GPU Technology Conference 2012

nVidia's GPU Technology Conference is over, and a number of presentation slides have been uploaded. There were a quite a few interesting talks relating to graphics, robotics and simulation:

• Simon Green from nVidia and Christopher Horvath from Pixar presented 'Flame On: Real-Time Fire Simulation for Video Games'. It starts with a recent history of research on CG fluid systems, and gives five tips on better looking fire: 1. Get the colors right (e.g. radiation model), 2. Use high quality advection (not just bilinear filtering), 3. Post process with glow and motion blur. 4. Add noise. 5. Add light scattering and embers. They then go into more detail on Tip #1 looking at the physics behind the black-body radiation in a fire, and the color spectrum.
• Elmar Westphal of PGI/JCNS-TA Scientific IT-Systems presented 'Multiparticle Collision Dynamics on one or more GPUs', about multiparticle collision dynamics GPU code. He starts by explaining the overall algorithm, and explaining step-by-step what performs well on the GPU. Specific GPU optimisations explained include spatial subdivision lists, reordering particles in memory, hash collisions, and finally dividing workload between multiple GPU's. An interesting read.

• Michal Januszewski from the University of Silesia in Katowice introduces 'Sailfish: Lattice Boltzmann Fluid Simulations with GPUs and Python'. He explains lattice boltzmann fluid simulation, and some of the different configurations of lattice connectivity and collision operators. Moves into code generation examples, and gives a brief explanation of how the GPU implementation works.
• Nikos Sismanis, Nikos Pitsianis and Xiaobai Sun (Aristotle University, Duke University) cover 'Efficient k-NN Search Algorithms on GPUs'. Starts with an overview of sorting and K-Nearest Neighbour (KNN) search algorithm solutions, including ANN (approximate NN) and lshkit and moves into results including a comparison of thrust::sort with Truncated Bitonic sort. Software is available at http://autogpu.ee.auth.gr/.
• Thomas True of nVidia explains 'Best Practices in GPU-Based Video Processing' and covers overlapping copy-to-host and copy-to-device operations, and an example of processing bayer pattern images.
• Scott Rostrup, Shweta Srivastava, and Kishore Singhal from Synopsys Inc. explain 'Tree Accumulations on GPU' using parallel scatter, parallel reduce and parallel scan algorithms.

• Wil Braithwaite from nVidia presents an interesting talk on 'Interacting with Huge Particle Simulations in Maya using the GPU'. He begins with a brief runthrough of the workings of the CUDA SPH example, and then moves onto the particle system including Maya's body forces (uniform, radial, vortex), shape representations (implicit, covex hull, signed distance fields, displacement maps), collision response, SPH equations, and finally data transfer. Ends with a brief overview of rendering the particles in screen space. Neat.
• David McAllister and James Bigler (nVidia) cover the OptiX internals in 'OptiX Out-of-Core and CPU Rendering' including PTX code generation and optimisation, and converting the OptiX backend to support CPU's via Ocelot and LLVM. An interesting result, LLVM does better at optimising "megafunctions" than small functions, but not entirely unexpected given how LLVM works. The presentation finishes with an overview of paging and a tip on bounding volume heirarchies. Good to see Ocelot in the mainstream.

• Eric Enderton and Morgan McGuire from nVidia explain 'Stochastic Rasterization' (ala 'screen door transparency' rendering) via MSAA for motion blur, depth of field and order-independent transparency, by using a geometry shader to bound the shape and motion of each tri in screen space, and setting up the MSAA masks. Nice.
• Cliff Woolley presents 'Profiling and Tuning OpenACC Code' (by adding pragmas to C / Fortran code, ala OpenMP) using an example of Jacobi iteration, and there were a number of other talks on the topic.
• Christopher Bergström introduced 'PathScale ENZO' the alternative to CUDA and OpenCL.
• Phillip Miller from nVidia did an broad coverage of 'GPU Ray Tracing'. He starts with a myths and claimed facts on GPU raytracing, highlights some commercial GPU raytracers (and the open source OpenCL LuxRenderer) and goes into some details that are better explained in the OptiX Out-of-Core presentation.
• Phillip Miller follows with 'Advanced Rendering Solutions' where he takes a look at nVidia's iray, and where they believe they can introduce new capabilities for design studios and find a middle ground with re-lighting and physcially based rendering.

• Peter Messmer presents 'CUDA Libraries and Ecosystem Overview', where he provides an overview of the linear algebra cuBLAS and cuSPARSE libraries performance, then moves to signal processing with cuFFT and NPP/VSIP for image processing, next is random numbers via cuRAND and finally ties things up with Thrust.
• Jeremie Papon and Alexey Abramov discuss the 'Oculus real-time modular cognitive visual system' including GPU accelerated stereo disparity matching, likelihood maps and image segmentation with a parallel metropolis algorithm.

• Jérôme Graindorge and Julien Houssay from Alyotech present 'Real Time GPU-Based Maritime Scenes Simulation' beginning with ocean simulation and rendering from FFT based wave simulation using HF and LF heightmap components. They then cover rendering the mesh, scene illumination and tone mapping, and a sneak peak at boat interaction. The ocean simulation video is neat.
• Dan Negrut from the Simulation-Based Engineering Lab at the University of Wisconsin–Madison gives an overview of the labs multibody dynamics work in 'From Sand Dynamics to Tank Dynamics' including friction, compliant bodies, multi-physics (fluid/solid interactions), SPH, GPU solution to the cone complementary problem, ellipsoid-ellipsoid CCD, multi-CPU simulation, and finally vehicle track simulation in sand. Wow. Code is available on the Simulation-Based Engineering Lab website.
• Max Rietmann of USI Lugano looks at seismology (earthquake simulation) in 'Faster Finite Elements for Wave Propagation Codes' and describes parallising FEM methods for GPUs in SPECFEM3D.
• Dustin Franklin from GE introduces GE's MilSpec ruggedised Kepler-based GPU solutions and Concurrent Redhawk6 in 'Sensor Processing with Rugged Kepler GPUs'. Looks at some example applications including hyperspectral imaging, mosaicing, 360 degree vision, synthetic aperture radar processing, and space-time adaptive processing for moving target identification.
• Graham Sanborn of FunctionBay presents 'Particle Dynamics with MBD and FEA Using CUDA' and gives a brief overview of their combined CPU/GPU multi-body FEA system and briefly describes the contact, contact force, and integration steps.
• Ritesh Patel and Jason Mak of University of California-Davis cover the Burrows-Wheeler Transform, Move-to-Front Transform and Huffman Coding in 'Lossless Data Compression on GPUs'. They find merge sort for BWT performs best on the GPU, explain the parallel MTF transform and Huffman in illustrative detail and tie things up with benchmarks, unfortunately GPU is 2.78x slower than CPU.
• Nikolai Sakharnykh and Nikolay Markovskiy from NVIDIA provide an indepth explanation of their GPU implementation of solving ADI with tridiagonal systems in '3D ADI Method for Fluid Simulation on Multiple GPUs'.
• Enrico Mastrostefano, Massimo Bernaschi, and Massimiliano Fatica investigate breadth first search in 'Large Graph on multi-GPUs' and describe how best to parallelise it across multiple GPU's by using adjacency lists and level frontiers to minimise the data exchange.
• Bob Zigon from Beckman Coulter presents '1024 bit Parallel Rational Arithmetic Operators for the GPU' and covers exact 1024 bit rational arithmetic (add,sub,mul,div) for the GPU. Get the 1024 bit arithmetic code here.
• Roman Sokolov and Andrei Tchouprakov of D4D Technologies discuss 'Warped parallel nearest neighbor searches using kd-trees' where they take a SIMD style approach by grouping tree searches via voting (ballot)
• David Luebke from nVidia takes a broad look at CG in 'Computational Graphics: An Overview of Graphics Research @ NVIDIA' and provides an overview of research which is featured in a number of previous talks and other GTC talks including edge aware shading, ambient occlusion via volumes and raycasting, stochastic rendering, improved image sampling and reconstruction, global illumination, and CUDA based rasterization.
• Johanna Beyer and Markus Hadwiger from King Abdullah University of Science and Technology discuss 'Terascale Volume Visualization in Neuroscience' where each cubic mm of the brain scanned with an electron microscope generates 800 tereabytes of data. The idea here is to leverage the virtual memory manager to do all the intelligent caching work, rather than a specialised spatial datastructure for the volume rendering.
• Mark Kilgard introduces the NV_path_rendering extension in 'GPU-Accelerated Path Rendering', and demonstrates using the GPU to render PDF, flash, clipart, etc. Contains some sample code.

• Janusz Będkowski from the Warsaw University of Technology presented 'Parallel Computing In Mobile Robotics For RISE' a full GPGPU solution for processing mobile robot laser scan data through to navigation. Starts with data registration into a decomposed grid which is then used for scan matching with point-to-point Iterative Closest Point. Next is estimating surface normals using principle component analysis, demonstrated on velodyne datasets. This is used to achieve point-to-plane ICP and he demonstrates a 6D SLAM loop-closure. Finishes it all off with a simple gradient based GPU path planner.

Note that in recent days more presentation PDF's have been uploaded so there is still plenty to look through, and with all the content it's difficult to look through it all - take a look yourself! I'll leave you with a video from the GTC 2012 keynote on rendering colliding galaxies:

Game Developers Conference 2012 - Technical summary

GDC2012 is over, and this year there are a huge number of available presentations. You can download the Game Developer Conference 2012 presentations from the GDC vault, Jare / Iguana has also kept a link collection from GDC 2012. I've looked over all the technical publications available and put together this summary post. (Edit: I've updated this to cover some maths, physics, and graphics material I missed on the first pass - thanks Johan & Eric)

I'll start with graphics.

Louis Bavoil / nVidia and Johan Andersson / DICE have a presentation on "Stable SSAO in Battlefield 3 with Selective Temporal Filtering", ambient occlusion is a well established technique now, but they apply a quick way to use past data and the differences in Z buffer states between frames to intelligently reuse the AO results. They also look at filters and optimising blur functions. Similar to established tricks in the realtime raytracing demoscene.

Eban Cook / Naughty Dog presented "Creating Flood Effects in Uncharted 3", a technical artist look at water effects. Unfortunately realtime fluid simulation wasn't used, instead Houdini was used to pre-generate the game content. An overview of the shaders for water, water particles, froth particles, and lighting is given.

Light probe interpolation

Robert Cupisz / Unity discussed light probes, "Light probe interpolation using tetrahedral tessellations", in terms of choosing the appropriate probe and weights using Delaunay Triangulation / Tetrahedrons and Barycentric Coordinates by dividing scenes into convex hulls. Also covers projecting onto the nearest convex hull, covers it all with a fair bit of maths, this would be of interest to physics / collision detection programmers too. There is a collection of nice links and some sample code at the end.

Matthijs De Smedt / Nixxes covers "Deus Ex is in the Details" using DX11 tech. Covers AA (FXAA DLAA MLAA), SSAO, DOF (Gaussian blur), tessellation and soft-shadows.

Colt McAnlis / Google investigates post-compressing DXT textures in his talk "DXT is not enough", trying to out-do zipped DXT's with delta encoding. More info at this blog post or skip it all and download the DXT CRUNCH compressor here.

Matt Swoboda / Sony & Fairlight delves into Signed Distance Fields, a demoscene hot-topic last year, with the talk "Advanced Procedural Rendering in DirectX 11". Investigates converting polgyon mesh data and particle data into signed distance fields. Takes an in-depth look into a optimised marching cubes implementation for a fluid simulation with smooth particle hydrodynamics (SPH), and how to use signed distance fields to do ambient occlusion.

Physically based rendering in realtime 

Yoshiharu Gotanda / tri-Ace research makes a case for physically based rendering with a Blinn-Phong model in the presentation "Practical Physically Based Rendering in Real-time". An indepth look at the BRDF formulation they use.

Wolfgang Engel, Igor Lobanchikov and Timothy Martin / Confetti present "Dynamic Global Illumination from many Lights", just a bunch of pictures, not much information.

Carlos Gonzalez Ochoa / Naughty Dog covers "Water Technology of Uncharted". Covers the shader, animating the normal maps flow, and simulating the ocean water with Gerstner waves, b-spline waves, and wave particles. They go on to look at LOD with "Irregular Geometry Clipmaps" including fixing T joints, and then culling, skylights and underwater fog. Next physics, attaching objects (buoyant), and point queries. Finally, SPU optimization. Quite comprehensive.

Water technology of Uncharted

Ben Hanke / SlantSixGames describes the bone code in "Rigging a Resident Evil". Transforms are described with 9 functions and processed with an optimising compiler, allowing fast retargeting of animations.

Scott Kircher / Volition Inc expands on Inferred Lighting in "Lighting & Simplifying Saints Row: The Third" by looking into lighting for rain, foliage, dynamic decals, and radial ambient occlusion. Then moves on to automated mesh simplification using iterative edge contraction and takes an indepth look at selecting an appropriate error metric.

Nathan Reed / Sucker Punch Productions discusses "Ambient Occlusion Fields and Decals in Infamous 2", going into depth on how to solve the artifacts of this approach.

Marshall Robin / Naughty Dog covers the effects system tools in "Effects Techniques Used in Uncharted 3: Drake’s Deception".

Niklas Smedberg / Epic Games looks at PowerVR GPU processing pipeline and capabilities in "Bringing AAA graphics to mobile platforms" and provides a number of tricks'n'tips on optimising the performance of the mobile GPU, and highlights the cheap operations. In short: AA (fast), hidden surface removal (fast), alpha test (slow), render targets (slow), texture lookups (slow). Takes a more detailed look at material shaders, god rays, and character shadows. All in all, pretend its ~2002, and you'll be right.

Mickael Gilabert / Ubisoft and Nikolay Stefanov / Massive cover the GI system in Far Cry 3 in "Deferred Radiance Transfer Volumes". Light probes get precomputed directional radiance transfer data from a custom raytracer stored using spherical harmonics. Source code for the relighting system is presented, along with optimisations by using volume textures.

John McDonald / nVidia explains CPU/GPU synching for buffers in "Don’t Throw it all Away: Efficient Buffer Management" and provides advice on buffer creation flags.

Bryan Dudash / nVidia suggests using average normals to overcome tesselation issues in "My Tessellation Has Cracks!".

Mastering DX11 with Unity

Renaldas Zioma / Unity and Simon Green / nVidia present "Mastering DirectX 11 with Unity". Starts by looking into Unity's physically based shaders (Oren-Nayar, Cook-Torrance, and energy conservation, then blurry reflections and combining normal maps). Next up, Catmull-Clark Subdivision, tetrahedra light probes (See Robert Cupisz's talk), HBAO, APEX destruction, Hair simulation with guide hairs, Explosions using signed distance fields with noise and color gradients,and finally velocity buffer motion blur.

Tobias Persson / Bitsquid discusses lighting billboards in "Practical Particle Lighting". Looks at normal generation and per-pixel lighting for billboards (including code snippets), applying shadow maps with a domain shader, and shadow casting

Karl Hillesland / AMD investigates realtime Ptex (per-face texture mapping) in "Ptex and Vector Displacement in AMD Demos", and efficient retrieval from the texture atlas, including all MIPs.

Jay McKee / AMD presents the "Technology Behind AMD’s
Leo Demo". He details some of the code behind the forward rendering of 3000 dynamic light sources using a depth pre-pass, light culling (tile-based compute shader to output light list), and light accumulation with materials phase. Basically moves the light management code from CPU to GPU.

Terrain in Battlefield 3

Mattias Widmark / DICE presents "Terrain in Battlefield 3: A modern, complete and scalable system". Begins with an overview of the features for the terrain system (heightfield based, procedurally generated, spline decals, decoration (tree,rock,grass), destruction, water), and presents their quadtree terrain data structure, paying particular attention to LOD. Next, CPU/GPU performance is investigated, and a clip-map based virtual texture system is presented. The large terrain data set is managed by intelligently streaming data to the required detail ('blurriness'), and co-locating data (heighfield/color/mask lumped together, next to the next level of relevant LOD data), which is also compressed (RLE/DXT1). Nodes are then prioritized based on distance, culling, and updates (e.g. destruction). Finally, mesh generation, stitching and tessellation with displacement on the GPU.




Moving on to physics.

Erin Catto covers "Diablo 3 Ragdolls", including representing ragdoll bones, initialising ragdolls from animations, and interacting kinematic and dynamic objects.

François Antoine / Epic talks about Gears of Wars 3 destruction physics in "Pushing for Large Scale Destruction FX" and suggests using particles for dust and debrie, and simplifying meshes for destruction.

Stephen Frye / EA looks at ragdolls in the presentation "Tackling Physics". Highlights aspects of ragdolls that look unrealistic, and suggests adding joint limits and motorized constraints at joints to simulate muscles. Gives two approaches to solving the control problem, first using external forces, second calculating the appropriate torque from world space.

Graham Rhodes / Applied Research Associates presents "Computational Geometry" where he looks at half-edge data structures for triangulating a polygon, splitting a face, splitting an edge, intersection of an edge and a plane and generating a convex hull.

Richard Tonge / nVidia covers "Solving Rigid Body Contacts" and starts with a gentle introduction to rigid body state space and progressively builds a signal-block-diagram of solving a single contact restraint. Then looks at each block in the diagram and deciphers the physics behind it. He then looks at solving multiple contacts, and explains why you can't apply a linear solver to the problem (contacts break), and presents the LCP, and an alternative approach; sequential impulses. He then gives a whirlwind tour of GPU solvers.

Gino van den Bergen / DTECTA presents "Collision Detection", first covering shapes, then configuration space, distance tests, Seperating Axis Tests, and takes a closer look at the GJK algorithm.

Jim Van Verth / Insomniac gives a nice introduction to Navier Stokes in "Fluid Techniques", breaking down the terms for external forces, viscocity, advection and pressure visually. Then looks at three major representations for fluids, grid, particle and surface (wave) based.

Takahiro Harada / AMD examines how heterogeneous compute architectures can achieve large scale dynamic simulations in "Toward A Large Scale Simulation". Begins with an overview of GPU architecture, and GPU rigid body simulation in three key phases: broad-phase, narrow-phase and constraint solving for a system of 128,000 particles and 12,000 convex bodies. He presents a design for overcoming data transfer and minimising synchronisation points whilst dividing the workload between CPU and GPU.

Erwin Coumans / AMD investigates destructive physics in the aptly titled "Destruction". He begins with generating voroni diagrams for shattering geometry and boolean operations, and moves into generating collision shapes with convex decomposition and tetrahedralization. Then moves on to realtime approaches with real-time booleans and breakable constraints and finite element
methods.



Looking at AI.

Bobby Anguelov / IO Interactive, Gabriel Leblanc / Eidos-Montréal and Shawn Harris / Big Huge Games present "Animation-Driven Locomotion For Smoother Navigation". They start with the standard motion graphs and transitioning/blending between animation cycles. Then take an indepth look at footstep planning (IK, Foot sliding) and come up with a system for deciding where steps should be taken to fulfil the navigation goal. They then investigate modifying navigation paths to better fit the animation cycles, and finish by looking into collision avoidance.

Daniel Brewer / Digital Extremes looks at agent perception, reaction, combat chatter, buddy systems and collision avoidance using velocity space Optimal Reciprocal Collision Avoidance in "Building Better Baddies".

Brian Magerko / Georgia Tech covers "How to Teach Game AI from Scratch" including competitions (Mario AI, Google Ants, Poker AI, Starcraft AI).

Dave Mark / Intrinsic and Kevin Dill / Lockheed Martin investigate some examples (snipers, guards) of Utility-Based AI in "Embracing The Dark Art of Mathematical Modeling in Game AI".

Kasper Fauerby / IO Interactive explains "Crowds in Hitman:Absolution" including cell maps, boids, animation and PS3 implementation details. The crowd AI uses a state machine with steering behaviours (pending walk, walk, panic), and behaviour 'zones' with information from the navigation system to select behaviours. Near-optimal Character Animation with Continuous Control was used for animation.

Elan Ruskin / Valve looks at empowering writers and dialog in TF2, Left4Dead, etc, in "Rule Databases for Contextual Dialog and Game Logic". Begins with player triggered lines (extended by environment, memory etc.) and avoiding fill-in-the-blank dialog by using databases. Rules, queries, responses and writers tools are examined next, and ties things off with database query optimisations.

Mike Robbins / Gas Powered Games examines "Neural Networks in Supreme Commander 2", with 34 inputs and 15 output actions and a single hidden layer (98 neurons), with a fitness function composed from 17 inputs trained to control combat platoons.

Ben Sunshine-Hill / Havok investigates LOD for AI in "Perceptually Driven Simulation", and makes a case for using probability of noticing a difference instead of distance as a LOD measure, and presents a market-based "LOD trader" for selecting the appropriate LOD given the constraints on hand.

Moving along to programming and math.

Adisak Pochanayon / Netherrealm covers debugging and timing issues in "Runtime CPU Spike Detection using Manual and Compiler-Automated Instrumentation". First up, manual instrumentation and wrapper functions, Then detours, and automated instrumentation (compiler flags) with an indepth look at the 360. Finally, profiling with threshold functions.

Pete Isensee / Microsoft details how rvalue in C++11 (T&&) can eliminate temporaries in "Faster C++: Move Construction and Perfect Forwarding".

Scott Selfon / Microsoft reviews audio compression technologies in "The State of Ady0 Cmprshn", starting with time-domain compression with PCM (raw, A-Law, U-Law, ADPCM), then frequency-domain compression and discusses the artifacts generated by both, then evaluates the performance of different codecs.

Robin Green / Microsoft and Manny Ko / Dreamworks present "Frames, Quadratures and Global Illumination: New Math for Games". Beings with a review of spherical harmonics, Haar wavelets, and Radial basis functions. Builds up to 'Spherical Needlet' wavelets, by exploring different basis functions ('frames')

Gino van den Bergen / DTECTA presents dual-numbers in "Math for Game Programmers: Dual Numbers", beginning with a look at complex numbers. Automatic differentiation with dual numbers is then described, with code, and examined in curve tangents, directed line geometry (triangle/ray intersections, plucker coordinates, angles), and rigid body transforms/skinning (dual quaternions).

Jim Van Verth / Insomniac explains rotation formats in "Understanding Rotations", including angle (2d) Euler angles, Axis-angle, Matrix (2d/3d), complex (2d) and Quaternion (3d). Interpolation is considered for each case (including slerp).

Eric Lengyel / Terathon presents exterior (Grassmann) algebra in "Fundamentals of Grassmann Algebra". This includes the wedge product, bivectors, trivectors and multivectors. Moves on to cross product transforms, dual-basis 'anti-vectors', regressive 'antiwedge' product, and demonstrates how these can be used in homogeneous and plucker coordinate systems. This leads on to basic intersections (line, plane, point) and distances (point plane, two lines) and finally ray-triangle intersection using bivectors to avoid barycentric coordinates.

Squirrel Eiserloh / TrueThought presents "Interpolation and Splines". Takes us back to basics by looking at averaging and blending, and moves onto interpolation. Begins with quadratic and cubic Bézier curves, then moves into splines and discusses continuity. Cubic Hermite splines are up next, and how to convert between Bézier and Hermite, then Catmull-Rom splines and finishes with the more general Caridnal splines.

John O’Brien / Insomniac covers "Math for Gameplay / AI". Starts with object intersection tests (sphere-sphere, sphere-plane, AABB-AABB, AABB-ray, capsules-capsule, capsule-ray) and projecting onto a plane in a gun turrent AI example. Next up, Bayes' Theorem and conditional probability, followed by fuzzy logic.

The Web up next

Corey Clark and Daniel Montgomery present "Building a Multi-threaded Web-Based Game Engine" covering both client side (WebGL, WebSockets, etc) and server side (NodeJS, Hosting, etc).

Michael Weilbacher / Microsoft looks at server issues in "Dedicated Servers in Gears of War 3".

Michael Goddard "Developing a Javascript Game Engine"
using component based architecture. Takes an indepth look at events/promises and loading content.

Mike Dailly / YoYo investigates packing textures and command list execution for improving performance in "The Voodoo Art of Dynamic WebGL".

Marc O’Morain / Swrve takes a look at a number of issues (including iOS multitouch) in "Building Browser Based Games Using HTML5".

And rounding up everything else

Caruso Daniel explains the "Forza Motorsport Pipeline". Importing assets into the game.

GuayvJean-Francois investigates sound diffraction and absorption in "Real-time sound propagation".

Mike Lewis presents the challenges of multithreading for MMOs "Managing the Masses".

Sean Ahern looks at building better game engine tools in "It stinks and I don't like it"

Clara Fernández-Vara, Jesper Juul, and Noah Wardrip-Fruin make a case that "Game Education Needs Game History"

Chris Jurney presents his idea "Motion Blobs", a fast and crude kinect data "gesture" system, essentially an extension of the typical 2D approach to 3D. Steps are to calculate motion via background subtraction, filtering (open/close), labeling, and then correlation.

Alexander Lucas explains automated testing at Bioware in "The Automation Trap And How Bioware Engineers Quality"

Alex Mejia looks at camera movement in "Saints Row : The Third real time capture tools".

Scott Philips presents "Designing Over the Top SAINTS ROW: THE THIRD Postmortem", and highlights the importance of pre-visualization and playtesting.

Ron Pieket / Insomniac looks at eliminating downtime in "Developing Imperfect Software" via a 'Structured Binary' approach to building engine data by taking advantage of a Data Definition Language.

Benson Russell takes a look at Naughty Dog's approach to polish in "The last 10, going from good to awesome", in essence longer alpha and beta tests.

Luke Muscat takes a look at the lessons learnt while updating Fruit Ninja in "Iterating Design And Fighting Fires: Updating Fruit Ninja And Jetpack Joyride"

Tatyana Dyshlova talks about managing 300+ artists working on 500 car models in "Racing to the Finish"

Summary
Quite a collection this year, but overall seems to be less exciting content than previous years. For graphics, it seems that signed distance fields and physically based rendering is the new theme, AI is still playing catchup and character animation cycles are still a hot topic, following that theme, physics is also looking at characters and ragdolls, with destruction being the hot topic, and the web is focusing on WebGL.

Half year catchup on Graphics, GPUs, Compilers, etc.

Another slow month on the blog. More than half way through the year, so its time to catch up on the backlog of news. Only covering graphics, games, physics and GPGPU and compilers. Expect a number of posts on robotics soon!

• GitHub is now more popular than SourceForge.
  
• Fabian 'ryg' Giesen has put together an in-depth explanation of the graphics hardware pipeline.
  
• nVidia released an extension to allow OpenGL direct access to DirectX buffers. Now you can write your graphics programs in both OpenGL and DirectX - pick whichever is easiest.
  
• nVidia released their 11th Graphics SDK - DirectX 11 only.
  
• Aras did a blog post on visualising mip-map levels and released the code to his shader.
  
• Redirect OpenGL from a remote machine with this VirtualGL tutorial.
  
• Morphological Anti-Aliasing paper with source code.
  
• Tim Lottes released his FXAA anti-aliasing source code
  
• José María Méndez wrote a fantastic article on a simple method to implement screen space ambient occlusion.
  
• Improve your ambient occlusion with occlusion normals to enable dynamic shading.
  
• A simple GLSLShader handling class
  
• Dave has a post on how you can generate game characters with a webcam.
  
• Source code from the Game Development Tools book. From texture generation and CSG to Continuous Integration, Perforce and XML.
  
• Steven Wittens has a fantastic series of posts on procedurally generating planets and worlds.
  
• Amit's blog post on polygon map generation using Voroni and Delaunay is worth a read.
  
• The old gameUltima 6 technical documents have been released. An interesting look at game design and programming decisions made in 1990. This should help nuvie, which has already made great progress.
  
• Oldskool demoscener Trixter wrote an interesting post onC64 vs IBM PC, and argues the C64 was a faster computer.
  
• Democoder Ferris/YUP did an interesting post on
  creating a tiny 1k graphics demo.
  
• John Ratcliff updated his Hierarchical Approximate Convex Decomposition utility library.
  
• Tim Ventimiglia and Kevin Wayne did an interesting post onusing the Barnes-Hut algorithm to accelerate n-body simulations.
  
• Pierre Terdiman has a great post on fast separating axis tests to speed up your collision detection for convex objects.
  
• PhysBAM source code - there is plenty of great stuff in here, so I'm sure to do a whole blog post on this later. It covers maths (e.g. ODEs, fourier transforms), spatial subdivision (KD trees, octrees), collision detection, raytracing and so much more.
  
• OpenCloth is a new library for cloth simulation algorithms.
  
• nVidia APEX SDK is now free. It has a number of functions that help with clothing and destruction physics.
  
• PhysxLab is a digital content creation tool to help you take advantage of the APEX sdk destruction features.
  
• The Oren Game Engine blog has a great post onimplementing destruction fractures.
  
• A realtime raytracer with pure C++, OpenMP and CUDA written by Thanassis Tsiodras is accompanied by some interesting analysis.
  
• Microsoft Accelerated Massive Parallelism (C++ AMP) appears to be the microsoft attempt at competing with CUDA, OpenCL and some of the libraries ontop of those technologies.
  
• Microsoft also released concurrent containers, parallel versions of STL algorithms.
  
• WebCL - OpenCL for the web, at Nokia research.
  
• AMD's OpenCL University kit covers some OpenCL and GPU basics.
  
• AMD Accelerated Parallel Processing (APP) SDK (formerly ATI Stream) has had a few updates, currently 2.4 is out.
  
• AMD gDEBugger is now free for debugging OpenGL and OpenCL programs.
  
• Intel SPMD Program Compiler is designed to generate optimal SIMD programs from a C-like language.
  
• PathScale EKOPath 4 is an optimising compiler, now free for linux, BSD and Solaris.
  
• Yang Chen wrote an amazing post comparing compiler optimizations.
  
• Helpful hints on the unix command xargs
  
• FreeArc is an amazing open source compressor. Fast and fantastic compression ratios.
  
• Google's excellent diff/match/patch tools
  
• Visual hashing explained, how to detect similar images.
  
• Ocropus is a open source library for Optical Character Recognition (OCR).
  

Finally, here is the SIGGRAPH 2011 technical papers highlights video, it contains a number of interesting advances in physics simulations and modeling.

Catchup Post: Robotics and Physical Simulations

A number of robotics related bits of interest from the last few months:

• Articulated Swimming Creatures by Jie Tan et. al actually performed work I had planned for my thesis, but never did complete. They simulated various creatures using different fluid simulation methods, and found they get different results. This was the same thing I found, and generalised via PAL and used to generate control algorithms that can transfer to the real world for an underwater vehicle.
  
• Predator: A Visual Tracker that Learns from its Errors by Zdenek Kalal went viral. I think it was a bit hyped (thanks to a clever name), but the TLD algorithm is interesting, and there are some worthwhile items to note. First of all it is an open source visual tracker, and that there is a freely available
  Google Tech Talk on TLD. In essence, Zdenek asserts that a tracker based on similarity of image patches will always lose its target and demonstrates trackers with learnt models from image data perform very well. (Similar to how models improve tracking in OpenTL). Zdenek et al. describe a way to generate more test sets using two experts (positive - objects must remain nearby, negative - only one true location per frame) and leverages boosting to get results. The total flow of operations are then: 1. Tracking and prediction, 2. Expert systems plus Detection, into Learning. 3. Re-Detection, using learnings.
  
• Paul Firth published a great introductory article on Physics Engines. Very handy. While your at it, Wolfgang Engel did a great post on some maths basics.
  
• Hierarchical Approximate Convex Decomposition of 3D Meshes (HACD) (HACD paper) is a method for representing objects as compound convex hulls (speeds up collision detection), that seems to outperform any other method I have seen.
  
• C2A by Min Tang et. al is a method for speeding up continuous collision detection with conservative advancement. A good paper, and source code is available.
  
• PAPPE is a Pascal Physics Engine.
  
• Barbara Solenthaler and Markus Gross published work on Two-Scale SPH Particle Simulation, an obvious idea (speedup simulations by mixing level of detail for SPH, they get about 2.2x speedups), someone had to do it. The videos are interesting nevertheless.
  
• On the topic of SPH, PhysXinfo has an article on the latests nVidia PhysX/Novodex/ETH research on fluid systems, of particular interest is Solid Simulation with Oriented Particles. Another interesting post is by Miles Macklin on fluid simulations.
  
• Intel released 'Colony' a crowd-simulation system, comes with source code.
  
• Lectures on machine learning with Matlab. Covers SVM, NN, EM, Bayesian methods, and image analysis.
  
• Ant colony optimization will be the next google AI challenge.
  
• An XML Unified Robot Description Format (URDF), again, like many other formats before it it has inherit limitations. COLLADA 1.5 Kinematics (library_kinematics_models) is probably a better choice.
  
• On the topic of XML, and other data interchange formats JSON cpp is a C++ library to handle exchanging JSON data.
  
• ACRA, the Australasian Conference on Robotics and Automation will take place in December in Melbourne.
  
• And just incase you've been hiding under a rock for the last while, the next big DARPA competition is the ARM manipulation program. Lots of interesting results are coming out of that project, but thats for another time.
  

Finally Heat-1 the space rocket build by danish amateurs Copenhagen Suborbitals successfully launched. (TED talk here). See the video below.

March update

I didn't want to have a month without a post, so here are some links for the month:

• GDC 2011 is over again. I'll do a breakdown soon, but meanwhile take a look yourself at DICE publications on Battlefield 3, nVidia's GDC publications, AMD GDC and ofcourse the official GDC vault (free). (Maciej Sinilo has a nice collection here).
  
• Game Physics Pearls has been published by Gino van den Bergen and Dirk Gregorius. Dirk is a very knowledgeable guy, and Gino wrote SOLID, so I'm sure it's great.
  
• ScienceBooksOnline has a collection of free books.
  
• Paul Firth has a great interactive blog post on contact resolution, and introduces a method used in Little Big Planet he calls "Speculative Contacts".
  
• PhysX info has a comparison of different clothing simulation systems.
  
• GLM is an OpenGL syntax math library.
  
• Cairo is a 2D graphics library that supports both OpenGL and PDF output.
  
• An MIT WebGL tutorial.
  
• How to convert your HTML5 page into a native OSX app.
  
• Paul Grenfell added another small raycasting OpenProcessing demo.
  
• Photoshop filters implemented in GLSL
  
• Herwig Hauser has an amazing gallery of 3D algebraic surfaces - useful for 4k productions.
  
• On that topic, Auld has a great snippet on miniature GLSL code for moving a camera.
  
• 0 AD is an open source 'Age of Empires' style game.
  
• Ninite is like apt-get for Windows. (Installation package manager)
  
• A siggraph paper on the miniature effect
  
• Bundler is an open source tool to generate structure from motion from unordered images. (It was published in 2006, but now you can look at the code)
  
• GPU Ocelot 2.0 supports AMD devices now. CUDA for AMD.
  
• Microsoft's paper on the Kinect bodypart tracking algorithm.
  
• Looking for a place to publish? Wiki Call for Papers collects conference paper submission deadlines and more. (Neat!)
  

The pick of the month has to be the new Festo production, the SmartBird ornithopter. (Official site has a PDF spec-sheet). Video below:

Newton Physics Engine

In an unexpected move the Newton Physics Engine has been open sourced with the zlib licence. I haven't been following this engines developments closely since the 1.x versions. Julio has released the 3.0 version over svn as well.

Finally, a chance to figure out some of Newton's strange behaviour I noticed in the PAL physics engine benchmarks.

Convex Hull Generation in Blender

Convex hulls are very useful for a number of optimized calculations such as fast intersection tests, fast spatial subdivision, and other early-out's used in computer graphics, computational physics and robotics.

When I implemented convex hull generation and convex decomposition in PAL I first used qhull and leveraged code from tokamak physics, but then used code by Stan Melax and John Ratcliff for PAL. Recently my work at Transmin has required generation of a number of Convex hulls, and so I combined these snippets of old code to create a plug-in for Blender.

The Blender plugin creates a bounding convex hull of the selected object.
It calls an external executable 'convex' which creates a convex hull based on an intermediate OBJ file.

Installing the plugin requires you to compile the code to generate the 'convex' executable, and copying the python code into Blender's scripts directory.

To compile the C code on linux/osx:

g++ createhull.cpp hull.cpp -o convex

Place the object_boundinghull.py script in your ".blender/scripts" directory.

On OSX Blender default installs to:

/Applications/blender-2.49b-OSX-10.5-py2.5-intel/blender.app/Contents/MacOS

Once the plugin is installed you can start creating convex hulls. You can select an object in blender and cut it into smaller objects to manually decompose the hulls. To do this, you can use the Knife tool (K) or split objects in edit-mode with 'P'. (Selection tools like 'B' and manual alignment of cameras ('N', Numpad 5) will help a lot).

Once you have the objects you would like to generate hulls for select one, and run the "Bounding Convex Hull" script. It will ask you to confirm the creation of the hull. The new hull will have the same name as the original object and have ".hull" appended to its name.

The plugin will generate a new object that represents the convex hull of the selected object, with the same transforms as the original object. (Ctrl-A to apply all down to the mesh, note: Blender 2.49 does not let you apply translation transforms, but Blender 2.5+ does). You can then decimate the hull to reduced the number of tri's used to represent your object. (Editing F9, under modifiers, select 'Add Modifier', decimate, and reduce the ratio).

Now your ready to export your scene for all your raytracing and collision detection needs!

Thanks to Transmin Pty Ltd for allowing me to release this plugin back to the Blender community under the GPL.

Follow the link to download the Blender Bounding Convex Hull plugin to generate editable bounding volumes directly in Blender.

Circular Motion in 2D for graphics and robotics

For a number of applications circular motion in 2D is useful, in particular simplified kinematic representations for mobile robot simulation and control. There are a number of different ways of representing this motion.

First it is helpful to remember a position on a circle can be described parametrically by:
[x,y] = [r*cos(theta), r*sin(theta)]
or alternatively, r =sqrt( x^2 + y^2).

1. As a circular variation of the standard 2D particle, we just add an angular velocity (omega) and angular orientation (theta). For a standard 2D particle we can describe its velocity (v) in terms of acceleration (a) and a delta in time (dt) (v += a*dt; x+= v*dt). We can modify this to include the parametric circle representation:
   
   

   theta += omega * dt;
   x+=v*dt*cos(theta);
   y+=v*dt*sin(theta);
   

2. The problem with the above method is that it is in-exact and relies on an integrator. The 2D velocity/angular velocity representation can easily be fully solved analytically. The radius of a circle produced by a given velocity (v) and angular velocity (omega, or w) is:
   r = | v / w |
   We can modify the parametric representation to include an offset for the centre of motion:
   [x,y] = [r*cos(theta) + xc, r*sin(theta) + yc]
   Thus, given an initial x,y,theta we can find the centre of the circle of motion as:
   
   

   xc = x - (v/w)*sin(theta)
   yc = y + (v/w)*cos(theta)
   

   Now we can update the position of the robot:
   
   

   theta += w * dt;
   x = xc + (v/w) sin(theta)
   y = yc - (v/w) cos(theta)
   

   We can expand this into a single line as:
   
   

   x+= -(v/w)*sin(theta) + (v/w)*sin(theta+w*dt)
   y+= -(v/w)*cos(theta) - (v/w)*cos(theta+w*dt)
   theta += omega * dt;
   

   
   Which is the form many robotics papers use.
   
3. Finally, we may wish to represent the motion in terms of two given x,y coordinates and solve for the translation and rotation required to reach them (as is the case for odometry calculations). In this case, we can represent any movement from an original set of coordinates [x,y,theta] to a new set [x',y',theta'] as first a rotation and translation to bring you to any new x' and y', followed by another rotation to bring you to the final theta'. Using triangle trigonometry this is:
   
   

   deltaRot1 = atan2(y'-y,x'-x) - theta
   deltaTrans = sqrt( (x-x')^2 + (y-y')^2 )
   deltaRot2 = theta' - theta - deltaRot1 
   

There are of course many more ways of representing circular motion, but the above are the most common in computer graphics and robotics.

Catchup Post: Graphics & GPU's & Physics

A long overdue catchup post for various interesting things I've spotted over the last two or three months. SIGGRAPH recently finished, so it really deserves a round-up, although I haven't had time to review all the interesting things.
The annual tutorial on
realtime collision had some interesting presentations, I quite liked the one from Erwin Coumans (Bullet) this year - it gives a good overview of the recent advances in the Bullet engine including the GPU optimizations. Simon Green also has a presentation on CUDA SPH rendering (also see Jihun Yu's particle fluid surface reconstruction) and another open source GPU SPH simulation from HPC lab.
The realtime graphics tutorial, stylized rendering, volumetrics, and programmable shaders has some great stuff that I'll look into in more detail in a future post. Ofcourse there is also always the SIGGRAPH 2010 papers list, and SIGGRAPH asia papers (again more on this later..).

Some GPGPU software/links:

• AMD's Stream SDK - the new version allows printf in OpenCL kernels - very handy for debugging and OpenCL1.1 support.
  
• AMD's OpenCL sample page.
  
• an interesting article on larrabee's demise
  
• CUDA Vision Library - another library, but this one has quite a few functions including optical flow and hough transforms plus some color space conversions.
  
• AMD OpenCL tutorial.
  
• OpenNL has some GPU based sparse matrix structures and iterative linear systems & least-squares solvers, etc.
  
• Back40 has a fast radix sort.
  
• OpenCL and OpenGL interoperability particle system example.
  
• and a now-old-hat story on theGPU supercomputer in the top 500 list.
  

and MPTL is a parallel version of the STL algorithms.


Some physics links:

• A new version of the PhysX SDK is available with some SSE optimizations and the source code to the tetgen program. A new version of the PhysX visual debugger is also available.
  
• Creature Control in a Fluid Environment - an interesting paper, reminds me that I should really publish my PhD at some point...
  
• While we are on the topic of underwater physics, Underwater Cloth Simulation with Fractional Derivatives is worth a look.
  
• Example based wrinkles for cloth simualtion an interesting take on one of the more difficult aspects of good cloth simulation.
  
• FASTCD - fracture aware collision detection - a lot of good things coming out of KAIST recently in this field.
  
• Dynamic Local Remeshing for Elastoplastic Simulation, is a Finite Elements method for achieving a range of physical material behaviors. Neat.
  

Some graphics links:

• Alex describes the making of the Ergon 4k intro
  
• ryg has a great post on optimzing packed pixel blend operations for non-SIMD systems.. nifty! I wish I knew this previously! (ryg also has an interesting post on morton-codes, which you can use for organizing your data for easy n-dimensional nearest neighbor retrieval. See codexon's explanation.
  
• I stumbled upon this interesting description of a global illumination shader including ambient occlusion, GI, bump maps, etc.
  
• Kyle has a post on his implementation of
  animating water with flow-maps
  
• The excellent page on screen space ambient occlusion at Meshula has been updated.
  
• NASA released a collection of NASA 3d Models
  
• Auld's blog has some interesting posts describing his 4k modeling tool, with some input from iq.
  
• GL minify to compress GLSL shaders.
  
• Steve Hollasch has a nice
  collection of interesting graphics-related newsgroup posts.
  

And finally a documentary on the history of the Future Crew demo group and Second Reality. Brings back the memories.

Applying forces

In many robotics, graphics, and physics applications some object must be 'moved' by applying a force. Doing this the naive way will often result in very unstable behaviour. There are a number of very simple steps that can be taken to improve the situation. First of all, don't just directly update the position from some overall calculated force (or rather, impulse in this case), instead accumulate a velocity using standard integration. That is:

velocity += acceleration*dt
position += velocity*dt

This is a good first step, and many people stop there and discover that they are still left with large oscillation problems. This is due to the poor first-order integrator (Euler) and the lack of damping. Adding damping and velocity limiting will help:

velocity += acceleration*dt
velocity = clamp(velocity, min, max)
velocity *= dampen //eg: 0.98
position += velocity*dt

Hopefully your system is acting closer to how you expected. At this point if you still have some minor oscillation and odd edge cases you can probably solve them through more advanced techniques. If your still not getting a behaviour close to what you want then try a completely different approach.

The final quick and easy step to improve performance is to improve the integrator. A simple leap-frog (velocity-verlet) integrator will provide decent performance (no need to go to RK45!):

velocity += acceleration*dt
velocity = clamp(velocity, min, max)
velocity *= dampen //eg: 0.98
position += velocity*dt + 0.5*acceleration*dt*dt

Done!

Now all your robot path-planning, navigation, graphics particle systems, and cloth-simulations will be up and running. Plenty of research papers to read if you want to keep improving it!

I'll leave you with this real life video illusion of marbles rolling up a slope:

Inverting Matrix - SVD (singular value decomposition)

Every once in a while you find yourself needing to solve a set of equations, or invert a matrix, or worse yet, invert a non-square matrix (eg: pseudo-inverse for manipulator inverse kinematics path control (See: Minerva IK control image on right, work I did at TUM) or kalman filtering). This is when a handy mathematical tool 'singular value decomposition' comes in to play.

In essence the SVD decomposes a matrix 'M' into three other matrices with special properties, making them easier to manipulate. The SVD equation is:

Where:

• U is a matrix whose columns are the eigenvectors of the M * M transposed matrix. (AKA left eigenvectors)
  
• S is a diagonal matrix whose diagonal elements are the singular values of M.
  
• V is a matrix whose columns are the eigenvectors of the M transposed * M matrix. (AKA right eigenvectors)
  

Discussing eigenvalues and eigenvectors I'll leave for another time, but they are quite straight-forward to calculate (get the matrix subtract a constant * I , take the determinant, equate to zero and solve, that gets you the eigenvalues!).

Now, how do you use the SVD to invert a matrix? Using a few matrix (inversion) identities (See the Matrix Cook Book, basic identity 1):

So now we just need a way to invert a diagonal matrix, which couldn't be easier. To invert a square diagonal matrix you simple invert each element of the matrix.
What if the matrix isn't square?
Well for that, we can just use the pseudo-inverse: we just invert each element of the matrix, and then transpose it. Done!


A good tutorial on the SVD can be found here by Dr. E. Garcia

Pixelux Digital Molecular Matter engine - Free license soon!

AMD have just announced there will be a free version of the DMM engine. It sounds like it will be closely integrated with Bullet Physics and provide OpenCL support.

I'm looking forward to this as DMM is the only realtime finite-element (FEM) based physics engine around. I'm interested to see how well it works.

Hopefully I can get a copy soon and some time to integrate it into the Physics Abstraction Layer.

Here is a video of DMM to refresh your memory:

Intersection of a Convex Hull with a line segment

A ray, or line segment can be represented parametrically as:
S(t) = A + t(B-A)
Where A and B are the endpoints of the segment, and t is the parameter that ranges from –infinity to +infinity for a ray, or just 0..1 for a segment.

A plane can be represented as n.X = d, where n is the plane’s normal, and d is the offset. (Given the plane’s normal, and a single point on the plane, P, we can calculate: d = -n.P)

A convex object can be represented as the area contained within a set of planes. Thus, to find the intersection between a line segment and a convex object, we just need to clip it against all the planes that form the convex object.

First, substitute the line equation into the plane, and solve for t:
i.e.:
n.(A+t(B-A)) = d
n.A + t*n.(B-A) = d
note: using identity ru.sv = rs(u.v), where u,v are vectors, and r,s are scalars
re-arrange to solve for t, the intersection point along the line:

We can determine if the plane faces the segment or not by evaluating the dot product of the plane’s normal, and the line segment’s direction vector.

From this we can determine which point of an intersecting line segment to influence. If the plane is facing the segment direction, then we can clip against the end point, otherwise we can clip against the start point.

As we are testing the intersection against a convex object we can simply keep clipping against each plane and altering the segment endpoints until we have the minimum remaining line length, or the intersection length becomes empty (there is no intersection).

In pseudo-code the entire operation is:

AB = B – A
tFirst = 0
tLast = 0
for all planes:
 denom = N dot AB
 dist = d – N dot A
 t = dist/denom
 if (denom>0 )
  if (t>tFirst) tFirst = t;
 else
  if (ttLast)
  No Intersection

Solving Linear Systems

In school you probably learnt how to solve systems of linear equations with techniques like Gaussian elimination, and Row-Reduced Echelon Form (RREF). However a simple, brute-force way to solve linear systems on a computer is through iteration.

Say we wish to solve the following equations:

4x -  y +  z = 7
 4x - 8y +  z =-21
-2x +  y + 5z = 15

Then we can re-write them as:

We can solve these with Gauss-Seidel iteration just by plugging in the current x,y,z values we calculate from these equations (and begining with an initial estimate.)

Thus, the Gauss-Siedel method in C-code looks something like:

#include <stdio.h> 

int main() { 
//a sparse way of representing the equations 
float eq[3][4];
eq[0][0] = 7/4.0; eq[0][1] = 0; eq[0][2] = 1/4.0; eq[0][3]= -1/4.0;
eq[1][0] = 21/8.0; eq[1][1] = 4/8.0; eq[1][2] = 0; eq[1][3]= 1/8.0;
eq[2][0] = 15/5.0; eq[2][1] = 2/5.0; eq[2][2] = -1/5.0; eq[2][3]= 0;

float x,y,z; 
x=1;y=1;z=2; //initial guess

//10 iterations of gauss-seidel 
for (int i=0;i < 10;i++) {
  x = eq[0][0] + eq[0][2]*y + eq[0][3]*z;
  y = eq[1][0] + eq[1][1]*x + eq[1][3]*z;
  z = eq[2][0] + eq[2][1]*x + eq[2][2]*y;
  printf("%f %f %f\n",x,y,z); 
} 

return 0; 
}

Producing this output:

1.500000 3.625000 2.875000
1.937500 3.953125 2.984375
1.992188 3.994141 2.998047
1.999023 3.999268 2.999756
1.999878 3.999908 2.999969
1.999985 3.999989 2.999996
1.999998 3.999999 3.000000
2.000000 4.000000 3.000000
2.000000 4.000000 3.000000
2.000000 4.000000 3.000000

Converging towards the solution nicely. (Things don't always converge, only when Ax=B, A is diagonally dominant - but that is another story)

Jacobi iteration does not converge as quickly, but is easy to execute in parallel. With Jacobi iteration you simply use the last iterations x,y,z value instead of updating it.

See? Solving systems of equations is easy.

Vortex Slides

Michel Carignan from CM Labs Vortex has kindly provided me with the slides to his presentation on Vortex.

edit: update, CM Labs can not publicly distribute the slides, but they are still available upon request.

Critical Mass Labs Presentation

Together with Ronald Jones from iVEC, I organized a presentation from CMLabs.

Michel Carignan, lead product engineer from CMLabs, discussed the internal structure of Vortex, a real-time physics-based simulation engine with collision detection. Michel covered issues in maintaining interactive performance with complex dynamical systems, and a number of applications from the areas of vehicle simulation, robotics and control.

Details of the constraint solver, collision detection, scene graph interaction, and the interactive editor were covered.

Vortex has a number of interesting features designed to support the simulation of cranes / booms with rigid-body chains for representing wires, etc. The simulation system features a highly accurate and fast solver (iterative/LCP, so I'm not sure what is so special about it..) and most constraint interactions are modeled as simple spring-damper systems. The package does not support continuous collision detection, but has 'Fast' objects, which perform iterative collision detection. A simple way to save computation time, while still achieving the goals of a CCD system, by putting some labor onto the programmer.

Constraints can be 'relaxed' to different degrees, enabling 'wobbly' links, eg: ropes. Each constraint can have a maximum force allowed, and this enables frictional forces with the ground to be simulated in a generic manner.

Vortex also has a few additional novel features including SPH fluids (and normal RB hydrodynamics), simulation of sonar sensors, cameras, etc.

One area where CMLabs seems to have put a lot of effort is the validation of the physics engine - quite an interesting topic, especially in validating motor models, etc.

The key new feature seems to be an interactive editor, however I was disapointed to hear they were building on their own file format and not supporting COLLADA (or let alone any other common 3d package like SolidEdge or Havok's physics format)

In any case it was an interesting talk, but unfortunately I had to leave early. Hopefully I can get the slides.