Houdini 16.5 Nodes VOP nodes

Two Way Switch VOP node

Takes an integer input.

This operator takes an integer input. If this input value satisfies the Condition parameter, the output is set equal to the first input value. If the integer input does not satisfy the Condition parameter, the output is set equal to the second input value. This provides a simple way to switch between two values and simulate an if-then-else construct.

Examples

The following examples include this node.

Street Crowd Example Example for Crowd Solver dynamics node

Crowd example showing a street setup with two agent groups

The setup creates two groups of agents. The yellow agents are zombies which follow a path of the street. The blue agents are living pedestrians that wander around until they come into proximity of the zombies and then they swtich into a running state.

Triggers to change agent states are setup in the crowd_sim dopnet. The zombies group uses proximity to the stoplights and the color of the light to transition into a standing state when lights are red. The living group transition into a running state when they get close to the zombie agents.

Note

The animation clips need to be baked out before playing the scene. This should happen automatically if example is created from Crowds shelf. Otherwise save scene file to a location of your choice and click Render on '/obj/bake_cycles' ropnet to write out the files. The default path for the files is ${HIP}/agents.

DensityViscosity Example for FLIP Solver dynamics node

This example demonstrates two fluids with different densities and viscosities interacting with a solid object.

FlipColorMix Example for FLIP Solver dynamics node

This example demonstrates the use of the Flip Solver to mix the colors of a red fluid with a blue fluid to form a purple fluid.

FlipColumn Example for FLIP Solver dynamics node

This example demonstrates how a mixture of fluid colours can have their colour changed by a collision with a static object.

DiffuseSmoke Example for Gas Diffuse dynamics node

This example demonstrates how to diffuse the density of a smoke simulation using the Gas Diffuse DOP.

grass

This example simulates grass being pushed down by an RBD object. Fur Objects are used to represent the blades of grass and Wire Objects are used to simulate the motion. When a single Fur Object is used to represent the grass, neighbouring blades of grass will have similar motion. Additional objects with different stiffness values can be used to make the motion less uniform. When "Complex Mode" is enabled, two objects are used to represent the grass. The stiffness of each set of curves can be controlled by adjusting the "Angular Spring Constant" and "Linear Spring Constant" parameters on the corresponding Wire Objects.

CurveForce Example for POP Curve Force dynamics node

This example demonstrates the use of the POP Curve Force node to control the flow of a particle sim AND a flip fluid sim.

Volume Rendering - Metaballs as Volume Example for Mantra render node

Metaball geometry can be natively rendered as a volume in mantra. Metaball rendering can be enabled by checking the Metaballs as Volume parameter on the Geometry tab of a geometry object. Any point attributes on the metaballs will be interpolated to the shading position in the same manner that point attributes are interpolated for metaball surfaces.

Here is an example using randomized point color attributes:

Controlling Shadow Quality/Performance

Shadow map generation uses the Pixel Samples and Shadow Step Size parameters (in the Mantra Render Operator) to control quality and performance in exactly the same way they are used for surfaces. Since volumes often cast soft, diffuse shadows, it is often possible to use low-resolution deep shadow maps when rendering volumes, leading to much faster render times. Shadow map Resolution can be changed on the Shadow tab of a Houdini light.

RampReference

This example demonstrates the use of ramps and referenced ramps which are animated over time.

Down Hill Lava Flow Example for Material shader node

In this file we create a downhill lava flow with crust gathering and hardening at the base of the slope. All of the animation is achieved through the shader itself, and all of the geometry is completely static.

Note

Most of the parameters for the lava material are overridden by point attributes created in the surface nodes.

FirePit Example for Material shader node

Note

No geometry is animated in this file. All animation is achieved by animating the textures

Flames are grids so that UV textures can easily be applied, they are then warped around a metaball using a magnet SOP. The flames are then assigned to either a yellow or blue Flames texture. The Flames' opacity mask wrap is set to Decal to prevent the texture from repeating and showing a single pixel ring at the top of the flame geometry. I'm also using a mask file named flameOpacMap.jpg to enhance the flames' shape at the top. The noise offset has been animated over $T with an greater emphasis on the Y axis so that the flames look like they are rising. This is the same reason the Noise jitter is larger for the Y axis as well.

The coals are spheres that have been copy stamped onto a deformed grid. Using Attribute Create surface nodes I am able to override and copy stamp the lava texture’s parameters at the SOP level so that local variables, such as $BBY, can be used to animate the texture. This way the texture’s crust and its crust values can be used only to form the tops of the coals. This reserves the lava aspect of the texture to be used on the bottoms of the coals. The lava intensity (Kd attribute) is then stamped and animated to create the look of embers on the bottom of coals glowing.

StyleDisplacement Example for Material shader node

This is an example file showing an object made up of two quads, one with a bump map, the other with true displacement. This object is duplicated, and the second copy uses a style sheet to reverse the material assignments on the two quads.

BlendAttr Example for Attribute Composite geometry node

This example demonstrates how to blend attributes using the Attribute Composite SOP.

RandomMaterial Example for Attribute String Edit geometry node

This example demonstrates how to use the Attrib String Edit SOP to modify String primitive attributes and randomize the colours on a grid on a per-primitive basis.

FurBallWorkflow Example for Fur geometry node

This example demonstrates how the Fur SOP and Mantra Fur Procedural can be applied to an animated skin geometry. CVEX shaders are used to apply a custom look to the hairs based upon attributes assigned to the geometry.

FurPipelineExample Example for Fur geometry node

This example illustrates how custom shaders can be used to define the appearance of fur generated by the Fur SOP.

PaintPoints Example for Paint geometry node

This example demonstrates how to paint scattered points onto the surface of your geometry with a set number of points per area.

AlphaOmega Example for Points from Volume geometry node

This example demonstrates how to use a Points From Volume SOP to create a target goal for a flip simulation and make it fill a given piece of geometry.

UnpackWithStyle Example for Unpack geometry node

This example demonstrates the Unpack SOPs ability to evaluate style sheet information while unpacking. Nested packed primitives are used to demonstrate partial unpacking while still preserving styling information. This example also demonstrates the use of a Python SOP to extract information from the per-primitive style sheets.

volumesurface_explicitgrade Example for Volume Surface geometry node

This example shows how to use the Volume Surface SOP to surface an SDF using another volume to specify the triangle sizes.

VOPpointgroup Example for Add Point to Group VOP node

Example of building point Groups in a VOP SOP where every other point is added to a new group.

Only point groups are supported in VOPs.

The VOPs you need to learn are:

Add Point To Group VOP, Create Point Group VOP, and Point In Group VOP

WornMetal Example for Curvature VOP node

This example shows how the curvature vop can be added to a shader network to add a worn or distressed look to your material.

PointCloudLookup Example for Point Cloud Iterate VOP node

This example shows how to accomplish point cloud lookups for volumes using pcfilter and pciterate. It demonstrates how to iterate over and import values returned by a query.

ParticleVolumeCollision Example for Volume Sample VOP node

This example demonstrates how to set attributes on a particle based on the value of a volume at the particle’s position.

To accomplish this, you can use a VOP POP to edit the particles, using the Volume Sample from File VOP to sample the volume.

In the example, particles are colored differently based on whether they are "in" or "out" of the volume, where "in" is defined in the example as "the value in the volume is > 0 at the position of the particle", but could easily be changed.

See also

VOP nodes