Gas Microsolvers and DOPs in Houdini

Jul 5, 2024

Gas Microsolvers and DOPs in Houdini

Introduction

  • Presenter: [Name not provided], Head of FX at Rise Visual Effects Studios
  • Main Topic: Gas Microsolvers and DOP data in Houdini
  • Location: Hosted by Rise Visual Effects Studios

Motivation for the Presentation

  • Lack of example files and tutorials for microsolvers in Houdini.
  • Existing resources: One masterclass by Jeff Wagner that's quite old but very good.
  • Recent initiative to create own setups and example files for every microsolver from A to Z.

Outline of Presentation

  1. Empty Object DOP and Top Geometry Spreadsheet
  2. Microsolvers: Scalars, Vectors, and Distance Fields
  3. Key Microsolvers Explained

Key Concepts

  1. Empty Object DOP: Initial data container for all simulations.
  2. Geometry Types: Scalar fields, vector fields, and distance fields.
  3. Microsolvers: Basic building blocks for simulations including Pyro, FLIP, and POPs.

Detailed Breakdown

Empty Object DOP

  • Purpose: Data container in DOP simulations.
  • Attributes: Fields, sources, colliders, subsolvers, and visualization data.
  • Visualization DOP: Required to display data in the viewport.

Gas Microsolvers Overview

  • Granularity: Low-level mechanics of any simulation (Pyro, FLIP, POPs, etc).
  • Complexity: Diving deeper into solvers reveals multiple layers, crucial to understand the fundamental 112 microsolvers.

Key Microsolvers Examples

Gas Advect CL

  • Function: Advects any field or geometry using a given velocity field.
  • Trace Methods: Euler, Midpoint, RK3, RK4, and OpenCL methods.
  • Application: Advecting Vellum cloth using a pyro simulation.

Gas Analysis DOP

  • Function: Compute properties (curvature, gradient, divergence, etc) of input fields.
  • Example: Computing divergence of a velocity field and visualizing it.
  • Relevance: Used extensively in fluid dynamics.

CSG Operations and Arithmetic

Gas Calculate DOP

  • Function: Perform operations on any pair of fields (e.g., copy, add, multiply).
  • Example: Copying and multiplying density fields in a Dop network.

Gas Linear Combination DOP

  • Function: Combines fields or attributes in various ways.
  • Examples: Integrating force into velocity and position for custom solvers.

Constructive Solid Geometry Operations

  • Function: Build geometries from SDF operations like max, min, etc.
  • Tools: VDB Combine SOP, VDB Convex Clip SOP.
  • Example: Combining a sphere and box SDF.

Specialized Microsolvers

Gas Seed Marker DOP

  • Function: Creates marker particles along an implicit surface.
  • Use Case: Representing surfaces in simulations.
  • Tools: Seed marker particles along implicit surfaces.

Gas Seed Particles DOP

  • Function: Create particles inside an implicit surface.
  • Example: Filling an SDF object with points and visualizing.

Gas Intermittent Solve DOP

  • Function: Solves operations at specific intervals instead of every frame.
  • Example: Reduced computation for certain solvers in multi-step simulations.

Practical Applications

Helmholtz Decomposition

  • Concept: Any vector field can be broken into solenoidal (divergence-free) and irrotational parts.
  • Application: Helmholtz Theorem in fluid dynamics.

Efficiency and Performance in Simulations

  • Optimization Examples: Vertical forces to counteract blurring, and performance comparisons between stock Pyro solvers and custom setups.

Conclusion

  • Credits: Detailed various microsolvers but had to omit some due to time constraints.
  • Hiring Notice: Rise Visual Effects Studios is hiring. Visit jobs.risefx.com.
  • Q&A Session: Discussed various user questions about microsolvers, custom solvers, and performance.