Particle Playground effect



The Particle Playground effect lets you animate a large number of similar objects independently, such as a swarm of bees or a snow storm. Use the Cannon to create a stream of particles from a specific point on the layer, or use the Grid to generate a plane of particles. The Layer Exploder and Particle Exploder can create new particles from existing layers or particles. You can use any combination of particle generators on the same layer.

David Van Brink provides a video walkthrough and downloadable example project on the omino website that show several things that you can do with the Particle Playground effect, including how to use the Kinetic Friction ephemeral property mapper.

Brian Peterson provides a tutorial on the Videomaker website that shows how to use the Particle Playground effect to create a flock of birds.

This effect works with 8-bpc color.

Particles shooting out of the spacecraft layer (upper-left), text characters used as particles shooting out of a ray gun (lower-left), and Layer Exploder used on spacecraft layer (lower-right)

Start by creating a stream or plane of particles, or by exploding an existing layer into particles. Once you have a layer of particles, you can control their properties, such as speed, size, and color. You can replace the default dot particles with images from an existing layer to create, for example, an entire snowstorm from a single snowflake layer. You can also use text characters as particles. For example, you can shoot words across the screen, or you can create a sea of text in which a few letters change color, revealing a message.

Use Cannon, Grid, Layer Exploder, and Particle Exploder controls to generate particles. Use Layer Map controls to specify a layer in place of each default dot particle. Use Gravity, Repel, and Wall controls to influence overall particle behavior. Use Property Mapper controls to influence particle properties. Use Options to set options, including options for substituting text characters in place of dots.

Note: Because of the complexity of Particle Playground, you may experience long computation, preview, and render times.

Use Particle Playground

  1. Select the layer on which you want particles to exist, or create a new solid layer.
  2. Choose Effect > Simulation > Particle Playground. The layer becomes an invisible layer in which only the particles are visible. Animating the layer in the Timeline panel animates the entire layer of particles.
  3. Set up a particle generator to determine how particles are created. You can shoot a stream of particles from the Cannon, generate a flat plane full of particles from the Grid, or use the Layer Exploder to create particles from an existing layer. If you’ve already created particles, you can apply the Particle Exploder to explode them into more new particles.
  4. Select your particles. By default, Particle Playground creates dot particles. You can replace the dots with a layer already in the composition or with text characters you specify.
  5. Specify the overall behavior of some or all particles. Use Gravity to pull particles in a specified direction, Repel to push particles apart from or toward one another, or Wall to contain or exclude particles from a certain area.
  6. Use a layer to specify the behavior of individual particles. You can modify controls that change particle motion, such as speed and force, and controls that change particle appearance, such as color, opacity, and size.

    The Particle Playground effect renders with anti-aliasing when the layer to which it is applied is set to Best quality. It also applies motion blur to moving particles when both the Motion Blur layer switch and the Enable Motion Blur composition switch are on.

    When you use a layer as a source for particles, Particle Playground ignores any changes you’ve made to that layer within that composition, such as changing the Position values. Instead, it uses the layer in its original state. To keep changes for a layer when you use it as a particle source, precompose the layer and use the precomposition layer as the control layer. (See Compound effects and control layers.)

Particle content and particle generators

Particle Playground can generate three kinds of particles: dots, a layer, or text characters. You can specify only one kind of particle per particle generator.

Create particles by using the Cannon, the Grid, the Layer Exploder, and the Particle Exploder. The Grid creates particles in an organized grid format with straight rows and columns. The exploders create particles randomly, like firecracker sparks.

The particle generators set the attributes of particles at the moment they are created. After creation, Gravity, Repel, Wall, Exploder, and Property Mapper controls influence particle behavior. For example, if you want particles to stick to grid intersections, you might use the Static Friction option in the Persistent Property Mapper to hold particles in place. Otherwise, as soon as particles are created, they begin moving away from their original grid positions.

Cannon controls

The Cannon is on by default; to use a different method to create particles, first turn off the Cannon by setting Particles Per Second to zero. The Cannon creates particles in a continuous stream.

Position
Specifies the (x,y) coordinates from which particles are created.

Barrel Radius
Sets the size of the barrel radius for the Cannon. Negative values create a circular barrel, and positive values create a square barrel. For a narrow source, such as a ray gun, specify a low value. For a wide source, such as a school of fish, specify a high value.

Particles Per Second
Specifies how often particles are created. A value of 0 creates no particles. A high value increases the density of the particle stream. If you don’t want the Cannon to fire continuously, set keyframes for this control so that the value is 0 at the times when you don’t want to create any particles.

Direction
Sets the angle at which particles are fired.

Direction Random Spread
Specifies how much each particle’s direction deviates randomly from the cannon direction. For example, specifying a 10-degree spread sprays particles in random directions within +/–5° of the cannon direction. For a highly focused stream, such as a ray gun, specify a low value. For a stream that widens quickly, specify a high value. You can specify up to 360°.

Velocity
Specifies the initial speed of particles in pixels per second as they emanate from the Cannon.

Velocity Random Spread
Specifies the amount of random velocity of particles. A higher value results in more variation in the velocity of particles. For example, if you set Velocity to 20 and Velocity Random Spread to 10, particles leave the Cannon at velocities ranging from 15 to 25 pixels per second.

Color
Sets the color of dots or text characters. This control has no effect if you use a layer as the particle source.

Particle Radius
Sets the radius of dots, in pixels, or the size of text characters in points. This control has no effect if you use a layer as the particle source.

Grid controls

The Grid creates a continuous plane of particles from a set of grid intersections. The movement of Grid particles is completely determined by the Gravity, Repel, Wall, and Property Mapper settings. By default, the Force control of Gravity is on, so Grid particles fall toward the bottom of the frame.

With the Grid, a new particle appears on every frame at each grid intersection. You can’t adjust this frequency, but if you want to turn off the Grid or make the Grid stop generating particles at specific times, set the Particle Radius/Font Size control to 0, or use keyframes to animate the value of the Particles Across and Particles Down controls. To make more particles appear in each frame, increase the values for Particles Across and Particles Down.

Note: By default, the Cannon is on and the Grid is off. If you are using the Grid and want to stop the Cannon from generating particles, turn off the Cannon by setting its Particles Per Second value to 0.
Position
Specifies the (x,y) coordinates of the grid center. When a grid particle is created, it is centered over its grid intersection, regardless of whether it is a dot, a layer, or a text character. If you’re using text characters as particles, the Use Grid option in the Edit Grid Text dialog box is on by default, placing each character on its own grid intersection, so normal character spacing, word spacing, and kerning do not apply. If you want text characters to appear at the grid position with normal spacing, use a text alignment other than the Use Grid option.

Width, Height
Specify the dimensions of the grid, in pixels.

Particles Across, Particles Down
Specify the number of particles to distribute horizontally and vertically across the grid area. Particles are generated only when the value is 1 or more.
Note: If the Width, Height, Particles Across, and Particles Down controls are not available, the Use Grid option has been turned off in the Edit Grid Text dialog box.

Color
Sets the color of dots or text characters. This control has no effect if you use a layer as the particle source.

Particle Radius/Font Size
Sets the radius of dots in pixels or the size of text characters in points. This control has no effect if you use a layer as the particle source.

Layer Exploder and Particle Exploder

The Layer Exploder explodes a layer into new particles, and the Particle Exploder explodes a particle into more new particles. In addition to explosion effects, the exploders are also handy for simulating fireworks or for rapidly increasing the number of particles.

The following guidelines can help you control particles resulting from an explosion:

  • A layer is exploded once for each frame. By default, this creates a continuous shower of particles for the duration of the composition. If you want to start or stop a layer explosion, animate the Radius of New Particles control by using keyframes so that its value is zero at times when you don’t want particles to be created.

  • If the source of the layer is a nested composition, you can set different Opacity values or In and Out points for the layers within the nested composition to make the exploding layer transparent at different points in time. The Layer Exploder does not create particles where the source of the layer is transparent.

  • To change the position of the exploding layer, precompose the layer with its new position (use the Move All Attributes Into The New Composition option), and then use the precomposed layer as the exploding layer.

  • When you explode particles, the new particles inherit the position, velocity, opacity, scale, and rotation of the original particles.

  • After layers or particles explode, Gravity, Repel, Wall, and Property Mapper controls influence the movement of particles.

    Some Persistent Property Mapper and Ephemeral Property Mapper options can make explosions more realistic. For example, change Opacity to make the resulting particles fade out, or change the Red, Green, and Blue color channels to make resulting particles change color as they appear to cool.
Explode Layer
(Layer Exploder only) Specifies the layer you want to explode. To make the video disappear the moment the particles appear, either turn off the video for the layer or trim the Out point of the layer.

Radius Of New Particles
Specifies the radius of the particles resulting from the explosion. This value must be smaller than the radius of the original layer or particle.

Velocity Dispersion
Specifies, in pixels per second, the maximum speed of the range within which Particle Playground varies the velocity of the resulting particles. High values create a more dispersed or cloudlike explosion. Low values keep the new particles closer together and can make the exploded particles resemble a halo or shockwave.

Affects
Specifies which particles the Layer Exploder and Particle Exploder affect.

Layer Map controls

By default, the Cannon, Grid, Layer Exploder, and Particle Exploder create dot particles. To replace the dots with a layer in the composition, use the Layer Map. For example, if you use a movie of a single bird flapping its wings as a particle source layer, After Effects replaces all dots with an instance of the bird movie, creating a flock of birds. A particle source layer can be a still image, a solid, or a nested After Effects composition.

A multiframe layer is any layer with a source that varies over time, such as a movie or a composition. When you map new particles to a multiframe layer, use the Time Offset Type control to specify how you want to use the frames of the layer. For example, use Absolute to map an unchanging image onto a particle, or use Relative to map an animating sequence of frames onto a particle. You can randomize both Absolute and Relative across particles.

Note: When you choose a layer for Layer Map, Particle Playground ignores any changes that you made to that layer within that composition. Instead, it uses the layer in its original state. To keep transformations, effects, masks, rasterization options, expressions, or keyframe changes for a layer when you use it as a particle source, precompose the layer.
Use Layer
Specifies the layer you want to use as the particles.

Time Offset Type
Specifies how you want to use the frames of a multiframe layer. For example, if you are using a layer of a bird flapping its wings and you choose Relative for Time Offset Type with a Time Offset of 0, the flapping wings for all the instances of the bird are synchronized. While this may be realistic for a marching band, it is not realistic for a flock of birds. To make each bird start flapping its wings from a different frame in the layer, use Relative Random.
Relative
Starts playing the layer at a frame based on the Time Offset you specify, relative to the current time of the effect layer; then advances in step with the current time of the Particle Playground layer. If you specify a Time Offset of 0, all particles show the frame that corresponds to the current time of the effect layer. If you choose a Time Offset of 0.1 (and your composition is set to 30 fps), each new particle displays the frame that is 0.1 seconds after the previous particle’s frame. Regardless of the Time Offset you specify, the first particle always displays the frame of the source layer that corresponds to the current time of the effect layer.

Absolute
Displays a frame from the layer based on the Time Offset you specify, regardless of the current time. Choose Absolute when you want a particle to show the same frame of a multiframe source layer for its entire lifespan, instead of cycling through different frames as the effect layer advances in time. For example, if you choose Absolute and specify a Time Offset of 0, every particle shows the first frame of the source layer for its entire lifespan. If you want to show a frame other than the first frame, move the layer earlier in time until the frame you want to show corresponds to the In point of the Particle Playground layer. If you specify a Time Offset of 0.1, for example, each new particle displays a frame that is 0.1 second after the frame of the previous particle (or every third frame of a 30-fps animation).

Relative Random
Starts playing the layer from a frame chosen at random, within the range between the current time of the effect layer and the Random Time Max you specify. For example, if you choose Relative Random and specify a Random Time Max of 1, each particle starts playing from a layer frame chosen at random from between the current time and 1 second after the current time. If, for another example, you specify a negative Random Time Max value of - 1, the Random Time Max is before the current time, so that the range within which new particles start playing advances as the current time advances. However, the range is always between the current time and one second earlier than the current time.

Absolute Random
Takes a frame at random from the layer, by using a time in the range from 0 to the Random Time Max you specify. Choose Absolute Random when you want each particle to represent a different single frame of a multiframe layer. For example, if you choose Absolute Random and specify a Random Time Max of 1, each particle shows a layer frame from a random time between 0 seconds and 1 second into the duration of the layer.

Time Offset
Specifies the frame from which to start playing sequential frames from the layer.

Affects
Specifies which particles the Layer Map controls affect.

Replace default Cannon particles with text

You can use text characters as particles. For example, you can type a message that the Cannon shoots across the frame. You can also change the attributes of any three sets of characters. For example, you can make some of the characters larger or brighter than others.

  1. In the Effect Controls panel, click Options.
  2. Click Edit Cannon Text.
  3. Type text in the box, and then set the following options:
    • For Font/Style, choose the font and style for Cannon characters.

    • For Order, click to specify the sequence in which characters exit the Cannon. The sequence is relative to the character order typed in the box. For example, if the Cannon Direction is set to 90° (making it point to the right), English text must exit the Cannon last letter first to be in readable order. Therefore, select Right to Left.

    • For Loop Text, select to continuously generate the characters you typed. Deselect to generate only one instance of the characters.

  4. Click OK to close the Edit Cannon Text dialog box, and then click OK to close the Particle Playground dialog box.
  5. Click the right-facing triangle next to Cannon so that it points downward.
  6. Click the Font Size value, type a value of 10 or greater, and press Enter (Windows) or Return (Mac OS).

    If you want to stop replacing default particles with text, delete all text from the box in the Edit Cannon Text dialog box.

Replace default Grid particles with text

  1. In the Effect Controls panel, click Options, and then click Edit Grid Text.
  2. Set the following options:
    • For Font/Style, choose the font and style for Grid characters.

    • For Alignment, click Left, Center, or Right to position text in the box at the Position specified in the Grid control, or click Use Grid to position each letter in the text on consecutive grid intersections.

    • For Loop Text, select to repeat the characters you typed until all the grid intersections contain one character. Grid intersections are specified by the Particle Across and Particle Down controls. Deselect to generate only one instance of the text. (This option is available only if you select Use Grid alignment.)

  3. Type text in the box. If Use Grid alignment is selected and you want to skip a grid intersection, type a space. To force the next character down to the next grid row, press Enter (Windows) or Return (Mac OS).
  4. Click OK to close Edit Grid Text, and then click OK to close the Particle Playground dialog box.
  5. Click the right-facing triangle next to Grid so that it points downward.
  6. Click the Font Size value, type a value of 10 or greater, and press Enter (Windows) or Return (Mac OS).

If you want to stop replacing default particles with text, delete all text from the box in the Edit Grid Text dialog box.

Using Selection Text values to differently affect subsets of text

You can differently affect only certain subsets of text particles by specifying Selection Text values. To open the Particle Playground options dialog box, click Options at the top of the Particle Playground entry in the Effect Controls panel. (This is the same place where you can specify the text used by the Grid or Cannon emitters.) Then enter text in one or more of the Selection Text fields, and click OK. After doing this, you can then choose one of the Selection Text sets from the Character menu under one of the Affects property groups. For example, you can make gravity only affect the letter e by entering e in Selection Text 1 and then choosing Selection Text 1 in Gravity > Affects > Characters.

Note: The string matching is case-sensitive, and it does include punctuation marks and other symbols.
As with all text features, consider using this feature with symbol fonts, like wingdings.

Changing a particle over its lifespan

Some controls affect the particle from birth: Cannon, Grid, Layer Exploder, and Particle Exploder. Others affect the particle after birth and over the course of its lifespan: Gravity, Repel, Wall, Persistent Property Mapper, and Ephemeral Property Mapper. To have full control over particle movement and appearance, you must balance these controls.

For example, if you want to use the Cannon to shoot sparks that fade over time, it may seem that you need only animate the Color control of the Cannon. However, using this method, you change only the color of each new particle as it’s created. To control the color for the lifespan of particles, create a layer map and use one of the Property Mappers to alter the color channels of the particles.

The following list covers common particle behavior and how you can influence it.

Speed
At particle creation, particle velocity is set by the Cannon and the exploders; Grid particles have no initial speed. After particle creation, use the Force control in the Gravity and Repel control groups. You can also influence the speed of individual particles by using a layer map to set values for the Speed, Kinetic Friction, Force, and Mass properties in the Property Mappers.

Direction
At particle creation, the Cannon includes particle direction; the Layer Exploder and Particle Exploder send new particles in all directions; and Grid particles have no initial direction. After particle creation, direction can be influenced by the Direction control in the Gravity control group or by specifying a Boundary (mask) in the Wall control group. You can also influence the direction of individual particles by using a layer map to set values for the Gradient Force, X Speed, and Y Speed properties in the Property Mappers.

Area
Use a Wall mask to contain particles to a different area or to remove all barriers. You can also restrict particles to an area by using a layer map to set values for the Gradient Force property in the Property Mappers.

Appearance
At particle creation, the Cannon, Grid, Layer Exploder, and Particle Exploder set particle size unless you replace the default dots with a layer map. The Cannon and Grid set the initial color, while the Layer Exploder and Particle Exploder take color from the exploded dot, layer, or character. The Options dialog box affects the initial appearance of text. After particle creation, you can use the Property Mappers to set values for Red, Green, Blue, Scale, Opacity, and Font Size.

Rotation
At particle creation, the Cannon and Grid set no rotation; the Particle Exploder takes rotation from the exploded dot, layer, or character. Use Auto-Orient Rotation to make particles rotate automatically along their respective trajectories. For example, a particle can point up as it climbs an arc, and point down as it descends. Rotation isn’t easily visible for a dot particle. It is easier to observe only when you replace the dot particle with text characters or a layer. After particle creation, use a layer map to set values for the Angle, Angular Velocity, and Torque property in the Property Mappers.
Note: The appearance and rotation of a layer map particle changes in relation to the original appearance and rotation of the mapped layer. For example, if you replace the default dot particles with a movie of a spinning wheel, the spinning-wheel particles appear to spin when no particle rotation is applied.

Gravity controls

Use Gravity controls to pull existing particles in a direction you specify. Particles accelerate in the direction of gravity. Apply in a vertical direction to create falling particles, such as rain or snow, or rising particles, such as champagne bubbles. Apply in a horizontal direction to simulate wind.

Force
Specifies the force of gravity. Positive values increase the force, pulling particles more strongly. Negative values reduce the force.

Force Random Spread
Specifies a range of randomness for the Force. At zero, all particles fall at the same rate. At a higher value, particles fall at slightly different rates. Although pure gravity accelerates all objects equally, increasing the Force Random Spread value can produce more realistic results with subjects such as leaves falling through air, where enough air resistance exists to vary the rates of descent of the leaves.

Direction
Specifies the angle along which gravity pulls. The default is 180°, which simulates the real world by pulling particles toward the bottom of the frame.

Affects
Specifies a subset of the layer’s particles to which Gravity applies.

Repel controls

Repel controls specify how nearby particles repel or attract each other. This feature simulates adding a positive or negative magnetic charge to each particle. You can specify which particles, layers, or characters are the repelling force and which are repelled.

Note: If you want to repel an entire layer of particles away from a specific area, use the Property Mapper controls, Wall or Gradient Force.
Force
Specifies the repel force. Greater values repel particles with more force. Negative values result in particle attraction.

Force Radius
Specifies the radius (measured in pixels) within which particles are repelled. Another particle must be within this radius to be repelled.

Repeller
Specifies which particles act as the repellers or attractors to another subset you specify by using the Affects control.

Affects
Specifies a subset of the layer’s particles to which repulsion or attraction applies.

Wall controls

Wall controls contain particles, limiting the area within which particles can move. A wall is a closed mask that you create by using a mask tool, such as the Pen tool. When a particle hits the wall, it bounces off at a velocity based on the force with which it hit.

Boundary
Specifies the mask to use as the wall. You can create a new mask by drawing one on the effect layer.

Affects controls

Many Particle Playground controls include Affects controls. Affects controls specify which particles the encompassing control affects. For example, the Affects controls within the Particle Exploder controls specify which particles the Particle Exploder affects.

Particles From
Specifies the particle generator or combination of particle generators whose particles you want to affect.

Selection Map
Specifies the layer map that influences which particles are affected.
Note: The simulation space is not bounded by the dimensions of the layer to which Particle Playground is applied. You may need to use a selection map that is larger than the Particle Playground layer so that the selection map affects dots that are not visible.

Characters
Specifies the characters you want to affect. This control applies only if you are using text characters as the particle type.

Older/Younger Than
Specifies the age threshold, in seconds, above or below which you want to affect a particle. Positive values affect older particles, and negative values affect younger particles. For example, a value of 10 means that as soon as a particle reaches 10 seconds, it changes to the new value.

Age Feather
Specifies the age range in seconds within which the Older/Younger Than value is feathered, or softened. Feathering creates a gradual, rather than abrupt, change. For example, if you set Older/Younger Than to 10 and Age Feather to 4, about 20% of particles start changing when they’re 8 seconds old, 50% change when they’re 10 seconds old (the Older/Younger Than value), and the remainder change by the time they’re 12 seconds old.

Use Particle Playground Property Mapper controls

You can control specific properties of individual particles by using a layer map and either the Persistent Property Mapper or the Ephemeral Property Mapper. You can’t alter a specific particle directly, but you can use a layer map to specify what happens to any particle that passes over a specific pixel in the layer. Particle Playground interprets the brightness of each layer map pixel as a specific value. The Property Mapper associates a specific layer map channel (Red, Green, or Blue) with a specific property, so that as a particle passes over a certain pixel, the brightness value at that pixel modifies the property.

A particle property can be modified in either a persistent or an ephemeral way:

  • A persistent change to a particle property retains the most recent value set by a layer map for the remaining lifespan of the particle, unless the particle is modified by another control such as Repel, Gravity, or Wall. For example, if you use a layer map to modify particle size and you animate the layer map so it exits the frame, the particles keep the last size value set by the layer map after it exits the frame.

  • An ephemeral change to a particle property causes the property to revert to its original value after each frame. For example, if you use a layer map to modify particle size and you animate the layer map so that it exits the frame, each particle returns to its original size value as soon as no layer map pixels correspond to it. Similarly, if you apply an operator such as Add, each time a particle passes over a different layer map pixel, the value of the layer map pixel is added to the original value of the particle.

In both the Persistent and Ephemeral Property Mappers, you can control up to three particle properties independently by using a single RGB image as a layer map. Particle Playground achieves this independent three-component control by extracting brightness values separately from the red, green, and blue channels in the image. You don’t have to use all three channels if you want to modify only one property. To change only one property or change up to three properties using the same values, use a grayscale image as the layer map because the RGB channels are identical.

In combination with keyframes or expressions, the Property Mappers provide complete control over individual particle properties in space and time. Using layer maps, you can change particle properties at any location within a frame. By applying keyframes or expressions to Property Mapper options and animating a layer map, you can control how particle properties change.

  1. For Use Layer As Map, choose a layer map to use as the source for values that modify particle values. The layer map must be part of the composition.
  2. To apply the effect to a subset of particles, specify the Affects controls as necessary.
  3. Choose a property for each of the Map Red To, Map Green To, and Map Blue To controls. You don’t have to map properties to all of the color channels. For example, if you want to change scale over an image map, you can map the color red to scale without setting other properties.
  4. Specify the minimum and maximum values you want the layer map to produce for each Map To group. Min is the value to which a black pixel is mapped, and Max is the value to which a white pixel is mapped. The complete tonal distribution between Min and Max is then scaled proportionally.
  5. If using the Ephemeral Property Mapper, you can apply an operator to the value of a particle property and the value of the corresponding layer map pixel.
    Note: Because particle properties use many kinds of units, such as pixels, degrees, and seconds, you may want to compress or expand the range of values from the layer map so that all the resulting values are usable in the measurement system of a specific particle property. First, use the Min and Max controls, which define the range of values to use from the layer map. If further adjustment is necessary and you’re using the Ephemeral Property Mapper, use the Operator control and choose a mathematical operator to amplify, attenuate, or limit the effect of a layer map.

    In both the Persistent and Ephemeral Property Mappers, you can use the alpha channel of a layer map to make more subtle changes to the value of a particle property. For example, particles over a layer-map pixel in which the alpha channel value is 255 are fully affected, while lower values affect particles less. Layer-map pixels that are completely transparent have no effect on particle properties.

    When you choose any of the following properties, Particle Playground copies the value from the layer map (that is, the layer selected in the Use Layer as a Map menu) and applies it to the particle.

    None
    Modifies no particle property.

    Red, Green, Blue
    Copy the value of the red, green, or blue channel of a particle within a range of 0.0–1.0.

    Kinetic Friction
    Copies the amount of resisting force against a moving object, typically within a range of 0.0–1.0. Increase this value to slow down or stop moving particles, as if braking.

    Static Friction
    Copies the amount of inertia that holds a stationary particle in place, typically within a range of 0.0–1.0. At zero, a particle moves when any other force, such as gravity, is present. If you increase this value, a stationary particle requires more of another force to start moving.

    Angle
    Copies the direction in which the particle points, in degrees relative to the particle’s original angle. The angle is easily observable when a particle is a text character or a layer without radial symmetry.

    Angular Velocity
    Copies the velocity of particle rotation in degrees per second. This setting determines how fast a particle rotates around its own axis.

    Torque
    Copies the force of particle rotation. The angular velocity of a particle is increased by a positive torque and is increased more slowly for particles of greater mass. Brighter pixels affect angular velocity more forcefully; if enough torque is applied against angular velocity, the particle starts spinning in the opposite direction.

    Scale
    Copies the scale value of a particle along both the x and y axes. Use this control to stretch a particle proportionally. A value of 1.0 scales the particle to its full size; a value of 2.0 scales it 200%, and so on.

    X Scale, Y Scale
    Copy the scale value of a particle along the x or y axis. Use these properties to stretch a particle horizontally or vertically.

    X, Y
    Copy the position of a particle along the x or y axis in the frame, in pixels. A value of zero specifies a position at the left of the frame (for X) or at the top of the frame (for Y).

    Gradient Velocity
    Copies the velocity adjustment based on areas of a layer map on both the x and y planes of motion.

    X Speed, Y Speed
    Copy the horizontal speed (x-axis velocity) or vertical speed (y-axis velocity) of a particle in pixels per second.

    Gradient Force
    Copies the force adjustment based on areas of a layer map on both the x and y planes of motion. The pixel brightness values in the color channel define the resistance to particle force at each pixel, so the color channel acts like a layer map of hills and valleys that decrease or increase particle force. In the layer map, areas of equal brightness result in no adjustment, similar to flat land. Lower pixel values represent less resistance to a particle’s force, similar to a downhill grade. Higher pixel values represent more resistance to a particle’s force, similar to an uphill grade. For best results, use a soft-edged layer map image.
    If you are using a layer map for Gradient Force where flat areas equal no adjustment, and you are using the Min and Max controls (not the Min or Max operators) to set the range of values for Gradient Force, set them to positive and negative values of the same number (for example, –30 and +30). This ensures that the middle of the range remains centered at zero.

    X Force
    Copies the coercion along the x axis of motion. Positive values push a particle to the right.

    Y Force
    Copies the coercion along the y axis of motion. Positive values push a particle down.

    Opacity
    Copies the transparency of a particle, where zero is invisible, and 1 is solid. Adjust this value to fade particles in or out.

    Mass
    Copies the particle mass, which interacts with all properties that adjust force, such as Gravity, Static Friction, Kinetic Friction, Torque, and Angular Velocity. It takes greater force to move particles with a larger mass.

    Lifespan
    Copies the elapsed length of time a particle exists, in seconds. At the end of its lifespan, the particle is removed from the layer. The default lifespan is effectively immortal.

    Character
    Copies the value that corresponds to an ASCII text character, making it replace the current particle. Applies only if you’re using text characters as particles. You can specify which text characters appear by painting or drawing shades of gray on the layer map that correspond to the ASCII characters you want. A value of zero produces no character. For US English characters, use values in the range 32–127. The range of possible values can accommodate Japanese characters. For more information about the ASCII character values for a font you’re using, see the documentation for the font, use a utility such as Character Map (Windows), or contact the font manufacturer.
    Note: If you simply want to make certain characters spell a message, it’s much easier to type the text directly in the Options dialog box. The Character property is more useful as a secret message effect in which you scramble text characters.

    Font Size
    Copies the point size of characters. Applies only if you’re using text characters as particles. Increase this value to make characters larger.

    Time Offset
    Copies the Time Offset value used by the Layer Map. Applies only if you used the Layer Map control to specify a multiframe layer (such as a movie) as a particle source.

    Scale Speed
    Copies the scale of a particle. Positive values expand the particle, and negative values shrink the particle. Particles expand or shrink by a percentage per second.

Min and Max controls for Property Mappers

When the overall range of layer map brightness values is too wide or narrow, use Min and Max to stretch, compress, or shift the range of values produced by the layer map. The following examples describe when you may want to adjust Min and Max:

  • You want to set the smallest font size for your text to 10 points and the largest size to 96 points. Set the Min value to 10 and the Max value to 96.

  • You set the initial color of a particle and then use a layer map to change particle colors. If you find that the color changes aren’t dramatic enough, you can lower the Min value and raise the Max value to increase the contrast of the color changes.

  • You set the initial velocity of a particle and then use a layer map to affect the X Speed value. However, you find that the difference between the fastest and slowest particles is too great. By raising the Min value and lowering the Max value for the layer map channel that is mapped to the X Speed value, you narrow the resulting range of particle speeds.

  • You use a layer map to affect the Scale property of particles and find that the smallest particles aren’t small enough while the largest resulting particles are too large. In this case, the entire output range needs to be shifted down; lower both the Min and Max values.

  • You have a layer map that modifies particles in the opposite direction from the one you want. Swap the Min and Max values, which has the same result as inverting the layer map.

    Note: The alpha channel of the layer map is used as the selection map for the Persistent and Ephemeral Property Mappers.

Operator controls for the Ephemeral Property Mapper

When you use the Ephemeral Property Mapper controls, Particle Playground replaces the value of a particle’s property with the value represented by the layer map pixel at the particle’s current location. You can also amplify, attenuate, or limit the resulting values by specifying a mathematical operator and then using both the value of a particle’s property and its corresponding layer map pixel value.

Set
Replaces the value of a particle property by the value of the corresponding layer map pixel. For example, to replace the value of a particle property with the brightness value of the corresponding pixel on the layer map, use Set. This operator is the most predictable and is the default.

Add
Uses the sum of the value of a particle property and the value of the corresponding layer map pixel.

Difference
Uses the absolute value of the difference of the value of a particle property and the brightness value of the corresponding pixel on the layer map. Because it takes the absolute value of the difference, the resulting value is always positive. This operator is useful when you want to limit values to only positive values. If you’re trying to model realistic behavior, the Difference operator may not be ideal.

Subtract
Starts with the value of a particle property and subtracts the value of the brightness value of the corresponding pixel on the layer map.

Multiply
Multiplies the value of a particle property by the brightness value of the corresponding pixel on the layer map and uses the result.

Min
Compares the brightness value of the layer map to the value of the particle property and uses the lower value. To limit a particle property so that it is less than or equal to a value, use the Min operator and set both the Min and Max controls to that value. If you use a white solid as a layer map, you need only set the Max control to that value.

Max
Compares the brightness value of the layer map to the value of the particle property and uses the higher value.

To amplify existing values of properties, try applying the Add operator with positive values or the Multiply operator with values above 1.0. To attenuate (tone down) property value changes, try applying the Multiply operator using values in the range 0.0–1.0.

Control layers for Particle Playground

Particle Playground can use a control layer to control a particle property, such as opacity. For general information about creating and using control layers, see Compound effects and control layers.

Regardless of the color depth of the image that you use as a control layer, Particle Playground always uses its red, green, and blue channels as if each were an 8-bpc grayscale image. If you create a control layer using colors, the Property Mapper property groups in Particle Playground can extract the brightness values from each RGB color channel separately.

The alpha channel in a control layer modifies the color values in the control layer before Particle Playground uses the control layer’s pixel values. Areas where the alpha channel value is 0 (transparent areas of a control layer) don’t affect particle values. Areas where the alpha channel has a value greater than 0 (semitransparent and opaque areas of a control layer) affect the particle value to a degree proportional to the value of the alpha channel. When you use the Persistent and Ephemeral Property Mapper property groups, the range set for the Min and Max controls also affects the value applied to a particle.

Particle Playground can extract brightness values separately from the red, green, and blue channels in an image. If you want to create different layer maps for each channel, use a program that can edit individual color channels, such as Adobe Photoshop, and then paint or paste each layer map into its own channel. Save the control layer as an RGB image in a format After Effects can import. The image may look unusual when viewed in RGB mode, because it’s intended to be used as a single hidden layer containing three different layer maps, not as a visible image layer.

If you already have three separate images, you can combine them into a single RGB file by using the Set Channels effect. Set Channels can load each image into its own channel in a combined file, making it suitable for use as an RGB layer map.

Improving performance with Particle Playground

Keep in mind the following when working with the Particle Playground effect:

  • When you’re generating a Particle Playground effect, keep an eye on the Info panel to see how many particles are being produced. If an effect contains more than 10,000 particles, it can greatly slow rendering. If you notice performance problems, set Particles Per Second and/or Particles Down to relatively low values (in the range 1–100).

  • The Grid and Layer Exploder generate particles on every frame, which may generate too many particles for the effect you’re creating and slow down rendering. To avoid continuous particle generation, animate these controls to decline to zero over time: Layer Exploder, Radius of New Particles, Grid Width and Height, Particle Radius, and Font Size. Then Particle Playground generates new particles only at the start of a sequence.

  • When you apply a Particle Playground effect to a layer, the particle positions aren’t limited to the bounds of that layer. To control particles that you can’t see or that appear near the edge of the image, use a Selection or Property Map that’s larger than the area of the Particle Playground layer. Also, note that After Effects takes the alpha channel of an image map into account. If you want transparent areas of your map to affect the particles, precompose the map layer with a black solid behind it.

    To specify field rendering with a Particle Playground effect, select Enable Field Rendering in the Particle Playground options dialog box. Then Particle Playground calculates the simulation at double the frame rate of the current composition, which is what field rendering requires.