Particles

Particles are objects with a very simple geometric description. Due to their simplicity, they are memory efficient and a large number of them can be created.

Phenomena such as water drops, fur, fog and fire, can be simulated using particles. Particles can be rendered in a variety of ways: as small dust particles, lens flares or foggy spheres, to name a few examples.

Despite their simplicity, the rendering engine of Realsoft 3D can make particles look very interesting.  For example, particles can be textured just like other geometric objects.
 

Creating particles

The Particle tool allows you to create particles interactively.

To create a flock of particles:

1. Activate the particle tool.

When you activate the tool, the Control Bar shows you a number of particle specific options.

Particle tool activated, the Control Bar shows you creation specific options.

2. Specify desired options from the Control Bar. To get started, just use the default values. Then create particles interactively through the view window by holding down the left mouse button while moving the mouse.

When done, accept the tool by clicking the right mouse button and selecting 'Accept' from the opened pop-up menu.
 
 
1D and 2D particles
 

You can also 'airbrush' particles on the surface of the selected objects. To do this, set the 'Surface' option of the particle tool. Orientation of 2D and 3D particles will then be determined by the orientation of the underlying surface. This option allows you to create easily fur and hair for objects.
   

Below is a description of particle tool specific options.

Class

The type of the created particles. Currently three kinds of particles can be created:

• 1D. 1D particle is defined by a single point. Rendering engine can render 1D particles as points, circles, stars etc. 1D particles look the same from all directions.
• 2D. A 2D particle consists of two points. So, it has properties such as 'direction' and 'length'. Real world objects like water drops, which have a symmetry axis, can be rendered using 2D particles. Also, polarity can be simulated (particles can have positive and negative ends).
• 3D. The geometry of 3D particles is represented as a coordinate system. In other words, 3D particles can be scaled, rotated and skewed. They can be used for rendering objects, which look different from all the three main directions. Please note that the current scan line shaders do not render 3D particles visible.

Pen 

Currently there are three pens available:

• Pencil. This creates one particle for each mouse movement.
• Brush. The number of particles created for each mouse movement can be defined through the 'Count' field.
• Object. This creates particles along a selected NURBS curve. The number of particles generated for each mouse move event can be defined using the 'Count' control.

A NURBS curve used as a pen for creating 1D particles
 
Brush

Modifying particles

Particles can be modified just like any regular objects, such as spheres and NURBS curves.

For example, you can modify the created particle flock by using the move tool with 'Collision Deformation' option set.

Select the particle object and activate the move tool with collision deformation option

Particle object moved against a sphere 
 

When you select a particle object, the control bar automatically shows you all particle specific tools. 

You can also enter the edit mode to single point edit the particles.

Some of the particles selected in edit mode

You can use any of the available tools, such as move, rotate or bend, to modify the selected particles. You can duplicate points simply by dragging them while holding down the copy modifier key 'Ctrl'.

 

Properties of particles

All common object properties, such as name, color or mass, can be modified through the property window.

The color of a particle object can be defined in the usual way using the property window's 'Col' tab.

The default scanline shading of particles does not look especially pretty.

1D and 2D particles rendered

Particle specific options can be controlled through the Property Window's 'Spec' tab. There are three sub tabs:

Particle specific properties

Rendering tab 

Particles can be rendered using scanline, post processing and ray tracing techniques. These are not exclusive: you can render a scanline particle and add a post effect on top of it. For more information about how to define visual appearance of particles, see the 'Post processing' chapter.

Scan line rendering

The color, optical and other surface properties of scanline rendered particles can be defined in the same way as those of any regular objects - by using the material system.

For example, you can texture map scanline particles using the 'wood' material of the default material library.

To texture particles:

1. Create a set of particles. Select the particle object.
2. Drag&drop a material from the Materials tab of the Select window into the view window. As usual, this creates the following object hierarchy:

 
Texture mapped 2D particles. Wooden particles consists of two sub objects: '2D particle' and 'wood'
 
Particles have a well defined surface parameter space, and therefore you can use UV mapping to map materials to particles. The UV space of 1D particles is two dimensional. The 'u' coordinate is defined in the 'radius' ' direction. It is zero in the center of a 1D particle and runs to one with the radius. The 'v' coordinate increases with the order number of individual particles: the first created particle has the v coordinate value 0, and the last particle has v equal to one.

UV mapped particles. Color changes by the 'u' coordinate. 
 

The UV space of 2D particles is three dimensional. 'U' runs along the length of a particle. 'V' runs perpendicular to the direction of the particle (from the axis towards the edge). The 'W' coordinate runs with the order number of the particle. Using the UV coordinates, you can define materials, which for example, make 2D particles look like 3D cylinders, cones, or hairs. And of course, 2D particles can also be bump mapped, clip mapped, they can be transparent or reflect light.

2D particles whose color fades with 'v' coordinate making them look like 3D cones.

 

Bump mapped 2D particles

Scan line rendered 1D and 2D particles are visible in ray racing. For example, other objects can cast shadows on particles.

The only drawback with scan line rendered particles is that they are quite memory consuming. However, a high render box count in rendering decreases memory consumption.
 
Summary: defining material properties for scanline particles does not differ much from defining material properties for any regular geometric object such as a sphere or a NURBS mesh.

Post Processing

In addition to scan line rendering, also post processing can be used for rendering particles. To do this:

1. Select the desired particle object
2. Drag&drop a post particle effect from the select window into the view window.

Drag&drop the desired particle effect into the view window to map it to the selected particle objects

As expected, this creates the following object hierarchy:

Star filtered particles consist of a particle object and a star filter mapping object
 

Rendering this shows a number of stars.

A star effect mapped to 1D particles and rendered

Note that both rendering methods (scanline & post processing) can be used simultaneously. For example, you can use the scan line particles to render hairs and then use post processing to make the hairs glow. 
 
Geometry tab

The 'Geometry' tab controls particle specific properties such as size and length.

Particle specific properties

The 'Geometry' tab consists of the following fields:

Count

Controls the number of particles. If you increase the count, position and other properties of added particles are computed by interpolating the existing particles.

Properties

This list view allows you to select and define particle specific properties, such as length and speed.

Particle properties

The rest of the fields in this tab are used for defining initial values and other properties for the selected property.

This gadget shows the value of the selected property.

For example, to modify the length of 2D particles:

1. Select the 'Length' property from the 'Attribute' list.
2. Enter a desired length to the 'Value' field.

Pointwise

Each property can have a uniform value or it can be defined per particle. Uniform means that the all particles in the object share the defined property. For example, by setting the particle length  property to 0.1, all particles become 0.1 meters long.

By checking the 'Pointwise' box, you can assign an individual value for each particle.

This gadget selects a channel for holding the value of a pointwise property in rendering. For example, you can define that a dynamic float channel 'Age' holds the value of the 'Life Time' attribute of particles. Then you can make a simple VSL material, which reduces the color of particles by the 'Age' channel.

2D particles here and there 
 

Constructor tab

Constructor

This control allows you to control the shape of the particle flock using other geometric objects.  'Distribute over surface' option distributes the particles over the surface of the sub objects.  To use this feature:

1. Create some 2D particles and create a sphere inside the particle object.

2. Select the particle object and open the property window. Go to the 'Spec/Geometry' tab and activate the 'Distribute over surface' constructor.

3. Modify the sphere. Particles remain distributed over the sphere.

Animating particles

Particles can be animated in the same way as any geometric objects.

Key framing and Morphing Particles

Particles can be key framed the same way as other geometric object. For example, to 'morph' particles, simply turn on animation recording and single point edit the particles.

Path Animations

Particle objects also support path animations.

For example, you can use point wise mapping to map particles to a path to achieve animated path deformations:

1. Create a set of particles with the Particle tool.
2. Create a NURBS curve.
3. Select the particle object and then the curve object and apply the pull down menu 'Animation/Path/Pointwise'.
4. Select the particle object and drag&drop a desired post particle effect (such as the 'star' effect) into the view window.  You get a bunch of stars traveling along the path.

Particles following a  path

Simulations

Particles are often animated using the simulation system. For example, you can use a number of 1D particles as meteorites acting under the influence of a gravity field caused by a planet.

To do this:

1. Create a number of 1D particles representing meteorites.
2. Create a sphere representing a planet.
3. Multi select the sphere and the particles and apply the tools 'Animation/Simulations/Gravity' and 'Animation/Simulations/Collision Detection'. Open the Property Window for the sphere, go to the simulation tab, and change 'Gravity' and 'Collision Detection' to 'Cause'.
4. Select the particles and apply the tool 'Animation/Physical Properties/Warm butter'.
5. Set the frame count to 500 and play the animation.

Note: using the simulation system to control particles does not differ from using the simulation system to control any regular object. However, note that particles don't have 'volume', and therefore two particles cannot collide. Particles can collide with true 3D objects, such as spheres, without any problems.