Particles and Bristles

The Particle Tab
Particle Settings
Animating Particles
Particle Example

Optipustics (aka Particles) are the silly-named procedural brushes that do a variety of things, from rendering grass and trees to realistic bristle brushes, animate waterfalls, fairy dust, and fire.

Optipustics can be used to generate particles along the mouse path, which can split into more trails over time. They can also change color according to the Gradient settings. This is a great feature for making foliage effects of many kinds, as well as grass, bushes, hair, fur, water fountains, fireworks and such. Particles can have mass and be subject to gravity, causing the branches to show weight and bend down. Or up depending on the value of gravity.


There are four modals on the Optipus panel: Particles, Bristles, Orbicles, and Foliage

The Particle tab

There are a number of preset effects possible with Optipustics. You can try them for yourself by clicking on the ‘Settings’ button at the bottom.

You can also create your own settings and save them with the 'save' button at the bottom.

  You'll have to be sure you have checked the Enable button before you can draw with Optipustics.

These are just a few of the settings at your disposal.

The Particle Settings

Max particles controls how many particles are emitted at a given time.  It is the maximum number of particles that can be in circulation.  When a particle dies (reaches the end of it's lifespan) it is recycles and available to be used again.

Max particles at 20

Max particles at 500

When you move the mouse to draw a path, there is not an infinite granularity to the information uses to duplicate that motion by the computer.  Actually, a relatively small number of samples are taken from the mouse or tablet, possibly 20-60 per second.  Then the computer uses these samples to draw your path.

In the case of the particle brushes, particles are emitted at each of these samples.  Setting the Particles per emission has an effect on the number of branches, or blades of grass that shoot out of your basic path.

Using the same value for Particles per emission and Max particles will cause the particle system to emit all available particles at the same time, causing them to clump up.  You won't see anymore particles until all of them have recycled.


This set of controls have to do with the physical properties of your particles.

Mass is a property of matter that is equal to the measure of  its resistance to changes in velocity.  While mass will not effect the speed of a particle falling, if will have a significant effect on the way it reacts to various forces.  For example, a feather and a bowling ball will fall at the same speed in a vacuum, but the bowling ball will fall much faster in an atmosphere because its mass causes it to overcome wind resistance more than the feather.

Gravity can be an arbitrary value.  It is not an exact simulation of nature, but it operates with the same principles.  A negative number will cause particles to fall, while a positive number will cause particles to rise.

Initial velocity is a speed value given to particles when they are emitted.  Particles are shot of at a random vector using this speed.

Terminal velocity is the maximum speed at which a particle can travel.  In the real world, maximum velocity is caused by wind resistance, where the force of the resistance to the air equals the force of gravity pulling the object down.  In the case of the particle system, the maximum speed is simply clipped to the terminal velocity.

Drag is similar to wind resistance.  It is a value that is used to scale the overall effect of every physical action a particle takes.  The value is in the range of -1 to 1.  A negative value will cause a particle to do the opposite of what it is supposed to do.

The lifespan controls how long the particle stays active.  The longer it's around, the longer tail it will draw.

Splits is the number of times a particle will branch into other particles when it dies.  After a particle has used up its lifespan, and it hasn't used up its splits, then it will split into 2 new particles, each of which have 1/2 the lifespan of the parent.

Split angle is the angle at which the baby particles will shoot off when they are created.  One is shot in a positive angle relative to the parent, and one is shot at a negative.

This value randomizes all of the above settings to give a somewhat unpredictable behavior to the particles.

Use mouse velocity adds a velocity to the initial velocity value, based on the speed of the mouse as you draw a brush stroke.  This value is only applied when particles are created, and not as they are moving through space.

Particles follow mouse causes the vector of the mouse to influence the particles, with the result of particles swarming in the same direction as the mouse pointer.  This can drastically alter the motion of branches as they travel.

A gradient can drastically alter the color and appearance of your particles.  You can select any of the 8 gradients with the Gradient index slider.  You can edit a gradient by clicking on the gradient swatch above.

With the gradient or sweep editor, you can create a color gradation that will be applied to your particle.



The opacity channel on the gradient editor can be used to fade the branches out.

When you use particles for grass and fine foliage effects like needles on a cactus, which tend to fade to very thin at the tip,  you can further enhance that effect by adding progressive transparency to it.

In some cases you'll use it to actually make the bushes become semi-transparent to see through them. In other instances it will convey the impression of extremely fine fair or fur. Perhaps a broken spider web?

You can also use it if you simply want to make your foliage fade, as if in the distance.  This can be useful for drawing foliage on 3d landscapes, where the objects in the distance would tend to fade.

The Style setting determines what kind of brush is used to draw the particles.

Line refers to a single pixel width anti aliased line.  Brush will use your current brush settings, whatever they may be.  Nova is an effect like a star or lens flare that can be used for fairy dust like effects.

The Size parameter applies only to the Nova style.  You can change the size of the brush style by changing the size of your current brush.  The line style will always be one pixel width.

Using a natural brush with particles.

Nova used for an animation of fairy dust.  See below for an example of animating particles.

The shading parameter determines if your particles receive a shading effect or not.

Example with and without shading.

Animating Particles

It's easy to draw foliage and other cool effects with particles, but you can also animate them to create fire, smoke, waterfalls, or fairy dust.  Below, we'll go through a simple example of using the Stroke Player with particles.  Lets start by clearing our image to black.

The first step in animating anything is to allocate a number of frames for your animation.  Select Create from the Animation menu, and you will be presented with a small panel asking you for the number of frames you would like to have.  Enter 30 for this example.

The 30 empty frames will be created for you, and the animation Control panel will also be opened for you.

You can use the slider on this panel to scroll (or scrub) through the frames of your animation.  This will get a lot more interesting when we have actually animated something.


We'll start by loading in the 'Grass' preset.  This will give us a good start on some basic particles.  Be sure to uncheck the Shading checkbox.  We won't need it for this example.

We will now edit the gradient so we have more of a fiery set of colors.

You can use drag and drop to drop colors onto the area that looks like a ruler at the bottom.  Put a light color on the left, and black on the right.

Feel free to edit the opacity so it falls off to 0 to the right side.

We should now have something that looks like this.

To begin animating, all we have to do is draw a motion with the mouse.  It might look something like this:

Now undo it.  We just wanted the brush motion, not the actual image created by it.

Open the Stroke Player from the Animation panel.

Set the Playback type to 'All frames'  This will play back your brushstroke, advancing the frame number as appropriate to cause the stroke (and the particles) to move through the animation.

Now press replay and wait for the brush stroke to be dawn.

You should now see your particles.  You can repeat the stroke at anytime.  you can even change the parameters of the particles, for example, switching to the nova style, and replaying the stroke.

You should now be able to scrub through your animation, or play it back with the play button on the animation control panel.

Particle Example (in a Previous version)


The bristle brush tab give you the controls for the bristle brush simulation.  In the real world, a bristle brush is a stiff bristled brush, often made from hogs hair, synthetic fibers, or even hemp.

The Bristle brush attempts to simulate this kind of brush in a simple to use way.  There are a number of presets on the panel to get you started.

Be sure to check the Enabled button to use the bristle brushes.

The Bristle setting controls how many hairs there are n the brush.  Setting this to a low value may give you a wispy effect, while a high value may give you a bold effect.

The radius is the size of the brush (in pixel)

Color bleed controls the amount of pigment in the painting medium.

Mix colors controls how the pigment mixes with the colors on screen.  These two settings are dependent on each other.  you can use them to get a paint that is fully opaque, or that is completely translucent and only blends the colors underneath.

The Presets area gives you a number of built in settings.  There are 10 settings for brush sizes and seven settings for paint quality.

The paints range from semi opaque, non mixing,  to fully opaque, somewhat smeary, and finally to only smeary with no pigment.

Tablet pressure is supported by default.  There are no button to switch on.  Pressure is the most obvious effect you will notice.  Tilt will also be taken into account, if available.

The usual convention of painting with the right and left buttons is also supported.

The Foliage tab

Creating foliage with the Foliage tool can be as simple as loading a preset and drawing.

You have a fine level of control over how your foliage is rendered, including the size of the pen, an overall fog level that blends the pen with a single color. This is adjustable with a “Fog amount” parameter. A “Gain” parameter controls the overall brightness of the rendering pen.

There's also a “Color cue” parameter that can be compared with fog, but instead of being a single color that the pen is blended with, the depth of the 3-D particles are taken into account, and branches that are farther away are rendered with more of the depth color. That color is defined by the current primary drawing color.

Create alpha lets you create a selection around everything you draw with the foliage tool. It can then be picked up as a brush, or further manipulated.

If you so desire, you can edit every parameter of every rule used to draw the trees and other foliage types that are possible using the rules library.