The Sprite Emitter effect is an all-purpose emitter. You can plug it into a drawing layer to generate particles that look like your drawing layer. You could also just output dot particles if you have no image layer connected. There are many parameters to control how particles are emitted.
Sprite Emitter Properties
Trigger: An on/off switch using binary code. 1 = on, 0 = off.
Number of Particles: This is where you can define how many particles will be emitted on each frame.
Probability of Generating Any Particles: This is a probability percentage between 0 and 100. If the probability is set to 100%, it will generate the Number of Particles specified. If you set the percentage to 50%, then there's only a 50% chance that it will generate the number of particles set in the Number of Particles. You can play with this value to add random spacing to the generation of particles.
Streak Seed: The number of streaks to generate.
Source Sampling Time Offset: Sets the streak start at a different time to offset its position.
Source Sampling Duration: This parameter is the key to generating streaks. If set to 0, the behaviour is the same as before. If set to -10 for example, it will sample the input region (in this example the Planar-Region) 10 frames in the past. If in this mode, the Number of Particles parameter is the number of streaks to generate. If you want to generate five streaks for example, you need to set the Streak Size to a value different than 0, otherwise all the streaks will be at the same spot.
Source Samples Per Frame: The number of subdivisions for each frame. A value of 1 generates a particle for each frame. A value of 16 generates a particle on each 1/16th of a frame.
Streak Size: The radius of the sphere used for sampling the offset of the streak.
Region Size for Baked Particle Input: The Baked Particle Input property refers to when you use a Baker as an input to a Sprite Emitter. You can do this when you want to generate particles from other particles. When you do this, you have the option of setting a sphere around the source particle from which the new particle system will generate particles. That is the region which is referred to in this value. If you look at the following example, you'll see that the purple smiley faces are generating smaller green, blue, and yellow smiley faces. This is done by plugging the Baker from the purple smiley faces into the Sprite Emitter of the other smiley faces. See the following images:
You may want to design a variety of different drawings that will vary the appearance of your particle system. To do this, you should put each drawing on its own cell in the drawing layer. Each drawing will then be a new Type of particle.
Type Generation Strategy:
Lets you sequentially or randomly assign a type (moving from one drawing to the next).
Particle Type 0:
This is the frame number of the first drawing. If you have a 5-frame cycle that starts on frame 1, you would put a 1 here.
Particle Type 1:
This is the frame number of the last drawing. If you have a 5-frame cycle that starts on frame 1, you would put 5 here.
Age at Birth: A different start frame number can be entered in this field. This means that a particle can start with a different drawing than the drawing that you have on frame 1.
Age at Birth Standard Deviation: Allows a random deviation for the birth of the particles. If you have a 5-frame cycle that starts on frame 1, but you want the particles to be of a random type, then you may want to set the Age and Birth to 3 with a standard deviation of 2. That means that particles will randomly be born at any frame from 1 to 5.
Set Maximum Lifespan: Makes particles die automatically.
Maximum Lifespan: This is how long the particle will exist before dying.
Maximum Lifespan Sigma: The lifespan variation of particles. If set to 0, all particles will have the same lifespan. A larger value means that particle lifespans will be distributed over a larger range.
Particles Mass: Define a mass for the particles. This mass will affect how the particles interact with gravity.
Copy Particle Velocity for Baked Particle Input: If you select this option, the velocity of the parent system will be applied to the child system when a Baker is used as the region for a Sprite Emitter.
Add Particle Age for Baked Particle Input: If you select this option, the age of the parent system will be inherited by the child system when a Baker is used as the region for a Sprite Emitter.
Align Initial Velocity: This aligns the initial velocity with the region from which the particles are being emitted. If you are emitting from a sphere, then the particles will all start out moving away from the centre of the sphere.
Minimum Initial Rotation: Define a minimum rotation in degrees that the particle can have when it is generated. There is also a separate Rotation-Velocity node in which you can define this parameter.
Maximum Initial Rotation: Define a maximum rotation in degrees that the particle can have when it is generated.
Rendering Strategy: Select a method to determine the particle type defined for each particle that is created.
For example, you can set the Particle Type to go from 1 to 100 in the Generation tab. Then use the Selector to remap the particle types to a certain drawing. So for example you could create five drawings, labelled 1 to 5, and use the selector to create mainly 1s, no 2s, a few 3s, 4s, and a very few 5s. What it's doing is looking at the X-axis to find what the particle "type" is, then looking at the Y-axis to find out which drawing to assign to that "type." When you use 1 to 100 as a type, then when you're setting the values, they act as a percentage.
Selector: Animates the Selector in conjunction with the Rendering Strategy to adjust the parameters that control the particle’s appearance at birth and over time.
Cycling: If you're using rendering strategies like Frame Number or Age, you may want to cycle the drawings. For example, if you are using Frame Number, but you've only got 5 frames worth of drawings in your Sprite, then if you use "No Cycle," your Particles will disappear after frame 5. You can choose to cycle Normally (1-2-3-4-5-1-2-3-4-5) or Back and Forth (1-2-3-4-5-4-3-2-1).
Number of Drawings in Cycle: Lets you indicate how many frames from your Sprite you'd like to cycle.
Size over Age: Lets you determine the size of the particle as it ages. Attach a function to this attribute if you want to, for example, have the particles get smaller as time goes on.
Directional Scale: Scales the particle in the direction of its movement.
Directional Scale Exponent Factor: Sets an exponent here for how much you want that particle to scale.
Align with Direction: Aligns the particle in the direction of its movement.
Axis to Align: Select the axis that you want to align. This axis refers to the axis of the Drawing grid from the Drawing node plugged into the emitter.
Flip X Axis to Match Direction: You may want to have the particle align to the X direction of movement. You can see this property being used in the Lemmings example.
Flip Y Axis to Match Direction: Similar to flipping the X axis, you may want to flip the Y axis of a drawing to match the direction of the particle movement..
Use Rotation of Particle: Enables rotation on the particle.
Keep Volume: When you choose to do a Directional Scale, this will automatically maintain the volume of the particle by squashing it proportionally to how much it stretches as a result of the directional scale.
Colouring Strategy: Lets you choose how to define the colour of the particle.
Red, Blue, Green, Alpha: This is where you can attach functions to the Red, Blue, Green and Alpha values. You can also click on the colour swatch to adjust the colour.
Blur: Lets you determine the Blur to apply to the particles.
Blur Intensity: Lets you set a value or attach a function to animate the blur according to the type of blur that was defined from the drop-down list.
Falloff Rate: The distance where the blur fades from the edge of the image. Select a value between 0 and 1. A falloff rate of 0 causes the blur to fade out slowly, distributing the blur evenly from the edge of the drawing to the farthest edge of the blur. A falloff rate of 1 causes the blur to fade out quickly so that the blur is heaviest at the edge of the drawing.
Blend Mode: Defines a blend mode for the particles to get cool effects.
Blend Intensity: This is a percentage of how opaque you want the particles to be blended. 50 = 50% transparent. 100 = opaque.