Making of the “spinning house” sequence in Twister (1996)

Earlier this year filmmaker Stu Maschwitz posted on Twitter a series of messages recounting the work he did, as a then junior visual effects artist, on the scene of the house crashing on the road in the 1996 summer blockbuster, Twister. He later copied them to his website: go read it there.

The story comes with a fair amount of detail, hacks and tricks to make the best of the technical limitations of the time, and gives an idea of the amount of work such a scene in a prominent Hollywood film entails.

Unreal Engine experimental scene videos

Since the beginning of 2014, there has been a lot of videos demonstrating the realism that can now be achieved with Unreal Engine 4.

Often, these videos showcase a static scene or even concentrate on a single detail: lighting in an architectural structure, the look of rain hitting the ground, or some wet pebble on the beach.

Physically based rendering, global illumination and screen space reflections seem to manage to trick the brain an get it confused between what is real and what isn’t. Even when some artifacts get salient, like reflections popping in and out or changing with camera orientation, we are quick to forget them and find the image very believable.

Here are some of these videos, by Alexander Dracott, Koola, and Benoît Dereau.

Unreal 4 Lighting Study: Forest Day from Alexander Dracott on Vimeo.

John Carmack on physically based rendering at QuakeCon 2013

In this (slightly over) one hour talk, 1½ hour including Q&A, John Carmack walks through the physics of light, the early days of rendering, the current state of the art, and the direction it is headed at. In short: until we can afford path tracing, we’re approximating it.

The rendering tools in the film industry

Here is a list of articles published by fxguide, giving fascinating insights into the tools used by the film industry in terms of rendering.

  • Ben Snow: the evolution of ILM’s lighting tools (January 2011)
    A presentation of the evolution of the technology and tools used at Industrial Light and Magic, over the course of the years and movies, from the mid-90s to nowadays.
  • Monsters University: rendering physically based monsters (June 2013)
  • The Art of Rendering (April 2012)
    A description of the different techniques used in high end rendering and the major engines.
  • The State of Rendering (July 2013): part 1, part 2
    A lengthy overview of the state of the art in high end rendering, comparing the different tools and rendering solutions available, their approach and design choices, strengths and weaknesses as well as the consequences in terms of quality, scalability and render time.

(Brace yourselves for the massive tag list hereafter.)

Simple light setup for outdoor environments

On his website, Iñigo Quilez (known for a wide range of notable contributions at RGBA, BeautyPi and Pixar; talk about an over-achiever! but I digress already), recently described the light setup he often uses for outdoor environments.

Capture of his technique in action

From the article:

This articles describes the lighting rig I use when doing such tiny computer graphics experiments with landscapes. It’s basically made of 3 or 4 directional lights, one shadow, some (fake or screen space) ambient occlusion, and a fog layer. These few elements tend to behave nicely and even look fotoreal-ish if balanced properly.

Setting up lights is not an easy task, so this article is a very welcomed insight. I especially like the trick of using an opposite directional light to fake global illumination. I also very much agree on using actual fill lights. Constant ambient alone is not enough, as you lose any sense of volume in the shadowed parts.

I am not too fond of the shadow penumbra trick though, which he described previously already. I must admit it indeed gives a warm look, but it doesn’t make any physical sense. So I suspect this should rather belong to the tone mapping part of the rendering, just like the square root he used to apply to the diffuse fall-off really was really working around the lack of gamma correction.

The recommendation to keep albedo near 0.2 is an interesting one. Indeed, your typical rock and grass albedo is nowhere near the albedo of snow (a quick look at Wikipedia gives this comparison chart). But if it is stored in a texture in a typical rendering pipeline, the question of precision lingers. I wonder how big game studios typically address this.

A list of important graphics research papers

This is an announcement that got all my attention. Since Twitter is a mess to find anything older than a day, here is the list so far:

  1. A Characterization of Ten Hidden-Surface Algorithms, Sutherland et al., ACM Computing Surveys, 1974
  2. Survey of Texture Mapping, Paul Heckbert, IEEE Computer Graphics and Applications, 1986
  3. Rendering Complex Scenes with Memory-Coherent Ray Tracing, Matt Pharr et al., proceedings of SIGGRAPH, 1997
  4. An Efficient Representation for Irradiance Environment Maps, Ramamoorthi & Hanrahan, proceedings of SIGGRAPH, 2001
  5. Decoupled Sampling for Graphics Pipelines, Ragan-Kelley et al. ACM Transactions on Graphics, 2011
  6. The Aliasing Problem in Computer-Generated Shaded Images, Franklin C. Crow, Communications of the ACM, 1977
  7. Ray Tracing Complex Scenes, Kay & Kajiya, proceedings of SIGGRAPH, 1986
  8. Hierarchical Z-buffer Visibility, Greene et al., proceedings of SIGGRAPH, 1993
  9. Geometry Images, Gu et al., ACM Transactions on Graphics, 2002
  10. A Hidden-Surface Algorithm with Anti-Aliasing, Edwin Catmull, proceedings of SIGGRAPH, 1978
  11. Modeling the Interaction of Light Between Diffuse Surfaces, Goral et al., proceedings of SIGGRAPH, 1984
    “The first radiosity paper, with the real physical Cornell box (which I’ve actually have seen in real life!)”
  12. Pyramidal Parametrics, Lance Williams, proceedings of SIGGRAPH, 1983
  13. Rendering synthetic objects into real scenes: bridging traditional and image-based graphics with global illumination and high dynamic range photography, Paul Debevec, proceedings of SIGGRAPH 2008
    “Influence on gfx proportional to title length!”
  14. A parallel algorithm for polygon rasterization, Juan Pineda, proceedings of SIGGRAPH, 1988
  15. Rendering from compressed textures, Beers et al., proceedings of SIGGRAPH 1996
    “This one (out of 3) of the 1st texture compression papers ever! Uses VQ so probably not something you want today, but major eye opener!”
  16. A general version of Crow’s shadow volumes, P. Bergeron, IEEE Computer Graphics and Applications, 1986
    “Generalized SV. Nice trick”
  17. Reality engine graphics, Kurt Akeley, proceedings of SIGGRAPH 1993
    “Paper describes MSAA, guard bands, etc etc”
  18. The design and analysis of a cache architecture for texture mapping, Hakura and Gupta, proceedings of ISCA 1997
    “Classic texture $ paper!”
  19. Deep shadow maps, Lokovic and Veach, proceedings of SIGGRAPH 2000
    “Lots of inspiration here!”
  20. The Reyes image rendering architecture, Cook et al., proceedings of SIGGRAPH 1987
    “Sooo good & mega-influential!”
  21. A practical model for subsurface light transport, Jensen et al., proceedings of SIGGRAPH 2001
  22. Casting curved shadows on curved surfaces, Lance Williams, proceedings of SIGGRAPH 1978
    “*the* shadow map paper!”
  23. On the design of display processors, Myer and Sutherland, Communications of the ACM 1968
    “Wheel of reincarnation”
  24. Ray tracing Jell-O brand gelatin, Paul S. Heckbert, Communications of the ACM 1988
  25. Talisman: Commodity realtime 3D graphics for the PC, Torborg and Kajiya, Proceedings of SIGGRAPH 1996
  26. A Frequency Analysis of Light Transport, Durand et al., Proceedings of SIGGRAPH 2005
    “Very influential!!”
  27. An Ambient Light Illumination Mode (behind a paywall), S. Zhukov, A. Iones, G. Kronin, Eurographics 1998
    “First paper on ambient occlusion, AFAIK. Not that old…”

A GLSL version of smallpt

smallpt is a bare minimum path tracer written under 100 lines of C++, featuring diffuse, and specular reflection, and refraction. Using the detailed explanation slides by David Cline, I experimented porting it to GLSL on Shadertoy.

This proved to be an interesting experiment that brought a few lessons.

You can see the shader and tweak it here. By default it uses 6 samples per pixel, and 3 bounces, which allows it to run smoothly on average hardware. I found 40 samples per pixel and 5 bounces to give nice results while maintaining interactive framerate.

Path tracing, 40 samples per pixel, 5 bounces

Path tracing, 40 samples per pixel, 5 bounces

Update: since GLSL Sandbox has a feature, reading from the previous frame buffer, that Shadertoy is missing at the moment, I thought it’d be interesting try it to have the image converging over time. A little hacking later, a minute or so worth of rendering got me this kind of result: Given the effort, I am really pleased by the result.

Path tracing, 40 samples per pixel, 5 bounces

Path tracing, unknown number of samples per pixel, 7 bounces