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Allen Chou

Member Since 15 Jul 2010
Offline Last Active Apr 27 2016 01:28 PM

Topics I've Started

My Uncharted Journey: My Story from Gamer to Game Developer

22 March 2016 - 08:05 AM

Here is the original blog post.
This post is part of My Career Series.
Note: This post was written before Uncharted 4 went gold, so it might contain tones or implications that Uncharted 4 hasn’t gone gold yet. Sorry for the confusion.
I started working on Uncharted 4: A Thief’s End almost two years ago, and here we are, less than two months before release. This would be my first shipped title as a full-time game programmer (I shipped Planetary Annihilation during a summer internship). Looking back now, I realized that I’ve really come a long way since I first wanted to make games more than a decade ago. I would like to take this opportunity to write down this journey to share with you and as a note for myself.
I Wanted to Work at A Game Store
My first contact with video games was when my dad got me an original Game Boy as a present while I was in kindergarten. My only two games were Super Mario Land and Tetris. That’s when I got hooked on video games. Later, I saw my cousins getting a Super Nintendo (SNES) when I was in 2nd grade. I went over and played with them pretty frequently, but we had to take turns as the SNES only has two controllers. After bugging my parents, I finally got my own SNES to play with. My favorite games were the Super Bomberman series. I even went and got all of the Bomberman games on the Game Boy.
In 4th grade, one of my friends brought over his Nintendo 64 (N64) and Super Mario 64; that was my first time playing a 3D game and it blew my mind. My friend and I made a deal where I would buy games slightly more frequently than he would, and we took turns owning the N64 and the games every couple months.
Around this time, when asked what I wanted to do in the future, I would say that I wanted to work at a game store so that “I could play video games all-day during work.” This all changed when, in 5th grade, my homeroom teacher brought a PlayStation (PS1) to school to let us play while we waited for our parents to pick us up after school. One day, as we watched in awe as he showed off how good he was at playing games, he said:
“You know what’s more impressive than being good at playing games? Making games.”
That, was when I decided that I wanted to make video games.
My Pre-Programming Phase
Back then, I knew of almost no resources on how to make video games. The best thing I was able to do was make very basic animations that reacted to mouse clicks in Macromedia Flash 3, which I learned in computer classes. In middle school, I picked up a 3D modeling software called TrueSpace and started experimenting with building simple character models, which I hoped would be someday used in a game (of course this didn’t happen).
When I started high school, I joined the Computer Research Club, in hopes of finally learning the technology behind making video games. On the first club lecture, I discovered that I did not like programming and preferred making game art; programming seemed daunting to me and not as visually attractive as art back then. So, I was detached from the programming aspect of game development for a while and focused on learning Photoshop and 3ds Max.
I was introduced to deviantART by a friend of mine in Canada. I started making and submitting art work to deviantART (both 2D & 3D) quite frequently; also, I picked up a lot of spoken English and internet slang along the way. After noticing some Flash games uploaded to deviantART, my interest in making games with Flash re-kindled; I gave another try at programming, and once I got through the steep initial learning curve, it didn’t seem as daunting as it had before. I started using Swift3D to render 3D models into Flash vector format to put in games. My most complete project was a bunny dancing game called “R-Squared de Dance!” which, unfortunately, was never fully finished and was lost. I did submit to deviantART a Valentine’s Day wallpaper with all 4 characters, though.
My First Contact with A Naughty Dog Game
One of my friends visited me and brought his PlayStation 2 (PS2) from the US, along with a copy of Jak and Daxter. The PS2 games sold in Taiwan were mostly Japanese titles; this was my first time seeing a PS2 title from the US. I only heard about Crash Bandicoot back in the PS1 days and didn’t know that it was developed by the same studio that made Jak and Daxter. Shortly after, during my sophomore year in high school, I got a PS2 because I couldn’t resist the temptation after hearing all of my friends talking about their PS2 games during lunch breaks.
During a summer break, my family went to visit some friends in California. I saw that their kids also had a PS2, with a whole collection of US games I’d never seen before. Intrigued, I asked them to bring me to a local game store. They brought me to a GameStop, and on the shelves I spotted a copy of Jak X: Combat Racing. That “weird-looking green-haired guy with an orange giant squirrel-like sidekick” instantly reminded me of my first sight of the original Jak and Daxter. I thought it looked interesting and decided to give it a try, so I picked up the game.
Jak X brought me a cinematic gaming sensation I had never experienced before. That was when Naughty Dog made a mark on me. I started having crazy thoughts about how amazing it would be if I could work at Naughty Dog. So there I was, staring at Naughty Dog’s website, clicking the tempting hyperlink that read “Want to join us? Click here!” A question popped up: “Are you still a student?” After clicking “yes”, I landed on a page that basically told me that Naughty Dog did not have opening for interns and “If you want to join us after graduation, you should pay more attention in math classes.” This, was the pivotal moment that made me adjust my attitudes towards math classes. Math became my favorite subject in high school, and I put a lot of effort in mastering vectors, matrices, geometry, statistics, combinatorics, and probability.
Fun fact: I tried programming a solver for linear systems of two variables in ActionScript, so that I could use it to do my math homework. I did not handle divions-by-zero, and when the computer told me the answers were NaN’s, I thought it was mocking me for being a noob, which has similar pronunciation in Chinese to NaN.
In my last high school semester, our Chinese teacher asked us to write a mock-up letter addressed to our dream company, be it real or fictional, and describe “why they should hire you.” I was the only person writing a letter to a foreign company which, of course, was Naughty Dog. Back then in Taiwan, working for a game company was generally frowned upon by parents and teachers, as video games were “what made kids bad.” However, I did have good grades, so my teacher did not give me a hard time for wanting to work at a game company.
And there came the nation-wide joint college entrance exam.
Addiction to Naughty Dog Games
I did pretty well in the exam, so I basically got to choose whichever college and whatever major I wanted. Determined to make games and becoming interested in programming again, I told my parents that I wanted to major in Computer Science. My dad, however, advised against that and suggested that I major in Electrical Engineering. He said that, as a pediatrician, he spent seven years in medical school learning everything besides pediatrics, and focused on pediatrics after becoming a medical intern; his argument was that I should not hop directly into focusing on what I was most interested in with tunnel vision, and should learn other related disciplines first, so that I could have a broader view.
My dad was pretty convincing, so I agreed; I chose Electrical Engineering and focused on hardware stuff, including electronics and integrated circuit design. Meanwhile, I still took some classes from the Computer Science department. Having a low-level understanding of hardware did make it easier for me to learn programming and computer architecture. For instance, I learned how to build computer memory from logic gates, and that helped me understand how memory access works. I also got to learn the gate-level design of full-adders and multipliers, hence their differences and why one is more computationally expensive than the other.
After my parents sent my sister to attend high school in the US, I remembered the fun I had with Jak X, so I asked my sister to send me copies of the Jak trilogy. As I went through the three games, witnessing the incredible work put into the game design and storytelling, I admired Naughty Dog even more and officially became addicted to their games. I went to Naughty Dog’s website once more, and saw the reveal trailer of their secret PlayStation 3 (PS3) project, later known to be Uncharted: Drake’s Fortune. I wasn’t very into shooters, “but it’s Naughty Dog, it’s got to be good.” So I picked up a copy of Uncharted when I visited my sister in the US during a summer break; knowing that the PS3 was not region-locked, I waited until I returned to Taiwan to get a PS3.
I played Uncharted. It was fun and technically impressive; I mean, look at the WATER on Drake’s pants! However, it didn’t give me the same charm as the Jak trilogy. To me, it felt like just another visually impressive action shooter with endless waves of enemies for target practice. So Naughty Dog dropped off my radar for a while.
Two years later (junior year), I saw the E3 live demo of Uncharted 2: Among Thieves. It completely blew me away. Did Drake just slide down and jump out of a COLLAPSING BUILDING, while IN-GAME? That sealed the deal. I got the game on release and powered through it; it was such an incredible game: stunning visuals, fun gameplay, awesome storytelling, and lovable characters. This was when I re-gained interest in Naughty Dog.
Then, I graduated from college.
Going Abroad & Joining The Kennel
Before I started my one-year mandatory military service, I applied for the undergrad program at a college focused on game development, called DigiPen Institute of Technology. I’ve already written about my story at DigiPen, so I’ll fast-forward a little bit. Uncharted 3: Drake’s Deception came out during my second semester at DigiPen. In spite of a few flaws in storytelling, I still thought the game was fantastic, just when I thought I couldn’t like Naughty Dog more.
Soon after, Naughty Dog released the reveal trailer for The Last of Us. This game completely caught me by surprise; a serious post-apocalyptic survival game is quite different from Uncharted’s lighthearted adventures. I thought it was a nice change of mood and appreciated that Naughty Dog was willing to try something different. At PAX Prime 2012, I went to Naughty Dog’s booth that showed a live demo of The Last of Us. The interior of the demo room was set up to look like the rundown hotel where Joel and Ellie fought the hunters. The demo itself was an impressive demonstration of hardcore gameplay, where Joel and Ellie fought for survival while out-numbered and out-gunned. Such harsh circumstances and pressure imposed on the player was a first among Naughty Dog games. After the demo, I got an Ellie T-shirt and lined up to get an autographed poster by Neil Druckmann and Bruce Straley.
I got a copy of the The Last of Us right upon release. Being able to emotionally connect to game characters is such a rare and beautiful experience. Ellie felt like a real companion, not just some emotionless sidekick controlled by AI. The rich interactions between Joel and Ellie made the story feel so alive; they fought together, they cared for each other, they shared jokes, and they experienced the same emotions together. Not many games had reached such level of compelling storytelling. I gave Naughty Dog my deepest admiration and respect, again.
When studying at DigiPen, I always had the slightest hope that some day I might end up working at Naughty Dog. After successfully landing an internship at Uber Entertainment and attending various career workshops at DigiPen, I was confident that I could get a job straight out of college. I had all these plans in my head: getting a job around the Seattle area where DigiPen is (perhaps Wargaming, ArenaNet, or Sucker Punch), working in the industry for a few years, applying for job at Naughty Dog, and then finally working there if I was lucky.
Little did I know that destiny would speed up this plan a little bit for me, where I came straight to Naughty Dog after graduating from DigiPen. You can read this story in detail here.
So here I am, working at my favorite studio, making Uncharted 4. As a huge Naughty Dog fan, I feel so honored to be working on the closing chapter of Nathan Drake’s adventure.
This has really been an uncharted journey.
After Uncharted 4 is released, I will write about what I have been working on since I started at Naughty Dog. Stay tuned. smile.png

DigiPen: The Game School I Went To

24 July 2015 - 08:14 PM

Original Blog Post


Disclaimer: This post is all about my personal experience with DigiPen and is in no way intended to represent anyone else’s experience or opinions.

I went to DigiPen Institute of Technology to learn how to make games in 2011, and graduated last year (2014). I graduated one year earlier than my fellow classmates in the same year, because I transferred in some credits I had already earned at my previous college in Taiwan.

I have written one post about my life at DigiPen every year on a game design forum in Taiwan. Also, many of my DigiPen friends just graduated and have started their jobs in the game industry. So I thought, why not write a dedicated post about my experience at DigiPen in English on my blog?


Finding & Choosing DigiPen

When I was almost done with my bachelor’s degree in Electrical Engineering at my first college in Taiwan, I blindly followed what most of my other peers did: looking for a master’s program in the US to advance further in academia. As I was combing through the overwhelming amount of resources on the internet over a few days, an idea deep in my mind struck me: I chose a program in Electrical Engineering because it had always been my dream to make games, and Electrical Engineering was the closest I could get in Taiwan (next to Computer Science). So why on earth was I blindly searching for a path confined within academia, just because everyone else was doing the same thing? After four years of college, I numbed my senses and got lost a little, forgetting my original dream. Hadn’t I played the Jak & Daxter trilogy and made Naughty Dog my dream company in high school? Stupid. Stupid. Stupid!

So I threw away all my research on master’s programs, and simply started Googling “game school”. Several results turned up, and DigiPen was among them. I did some research and comparison on different curriculums and programs. As I learned about the vast number of various game-related courses there were, I became more and more convinced that a 2-year master’s program would not be long enough for what I wanted to learn. I ultimately chose DigiPen, which provides several 4-year undergrad programs, a learning environment exclusively for making games, and a large number of students in each year, which is a big enough pool to look for people to form a game team.

This wasn’t an easy decision to share with my parents. One stereotype about Chinese parents is unfortunately true: many Chinese parents expect successful academic progression from their kids, so they encourage – sometimes even force – kids to pursue higher degrees in academia. As far as I know, going for a second bachelor’s degree after already having earned one was unheard of in my circle. Fortunately for me, my parents are very reasonable people. After confirming with me for probably the fifth time that I was determined to do this, they finally said: “If going to this game school is really what you want, then you have our full support.” And I am forever grateful for their generous support.


DigiPen Is A Very Hard School

I will never forget the opening speech given by DigiPen’s president, Mr. Claude Comair, at the orientation.

“Look to your left. Look to your right. You won’t be seeing at least one of the people you just saw when you graduate…or not.”

This, as I learned later, is a very true statement, and he says it every year! Learning to make games at DigiPen is much more demanding than many people think. A quarter of freshmen can’t finish the first semester every year, and only about half of the students graduate on time; it’s worth mentioning, though, that some students choose to drop out because they have accepted job offers before finishing school.

Students are expected to attend classes and finish assignments just like regular college students do. However, on top of that, students need to use their own free time to work on game projects with a team. There are two game projects in the freshman year (one per semester), and one game project per year after that. Students can opt to intern at game companies instead of participating in student game projects in the final year.

Based on my experience, the things you learn from school, only account for 20% of the basic knowledge you need in the industry. What about the other 80%? You learn by forming study groups, conducting personal research and projects, attending club lectures, going to workshops, and last but not least, meeting with peers and professors. I learned about game physics and game engine architecture mostly through club lectures and research with peers.


Various Programs at DigiPen

When I started at DigiPen, there were 5 major undergrad programs, listed below. DigiPen has since added several new programs, including two sound & music programs for games.

  • Bachelor of Science in Real-Time Interactive Simulation (RTIS)
    This is basically a standard Computer Science program, plus extra courses focusing on game technology. The name of the program was changed during my sophomore year to Bachelor of Science in Computer Science in Real-Time Interactive Simulation, shortened BSCSRTIS, which is still quite a mouthful.
  • Bachelor of Science in Game Design (BSGD)
    Game design techniques, focusing more on the technical side of game design, e.g. scripting, gameplay programming.
  • Bachelor of Art in Game Design (BAGD)
    Similar to BSGD, but focusing more on the art side of game design, e.g. level design.
  • Bachelor of Fine Arts (BFA)
    As the name suggests, game arts.
  • Bachelor of Science in Computer Engineering (BSCE)
    Electrical engineering. Hardware stuff.

I was an RTIS student, so I have a better understanding of the RTIS program.



DigiPen is a 3-story building. On the first floor, there’s a cafeteria, some classrooms, including several bigger lecture halls, and a library (although not very large) full of books about making games (programming, art, game design, game history, you name it). You can also borrow games and various gaming hardwares from the library (for research purposes of course). On the second and third floors, there are more classrooms and the most important space of the school: the open lab.

The open lab consists of a big open space with tables and hundreds of computers. Students can use these computers to work on their assignments and game projects. Most game teams would stake out team spaces and use them throughout a game project cycle. In my first two years at DigiPen, I went to school at 9 in the morning and left around 11 at night almost every day. When I wasn’t in a class, I would be sitting in my team space, working on assignments, game projects, or conducting research. Good times.


Game Projects

Game projects account for special “game credits”. Throughout each project cycle, students have real milestones (Engine Proof, Prototype, First Playable, Alpha, Beta, and Gold), just like the industry. Upon each milestone, DigiPen’s game professors gather and sit through milestone presentations by every single team, usually non-stop throughout a couple days. Presentations are scored, and projects are also rated based on completion of Technical Certification Requirements (TCRs) and Design Certification Requirements (DCRs), all based on common industry standards.

These are very solid practices for presentation skills. During my first milestone presentation, I was so nervous that I sweated and trembled ridiculously. During my last presentation, not to brag, I was as calm as a pro.

We also learned to scope our games, as well as making the hard decision of cutting features before milestones.

In order to let students get a better taste of the industry, students are allowed to jump from one team to another; on the other hand, teams can hire or fire students. Students also have the option to go solo. If the game professors decide that a student has spent too much time without a team or a solo project, they can fail the student for game credits. A game team can also fail game credits if their game ends up incomplete.

A typical student game team consists of programmers from the RTIS program, a couple game designers from the BSGD or BAGD programs, some artists from the BFA program, and a producer. Producers have weekly meetings with game professors to learn production skills and discuss progress on the game projects.

Game teams can schedule a “team-on-one” with one of the game professors. A team-on-one is a 4-hour session with a professor, where everyone sits down, eats snacks, and talks about the game project casually. This is sort of like a reality check for the game project and a good chance to fix communication problems within the team, utilizing various team exercises. After every session, I always felt like my mind had been refreshed and my motivation rebooted.



Unlike ordinary colleges, most of the clubs at DigiPen are either about playing games or making games: Board Game Club, Shooting Game Club, Fighting Game Club, Game Graphics Club, Game Physics Club, Game Engine Architecture Club, etc.

Among them is a special club called the Playtesting Club. They hold playtesting sessions twice a week in the afternoon, setting up games on the computers in the open lab. Game teams can participate by putting up their games and let other students play. Playtesting sessions are valuable time spent in getting precious feedback on your game from fellow classmates. By the way, you can get a voucher for a free entree from the cafeteria if you playtest three games. Why wouldn’t you participate?


Integration with Industry

DigiPen has a very tight relationship with the game industry. Many of the faculty are industry veterans; some are still in the industry and teaching at DigiPen part-time.

Spring breaks and fall breaks are always aligned with the Game Developer Conference (GDC) and the Electronic Entertainment Expo (E3), so students and faculty are free to attend these important industry events.

I cannot stress enough the importance of attending GDC. You can make professional connections there, and it is a great place for job hunting. My current job at Naughty Dog would not have been possible had I not run into Naughty Dog’s recruiter at GDC in 2013. I also write down some GDC social tips; if you’re interested, you can check them out here and here.


Career First

If there’s one thing at DigiPen that is more important than preparing students for the industry, it is putting them into the industry. This is a general consensus among faculty. A student’s opportunity to break into the industry takes top priority.

For instance, my on-site interview with Naughty Dog coincided with a midterm. My professor thought the interview was much more important than her midterm, so she let me go to the interview and take the midterm another day without penalty. I also missed some other classes that day, and all professors were totally fine with it.


Career Services Center

In my opinion, the Career Services Center is one of the best resources DigiPen provides.

You can schedule a meeting with a dedicated professional at the center. During the meeting, you can discuss how to write your resume, design your website and business cards, practice interviews, and so much more. I went to over 20 meetings before I finalized my resume, personal website, and business cards.

When I had my phone interviews with Naughty Dog, they kindly let me borrow a meeting room. They also helped me draft a very professional-looking turn-down letter to a Microsoft offer I received.

Almost every week, the Career Services Center would invite a game company over to the school’s biggest lecture hall for a “company day”. They would talk about the company and what they look for in job applicants. Sometimes, companies even hold interviews right on-campus!

The school holds various workshops, some designed for current events. For instance, most DigiPen students are quite shy; in one of my years at DigiPen, a few weeks before GDC, where people get socialized and make connections with people from the industry, they invited some people from the industry and held a miniature mixer to let students practice having conversations with professional game developers. Every now and then, they also hold workshops focusing on self-presentation, helping students understand how to appear more professional with their social skills, resumes, websites, business cards. I really learned a lot of great tips from these workshops, including how to tailor resumes to specific companies, and what to look out during interviews.

I recently learned that the school has started officially offering classes dedicated to professional communication taught by Sonia Michaels, including everything from resumes to business cards to professional networking and, of course, conference behavior.

The Career Services Center is also responsible for DigiPen’s annual career fair, which is famous for being quite different from regular colleges. Instead of having students walking around company booths, students set up booths and recruiters walk around to hunt for prospective hires. It is not uncommon for a student to end up with multiple job offers after the career fair.

The placement rate of the RTIS program in the past four years ranges from 84% to 90%, i.e. at least 8 out of 10 RTIS students graduated with a job offer already in hand in the past four years.


The End

These are the things I have to say about DigiPen off the top of my head.

I’ll end with a list of my friends from DigiPen, most of whom recently graduated and got jobs, in case you would like to follow them.

Is gamesdevil.net an imposter of gamedev.net?

30 June 2015 - 06:56 PM

If you go to gamesdevil.net, you'll see it's 100% mirroring the content of gamedev.net.

Is this an imposter site that is potentially a phishing site?


P.S. All pages are up to date and all links work. The only difference is the domain name.

Game Math: More on Numeric Springing

26 April 2015 - 02:39 AM

Original Blog Post with Pretty Equations
This post is part of my Game Math Series.  
Previously, I talked about numeric springing and provided some examples.  
I have been saving up miscellaneous topics I would like to discuss about numeric spring, and now I have enough to write another post. Here are the topics:  
1. Using The Semi-Implicit Euler Method  
2. Numeric Springing vs. Tweening  
3. Half-Life Parameterization  
Using The Semi-Implicit Euler Method
Recall the differential equation for a damped spring:  
(d^2 x)/(d t^2) + 2 zeta omega (d x)(d t) + omega^2 (x - x_t) = 0  
And the equations for simulating such system obtained by the implicit Euler method:  
x_{i+1} &= Delta_x / Delta  
v_{i+1} &= Delta_v / Delta  
Delta = (1 + 2 h zeta) + h^2 omega^2  
Delta_x = (1 + 2 h zeta omega) x_i + h v_i + h^2 omega^2 x_t  
Delta_v = v_i + h ^2 (x_t - x_i)  
I presented the equations obtained by the implicit Euler method, because they are always stable. We can obtain a different set of equations that can also be used to simulate a damped spring system by the semi-implicit Euler method[/b]:  
v_{i+1} = (1 - 2 h zeta omega) v_i + h omega^2 (x_t - x_i)  
x_{i+1} = x_i + h v_{i+1}  
The equations obtained by the semi-implicit Euler method involve much less arithmetic operations, compared to the equations obtained by the implicit Euler method. There is a catch: the equations obtained by the semi-implicit Euler method can be unstable under certain configurations and the simulation will blow up over time. This can happen when you have a large zeta and omega. However, the zeta and omega on most use cases are far from the breaking values. You would almost never use an overdamped spring, so zeta is usually kept under 1. Even if zeta is set to 1 (critically damped spring), omega can be safely set up to 10 pi (5Hz), which is a very fast oscillation you probably would never use on anything.  
So, if your choice of zeta and omega result in a stable simulation with the equations obtained by the semi-implicit Euler method, you can use them instead of the equations obtained by the implicit Euler method, making your simulation more efficient.  
Here's a sample implementation:  
      x     - value             (input/output)
      v     - velocity          (input/output)
      xt    - target value      (input)
      zeta  - damping ratio     (input)
      omega - angular frequency (input)
      h     - time step         (input)
    void SpringSemiImplicitEuler
      float &x, float &v, float xt, 
      float zeta, float omega, float h
      v += -2.0f * h * zeta * omega * v 
           + h * omega * omega * (xt - x);
      x += h * v;
Numeric Springing vs. Tweening
Numeric springing and tweening (usually used with the famous Robert Penner's easing equations[\url] might seem very similar at first, as they are both techniques to procedurally animate a numeric value towards a target value; however, they are actually fundamentally different. Tweening requires a pre-determined duration; numeric springing, on the other hand, does not have such requirement: numeric springing provides a simulation that goes on indefinitely. If you were to interrupt a procedural numeric animation and give it a new target value, numeric springing would handle this gracefully and the animation would still look very natural and smooth; it is a non-trivial task to interrupt a tweened animation, set up a new tween animation towards the new target value, and prevent the animation from looking visually jarring.  
Don't get me wrong. I'm not saying numeric springing is absolutely superior over tweening. They both have their uses. If your target value can change dynamically and you still want your animation to look nice, use numeric springing. If your animation has a fixed duration with no interruption, then tweening seems to be a better choice; in addition, there are a lot of different easing equations you can choose from that look visually interesting and not necessarily have a springy feel (e.g. sine, circ, bounce, slow-mo).  
Half-Life Parameterization
Previously, I proposed a parameterization for numeric springing that consisted of 3 parameters: the oscillation frequency f in Hz, and the fraction of oscillation magnitude reduced p_d over a specific duration t_d due to damping.  
I have received various feedback from forum comments, private messages, friends, and colleagues. The most suggested alternative parameterizatoin was the half-life parameterization, i.e. you specify the duration when the oscillation magnitude is reduced by 50%. This seems like a fair suggestion; thus, I'll to show you how to derive zeta to plug into numeric springing simulations, based on a given half-life.  
I'll use lambda to denote half-life. And yes, it is the same symbol from both Chemistry and the game.  
As previously discussed, the curve representing the oscillation magnitude decreases exponentially with this curve:  
x(t) = e^ {-zeta omega t}  
By definition, half-life is the duration of reduction by 50%:  
x(lambda) = e^ {-zeta omega lambda} = 0.5  
So we have:  
zeta omega = -ln(0.5) / lambda  
Once we decide the desired lambda, we lock in omega and compute zeta:  
zeta = -ln(0.5) / (omega lambda)  
And here's a sample implementation:  
    void SpringByHalfLife
      float &x, float &v, float xt, 
      float omega, float h, float lambda
      const float zeta = (-lambda / omega) * ln(0.5f);
      Spring(x, v, xt, zeta, omega, h);
Here's a graph showing lambda = 0.5 and omega = 4 pi (2Hz). You can clearly see that the oscillation magnitude is reduced by 50% every half second, i.e. 25% every second.  
I've discussed how to implement numeric springing using the faster but less stable semi-implicit Euler method, the difference between numeric springing versus tweening, and the half-life parameterization of numeric springing.  
I hope this post has given you a better understanding of various aspects and applications of numeric springing.

Apparently, Game Devs Are Considered Non-Threatening to US National Security at All

25 April 2015 - 04:00 AM

I would like to share an interesting story about my past two visits to American Institute in Taiwan (AIT).
For people in Taiwan to study or work in the US, they need a student visa or a work visa. Visas are acquired by interviewing with an official at one of the two AIT offices. Luckily, one of them is very close to where I lived in Taipei.
I went to AIT to get my student visa for DigiPen in 2011, as well as my work visa stamp for Naughty Dog in 2015. My experience with both visits told me that, apparently, game devs are considered non-threatening to US national security at all.
My Student Visa (2011)
This was my first time interviewing at AIT by myself. When I had visited the US with my family before this, it was my parents who did the talking at the interviews for visitor visas.
As I got in line at the AIT office, I started practicing the interview in my head, trying to prepare my self with acceptable answers for various possible questions related to national security. When I got closer to the interview booths, I tried to eavesdrop on the interviews to get a better idea on what sort of questions were asked.
For many people before me, they were asked tons of security questions, and a few of them got rejected. As I heard more questions and saw people getting rejected, I became more and more nervous.
Then, it was my turn.
I went up to the booth, and the interviewer took my documents.
"You're going to study in the US?"
"Yes, sir."
"This school. DigiPen. What are you studying there?"
"Making video games."
"Oh? What type of games do you play?"
"I said what type of games do you play?"
"Uh...mostly action games and platformers."
"Really? Like what?"
"Well...like the Assassin's Creed series...and the Uncharted series."
"Ah. I've never got to play Assassin's Creed, but I play a lot of Call of Duty."
"Um...I'm not that into shooters."
"I see. You should try."
"I did play some shooters, but not much."
"Okay. I see. Thank you."
Then the the interviewer stamped my passport and gave me my documents.
"So...." I was confused.
"You're good to go! The exit is right over there."
That was the entire interview. Not a single national-security question asked.
My Work Visa Stamp (2015)
After leaving DigiPen in April 2014, I started working at Naughty Dog in May 2014 without leaving the US. For the first few months, I was working under Optional Practical Training (OPT), which is an extension program that allows new grads to stay and work in the US for a year, with a possible 17-month extra extension.
Work visas are issued en mass around October by lottery. I got my work visa in October 2014 (the chance of getting one was about 50% in 2014). However, I had to get a physical work visa stamp on my passport from AIT if I wanted to leave the US and come back later. I had planned a trip to Korea earlier this year in March, so I had to arrange a visit back to Taiwan after Korea.
Again, I was in line at AIT. This time I was less nervous based on the experience from last time. Then, it was my turn for the interview.
"So you need a work visa stamp, huh?"
"Ooooh. Naughty Dog. I know this company. You guys make video games, right?"
Then the interviewer quickly stamped my passport and returned my other documents.
"Here you go. Have a nice day!"
And that was it. It took me less then a minute, which was unbelievably quick compared to other interviewees.
Apparently, game devs are considered non-threatening to US national security at all.
They probably don't know that some game devs (like Zombie Studios) make serious games for military training purposes. Oh well.