Poly Bridge: Just Starting Out With Stresses And Strains

So I’ve been having fun playing Poly Bridge [official site] this morning. I feel like it’s the sort of game you can sink into and tinker with while binge watching something on another screen or maybe listening to a podcast. But I’ve started to see the parts where I’ve not quite got the hang of how the physics works and where the game is better and worse at helping me figure out why that might be.

I’ve gone through the whole tutorial and was gradually working my way through the campaign levels, figuring out how to build a workable solution and then, often, refining it to reduce the budget or make it more efficient. Some was trial and error but largely I got the idea of what I was building and then it was a case of working out which bits weren’t pulling their weight. Or were pulling too much weight and weren’t attached to enough triangles.

I meandered my way to level 1.8. It’s called Overpass and you can use wood, steel and rope to get two cars over a stretch of water but leave enough room for a boat to pass through the middle.

I figured it out slowly but it occurred to me that the tutorial left a couple of things out (unless the man at the door trying to sell me a new fascia meant I missed something crucial). I get that you don’t want a player to be overwhelmed or that bombarding them with physics might be a misstep if you want your game to be approachable so I understand why you don’t get that stuff by default.

I mean there’s that advice mentioned by Hawking in relation to A Brief History Of Time that each equation you include halves readership. Obviously it’s about the idea of making things approachable and people’s responses to mathematical notation rather than a specific measurable fact (otherwise my A-level textbooks would probably have had readership of a fraction of a person). You can see why a game might prefer to keep the equations under the hood where possible.

So I understand the approach where you explain the basics and then let the player feel out more complex ideas out as they go. But it felt like a few bits of important information had been missed that point out where you go to start digging into those ideas.

For example, I don’t get why the tutorial itself didn’t tell the player that if you’re having trouble with a bridge you can use the options to slow down the part where you watch how it works in practice in conjunction with the button that toggles the ability to see how much stress is on each element. That lets you see how particular bits of the bridge are performing under pressure and adjust your design accordingly.

It does tell you that there’s a manual nestled in the side bar. The info about the stress toggle and the speeds of the replays is actually contained in the manual if you scroll right to the bottom of the tips and tricks chapter. But I don’t understand why that tip would be several optional clicks away rather than information you give as you launch the player into the campaign.

What happened with me is that I didn’t need to peek at the manual for a while because the first few levels are straightforward. By the time it would have been useful I’d forgotten it was there as it doesn’t “pop” on the menu sidebar. A reminder that it existed after I’d failed one bridge a few times would have been a handy prompt, I think.

I’d been struggling with a particular construction – Overpass – for a while and it was because how I thought particular elements would behave were a little different in practice than intuition. Skimming through the materials section of the manual opened that up to me which was cool but that slight tweak to how the game directs you to useful information would have made a difference.

At this point in my playthrough of the campaign the one thing I feel like I’m missing is an option that tells me a bit more about forces acting on the bridge. Sometimes you can see an area getting stressed and eventually collapsing – it turns from green to orange to red to destroyed… – but it’s not always immediately clear which forces are actually acting on that section and from which direction. Working that out is part of the puzzle, but I do miss the ability to annotate or to maybe switch to a mechanics textbook view where you can see the different forces at play and the direction in which they’re acting.

Maybe people would feel that would make it too easy or maybe it would be a hellish task to represent that stuff in a way that’s legible to the player. I feel like it would make it easier to understand why something is behaving in a way that seems counter-intuitive, though.

For example, I tried to strengthen a weaker section of one bridge using ropes just now as an additional support measure because hooray for tensile strength. It actually made the entire bridge collapse and I still haven’t quite figured out why – whether it was a weight thing or whether a different force was suddenly in play.

It’s not a pressing concern because I fixed the design a different way, but just being able to scan an overlay and go “Oh, I see! I totally forget about x force!” would make me feel like I’d understood my design choices better. Especially given it’s been *COUGHCOUGHCOUGH* years since I studied that mechanics A-level!

I want to stress* that I’m enjoying the game, by the way! I like the style and a lot of the simplicity of the presentation so far. I just wanted to point out what I’d missed or forgotten having worked through the tutorial in case that helps anyone else. As well as, I guess, bemoaning how little of my practically-oriented maths education I can apparently recall at a moment’s** notice.

* That was a pun – you can laugh now. I’ll wait.

** That was also a pun. Mechanics comedy is my new jam.


  1. Flatley says:

    While it’s in theory very straightforward to represent the difference between tension and compression using colors, there’s no really good way to do it in a perceptually pleasing manner — high tension can be red, but then what can high compression be. Blue? Blue is shorthand for “good.” (Most structural analysis programs use a red to blue scale because there really aren’t better choices.) I guess you could use red/yellow but that might be tough to distinguish.

    My solution of choice would be to offer a toggle between the default, unsigned “magnitude” color scale and a signed scale indicating tension or compression.

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      Philippa Warr says:

      I actually meant more of a traditional mechanics notation to show the direction of a force acting on an object. Arrows and so on when you select an individual element so you can tell what’s going on in a more granular way and learn from it.

      • corinoco says:

        Rivetting review. You really spanned all the major pillars of the program. A shear delight to read.

        [runs away]

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      Phasma Felis says:

      Why not just arrows?

      • unacom says:

        For simple structures arrows will do just fine. For a little more complex situations arrows will start to confuse the eye pretty fast. Mainly because it´s not just one direction of force per structural element, but compression as well as tension. Then, there´s momentum, shear, vibration…
        And I´m only thinking about the elements right now. There´s the nodes too (if they are considered).
        Man. I need to reinstall Bridge Builder fast [adds Poly Bridge to wishlist].

  2. pepsiman says:

    one of my structures lecturers showed red/blue for comp/tensile forces and thickness of strut for magnitude of forces.

    if you could go into a separate ‘mechanics view’ and maybe show that information?

    by the way how detailed does this game get? do the beams have bending moments or are they just comp/tens trusses?

  3. lepercake says:

    Sooo bridge builder? Pointifex? That’s what this is?

  4. Alasher says:

    link to steamcommunity.com

    It’s physics sucks badly: When building a bridge the only parts that add weight are roads and joints.
    The connecting struts, such as wood, steel, etc, do not add weight on their own, so a 2m piece of steel weighs the same as a 2m piece of wood, but really it’s just the joint that is adding that weight.

  5. James0 says:

    I really like bridge building games for some reason. But usually I get frustrated because they tend to force you into using simple, utilitarian designs. This one seems to actively encourage, er, “creativity”. There are some levels where you don’t have enough materials to build a proper bridge so you just have to build ramps that allow cars to jump over the gaps, and I remember at least one level where you can bounce the cars off a hot air balloon. The game accepts solutions that collapse immediately after the last car gets across, and ones in which the cars cross the finish line high in the air or on their backs. And you can do all kinds of fun things with the hydraulic parts: my favourite is to build bridges that disappear underwater to allow boats to pass.

    Though I suppose this could be considered a flaw by people who like their games realistic and boring.

    Disclaimer: I haven’t played it since it was in early access, so all of the above might be wrong.