Particles

Realsoft Graphics Oy		Particles
	Chapter 2. Modeling

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.

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.

Particle tool 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

This field controls the radius of the airbrush particle tool. The size is measured in pixels.

Count

Defines the number of particles created per each mouse movement when using the brush and selected object pens.

Project

This option controls the depth coordinate of particles added by the brush pen. Three choices are available:

Disc: Particles are created into the input plane. The result is a flat particle cloud.
Sphere: Each mouse movement adds a new spherical cloud of particles around the mouse position defined by the input plane. The diameter of the particle cloud is defined by the Brush gadget.
Surface: Particles are added to the surface of the selected objects. The surface also defines the orientation of the particles.

Size Defines the size of created particle items.

Rnd Size

Randomizes the size of created particle items. 0=constant size, 1=fully randomized size.

Rnd Dir

Randomizes the direction of created particle items. 0=fixed orientation, 1=quite random orientation dominated by original direction, 10=totally random orientation.

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:

1. Select the particle object and activate the move tool with the Collision deformation option.

2. Move the particle object against the sphere.

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

Particle tools

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

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'.

Some of the particles selected in edit mode

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. It includes three sub tabs, which are described below.

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.

Particle specific properties

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.

Texture mapped 2D particles. Wooden particles consist of two sub objects: 2D particle and wood.

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. This creates the object hierarchy shown in the example image.

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 by v coordinate making them look like 3D cones, and bump mapped 2D particles

Scan line rendered 1D and 2D particles are visible in ray tracing. 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

Star filtered particles

As expected, this creates the object hierarchy shown in the adjacent image.

Rendering this shows a number of stars.

Note that several 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.

A star effect mapped to 1D particles and rendered

Geometry tab

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

Max Count

Limits the maximal number of particles. The value is used, when a particle constructor is enabled, making the count vary over time.

Creation Rate

Defines how rapidly particle count increases, when a constructor is enabled. The value defines the total number of added particles during the whole animation. Note that the rate value can be animated, making the density of particle flow variable. A negative value stops particle recreation (particle count starts decreasing, when existing particles die).

Geometric particle properties

Properties

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

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

Common Value

This gadget shows the common 'per object' value of the selected property.

For example, to modify the size of 1D particles:

Select the Size property from the Attribute list.
Enter a desired radius to the Common Value field.

Uniform size defined for 1D particles

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.

By checking the Pointwise box, you can assign an individual value for each particle. For example, to modify the size of particles:

Select the Size property from the Attribute list.
Enter a suitable base value to the Common Value field. This value will initialize per point values.
Check the Pointwise option.
Set the particle object to edit state and select some particles from the view window.
Enter a new radius to the Point Value field.

2D particles here and there

Render Channel

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.

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:

2D particle object contains a sphere

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.

2D particles distributed over a 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 pointwise 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:

Create a number of 1D particles representing meteorites.
Create a sphere representing a planet.
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.
Select the particles and apply the tool Animation/Physical Properties/Warm butter.
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.


Recording and Executing Macros		Creating Leaves Using 3D Particles