Instancing and Rendering Particles

Direct Rendering

There are two approaches to direct rendering of particles systems in mantra. You can either render particle systems or render as points. If you are rendering particle systems, you must create your particle geometry in POPs. If you are rendering as points, you can render from any geometry.

Particle Systems

Particle system primitives created using a POP network SOP can be rendered directly in mantra. By default, particle system primitives are rendered as spheres.

Render as Points

In mantra, you can directly and efficiently render the points in a model without creating a particle system. Point rendering renders the points in a model as disks oriented toward the camera, with only a single shader evaluation per point.

Rendering geometry as points

Turn on Render As Points on the Geometry sub-tab of the Render tab of the object.
Render using a mantra output driver.

Rendering Attributes for Points and Particles

To change the rendering style of particle systems, use a Render POP.

Note	You must re-simulate the POP network for any changes in the render POP to take effect.

You can add attributes to points and particles by creating an Attribute SOP or Attribute POP and connecting it to the particle system.

The following attributes can be added to points, verticies, entire particle systems, and primitives:

Points

particle scale
width
velocity
orientation

Verticies

particle scale
width
orientation

Particle systems

particle scale
width

Primitives

particle scale
width

How to instance geometry on particles (particle replacement)

To...	Do this
Instance geometry on particles	Click the Instance button on the Drive Particles tab of the shelf. Click the particle system you want to be affected and press Enter to confirm your selection. Click the object you want the particles to be replaced with and press Enter to confirm your selection. You can see a preview by clicking the template flag in the network editor, which will replace each particle with a wire frame of the shape. For specific parameter help see the Instance node help.
Rotate the instanced geometry to an angular value	On the Instance node (see above). Set the Orientation to Fixed axis. Set the Angle parameter to the angle to rotate to, and the Axis parameter to the axis around which to rotate. Create a Rotation node and connect the particle flow to it. Set the Angle parameter to the angle to rotate to, and the Axis parameter to the axis around which to rotate.
Rotate the instanced geometry using torque	Click the Torque button on the Drive Particles tab of the shelf. Click the particle system you want to be affected and press Enter to confirm your selection. Torque is like sticking a handle on something and rotating it by pushing on the handle. Set the Position of the offset point which you will apply the force to, and the Force to the force to apply to the offset point. For specific parameter help see the Torque node help.
Make the instanced geometry look at an object	Create a Look At node and connect the particle flow to it. Set Lookat Mode to Lookat point. Set the Reference parameter to Referenced object. Set the Object field to the path to the object you want the particles to point towards.
Make the instanced geometry look at a plane	Create a Look At node and connect the particle flow to it. Set Lookat Mode to Lookat plane. Set the Reference parameter to World Space or This Object to choose in which space to interpret the direction. Set the Direction parameter to a vector describing the direction in which the particles should look.

How to set the rendered appearance of particles

To... Do this

Control the appearance of non-sprite particles

Use the tab menu to create a Render node.
Use the Particle type parameter to control what raw particles look like in the rendered image.
You can use the Render node to control the global size of all particles, or you can use the Property POP to set each particle’s scale (pscale) attribute.

Display sprites in the viewport

In the viewport options menu, choose Display > Display options, or press D.
Click the Particles tab.
Set Display particles as to Sprites.

Control the appearance of sprites

Create a Sprite node and connect the particle flow to it.
At the SHOP level, create a material with a VEX Decal and a Mantra: Sprite Procedural, and connect them to the Output Shaders node.
Assign a Texture Map to the VEX Decal in the parameter editor.
Go back to the SHOP level and drag your Material onto your particle system.

Note	You can rotate and scale the sprites by turning on the Rotate and Scale checkboxes and editing the values in the Sprite node parameter editor.

Note	Sprites always face the camera.

For specific parameter help see the Sprite node help.

If Resolve SHOP Path is on, the Sprite SHOP path is resolved relative to this node, and the spriteshop attribute is set to the full path of the shop. If it is off, no attempt is made to find the shop, and the exact string entered in the Sprite SHOP parameter is put into the spriteshop attribute. This will prevent the sprites from rendering properly in the POP Viewer. The Geometry and Object Viewers will still render the sprites properly if the SHOP paths are specified relative to the object that contains the POP Network.