ProcGen: Implementation considerations

This entry is about considerations and aspects you should think of when you are implementing  procedural generation (procgen) systems, beyond the pros and cons presented in the previous post (here).

Some of these could also be considered pros or cons and, in fact, some of you commented that. The main difference is that these are more case specific.

Here we go:

  1. Define objectives: If you are dealing with runtime (real or load-time) procedural generators in a game, you need to create rules in a way to guarantee that the game objectives are not compromised. The right rule set and logic can sometimes be tricky to fine tune and narrow down.
  2. Testing: As part of guaranteeing the previous line, runtime ProcGen systems require you to thoroughly test its results. The more freedom you give your ProcGen system to create content the more you need to test it. You really want to make sure the resulting content is plausible, so that nothing weird is generated or something that stops you from completing the game’s objective.
  3. Perception: The question is: do all these trees look alike? Is this room memorable? Or will the user distinguish similar type content? If you want them to, you should make sure you know what aspects and details help you to achieve this perception. GalaxyKate brought this to my attention and you can read her interesting post on it (and her experience on spore) on her Tumblr here.

  4. ProcGen by necessity: There are some types of games that require you to use ProcGen systems, like Infinite runners and Roguelikes, or games that learn and adapt with your inputs and gameplay. There are also other good to have situations like creating special effects or textures (like with Substance).


  5. Prototyping: If you have a ProcGen system or tool, it could help you to prototype game levels that require content in scale, like open-worlds. If you are using ProcGen at design-time you can use the resulting content as your starting point.

  6. Rewarding: Another thing you need to worry about is the sense of reward, if the generated content somehow influences it. Normally, you’ll want the game to give you a sense of accomplishment, be rewarding and fun. Again, testing is important. Tanya Short from Kitfox Games talked about it at GDC 2015 (below).

  7. Replayability: If you have a runtime ProcGen system that guarantees a good variation of your game experience every time you play it, that can increase the game’s longevity, meaning people would take longer to get bored of it. Gives it a sense of novelty that can, at times, surprise even its creator.
  8. Discussion value: You need to manage this value properly. Runtime ProcGen, depending on the cases, will give you less walkthrough material (sometimes more) to talk about with other gamers. This mainly because each player will have a different experience. On the other hand, there are other things you can discuss. Minecraft gives you a lot of creative power which you can share with others. Infinite games, for instance, use the point system to allow gamer comparison.
  9. Art perfection: It’s not easy to get ProcGen to produce art like a human artist would. It can be difficult for (random) runtime ProcGen art to satisfy 100% of the time. This mainly because it can be difficult to test all possible outputs and, if you decide to change one little variable, you can define a whole new set of outputs.

I hope you guys enjoyed this list. Let me know if you have any comments or other considerations that I missed 🙂

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ProcGen: pros and cons

In this post I discuss the pros and cons of using procedural generation (ProcGen). This type of analysis is a good way for you to understand when you should use it and it varies depending on what you want to do. Some case examples in my previous post here.

The root cause for some of these arguments in favor or against might be the same. Here are a few of the most common pro and con arguments:

([+] for pro, [-] for con, [+/-] for depends)

  1. [+/-] Efficiency: How fast we can design our scenes? Whether ProcGen is more efficient than manual content sculpting, really depends on what you are doing. If you want to model a single 3D building, for instance, then maybe ProcGen might not be as efficient as the manual method. On the other hand, if you are to create 10, 50 or 100 buildings for a city then you could reconsider. In short, ProcGen can have a larger overhead than manual modelling but after you “break even” timewise, ProcGen can become infinitely more efficient.
  2. [+/-] Cost: How much time and money does it take to create? When it comes to the cost of using manual vs ProcGen, efficiency plays a big role when you consider the saying “time is money”. Another factor that influences cost is whether you create your own ProcGen system or use existing solutions such as SpeedTree, Houdini or Sceelix (shameless plug). Although you need to pay for the licenses, it may compensate the time your team saves.

    from Sceelix
  3. [-] Control: The ease to define certain designs and properties. When you want to create content with total control and specific details your best bet is to create the content manually. For your time, wallet and sanity’s sake.
  4. [+] Monotony free: If you have to create 100 3D buildings by hand, that can be a very tiresome and repetitive job. This is a point commonly made by game designers in favor of ProcGen.
  5. [+] Scalability: The ease to create small scenes as well as large. Once you determine the properties and parameters of the content you want to generate procedurally (which generates the overhead previously mentioned), the time it takes a PC to generate any amount of content depends solely on the limitations of the PC. Basically, from making 10 building to 100 can be a matter of seconds.
  6. [+] Compression: As you may remember from the high ProcGen purity game from my previous post, a whole 3D first-person shooter level fit into a 96kb executable because all its content (3D meshes, textures, sounds) were generated procedurally. When the game loaded up it used up over 300mb of RAM.
  7. [+] Paranoia: Is this tree distribution random enough? Or the number of branches and sub-branches for that matter? Aaahhh… ProcGen can give you more peace of mind in that sense, if you feed truly random seeds to a properly bounded system. Testing is always important specially if generation is at runtime.

    Printscreen 131021993101893786.png
    from Sceelix
  8. [+] Consistency: The guarantee that elements follow the same style and working principles. Almost in the opposite side of the spectrum from the previous point: Do these trees look like they’re from different planets? If you have a well rounded ProcGen system or tool specification, you can better guarantee greater consistency between content of the same type than if you did them manually. If you don’t, it can be a problem. Again, testing is important.
  9. [+] Reusability: Being able to make the most out of your work. Some ProcGen systems have a high reusability factor. Changing a few parameters could generate a whole new set of content. This also brings value you should consider, if you decide to create one. The more you can reuse it, the better the investment is of creating or specifying one.
  10. [+/-] Manageability: The ease of controlling the resulting output. If you are talking about creating large quantities of content, ProcGen can give you centralized control over the overall result. If you are dealing with small quantities, manual creation will give you more control. Some ProcGen tools also give you more control by giving you visual languages (normally node-based) with parameterization.
  11. [+] Adaptability: change to obey the rules you defined in your system. If you make a building double its original height, then the number of floors could automatically double. If the ProcGen system you use is well developed, you may change one of its parameters and the resulting output will adapt to meet the constraints you have in place.

    from Sceelix

These are the broad strokes. There are also some general considerations you should have when you use procedural generation, but that I’ll leave for my next post.

If you remember more arguments beyond the ones I mentioned, or have any feedback, let me know 🙂

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Hello world! #procgen

Hello everyone!

Welcome to this blog dedicated to Procedural Content Generation aka Procedural Generation aka PCG aka ProcGen, mainly in the context of Game Development.

ProcGen is when you use computer instructions and algorithms to produce any type of digital content (3D meshes, textures, sounds, …). These can use degrees of randomness in its generation. There is no magic: you can implement something that uses this method or use existing tools that implement it for you.

No Man's Sky 1
From “No Man’s Sky”

There are obvious games that come to mind when you think of ProcGen – like “Spore”, “Minecraft” and “No Man’s Sky”. These use this technique in big quantities. But there are also other games that use ProcGen, here and there, and are not so obvious – for instance, “Assassin’s Creed: Unity”’s city block generator – which I will talk about.

Block Builder
“Assassin’s Creed: Unity”‘s city block generator

For the last year I have been finding out more and more about this technology from the game industry’s point of view. Talking to people and researching. In this blog, I will talk about a few of my conclusions. Feel free to contribute with your opinions! 🙂


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