Thursday, May 19, 2011

Game Programming Interviews and Tests: Entry Level Edition

I'm starting to realize that most of my blog posts begin with me making excuses about something as well as linking to somebody else's post or article. Spoiler alert, today will be no different. The excuse is that this post is not my follow-up to my last one about my initial adventures with off-screen particles, due to a lack of time to work on it while moving into a new place and also some disappointing results with mixed resolution rendering. So what I'm talking about instead is my experiences with interviewing for programming intern positions throughout this past Spring. A while back, Jaymin did a great post about programming tests and demos, but I feel like I might have some insights for aspiring entry-level game developers.

The Hunt

I started my hunt for getting professional development experience by testing the water by sending out a few intern applications during my second year of college. The first step to getting any job is to actually apply for it. Typically this happens online these days, especially for intern positions. This brings me to my first point: looking good on paper counts for something. No matter what, you have to look appealing enough for a company to think about investing the time to actually talk to you. This was evident because, even though I was completely unqualified at the time, I scored a programming test for the Insomniac core team. I'm sure the only reason that happened was because I didn't let my grades slip during my first two years of college (proving that even the most painful "general education" class in existence still counts for something), and I also had experience working on several game development projects around the University. In short, I looked good on paper. Having a well thought out resume and portfolio are crucial, and the evidence adds up both from responsiveness to online applications and responsiveness from studio representatives at job fairs, such as the annual career pavilion at GDC.

After making it past the first hurdle, there are typically a two things that happen next. You will almost always need to do a technical interview and a programming test, although the order that they happen can vary. The Insomniac test was proof that I wasn't qualified yet, but at least it showed me what I needed to do to get past that initial challenge of getting noticed in the ever growing pool of fresh applicants looking for work in game development. So what exactly is in a programming test and how should you prepare?

The Test

For an intern, most tests are emailed to you, and you typically have a specified period of time to send it back. I've had several tests structured as a small programming project, in the style of typical work required to make a video game from the ground up. Anything that requires a substantial amount of work for a single problem is usually very generic in nature, so don't expect heavy AI or Graphics problems if the position isn't specifically for that discipline. Some of the more “small project” style questions that I've had have included memory management, binary file I/O, basic 2D collision detection, and string parsing. Almost every test requires C/C++ to be used, so make sure you've had practice! Also, take Jaymin's advice about showing a smart answer instead of a correct answer. Most problems have many solutions, is yours clean and optimized, and does it handle a good spread of use cases?

Some tests are limited to just a few hours, and I tend to find those to be more towards the stressful end. Perhaps the hardest test that I ever took was a 17 page short answer onslaught crammed into the span of 3 hours. It had required sections on bug finding and solving (things like what to do if the game crashes in release only, in a soak test with no memory leaks, etc), short answer code writing (think bit twiddling, list reversing, basic assembly writing, etc), and math problems (involving vectors, matrices, and trig) together forming the first 12 pages, and then 4 optional sections on gameplay, graphics, core, and networking programming (the remaining 5 pages). For me, it highlighted just how different a test could be from the “small project” style test.


A technical interview tends to feel different in nature than a programming test, which was surprising to me the first time I had one. One thing that you should know before any interview is the difference between a struct and a class in C++, this is a question that gets asked over and over again, partly to break the ice. More than three quarters of my interviews have started with that question. Be prepared to know about inheritance, virtual functions, dot products, cross products, const correctness, cache use, and game engine design. Also make sure that you're prepared to talk about game projects you've worked on, especially those you have on your resume or portfolio. Typical questions about your work include asking about your individual contributions to group work, what kind of difficult problems have you overcome, and if what is something (maybe just part of a project) you've worked on that you wish you could go back and redo.

Something telling of being a programmer is that no one has ever asked me if I have played games made by their company, where as I know designers that have had tons of questions about redesigning games made by the company they were interviewing with. Don't sweat it if you haven't had a chance to pick up a company's latest game, spend your time refreshing yourself about the details of multiple inheritance and less commonly used C++ keywords instead. If anything, you might be asked what games you've been playing recently, just to make sure you play some games.


Be prepared to not have everything go smoothly the first couple jobs you interview for. I've botched tests and interviews alike, sometimes from things completely out of my control, but the important thing was that I kept working to improve myself as a programmer afterwards. Have you read Jason Gregory's excellent Game Engine Architecture? Do you have projects where you can show how you specifically contributed? Can you get involved with a mod group or a student club or a something to get experience working with others? Have you done projects completely on your own?

I've heard for a long time that game industry jobs require personal connections and luck, but to be honest you just have to be at a certain level of experience as programmer and be able to prove it. I've always maintained that the key is to get a feel for what that level is, and then set your goals accordingly. Make sure you feel like you're continually getting closer to that end goal of landing a job (and in a work environment that suits you best!). If it seems hard, that's because it's certainly no cake walk to get there in 3 or 4 years time. This is especially because until you have a game development job, you usually have to spend time doing things like going to class or working a non-games related job. I attended a talk at my university last Fall about interviews and tests for general software engineering jobs, and I left knowing that non-game industry interviews are laughably easy in comparison, even for "top-tier" companies. It's not easy, so keep at it!

Saturday, May 7, 2011

Adventures with Off-Screen Particles

This is hopefully going to be a two part post because I didn't get to fully explore it as much as I wanted to, as I've been losing my mind during another eventful week of final exams in college. I considered postponing this and pulling something out of my ass for today... but then I saw fellow contributor Wheezie had already stolen that spot with his post “What Did I Do Today?” If you haven't already, you should check it out to at least read the amazing comic that he put at the end of it. Especially because half of the time I don't think people who aren't designers understand what designers actually do. I mean, it's pretty clear that graphics programmers spend all their time inventing new acronyms for anti-aliasing techniques except for when they're tightening up the graphics on level 3, but designers- they're a whole different mystery. Wait, what was I actually going to be talking about in this post? Particles, that's right...


Particle systems are cheap, flexible, and easy to set up, especially if you're using Unity3D, as is often the case with the projects happening at my University. This is why on a lot of my projects that I've been on (small student projects with tight deadlines), a designer often picks up the task to reduce the workload of other team members. This was the case with one such project that I was working on the fall. That project was Dust.

As you might guess from the name, there's a lot of dust in Dust. So much so that it takes place in a desert. Some of the designers on the project were tasked with helping to build the ambience for the game with some particle systems. An innocent enough task, but when it came time to integrate the work into our initial prototype, it was clear something was awry.

The problem with video game content creation is that people often have to learn the hard way how their work can impact performance. In this case, we wanted substantially more particles than anything other than a top of the line computer could accommodate (like the one we had been working on). And to be fair, a game like Dust should have as many particles as we can manage to have without blowing perf. One of the biggest impacts on performance from large numbers of particles is overdraw, especially when the particles are filling large sections of the screen:

[caption id="attachment_5183" align="aligncenter" width="484" caption="Massive overdraw from dust particles"][/caption]

This is a shot of the Unity editor's visualizer for overdraw. The bright areas are spots where many pixels are being drawn over and over again. This is particularly an issue with particles because the system contains many overlapping quads, where pixels will be drawn over many times. Keep in mind that the given shot is from the current version of Dust, his systems were originally much, much heavier on overdraw.

Doing it Offscreen

A solution to this particular consequence of particle effects is presented in the fabulous GPU Gems 3 by Iaian Cantlay. The technique boils down to reducing the number of pixels being rasterized by rendering the particles to a texture that is then composited back into the main image. The rendering is done after a depth buffer has been formed, so that the pixels in the particles that fail the depth test can be discarded properly as you render them. This means that the color can be applied directly back into the scene, which is especially easy if your particles are additive like ours were.

I started considering it as a possible solution to allow for thicker particles in future iterations of the project when I read through Shawn White's post on his implementation in Unity for Off Road Raptor Safari HD. It didn't take too long for me to adapt my own implementation a week or so ago, but there are definitely several issues that come to light very quickly (many of which are discussed in the GPU Gems 3).

Problems / Solutions

[caption id="attachment_5189" align="aligncenter" width="450" caption="Zoomed in view of cracks from point sampled depth"][/caption]

Some of the issues that I immediately encountered were visible halos between solid objects (notably the boat that the player controls in Dust) and particles after compositing. One solution to this problem is to have the depth buffer, which is being down-sampled due to the low-res target, take the minimum or maximum depth to be used when downsampling. As noted in the gems article, this is really just a rule of thumb, but it did indeed fix issues with cracks.

[caption id="attachment_5190" align="aligncenter" width="450" caption="Zoomed in view of depth farthest heuristic"][/caption]

However, it made it apparent that the much more serious issue is the aliasing that occurs due to the buffer being a lower resolution. It's very obvious along the edge of the sail in Dust. My goal was to get the particles to render at quarter res, but right now only half res comes close to an acceptable quality. One thing I could do is render the edges at full res in yet another pass, but the big question in my mind is whether or not two passes for particles would still result in a performance increase. We already have to create a depth buffer specifically for the purpose of the off-screen particles, because we don't do deferred rendering, it's not used for much else.

Next Time

Hopefully by the time my next post rolls around (and I'm done with finals), I'll have some more results (and perf numbers) and give some insight onto whether or not we decide to actually use it in the game. On the plus side, we modified Dust's design recently to be more separated, so potentially we can split it so that it's only in effect where the particles are prevalent enough to warrant its use. Also, I'll try to set up some fresh test scenes that show the effects better, considering that upsampling the in game shots went horribly.