# Particles Deflector


*Particles Deflector* is a surface field that has no visual representation, but physically interacts with [Particle Systems](../../../../objects/effects/particles/index.md) (other objects are not affected) blocking the way for particles and making them bounce off the deflector's surface. Depending on the specified size, it can be either rectangular or square, plus it can be arbitrarily positioned or rotated to cover the necessary area.


Deflectors are **one-sided**, meaning the particles can only interact with one side (e.g., when falling on a deflector from above, while freely passing through them from the opposite side).


![](particles_deflectors.gif)


### See also


- The *[ParticlesFieldDeflector](../../../../api/library/objects/class.particlesfielddeflector_cpp.md)* class to manage *Particles Deflectors* via API


## Adding Particles Deflector


To add a *Particles Deflector* to the world via UnigineEditor, do the following:


1. In the Main Menu, choose *Create -> Particle System -> Particles Deflector*. ![](add_deflector.png)
2. Place the *Particles Deflector* in the world to cover the area where particles are to be cut out: > **Notice:** Make sure that the *Spacer interaction* flag is set for materials applied to grass or water.


## Editing Particles Deflector


In the *Particles Field Deflector* section (*[Parameters](../../../../editor2/node_parameters/index.md)* window -> *Node* tab), the following parameters of the *Particles Deflector* can be adjusted:


![](edit_deflector.png)


### Adjusting Deflector Form


| Size | Size of the deflector's plane surface. |
|---|---|
| Restitution | Restitution coefficient of the *Particles Field Deflector*. This coefficient defines the value of the bouncing impulse a particle will receive on a contact with the deflector (how fast a particle shall bounce from the deflector): - The minimum value of **0** means the particles do not bounce off, but rather slide along deflector surface. - The maximum value of **1** makes the angle of bouncing equal to the angle at which the particles fall. |
| Roughness | Roughness coefficient of the *Particles Field Deflector*. This coefficient defines roughness of the deflector surface the particles collide with, and the range of angles at which particles shall bounce from the deflector: - The minimum value of **0** means the surface is smooth and bouncing particles are scattered in a uniform direction. - The maximum value of **1** means the surface is uneven and bouncing particles are scattered in different directions. |
| Interaction Particle Mode | Interaction mode for the *Particles Field Deflector*. Interaction can be triggered on a contact of the deflector either with particle's center position or with its bounding box (this can be useful in case of length particles, for example). |


### Setting Bit Masks


The bit masks listed below enable you to fine tune interactions and functionality of a *Particles Field* to achieve the desired effect and optimize performance.


| Particles Field Mask | Bit mask enabling you to control interactions of the *Particles Deflector* with particles. The *Deflector* will affect particles generated by a Particle System only if they both have [matching masks](../../../../principles/bit_masking/index.md). |
|---|---|
| Viewport Mask | A *Viewport* mask. A bit mask for rendering the *Particles Deflector* in the current viewport. For the *Particles Deflector* to be rendered into the viewport, its mask should match the camera *[Viewport](../../../../principles/bit_masking/index.md#viewport)* mask (at least one bit). This can be used to selectively disable *Deflector* functionality for a certain camera view without disabling the *Deflector* itself (e.g. it is not necessary to cut out rain or snow inside a car, when the car is viewed from above). |