity, the Turbulent Displace and Roughen Edges effect.

Don't give too much consideration too my camera animation and a few other things. I know that they are not the best and are only for demo purposes. I'm sure you will come up with much better results. Perhaps you will share them with the rest of the people here at the creativeCOW and post a few images? in the meantime: Enjoy and feel free to ask your questions
regarding this tutorial in the After Effects forum at Creativecow.net



Please visit our forums at Creativecow.net if you found this page from a direct link.

Comments

Re: Particular - Frequently Asked Effects
by Gibber Magash
First off, I think there is a spelling error in your code. It says Postition instead of Position. I also keep getting the "Couldn't find effect 'Particular'" Error on the Velocity Layer "Source Text". I'm not sure what that is about. Perhaps you might have some advice.
Particular - Frequently Asked Effects
by Ralph Pritchard
I couldn't get my sky smoke to show. As soon as I put in the code the smoke stopped displaying. I followed your instructions to the letter but am mystified.

Ralph


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