Weighted, Blended Order-Independent Transparency

I'm leaving this up for historical reasons, but I recommend my more recent post on blended order-independent transparency for implementors.

Glass, smoke, water, and alpha-cutouts like foliage are important visual elements in games that are all challenging to render because they transmit light from the background. This post explains a new method called Weighted, Blended OIT for rendering all of these effects quickly and with pretty good quality on a wide set of target platforms. (As is common game developer jargon, I refer to all of these as "transparency" effects. The appendix of my earlier transparent shadow paper with Eric Enderton explains the subtle differences between them.)

The traditional approach is to sort the transparent polygons, and then render them in order from farthest from the camera to nearest to the camera. That sorting is itself slow, and causes further performance problems because it triggers more draw calls and state changes than otherwise needed and prevents common performance optimizations such as rendering amorphous surfaces like smoke at low resolution.

An Introduction to JavaScript for Sophisticated Programmers

Introduction

JavaScript (which is defined by the ECMAScript specification) is a just-in-time-compiled, memory-managed (garbage collected), dynamically-typed, functional programming language. Its greatest practical strength is its use on the web as the primary client-side programming language. This means that nearly every computing device with a display serves as both a target platform and a potential development environment. That is powerful and convenient.

Some Interesting New Game Art Styles

Little Big Planet 2

Expressive, also known as "non-photorealistic," computer graphics seek conscious stylization over mimesis. The world of animated films has long embraced non-mimetic styles, however relatively few games exhibited bold style after display resolutions and processor throughput became high enough to escape the (pleasant) confines of pixel art and flat-shaded polygons. Some noteworthy big-budget exceptions are Oni, Okami, Another World, Wind Waker, Prince of Persia, Jet Grind Radio, Ni No Kuni, Little Big Planet, Borderlands, and Mirror's Edge.

JavaScript Desiderata

Why JavaScript?

I teach the the programming portion of Williams CS107: Creating Games using codeheart.js, which is a minimal game framework for JavaScript. I use JavaScript because it has several practical advantages over other currently available languages for beginning students (as well as for my own jam games and prototypes):

The Skylanders SWAP Force Depth-of-Field Shader

Our depth of field effect in the game.

Mike Bukowski, Padraic Hennessy, Brian Osman, and Morgan McGuire (that's me) published in GPU Pro⁴ an early version of a depth of field shader that we developed while working together on Skylanders: SWAP Force™ at Vicarious Visions, and Activision studio.  This post describes the shader a bit more and includes links to updated sample code.

The Graphics Codex Web Edition

The essential reference for computer graphics is now available on all platforms through the Graphics Codex Web Edition.

Sample Radiometry diagram

“ Both readable and solid, the Graphics Codex provides the reader with the essence of 3D computer rendering.”—Eric Haines, Autodesk   coauthor of Real-Time Rendering

“ I own and use the Graphics Codex. Is it a reference tool, a companion to a textbook, an alternative to a textbook, or a self-study guide? It can work in any of these roles, but I think it is in fact a new thing. It's a thing we'll be seeing a lot of...dollar for dollar, it's the best scholarly information I have ever purchased.”—Peter Shirley, University of Utah
   coauthor of Fundamentals of Computer Graphics

Plausible Environment Lighting in Two Lines of Code

a group post by McGuire, Evangelakos, Wilcox, Donow, and Mara
(Because of intense interest in this post, we archived it as a technical report at http://graphics.cs.williams.edu/papers/EnvMipReport2013/ suitable for scientific citation)


This post describes a trick used in the G3D Innovation Engine 9.00 to produce reasonable real-time environment lighting for glossy surfaces. It specifically adds two lines of code to a pixel shader to reasonably approximate Lambertian and glossy reflection (under a normalized Phong model) of a standard cube map environment. This trick resulted from an afternoon discussion/challenge last week in the Williams Computational Graphics lab between Morgan McGuire (that's me), my summer 2013 research students, Dan Evangelakos (Williams), James Wilcox (NVIDIA and University of Washington), Sam Donow (Williams), and my NVIDIA colleague and former student Michael Mara.

There are many more sophisticated ways of computing environment lighting for real-time rendering (see Real-Time Rendering's survey or a more informal Google search). Unfortunately, those techniques tend to require an offline asset build step, so they can't be directly applied to dynamic light probes, which are particularly interesting to us...although there are some clever things that one can do with spherical harmonics to reduce the cost of that precomputation a lot. Those methods also tend to require a specific setup for the renderer that doesn't work with our default shaders. For research and hobbyist rendering, one often has to work with off-the-shelf or legacy assets. This situation also arises in production more than one might think, especially when working with games that run across a variety of devices.

A series of increasingly shiny teapots, before and after applying this technique.
In the before row, only the perfect-mirror (rightmost) teapot reflects the environment.

Z-Prepass Considered Irrelevant

The G3D Innovation Engine directly supports easy switching between forward, forward+, and deferred rendering. Most programs, including the starter sample, begin rendering with a z-prepass regardless of which mode they are operating in. This ensures that (except for translucent surfaces and partial coverage) shading occurs once per sample. The z-prepass operation is a depth-only render pass that bypasses the fragment shader (except when a surface has an alpha mask), and it processes fragment-bound scenes in about 1/3 the time of a regular shading pass on NVIDIA GPUs, which have special fixed-function support for depth-only rendering.

A Really Smart Enum in C++

For the G3D Innovation Engine, I wanted much richer enumerated type functionality than C++ enum (or even recent extensions) provide, without the template error nightmares and complexity of something like the Boost library's enums or X macros. I also did not want to use non-standard compiler extensions or an offline code generator; portability and minimal maintenance are important for my multi-platform code and small development team. I call my solution "really smart enums" because they extend the so-called C++ Intelligent Enum design pattern.  The solution that I used allows all of the following:

Tracewords Makeover

I'll be releasing Tracewords shortly.  This is a casual word game written with codeheart.js that is designed for one-handed (one-thumb, really) play on mobiles. I implemented the mechanics a year ago. To prepare for release I needed three major features:

Favorite Films from Annecy 2013

Top three:

1. Miss Todd

Miss Todd

Kristina Yee 2013
A paper-cutout musical, historical fiction (pleasantly heavy on facts), feminist tract, and fun story. That it was also a student graduation film is amazing. This was my favorite film of the festival.

2. Will
Eusong Lee 2012
The saddest and most emotionally effective short I have ever seen at the festival.  I cried and wanted to run from the theatre once it became clear where this was going.  If the last 15 seconds were cut, then it would be perfect.

3. La Grosse Bête
Pierre-Luc Granjon 2013
Well animated, with a compelling story. This also acts as a precise allegory in a world debating civil rights vs. security.  The timing and direction are flawless and masterful.

Other highlights:

Les Voiles du Partage 
Pierre Mousquet and Jerome Cauwe 2013
Mad Max meets Charles Bronson for a fast-paced dystopian satire. It is great to have some films that are just fun!

Rabbit and Deer

Nysuzi es Oz (Rabbit and Deer)
Peter Vacz 2012
2D meets 3D, and science is the original sin.

Duku Spacemarines
Nicolas Liautaud, Alice Suret-Canale, Hugo Paquin, and Nicolas Dubois 2012
For every student whose film or game design included "and one more awesome thing..."

Beach
Pawel Prewencki 2012
A simple vignette of the beach, with one cynical note.

Betty's Blues
Claymation and animated woodcut bringing to life a set of three blues songs; the stories are dark but presented more cheerfully than you might expect.

Trespass
Paul Wenninger 2012
A stop-motion live-action journey of epic scope; the music-video like novelty wears off after a minute and the impact then begins. I believe that the actor was also the director.  His performance is particularly impressive--it would be hard to maintain that composure over such long stop-motion scenes.

But Milk is Important

The Caketrope of Burton's Team
Axelandre Dubosc 2012
A chocolate cake zoetrope in homage to Tim Burton.

But Milk Is Import
Anna Mantzaris, Eirik Gronmo Bjornsen 2012
Shy guy meets shy girl in stop motion with lots of knitting and felt.

Kick-Heart
Masaaki Yuasa
Japanese insanity, with manga tropes.

History of Pets
Kris Genijn 2013
The pets don't fare so well in this funny and lighthearted tragedy.

A Girl Named Elastika
Guillaume Blanchet
The journey of a rubber band girl across a cork board in thumb-tack stop motion.  A fresh look and self-deprecating presentation.

Balance and Swing

Balance and Swing

Anne Beal 2012
A beautiful watercolor from RISD.

Aux Gambettes Gourmandes
A light powder (think sand and sugar painting) animation with a fun and accurate twist.

Boles
Spela Cadez 2013
Extremely smooth and self-contained Kafkaesque stop-motion. Women in Annecy shorts regrettably tend to caricatures: nurturing mothers, children, thin beautiful 20-something sex objects, grandmothers, or extremely fat.  This one had a much more interesting character.


The program this year seemed heavy on slow, depressing films about child abuse and refugees. These are seldom my own favorites because, while the subjects are of course important, they very hard to present in a novel or nonobvious way, and thus tend to disappoint as art and are underrepresented in my list.

I noted fewer films from North America and from Japan this year.  Monsters University was shown in 3D and was good, and technically perfect although I found the story and cinematography less compelling than Pixar's previous best films.  New work by Monty Python and Bill Plympton was good but not as exceptional as we have come to expect.

Bonus! A favorite from last year is now online: Una Furtiva Lagrima

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Morgan McGuire is a professor of Computer Science at Williams College and a professional game developer. He is the author of The Graphics Codex, an essential reference for computer graphics that runs on iPhone, iPad, and iPod Touch.

Big Graphics Codex changes in Aug & Sept

Over 1000 of 3D programmers, researchers, and graphics students already use the Graphics Codex app--I can see not only the original sales, but how many download the free updates each month. For the last two years the app has been essentially underground. Sales are driven solely by word of mouth and I have no advertising. This was a quiet start appropriate for an app that began by just releasing my course lecture notes in a mobile form factor, and only later grew towards comprehensive coverage.

Now that the Graphics Codex has 224 entries, including an entire course of lecture notes on physically-based rendering and new topics ranging from HTML5 to the biology of the human eye, it is time to upgrade both the app and the distribution strategy. In mid-August, I'll release version 2.0.  I have already submitted it to Apple and am just waiting for App-store approval for release. This contains a reworking of the UI code for responsiveness and clarity. Here's the full change log:

This really is a "2.0"--the entire scrolling, selection, and layout engines have been rewritten for performance and robustness.  The 1.9 version introduced the iOS 7 interface, which is retroactively available back to iOS 5.

I plan two more rapid-fire updates, for August and September. The first will include more UI features that need additional testing, such as the interactive graphs and retaining your place on a page when navigating between topics. Other UI features like printing are on the task list but may not make these short-term updates. I try to ship once a month with whatever is ready, rather than holding a release on a specific feature.

This update will be accompanied by an academic marketing campaign run by Alice Peters (cofounder of A K Peters), whom I've had the pleasure to work with on many projects in the past. It is time to get the word out about the app as the perfect complement for traditional textbooks in the classroom. In the last six years (long before it was publicly available!), I used the Graphics Codex in teaching at Williams as a companion to Fundamentals of Computer Graphics, Real-Time Rendering, and Computer Graphics: Principles and Practice in different semesters. I tuned the material for the app to work well with all three of these popular texts.

The September update will follow shortly after Apple's expected early-September product announcements. It will include additional iOS 7 support and increased coverage of GPU and rasterization topics. I'll post more information about this and another significant announcement about the Graphics Codex at the end of August.

Morgan McGuire is a professor of Computer Science at Williams College and a professional game developer. He is the author of The Graphics Codex, an essential reference for computer graphics that runs on iPhone, iPad, and iPod Touch.

Starfield Shader

I'm preparing assets for an upcoming mini-game jam/hackathon.  My current plan is to make a spaceship video game inspired by Galaxy Trucker, in which you build and then fly a ship.  This post is about the starfield shader that I created by modifying Kali's amazing Star Nest shader on Shadertoy to fit into the game framework.

The starfield

The starfield renders in 3.7ms at 1080p on GeForce 650M (the Kepler GPU in a 2012 Macbook Pro) on Windows 7 64-bit, including upsample time.  It is procedural, so it has effectively infinite extent and fine detail down to the pixel level, and has parallax as it scrolls.

I was only willing to spend 25% of the frame time on the background. To keep the performance high, I render downsampled by 2.5x in each direction to an RGB8 texture and then bilinearly interpolate up to full screen resolution.

Here's the GLSL shader:

// -*- c++ -*-
// \file starfield.pix
// \author Morgan McGuire
//
// \cite Based on Star Nest by Kali 
// https://www.shadertoy.com/view/4dfGDM
// That shader and this one are open source under the MIT license
//
// Assumes an sRGB target (i.e., the output is already encoded to gamma 2.1)
#version 120 or 150 compatibility or 420 compatibility
#include <compatibility.glsl>

// viewport resolution (in pixels)
uniform float2    resolution;
uniform float2    invResolution;

// In the noise-function space. xy corresponds to screen-space XY
uniform float3    origin;

uniform mat2      rotate;

uniform sampler2D oldImage;

#define iterations 17

#define volsteps 8

#define sparsity 0.5  // .4 to .5 (sparse)
#define stepsize 0.2

#expect zoom 
#define frequencyVariation   1.3 // 0.5 to 2.0

#define brightness 0.0018
#define distfading 0.6800

void main(void) {    
    float2 uv = gl_FragCoord.xy * invResolution - 0.5;
    uv.y *= resolution.y * invResolution.x;

    float3 dir = float3(uv * zoom, 1.0);
    dir.xz *= rotate;

    float s = 0.1, fade = 0.01;
    gl_FragColor.rgb = float3(0.0);
    
    for (int r = 0; r < volsteps; ++r) {
        float3 p = origin + dir * (s * 0.5);
        p = abs(float3(frequencyVariation) - mod(p, float3(frequencyVariation * 2.0)));

        float prevlen = 0.0, a = 0.0;
        for (int i = 0; i < iterations; ++i) {
            p = abs(p);
            p = p * (1.0 / dot(p, p)) + (-sparsity); // the magic formula            
            float len = length(p);
            a += abs(len - prevlen); // absolute sum of average change
            prevlen = len;
        }
        
        a *= a * a; // add contrast
        
        // coloring based on distance        
        gl_FragColor.rgb += (float3(s, s*s, s*s*s) * a * brightness + 1.0) * fade;
        fade *= distfading; // distance fading
        s += stepsize;
    }
    
    gl_FragColor.rgb = min(gl_FragColor.rgb, float3(1.2));

    // Detect and suppress flickering single pixels (ignoring the huge gradients that we encounter inside bright areas)
    float intensity = min(gl_FragColor.r + gl_FragColor.g + gl_FragColor.b, 0.7);

    int2 sgn = (int2(gl_FragCoord.xy) & 1) * 2 - 1;
    float2 gradient = float2(dFdx(intensity) * sgn.x, dFdy(intensity) * sgn.y);
    float cutoff = max(max(gradient.x, gradient.y) - 0.1, 0.0);
    gl_FragColor.rgb *= max(1.0 - cutoff * 6.0, 0.3);

    // Motion blur; increases temporal coherence of undersampled flickering stars
    // and provides temporal filtering under true motion.  
    float3 oldValue = texelFetch(oldImage, int2(gl_FragCoord.xy), 0).rgb;
    gl_FragColor.rgb = lerp(oldValue - vec3(0.004), gl_FragColor.rgb, 0.5);
    gl_FragColor.a = 1.0;
}

The preamble uses some G3D-specific shader preprocessing. #expect declares a macro argument, G3D allows multiple version numbers and promotes the highest one to the first line, and implements #include.  The compatibility.glsl file smoothes over differences between GLSL versions and between GLSL and HLSL.

At its heart is the "KaliSet" iterated function p := | p | / | p |² - k.  I tuned the constants for the specific look I was targeting and for performance.  It is of course very performance sensitive to the number of iterations of the inner loop and the number of volumetric steps.  I also extracted some of the expressions into uniforms in a way that the Shadertoy framework wouldn't have allowed for the original.  I tried using the max component or the average component in place of the expensive length() call, but this creates a 3-fold symmetry on some "suns" that is undesirable.

In my game, the background will move slowly as the ship flies. Very bright single pixels flicker in and out of existence as they are undersampled with the unmodified shader, so I suppressed these cheaply using derivative instructions and blending in against the previous frame.  The previous frame blending is primarily there to create motion blur and soften the background under motion to keep attention on the shops. I also wiggle the screen by a random offset of up to 1/3 pixel when the camera is still.  This makes stars appear to twinkle and closes the visual difference between the slightly-incoherent rendering under motion and when still.

Morgan McGuire is a professor of Computer Science at Williams College and a professional game developer. He is the author of The Graphics Codex, an essential reference for computer graphics that runs on iPhone, iPad, and iPod Touch.

iOS 7 Style for The Graphics Codex

I'm working on the release of version 1.9 of The Graphics Codex. The new features will be available on all supported versions of iOS, which means iOS 7 back through iOS 5.1. So, even iOS 5.1 and iOS 6.x will look like iOS 7!  I've wanted to implement a cleaner UI for a long time but felt that keeping the UI consistent with the latest version of iOS was important initially.

The new version contains interactive graphs and new graphics content as well as the new interface. It has the same fast interface, crisp text layout, and searchable index as the previous versions. All of the content is in the app, so that it works without a network connection.

Now that the iOS feature set is highly polished, I'm also looking at solutions for other platforms like Android.  I'll announce plans once I've worked out the technical details and know exactly how those versions will work.

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Morgan McGuire is a professor of Computer Science at Williams College and a professional game developer. He is the author of The Graphics Codex, an essential reference for computer graphics that runs on iPhone, iPad, and iPod Touch.

Pixel Art Evolution

I've been working on a dungeon crawl cooperative ARPG with my children in the evenings. Our emphasis is on design and interaction, not graphics. To keep art time low and accomodate the very small characters, I chose a 2D pixel-art style. I began by purchasing low fidelity 8x8 sprites from Oryx Design Lab and upsampling them using hq4x (in this case, using Darnell's Depixelizer). This enabled me to bring the implementation to playtesting  in a few hours. Having reasonable initial graphics was important for my co-designers, who aren't as willing to identify with programmer art.

As the game became more refined, I revisited the sprites and redrew many of them to add increased detail and match the features of their corresponding character portraits.

The images above show the evolution of two characters: the human female Ranger (currently named d'Arc) and the dwarven male Builder Crefftwyr.  This is frame 0 of each of their idle animations. The in-game shots are less sharp because the engine renders at fixed high resolution and then filters down to the current screen resolution. The result reminds me of the early game consoles of my own childhood when displayed on 1980's television.

To make the Ranger appear female, I narrowed the waist by one pixel on the upsampled size, pulled in her right cheek, and added long hair. To make the hair stand out, I traced a thin dark outline around her cowl. The final touch was adding a small mouth. Many of the other male characters (not shown) look acceptable without mouths, but somehow defining the mouth increased a sense of delicacy and precision in the face.  I tried adjusting the neckline of her shirt, but at scale it just read as a larger head and not an exposed neck.

The challenge in drawing the Builder was emphasizing the classic fantasy dwarven racial characteristics at small scale.  I pushed his head down so that he fit in 8x7 instead of 8x8 and then cheated and shaved another pixel off his legs in the upsampled 32x24 version.  Making the right-side eye triangular and drawing in an eyebrow gave the appearance of a large nose.  I thickened his arms by one pixel and raised the shoulders to increase the hunchback appearance.

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Morgan McGuire is a professor of Computer Science at Williams College and a professional game developer. He is the author of The Graphics Codex, an essential reference for computer graphics that runs on iPhone, iPad, and iPod Touch.

Upsampling Pixel Art with Alpha on OS X

It is easy to find low-resolution pixel art "sprites" for indie games, for example, by browsing the legally-distributed, Creative-Commons-licensed art at OpenGameArt.org. Such sprites are popular partly for their nostalgia factor for 30-something developers, but I think primarily because such low-fidelity graphics are easier both for indies to produce and to match surrounding image quality for. I use such art extensively in my teaching programming samples and jam games.

Unfortunately, in a world of high-resolution displays, 32x32 pixel art sprites are simply too small. Nearest neighbor upsampling retains the pixel quality but often (to my eyes) plays up the lo-fi nature a bit too much.  I prefer to increase sprite resolution using a pseudo-vectorizing filter such as Maxim Stepin's hq4x. It yields results like this:

Before

After

There are several open source implementations of hq4x available. Finding one that actually builds without a number of dependencies and supports your operating system (mine is OS X when doing artwork) is tricky, however.

I use Nelson's Windows + Linux implementation (which works fine for OS X if you compile from the Makefile) that simply wraps Maxim's code and doesn't introduce any library dependencies.  To install this on OS X:

1. Download the source from http://www.somebits.com/weblog/tech/hqnx/
2. Double-click to unzip the code 
3. Type "sudo make install" in the directory to compile the programs

The resulting script doesn't work correctly because it uses the Linux-specific tempfile command and because the hqnx code doesn't write correct .bmp files out.  I originally started patching this, but found that it was easier to simply invoke the hqx routines directly on .tga files, which it handles fine.  To upsample artwork simply use:

    hq4x source.tga destination.tga

This process does not preserve alpha (transparency). There are some variants that do support alpha, but again, it was easier for me to solve this problem in Photoshop. I paint backgrounds green (0, 255, 0) and then use the free Photoshop Green Screen filter.  You can also roll your own green (or other) screen removal code, since the algorithms were published by Smith and Blinn in 1996.

Here's the process for a spaceship that I downloaded from http://opengameart.org/content/modular-ships and then modified:

If you like this particular space ship, then you can download the set of 12 that I created by the process described here (as Public Domain content) at http://opengameart.org/content/2d-spaceship-sprites-with-engines.

In closing, I'd like to note that there is still a great need for all-in-one pixel art resampling, and providing this would be a great way for a junior game developer or Ph.D. student to gain great exposure. One could provide a simple, artist-ready tool that wraps hq4x and directly supports input alpha, or perform true vectorization for more significant upsampling, say, in the style of Depixelizing Pixel Art.

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Morgan McGuire is a professor of Computer Science at Williams College and a professional game developer. He is the author of The Graphics Codex, an essential reference for computer graphics that runs on iPhone, iPad, and iPod Touch.

Sol LeWitt and Voxel Ambient Occlusion

I've previously written about the relationship between the work of artist Sol LeWitt and computer science. Some representative geometric works by Lewitt include:

Note the exploration of the regular grid, mathematical patterns, tone and contrast, and light and shadow. The image that I created below follows in this vein of patterns in (exhaustive) combinatorial art and, I fancy, echoes LeWitt's interests.

Each tile in this image is a top view of a square of a white plane. The square is akin to the center of a Tic-Tac-Toe (UK: Naughts and Crosses) surrounded by up to eight white cubes in the adjacent squares. Those boxes are cropped out, so that only the effects of shadowing on the central square are present. That is, this is the complete set of ambient occlusion masks needed in a voxel system (such as Minecraft).

Each of the surrounding squares on the 3x3 grid of the Tic-Tac-Toe board may have a shadowing cube present or not. If you think of "there is a cube here" as the digit 1 and "there is no cube here" as the digit 0, then these patterns correspond to the possible values of an 8-digit binary number...there are 2⁸=256 of them. Of course, many of these are duplicates.  For example, once the horizontal and vertical squares are filled, no additional shadowing can come from corners.  So, there are 2⁴=32 tiles that look like the one in the lower-right.

I created these tiles using the G3D Innovation Engine to generate all possible scenes of this description and then applied the Scalable Ambient Obscurance algorithm (which is built into G3D) to efficiently generate the shadowing. I then used Image Magick's montage tool to combine them to produce this image.  The idea for generating tiles in this way is due to Mike Mara at NVIDIA. Below is an image showing their application for efficient illumination effects for the codeheart.js expert "orthovoxel" example. The left image has no ambient occlusion.  The right image uses these tiles to produce dynamic ambient occlusion in real-time.

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Morgan McGuire is a professor of Computer Science at Williams College and a professional game developer. He is the author of The Graphics Codex, an essential reference for computer graphics that runs on iPhone, iPad, and iPod Touch.

This may be a good time to learn some Computer Science

According to the US Bureau of Labor Statistics, students who start on a computer science degree are far more likely to find employment in the years after their graduation.  Other science and engineering fields will have a labor oversupply, but CS will be drastically undersupplied:



Morgan McGuire is a professor of Computer Science at Williams College and a professional game developer. He is the author of The Graphics Codex, an essential reference for computer graphics that runs on iPhone, iPad, and iPod Touch.

SSH with command-line password on OS X and Linux

Sometimes you have to connect via SSH or SCP to another machine inside of a script.  For example, when I update the codeheart.js website, I do so by running a script that builds the site, examples, and documentation, and then uploads them via SCP with multiple commands. Since the connection is launched by a script, it is inefficient..and annoying...to repeatedly type the password for SSH each time that the script needs it.  There are some common solutions to this problem, which don't happen to work well if your environment is OS X or Linux, or you don't have permission (or inclination) to modify the accounts to which you are connecting, or the accounts that you're connecting to have remotely-hosted file systems. Those common solutions are kerberos authentication forwarding/sshagent, TortoisePlink's windows SSH password option, and editing the known_hosts + authorized_keys files.

My solution is to use the Unix "expect" domain-specific language to trick SSH into communicating with a virtual terminal, and then programming the input that it receives until the connection is established.  The script below runs on OS X and Linux and allows you to supply a password on the command line.  I implemented this script to terminate with an interactive prompt, but you could instead close the connection after the remote command executes.

#!/usr/bin/expect -f
#
# syntax: sshnopassword password host command

set password [lindex $argv 0]
set host     [lindex $argv 1]
set command  [lindex $argv 2]

spawn ssh $host $command
expect {
  # Agree to modify known_hosts if prompted
  "(yes/no)?"   { 
      send -- "yes\r"
      exp_continue 
  }

  # Enter the password
  "*?assword:*" { 
     send -- "$password\r" 
  }
}

interact

Morgan McGuire is a professor of Computer Science at Williams College and a professional game developer. He is the author of The Graphics Codex, an essential reference for computer graphics that runs on iPhone, iPad, and iPod Touch.

Polymorphic vector operations for JavaScript

I wrote a small vector math (linear algebra/geometric) library codeheart.js because any kind of physical simulation for a game becomes awkward and redundant when implemented purely with scalar expressions. My current design is the result of several radically different experiments. I'm satisfied with the blend of special- and general-purpose code. It seems neither over-engineered nor too limited. The features that I sought were:

• Support functional addition, subtraction, Haddamard/array multiplication and division, dot product, magnitude, and direction
• To allow implementing polymorphic math routines, allow the same set of functions to operate on vectors:
• of any number of components
• with differently-named fields (e.g., xyz vs rgb vs. st)
• implemented as Javascript arrays
• from other libraries (especially box2d.js)
• ...and Javascript Numbers
• Simple for me to maintain
• Unlikely to exhibit hard to diagnose bugs (i.e., not too clever)