##### Tutorial #2

In the first tutorial we made an emitter move between a few points on the stage, but only in a straight line. What if we want the emitter to follow a more complex curved path?

To pick up where we left off, load the project that you saved at the end of the first tutorial. Select Open from the File menu, click the OPEN button on the main toolbar, or select the filename from the list of “most recently used” filenames on the File menu.

Before we add some curves to the emitter motion, wouldn’t it be nice to see what the emitter was doing while we are making changes? Well you’re in luck. You can turn on a “particle preview” by clicking on the SHOW PARTICLES button on the main toolbar.

You should now see all of the particles that this emitter has created. (If you don’t see any particles, jump to a higher frame number. If you still don’t see any particles, jump to a lower frame number since some emitters do not emit continuously.) A warning: depending on the speed of your computer and the number of particles on the stage, SHOW PARTICLES may cause a dramatic slowdown when redrawing the stage.

Okay, now let’s make a curve. Jump to frame 30 (the second position key of the project from tutorial #1). Now R-click on the emitter in the stage window. The menu that is displayed should look like this (if it doesn’t then make sure that the emitter is at a position key frame – use the Up/Down arrow keys):

For now ignore all of the other menu functions except for the Curved item. (This item is only visible when at a position key.) Click the Curved item. You have just converted the position key from a linear key to a curved or “spline” key.

There are three indications that a key is curved: 1) The path is now visibly curved on the stage; 2) R-click on the emitter again – the Curved item is now checked. 3) There are two spline controls visible.

##

## These spline controls can be clicked and dragged to change the curve of this key. Click on one of the controls (the small points at the ends of the dotted line) and drag it around. You can see that the controls move together when one of them is dragged – this is due to the fact that they are Connected by default. If you R-click on the spline control or on the emitter (while at a Curved position key) the Connected menu item is now enabled. If you select the Connected item, the control points become disconnected, and no longer move together.

##

## You’ll notice that once you disconnect the control points the Connected menu item is no longer enabled. How do you make the controls Connected again? You need to toggle the key linear (non-Curved), then back to Curved again.

There are shortcuts to the Curved and Connected functions that do not require the use of the context (R-click) menus. If you Alt-Click (hold down the Alt key while L-clicking) on an emitter when it is at a position key, it will toggle between linear and Curved. Similarly if you Alt-Click on a spline control, it will change from Connected to disconnected. ( that once it is disconnected, the only way to get it Connected again is to toggle it linear then Curved again.)

Did you try moving the emitter around when at the frame 30 position key while the key was Curved? Did you notice that when you moved it around the stage the path segments between the first and last position keys “followed” the key you were moving? Not sure what that means? Okay, jump back to frame 1. Change the position key at frame 1 to Curved (so now there are two position keys that are curved). Now jump back to frame 30 and move the emitter around the stage. Notice the difference in the way that the path segment between the first key and the key you’re moving behaves?

The image on the left is with the first position key linear (non-Curved) and the image on the right is with the first position key Curved.

If you are moving a position key around and notice that part of the path is not behaving as you expect, you should check the Curved state of the adjacent position keys. Just something to keep in mind.

# Easy does it!

Let’s go back to linear keys for a minute. If you look at the frame positions (dots) between two linear keys, you’ll see that they are equally spaced. That is, the emitter moves the same amount at each frame. What if you want the emitter to start moving slowly, then move more quickly? (Some applications refer to this as “ease in/ease out”, or as acceleration.) In Illusion there is no specific setting to accomplish this – but you can get the same results in many cases. How? By changing the keys to Curved, and adjusting the spline control points to get the frame spacing we want.

Start by reloading the same project file you loaded at the start of this tutorial. Change the first and second position keys to Curved (use the Up/Down arrows to move between them). Make the spline controls of the second position key Disconnected. Now move the control point for the first key so it is approximately on the line between the first and second position keys, and is about 1/3 of the way between the two. Do the same for the spline control of the second key (remember that spline controls are only visible when the emitter is at the position key). The result should be a very close approximation of a linear segment between the keys (as if they were both non-Curved).

Now to get the evenly-spaced dots the way we want them (closer together near the first key, and farther apart near the second key) we just need to drag the control point for the first key closer to the first key, and the control point for the second key farther from the second key. Here’s one way it could look:

So it’s possible to approximate the acceleration that we wanted.

Okay, so now we know how to make an emitter move both linearly and along a curved path. What if we need to make precise adjustments to a position key, for instance if it is slightly out of position from where we want it to be? That’s where we use the NUDGE buttons (on the nudge toolbar):

Clicking one of the NUDGE buttons moves the emitter one pixel in the direction the button indicates. Note that this is another way (besides dragging or using MOVE) to move an emitter. Remember that whenever an emitter is moved (even if only one pixel) and it is not at a position key, a position key will be created.

If we need to create a position key at the exact spot that an emitter is currently at – we wouldn’t try to use MOVE or drag the emitter. We would use NUDGE instead (we can NUDGE the emitter up then down and it will be at the same position, but a position key will have been created for it).

Let’s say we’ve just spent quite a bit of time adding position keys, moving them, nudging them and adjusting them until they were just right. Now we’ve realized that we’d like the entire path of the emitter to move some amount – we want the path to keep it’s same shape, but want it to start at a different location. It would take too much effort to move each individual position key, so what can we do? The solution is simple: hold down the CTRL key while you click and drag the emitter. This will move the entire emitter path without creating any position keys.

Note: you might find that turning off SHOW PARTICLES before using this trick makes things more responsive and therefore easier to position.

# Undo what you do

Suppose while you were trying that last trick of moving the entire emitter path (by holding the CTRL key) you released the key too early, and ended up creating a position key when you didn’t want to. How can you get rid of that key you just created? There are a few ways to do it.

One of them is to just delete the key from the stage. With the emitter at the position key, press Ctrl+D. This will delete the position key. Note that if you press Ctrl+D when not at a position key, nothing will happen. Also, you can’t delete the first position key (every stage object has a position key at frame 1).

There is also a way to delete a position key using the graph window, but we’ll cover that later when we talk about the graph window in depth.

The most “universal” way of fixing any mistakes you make (such as creating a position key that is not wanted) is to use the UNDO function. Most applications include some sort of Undo function, so the concept is probably not new to you. If you are not familiar with Undo, it simply reverses the last change or changes that you made. There is usually a REDO function that goes along with Undo, which restores the change – essentially an Undo of the Undo.

Illusion supports multiple Undo/Redo actions. To Undo, select Undo from the Edit menu or use the keyboard shortcut of Ctrl+Z. Do it now and see what happens to the emitter on the stage. Undo a few times in a row and you’ll see the last changes you made being reversed. Ok, now try Redo. Select Redo from the Edit menu, or use Ctrl+Y. Redo until you can Redo no more.

Only changes made to the stage or to the graph window can be Undone in Illusion.

When you use Undo, Redo is available until you make some new change to the project. The new change “overwrites” the actions that were Undone, making them no longer available for Redo. A little example to illustrate this. Let’s start a new project. Click on the NEW button of the main toolbar:

If your existing project hasn’t been saved, you will be asked if you want to save the project first. Then the project will be reset to its default state (the stage will be cleared). Note that you can’t Undo NEW, just as you can’t Undo OPEN or SAVE.

So we now have a clear stage. Select the Heavy Fire Sparkles library emitter again and add it to the stage (anywhere). Now move the emitter to another location on the stage (still at frame 1). Now jump to frame 20 and move the emitter somewhere else on the stage.

At this point we have three actions that can be Undone: 1) Adding an emitter to the stage 2) Moving the emitter 3) Moving the emitter and creating a position key. You should be able to use Undo three times, and end up with an empty stage again. You can Redo three times as well to get all of the changes back. Use Redo until all changes are back. Now Undo just one time – you should have the emitter at a single position on the stage.

Now just L-click somewhere else on the stage (not on the emitter) to add a second emitter. Our list of Undoable actions has just changed. It is now: 1) Adding an emitter to the stage 2) Moving the emitter 3) Adding a second emitter. Use Undo and Redo to see that the action of moving the first emitter to create a position key is no longer available. It has been overwritten by the action of adding the second emitter.

By default Illusion is set to keep 20 actions in the Undo list. If you want to be able to Undo more actions, you can change this number in the Preferences dialog (which we’ll talk about in a later tutorial). Note that setting this value higher requires more memory.

# Project Settings

We’re about to start digging into the “guts” of an emitter, but before we do let’s take a look at something completely different: the Project Settings dialog.

Click on the PROJECT SETTINGS button of the main toolbar:

This will open the Project Settings dialog:

Here you see the settings for Motion Blur (which we will leave for later), output frame rate for the project, background color for the stage and preview window, and stage size.

The frame rate value determines how many frames per second Illusion will display for playback and when saving output. Important: some emitters look quite different at different frame rates. Therefore, it is important to set the frame rate before you start doing any work on the stage with emitters, or you may not get the results you want.

The background color setting shows the current color of the background of the stage (and preview window). To change the color, just click on the color and a color picker dialog will be shown:

You can select the color by clicking and dragging in the two color windows, or by entering the color component values directly.

A note about background color: some particles (flagged as “intense” which will be covered later) look best on black backgrounds.

The Stage Size settings determine the size of the stage, which is the area that will be saved when saving output, and is the only area that displays particles. The drop-down list shows several common stage sizes. You can also directly enter the width and height values. If there is a stage size that you would like to add to the drop-down list, enter the values for width and height, then click the Add button. If there is a stage size in the list that you will never use and want to delete, first select it from the list, then click the Del button.

You can also view or edit the Project Notes using the Notes button. The Project Notes are a great place to store information about the project, and can hold quite a bit of text. (The Project Notes are also accessible from the main View menu.)

A note about frame rates. The windows that animate (the stage during playback, and the preview window when displaying a library emitter) will attempt to match the project frame rate. In many cases, the actual frame rate may be lower than the project frame rate. The status bar at the bottom of the Illusion window displays the achieved frame rate followed by the project frame rate in parentheses.

The achieved frame rate is determined by the speed of your computer, the presence of 3D video hardware, the number of particles, and (especially without supported 3D hardware) the size of the particles being drawn. There are other factors involved too, but they involve things that we have not covered yet (the presence of deflectors, blockers, and background images all have an effect on playback speed).

The Motion Blur options that we skipped earlier can be used to add more realism to animation. If you’ve ever seen a photograph of something that is moving quickly, you know that the image appears blurred. Fast-moving objects whether on film or viewed with the naked eye are usually not sharp – they are blurred. Because we understand this fact, fast-moving particles in Illusion should also blur in order to look more realistic.

Start a NEW project and add the Shooting Star emitter to the stage. To add motion blur to the project, simply check the Enable box in the motion blur options section of the Project Settings dialog. We’ll see a few more options appear.

Extra Frames is the number of frames that are averaged to produce the blur effect – the higher the number the smoother the blur, but the more time it takes to draw them.

Blur amount controls the amount of the frame over which the blur occurs. When set to 100%, the particles are blurred over the entire interval between the current frame and the next one. If set to 50%, the particles are blurred over only the first half of the interval between the current frame and the next one.

When particles flagged as “intense” (covered later) are motion blurred, the result may be a change in intensity of these particles. The Intensity Adjust slider is used as an additional scale factor to be applied to the visibility of “intense” particles only in order to help counteract this intensity change due to blurring.

### Digging In!

Okay, now we’ll start digging in to the “guts” of emitters and look at the properties that determine how they act, and also how the particles they emit will look and behave.

Clear the stage using the NEW button. Now select the Heavy Fire Sparkles emitter again. (I know – there are so many cool emitters to choose from! Why do we keep using this one? We just want to start with something simple at first so things don’t get too confusing.) Add a single emitter anywhere on the stage. Turn on SHOW PARTICLES and jump to frame 30. Now turn your attention to the Hierarchy window:

From this we can see that there is a single layer in the project (we’ll cover layers in a later tutorial), there is a single emitter on the layer called “Heavy Fire Sparkles 1”, and this emitter has a single Particle Type called “fiery”.

(When emitters are added to the stage, they will be given a name that is the library emitter name plus a number. This is to try and keep things straight when more than one emitter is on the stage. You can rename the emitter to something more meaningful to the project by clicking on the emitter name in the Hierarchy Window.)

Remember that emitters are made up of one or more particle types, and the particles that this emitter will emit are based on the settings of those particle types.

We won’t cover them in depth here, but let’s take a quick look at the particle type properties. Either double-click the “fiery” particle type or L-click on the little plus sign to the left of the work “fiery”. Now you should see all of the particle type properties. What’s important to note right now is that some of the particle type properties (the ones with the cyan and purple icons) have the same names as some of the emitter properties. The emitter properties (life for example) are a global “scale factor” that applies to the life settings of each of the particle types in the emitter. We’ll discuss this in depth in the next tutorial.

Okay, forget about the particle type properties for now. Now we’ll see how the hierarchy window and graph window work together. Click on Heavy Fire Sparkles 1 in the hierarchy. Now look at the graph window. It should show:

This shows the graph of the position keys that we were working with earlier.

Jump to frame 30 and drag the emitter to another point on the stage. You should now see a second position key in the graph window:

This should all be familiar from the earlier examples. Now something new. Suppose we wanted that position key to be at frame 40 instead of frame 30. One way to do that would be to Undo, then jump to frame 40, then move the emitter again. An easier way is to use the graph window. Just L-click on the position key at frame 30 (in the graph window) and drag it until it is at frame 40. That’s it. You’ll notice the stage change as well when you make this change – the density of the dots on the path segment will change because you are changing the number of frames over which the position of the emitter changes.

If you had a motion path of 2 segments (let’s say the one key is at frame 30 and the other is at frame 60) but the distance moved in the second segment was much smaller than in the first segment, the emitter would move more quickly over the first segment, then more slowly over the second. What if you want the emitter to move at the same speed over both segments? You can approximate this by dragging the middle position key in the graph window until the dots in both segments (looking at the stage) appear to have the same spacing.

Note that when the position keys are being displayed in the graph window, the graph is titled “Position” and the graph is shown as a horizontal line graph. If you click on the graph, nothing happens. The position graph is a special case – position keys are added via the stage, not using the graph. Let’s look at the graphs of some other properties.

Select the emitter Size property in the hierarchy window, and jump to frame 30. Turn on SHOW PARTICLES if it isn’t already.

You can see that the size graph is a horizontal line with a Y-value of about 73. What does this mean? Since this is the emitter size graph is a scale factor that is applied to all of the particle types it contains, this example shows that the size of the particles will be 73% of whatever size they were set to in the particle type size property.

The Y-axis values on graphs that display numbers along the Y-axis should be interpreted as percentage.

(Since the line is horizontal, we can also tell that the size value remains constant over all frames – more on this shortly.)

Now L-click on the red point in the graph window and drag it up and down. While you’re dragging it, notice the effect it has on the particles on the stage – they’re getting bigger and smaller. Okay, now drag it to about 70 again.

L-click in the graph window at about frame 60. You’ll see that a new graph point has been created. This is a key frame, very similar to the position keys that we’ve already created. The difference is that this key is a “data key” instead of a position key since a data value (size) is changing instead of position. “Data key” is the generic term for these keys created in the graph window – we’ll refer to them more specifically as the type of data they represent. In this case the key will be called a “size key”. As with position keys, at least one data key will exist for each property, and it will usually be at frame 1.

So now you should have a graph with two size keys (points) on it. Drag the second key so it is at frame 60 with a value of about 10%. Drag the current frame indicator so you can see what happens as the frames increase. What you should see is the particles eventually getting smaller and smaller. Important: Graphs that show frame numbers along the X-axis show values of properties for the particle at the moment the particle is created. They say nothing about what an individual particle will do over time.

In our example, particles created at frame 1 will have a size scale of about 70%. Particles that are created at frame 60 will have a size scale of about 10%. Particles that were created at frame 1 that may still be around at frame 60 still have a size scale of about 70%. Understand? Most of the graphs of emitter and particle type properties represent the values at the time the particle is created only. The only exception to this is the particle type graphs of properties “over life”. We’ll discuss that when we get into the particle type properties.

Okay, just click in the graph window and create a few more size keys – you can position them wherever you want.

The data key that is red is the selected data key, which will be important in a minute. Right now just L-click a data key and drag it left and right. Notice that it can’t be dragged past any neighboring keys. Also note that the first data key is fixed at frame 1.

Now why is one key selected (red)? Select any key except the first and then R-click anywhere in the graph window. You’ll see this menu:

Select the Delete menu item. The selected key has been deleted (remember that you can Undo changes made to the graph window).

What do the other menu items do? Reset simply deletes ALL keys from the graph (except the first). An interesting thing about using Reset when the position graph is being displayed – Reset causes all of the emitter position keys (except the first) to be deleted, but it also positions the emitter in the exact center of the stage.

The Scale function displays the following dialog:

This function allows you to either compress or expand the values or frames of the graph. For example if we wanted to double the values of each key of the graph we would select Scale Values (y), set the scale factor to 200% and click OK. If we wanted the changes to occur over a shorter number of frames (compress the time) we would select Scale Frames (x) and enter an appropriate scale factor – we’d use 50% to make the changes occur in half the length of time. (Note that only Values OR Frames are scaled when the OK button is pressed. Selecting Values and setting a scale factor then selecting Frames and setting a different scale factor then pressing OK scales the frames only.)

The Zoom menu function allows you to zoom in or out either Y (values) or X (frames). Zooming out allows you to see more of the graph, while zooming in is useful for more precise positioning.

The Reference menu function allows you to create a visible copy of the graph so you can coordinate the graphs of other properties to the graph of the referenced property. Let’s look at an example. With the current size graph selected, R-click and select Reference, then Create A. Then in the hierarchy window select emitter Velocity.

There are two reference graphs available, A and B. If a reference graph has been created, it can be toggled on/off using the Show A (or Show B depending on which graph you’re interested in) function. When a reference graph has been created it will be displayed in either light purple (A) or light green (B) and its title will show in the upper right corner of the graph window.

In our example you can see the size graph drawn as Reference A, and the velocity graph as the current graph. Now it will be a lot easier to coordinate changes in velocity to changes in size.

Note that the reference graph is just a snapshot image of the graph. If we were to go back and change the size graph, the reference graph we created from the size graph would not change.

Here’s a quick summary of the graph window. For the majority of graphs (except for position) you create a data key by clicking in the graph. You can drag data keys around, and can delete keys. You can zoom the graph, and create reference graphs. You can also scale the values or frame numbers of the data keys in a graph.

What if you want to move more than one data key at a time? You can’t select more than one data key in Illusion, but it IS possible to move all of the keys in a graph at once. To do this, hold the CTRL key before clicking and dragging a key. The mouse cursor will display the word “all” so you’ll know that you’re moving all of the data keys. Now just drag as usual. Once you’ve clicked, you no longer need to hold the CTRL key.

One other thing to point out about the graph window that you may have already noticed. When dragging a data key, the window will scroll automatically when you reach its edge. Obviously, you can also use the scroll bars to scroll the window.

# Back to the Hierarchy

Now that we know how the graph window works, let’s take a look at some of the things it will show. We’ll end this tutorial with the emitter properties that are available in the hierarchy window, and start the next tutorial with an examination of the rest of the emitter properties and the particle type properties.

The first group of properties are the emitter scale factors for the corresponding particle type properties. Life is how long a particle exists; Number is how many particles are created; Size is how big the particles are; Velocity is how fast the particles travel; Weight controls how fast the particles fall or rise; Spin is the amount of rotation that the particles have; Motion Randomness is how much randomness is applied to the particle motion; Bounce is how much the particles bounce when hitting a deflector.

(Remember that these emitter properties listed above are “scale factors” that are applied to every particle type of the emitter, and the values (y-axis) are percentages. If the corresponding particle type property is set to 0, then it does not matter what the emitter property is set to – the result will be 0. This will become apparent later, but it is an important point.)

The Zoom property is also a scale factor, but there is no particle type Zoom property. So what does it scale? Zoom scales both the particle type size and velocity to give the appearance that the particles are farther or closer to the viewer. Let’s start a new example to demonstrate this.

Start a new project (click NEW). Now select the Simple Explosion emitter. Before you add it to the stage, let’s try something new. Every emitter we’ve added so far has been added at frame 1, but that’s not necessary. You can add an emitter to the stage at any frame you want. It will not activate (start emitting particles) until the frame that you added it at.

Jump to frame 10. Now add an emitter toward the left side of the stage. Now jump to frame 30. Add a second emitter of the same type near the center of the stage. Now jump to frame 50 and add a third emitter near the right side of the screen. Rewind to frame 1 and press PLAY. You should se a series of three explosions, time delayed from each other. You should see that the hierarchy window now has three emitters in it, and that each emitter contains five particle types. There is a lot of data in the hierarchy window right now. Just ignore it for now, and let’s adjust the zoom settings.

# Natural Selection

We want to select the first emitter we placed on the stage. There are three different ways to select an emitter (when multiple emitters are on the stage). First, we can just click on it on the stage. (Don’t double-click it or you’ll be jumping ahead to the next tutorial.) This is the most common way of selecting an emitter, but it doesn’t always work. When two or more emitters are right on top of each other, it can be impossible to use the mouse to select the emitter you want. The second method of selecting an emitter is to select the emitter in the hierarchy window. By clicking on the emitter name or any of its properties, the emitter will be selected on the stage. (In the same way you may have noticed that when selecting an emitter via the stage the emitter becomes selected in the hierarchy too.) The third method for selecting an emitter is to use the keyboard shortcut of the TAB key to cycle between emitters. You may also use Shift+TAB to cycle through in the reverse order. Note that these keys only cycle through the emitters that exist on the same layer (layers will be covered later).

So select the first emitter using any of the three methods you prefer. Now select the zoom property in the hierarchy window. Make sure you select the zoom property for the correct emitter. If you don’t then you will see a different emitter selected on the stage.

Now look at the graph window. The zoom graph should show a horizontal line at 50%. Jump to frame 20 and make sure SHOW PARTICLES is on. Grab the key at frame 1 and drag it down to a value of about 20%. Notice that the entire explosion appears to get smaller, as if it is farther away. Now jump to frame 60 and select the third emitter (the one near the right side of the screen). Change its zoom graph so it is a horizontal line at about 100%. It should appear much larger as if it is closer to the viewer. Now REWIND to frame 1 and PLAY. You should see the same series of time delayed explosions, but now the first appears to be far away, the second is closer, and the third is right in your face!

You probably noticed that during playback the third explosion “covered up” part of the second one, which added to the illusion that the third blast was “closer” than the second. It’s important to note that emitters are drawn in the order they appear in the hierarchy window. The topmost emitter in the hierarchy is drawn last (on top). When we discuss layers, the same rule will apply – layer on top is drawn last (it’s closer to the viewer). The same goes for the particle types in an emitter – the topmost particle types are added last – although this does not always make a difference with particle types.

What if we wanted to make the second explosion the “closest”, and the third appear to be further away? First let’s change the zoom of the third emitter so it is 50% again (you can just use Undo). Then change the zoom of the second emitter to 100%. If you press PLAY you’ll see that it’s just not right – we need to change the order of the second and third emitters so the second emitter draws last. This is easy.

First, just collapse the hierarchy so it’s easier to look at. (Click on each of the small minus signs.)

Next R-click on the second emitter (Simple Explosion 2).

Ignore all of the menu items except for Move Up and Move Down for now. Since we want the explosion to be drawn last, it needs to be moved to the top of the hierarchy. Therefore, select the Move Up function. Since the emitter is now “on top” of the other two emitters, we’re finished.

REWIND and PLAY, and the second explosion should now appear to be the closest.

(When you R-Click in the hierarchy window, you don’t need to click on the emitter name. You can click on any part of the emitter, including the particle type or its properties, and the result will be the same. That is to say the menu that is displayed always applies to the emitter.)

We’ll save this project now. Select Save As from the File menu, and save this file as “Tutorial 2”.

Now that we’ve covered Zoom, let’s get back to the rest of the emitter properties in the hierarchy window.

The Visibility property controls the overall transparency of the emitter. The visibility of each particle type can also be set, so the emitter visibility is again a scale factor that is applied to each particle type. Select the visibility of one of the explosion emitters that are on the stage right now. Reduce its value and see how that affects the particles.

The Tint Strength property determines how much of the emitter tint color is blended into the particle type colors. The default tint color is gray (we’ll see how to change the tint color in the next tutorial) so you can adjust this value and see how the particles get tinted gray. Tinting is usually the easiest way to change the color of an emitter’s particles. Tinting can also be used to help simulate distance – applying a slight blue or gray tint to an emitter may make it appear to be more in the distance (when used in combination with the visibility and zoom properties).

The Emission Angle and Emission Range properties determine the direction in which particles are emitted. The best way to illustrate this is with another example. Start a NEW project, then select the Super Colorful emitter. Place it near the center of the stage. Jump to frame 80 or so and make sure SHOW PARTICLES is on.

Now select the emission range property. You’ll need to scroll the graph window up or zoom the graph window out until the data key at 360 (degrees) is visible. Drag the data key down to about 60 degrees. (Note that the units for the values on the y-axis of angle graphs are degrees instead of percent.) The particles are confined to a “beam” instead of emitting in all directions.

Now select the emission angle property. As you drag the data key up and down, you’ll see the beam of particles sweep around.

Let’s do a simple animation of the beam of particles completing three complete revolutions in 120 frames. First drag the initial data key down to 0 degrees. Now click on the graph window at frame 40. Drag the new data key up to 360. The beam has now completed one revolution in 40 frames. How do we make the second revolution? Just click on the graph somewhere around frame 50, then drag this new data key down to 0 and to the left. The data key can’t go past the frame of the previous key, so you’ll end up with a key at frame 41 with a value of 0. Now click at frame 80 and drag the key up to a value of 360. The graph window should look something like this:

REWIND and PLAY. You should see the beam of particles create a spiral pattern as the emitter makes two complete revolutions.

Repeat the process to add the third revolution: add a key at frame 81 with a value of 0, then a key at frame 120 with a value of 360. That’s it! The emitter now makes three revolutions in 120 frames as we intended.

Note that if the emitter rotated faster, there could be a visible pause when the beam reaches the 0 angle. This is because the emission angle is at the same value (0) for two frames in a row – the key with a value of 360, and the key at the next frame with a value of 0. The solution is to move the key with a value of 0 so it has a value of 5 or 10 – whatever is appropriate to get rid of the pause.

The Active property determines when an emitter is on (creating particles). In the “Tutorial 2” example with the three explosions, we added emitters at frames 10, 30, and 50. Load that project now and look at the active graph for each emitter. The active graph for the second emitter looks like this:

Since the emitter was added at frame 30, the emitter doesn’t go active until frame 30.

The active graph is different from the other graphs in that the first data key is not tied to frame 1. Also, every additional key added causes a toggle between active and inactive (on and off). Back to this in a minute.

If the active graph is used to turn an emitter on and off, why doesn’t the graph above show the point where the emitter turns off? The explosion emitter obviously stops emitting points 15 frames or so after it starts emitting. How can this be? The Simple Explosion emitter doesn’t stop emitting points by using the active graph – it uses the number graph. Here’s the number graph for that emitter with the active graph as a reference graph:

You can see that after only about 5 frames the number of particles starts decreasing to 0%, and by 10 frames after the start of the explosion there are no more particles being added.

The reason the active graph was not used to stop emitting particles in this case is that when an emitter goes inactive, all of its particles immediately disappear. Since the particles created in the explosion need to linger and fade out, we couldn’t use active to turn the emitter off. There will probably be very few cases where you will want to use the active graph to turn an emitter off.

The final emitter property available in the hierarchy window is Angle. This property does not usually apply to point emitters, and we haven’t talked about line and elliptical emitters yet, so we’ll come back to this in a later tutorial. If you’d like a quick example of an emitter that changes angle over time, look at the Sparkle Twirl emitter.

We’ll continue our look at the emitter and particle type properties in the next tutorial.