SPH - Spline

"Spline" is a very interesting emitter with many fields of application. Its shape can be adjusted with control points (CP) and tangents using the “Move” tool. This type can be seen as a hybrid between an emitter and a daemon, because you can add forces that influence the particles.

A standard "Spline" emitter shows three control points, surrounded by yellow circles. These circles represent the zones of influence of the various forces. Each of these zones can be adjusted individually and it is also possible to add or remove control points. Control points can also be animated, but it is better to use a parented helper object (e.g. a "Null" node) for this purpose, instead of manipulating them directly. Of course, you can apply any particle type (fluid etc.) to the spline emitter. Changing and adjusting a spline emitter’s shape takes a little practice, but if you are familiar with splines from other programs, it should not take very long to achieve full control. Moving one control point affects the shape of the entire spline.

To give you a better understanding of this emitter, it is necessary to know its parts and elements:

A. The small yellow dots are the spline’s control points.

B. Each yellow circle shows a control point’s radius. This radius can be seen as the zone of influence of the control point’s settings and parameters. Particles can also be deleted when leaving the yellow circle.

C. The light blue arrows indicate the emission direction for each control point.

D. The straight line from up to down represents the spline’s curvature or path. It will be adjusted dynamically while moving the control points.

E. The dots at the beginning and the end of the spline are tangent control points. They can be adjusted independently from each other.

Affect

This feature is normally only available with daemons, but since the control points are able to exert forces on the particles, it is necessary to introduce the options here. Particles can be affected in two ways: either by “Force” or “Velocity”. The first option applies an external force, resulting in an acceleration, while the second one only modifies the velocities of the particles without introducing an additional acceleration.

“Forces” takes a little time to display their full influence. This means that they accelerate the particles over a certain time span, depending on their strength. High forces exert stronger accelerations and the particles or bodies become faster and faster as long as the force acts on them. The result is a curved stream of particles.

“Velocity” directly affects the particles from the very beginning without any delay or deceleration. The result is an apparently stronger influence, because the deflection of the particles starts from the very first moment. In this case the result is a linear, diagonal stream of particles.

Creation

You can choose from three different options: “Axis”, “Tube” and “Edge”. Particles are always influenced by a control point’s settings, such as radius. “Axis” works similar to the “Linear” emitter and the entire spline is used to create particles. “Tube” creates a hose around the spline and with the “Kill leaving” option you can create a tube that is limited by the control points’ radius settings. “Edge” can be seen as a circular mode. The radius of the first (lowest) control point acts like a circle emitter, creating particles in upward direction parallel to the spline. Please have a look at the images below.

The "Spline" emitters "Creation" types: "Axis", "Tube" and "Edge".

Speed

This setting determines the speed of the particles during creation time. "Speed" is measured in metres per second [m/s].

Randomness

To avoid a uniform look, the particles can be randomly displaced while leaving the emitter.

Kill leaving

Particles will be automatically deleted while leaving the yellow circles.

EDIT

This is the button if you want to change the positions and settings of control points. If the edit mode is enabled, the button turns yellow and the parameters become accessible.

Insert CP

This button is used to create a new control point (CP). To add a new point it is necessary to select an existing point first. A new point is always created above the selected one. Custom points share exactly the same features and as their default “counterparts”.

Delete CP

Select a control point and click on this button to remove it. Adding or deleting a control point might change the spline’s shape! Please note that it is not possible to delete the three default points. This action only affects subsequently added points.

@ CP index

This field indicates the index of the currently selected control point. By entering a (valid) number you can jump directly to the desired point. Indices are enumerated from bottom to top. The control point indices will be automatically updated when you create a new point.

@ CP axial

This parameter introduces an axial force along the spline’s path near the selected control point.

@ CP radial

With this setting a radial force is added near the selected control point.

@ CP vortex

You can also create a vortex force around the currently selected control point.

@ CP radius

Alter the radius of the zone of influence for each control point individually. The radius is indicated by a yellow circle around the control point.

@ CP rotation

Use this parameter to change the emission direction. The light blue arrow, indicating this direction, becomes rotated around the spline’s path. This is great to create twisted emissions and avoid patterns.

@ CP link

By clicking on the hyphen, RealFlow opens a new node picker and you can choose the object that the selected control point will be parented to. You can even select animated objects to externally control the particular point – typically a control point is linked to a "Null" object. This workflow is much easier than directly changing the point’s position with the move tool.