How to Play Trestle
Trestle is a bridge construction physics puzzle — your goal is to design a truss span that survives a vehicle crossing without exceeding your material budget. Each level gives you a deck already spanning the gorge — a chain of joints every 20 pixels between two abutments pinned to opposite banks — plus a steel budget. You add your own joints anywhere on the canvas, snapped to a 20-pixel grid, then connect pairs of joints with struts (members) to brace that deck. A strut costs two and a half units per pixel of its length, so price is purely a matter of distance: long diagonals are expensive, short members are cheap, and the game refuses any strut you cannot afford. Once you are happy with your design, click Test to send a weighted vehicle rolling across the deck.
During the load test the game solves the method of joints — a classical structural analysis technique — at every frame. Each strut changes colour to show the force it carries as a fraction of the level's breaking limit: green below 55 percent, amber from 55 to 85, red above 85. Red is a warning band — a member does not actually fracture until it passes 100 percent. When one of yours does, the test stops dead, the member bursts, and the level is failed. The pre-built deck members are colour-coded too but are never checked for failure. A crossing that holds earns one star, doing it on 80 percent or less of the budget earns two, and 60 percent or less earns three — the rating is budget efficiency and nothing else.
Building a Good Truss
- Copy the classic Warren truss shape — diagonal struts alternating above and below a horizontal chord distribute load evenly and are efficient on most Trestle spans.
- Brace at the load points — watch where the vehicle wheels contact the deck and add a vertical or diagonal strut directly at those nodes to redirect force into the truss.
- Cost is length, exactly — a strut costs two and a half budget units per pixel of its length, so splitting a long diagonal into two shorter ones costs the same as leaving it whole. Extra joints buy better triangulation, not a discount; the way to save budget is to need fewer members, not shorter ones.
- Read the stress colours before deleting — amber is 55 to 85 percent of the limit, red is over 85 and close to the edge, and a green member sitting under 55 percent may be redundant and worth removing to recover budget.
- Reset early — it costs nothing and is usually faster than trying to patch a flawed design partway through.
What Makes Trestle Different
Where most bridge builders iterate a soft spring simulation until it settles, Trestle solves the structure directly: it assembles the global stiffness matrix for the whole truss and solves it by Gaussian elimination, once per frame. Members are still linear-elastic axial springs — that is what a truss member is — but the answer is a closed-form solution to that model rather than a relaxation that may or may not have converged, so the same design always reports exactly the same forces. The per-strut colour coding lets you diagnose your design failure by failure — you can see exactly which member broke and why, which makes fixing it a learning exercise rather than a guessing game. Twelve levels ramp the vehicle weight from 2,000 units on First Span to 5,200 on Grand Span while the per-member strength multiplier drops from 1.1 to 0.75, so the triangulation that carried the early gorges is nowhere near enough by the end.
Understanding Truss Types
The shape that works in Trestle is the Warren truss — diagonals meeting in a V at every loaded deck joint, with a chord carried on to both abutments. The Pratt and Howe trusses of the textbooks, and the king post and queen post, all hang a loaded joint from a single vertical member, and Trestle's solver will not let that stand: vertical equilibrium at a joint held by one member hands it the vehicle's entire weight, while a member fails above the level's limit — at most 0.88 of that weight. A lone vertical snaps at any rise and any budget, so two non-parallel members on every loaded joint is not a stylistic preference here, it is the only thing that holds. Because every member is given the same axial rigidity and its stiffness is that rigidity divided by its length, a short strut is stiffer than a long one and draws more load toward itself — which is why a dense knot of short members near an abutment can quietly become the thing that breaks. Experimenting with these patterns across the 12-level campaign is how Trestle teaches structural intuition without formal instruction. The stress colour map is your tutor — a single amber member is a warning; trace which joints it connects and ask whether adding one new strut could split the load in two.
Frequently Asked Questions
How do I build a bridge in Trestle?
Each level opens with the deck already built: a line of joints every 20 pixels from one abutment to the other, pinned at both ends. With the Joint tool selected, click anywhere on the canvas to add joints of your own above or below that deck — they snap to the 20-pixel grid, and the game refuses to stack one on top of another. Then switch to the Strut tool and click two joints to connect them; the cost comes off your budget the moment the member appears, and a strut you cannot afford is refused outright with an over-budget warning rather than putting you in the red. When the design looks right, click Test to send the vehicle across.
What do the stress colours mean during the load test?
Each strut changes colour according to the force it carries as a fraction of the level's breaking limit. Green is anything under 55 percent. Amber runs from 55 to 85 percent. Red starts at 85 percent, and it is a warning band rather than a death sentence: a member only actually fractures once it passes 100 percent of the limit, so a strut can sit red for an entire crossing and survive. Treat red as the member to reinforce next — add a joint that shortens its span, or a parallel strut to share the load. Note too that only struts you placed can break; the pre-built deck members are colour-coded but never checked for failure.
How do I earn three stars on a level?
Stars are awarded purely on budget efficiency, once the vehicle is across. Getting it across at all earns one star. Crossing on 80 percent or less of the budget earns two. Crossing on 60 percent or less earns three. A collapse scores nothing at all, and the result panel prints the exact percentage you used, so the whole optimisation is finding the cheapest arrangement of struts that still holds. Only your best result on a level is kept, so a later, leaner design can raise a level's rating but never lower it.
How does Trestle work out the forces?
It solves the whole truss at once using the direct stiffness method, the matrix form of linear-elastic structural analysis. Every member — deck and player-placed alike — contributes a stiffness equal to its axial rigidity divided by its length, resolved along its own direction. Those contributions are assembled into one global stiffness matrix, the two abutments are pinned, and the system is solved by Gaussian elimination with partial pivoting to find how far every joint moves. Each member's axial force is then read back from how much its two ends shifted relative to one another, and compared against the level's breaking limit to give the stress ratio behind its colour. That whole solve is redone on every animation frame as the vehicle's weight moves along the deck, which is why the colours ripple ahead of and behind the wheels.
Can I delete a strut after placing it?
Yes. Select the Delete tool and click any strut to remove it — its full cost goes straight back into the budget. On desktop you can also right-click a strut to delete it whatever tool is active. Only your own struts can be removed; the pre-built deck is not yours to take apart. Editing is locked while a load test is running, and it stays locked after a collapse, so the only way back is Reset — and Reset clears the entire bridge and refunds the whole budget rather than restoring your last design. After a crossing that holds, though, the design stays editable, so you can keep trimming struts and retest to chase a cheaper solve.
Does Trestle work on mobile?
Yes. The canvas scales down to your screen width and every interaction is a tap — tap to place a joint, tap two joints in turn to draw a strut between them, and with the Delete tool selected, tap a strut to remove it. There is no long-press gesture, and the right-click shortcut is desktop-only. The toolbar sits above the canvas at every width and wraps onto extra rows when the screen is narrow. No install required; load the page in any modern mobile browser.
Is there a leaderboard?
Yes. The leaderboard tracks your cumulative star count across all 12 levels, so the maximum score is 36. Your running total is submitted every time you complete a level successfully; a collapse submits nothing. The star total is the only figure sent, so replaying an earlier level to turn two stars into three raises your score, and there is no separate tiebreaker on budget spent.
