Sunday, June 19, 2011

Death of a Project

This is actually the follow up to my article on my adventures with Off-Screen Particles in Unity, but being that it ended with me deciding to kill the feature, I've decided that my process towards doing so would make a much more interesting post. I feel that knowing when to throw in the towel or radically change approaches is a good skill to have when developing any game, especially because this is the type of engineering endeavor where “seems right” and “ships on time” is so much more important than things like “is actually right” or “bridge you're engineering doesn't collapse when the wind blows”.


An important thing to keep in mind when you're working on a feature is the context of why you're doing it. This includes everything from how much time you can allocate for working on it to how much it impacts the user experience in your final product. In my case I was trying out a potential optimizations to hopefully allow an early prototype from a designer become feasible, which was not due to his heavy use of particles to create a dust storm, causing performance issues from heavy overdraw. This in itself is an important thing to keep in mind when doing an optimization, is whether or not what you're optimizing is actually a bottleneck in your game.

In my case, I knew the overdraw was becoming an issue because I: 1) reviewed possible reasons why our tons of particles could hurt our performance (to be fair, I was already a little familiar with the issue: knowledge is power!), 2)tested the effects of changing things like particle size, count, screen resolution, and 3) attempted to kill the designer for not using Unity' nifty overdraw visualization in the first place (Side note: attempting to kill a designer should only happen if you work in a strictly unprofessional environment, like a University lab, and will rarely have a direct impact on perf).

After identifying the problem, the next thing to do was decide how I could address it. Because the particles had only a minor impact on gameplay, the team cut it at the time and focused our efforts elsewhere for our deadlines at the time. However, I knew that being able to ramp up the particle density would really enhance the look and feel of the game, so I kept the problem as a side project.

Ramping Up

The project was slow to get started, due to it being on the back burners for some time. I started to really make progress on it when we were transitioning to hopefully ramp up our work on the game once again after many other projects that had been distracting team members for some months began to wind down (this is a continual problem in a University setting, but that's a story for a different day). I knew that the feature would be important if the proposed design changes happened, and that the work would be wasted if the designers went ahead and designed new zones without the feature at their disposal early on. With this in mind, the project quickly rose to a much higher level of significance. I spent a lot of time when I wasn't with the team cracking away at my work, and putting extra hours in at this point can often pay off.

Putting in that extra effort at the right time can really pay off. I quickly began to see measurable results and progress. The implementation that I discussed last time does have a substantial impact on a scene I brewed that's mostly particles at a density similar to what design wanted, resulting in a greater than 10 ms performance increase in my test scene at a 1280x720 screen resolution when rendering particles to a buffer smaller by 2x. I could do even better than that when using a 4x smaller buffer. That clearly identified two things: 1) that the feature warranted further refinement and 2) that I was right about the bottleneck, as the increase in perf proved that I was not wasting time going down the wrong path. However, in my first post I detailed artifacts that are noticeable in our particular game, and that I intended to explore the mixed resolution rendering as a solution to those issues.

Spotting the Wall

I knew that going to mixed resolution would require substantially more resources for the rendering and compositing of multiple passes, but would also allow me to get away with using a 4x decrease in our smaller buffer. So I started out with the intention of laying it out as simply and as efficiently as possible, and then tune from there.

After a little more work, I had it: mixed resolution off-screen particles. They had some room for quality improvements, but they definitely did a lot to fix the artifacts from before. I had also gained something else: my offscreen particles rendered with almost no increase in perf. I had lost all of my savings from my earlier work, which also meant that I may have moved my bottleneck as well.

I had a couple options at this point: 1) tediously work to increase perf and quality at the same time, 2) scrap mixed resolution and try to find another solution, or 3) kill it. The first option bears the weight of what would most likely be a lot of work on a project that I only have a limited amount of time to work on, and is especially difficult to do without source level access. I did try a couple quick and dirty thoughts on the second option, but going back to the drawing board has its own costs associated with it.

So I Killed It

It's not easy to kill something, especially when early work shows promise. However, it's an important thing to be able to do. I have other things to be poking around at in my spare time, and a feature that the game can live without is certainly not worth it. I had invested a reasonable amount of time into the feature already, but that didn't mean it was worth further pursuit. I suspect further work on it would be roughly equivalent to doubling the scope of the feature. Your time is always one of your most valuable resources, especially when code familiarity in itself makes you a valuable asset to your team. Getting stuck with your wheels spinning on a feature that isn't worth the benefits for the work isn't going to help anything, no matter what discipline you're in.

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