Span & Strain

Build a bridge across a golden-hour canyon, press GO, and watch a loaded vehicle test it.

How it plays

• Build. Drag from a joint to a grid point to lay a piece: Road, Wood, Steel, Cable or Spring. Each has its own cost per metre, maximum length, stiffness and breaking strain. Cables only pull; springs give and damp. A piece that is too long, already built or outside the build area turns red and is refused. Right-click or Delete removes, keys 1 to 5 pick a material, Ctrl+Z undoes and Ctrl+Y redoes. Play with mouse and keyboard; see Known limits for gamepad and touch. The budget turns red and GO locks when you overspend.
• Run. The bridge bends under the vehicle. Every piece shows its load in one of two colour families: stretched pieces glow blue, crushed pieces glow red to yellow, and both get brighter as they near breaking (the legend in the run HUD says so). Overloaded pieces snap into two red-hot halves with splinters, sparks and dust. The first break near the vehicle drops into slow motion with a camera push-in, and the HUD counts broken pieces. Once the vehicle has driven off, a standing bridge comes to rest within about 2 seconds.
• Win or lose. Reach the finish flag to win, rated 1 to 3 stars by how little of the budget you spent. Fall into the canyon or stall and you go back to build with your design kept.
• Progression. Five levels (First Crossing, Dry Gulch, High Wire, Midstream Pier, Red Rock Run), each with its own canyon look and vehicle: a light van, the cargo truck or a heavy three-axle tanker. Stars, best costs and unlocks are saved per player.

Known limits

These are things the game and its packages do not do properly yet:

• Touch is not finished. One finger to build and two fingers to pan or pinch exist in the build mode, but they do not work properly yet. On a touch screen the engine's own on-screen touch buttons also sit on top of the GO button. For now, play with mouse and keyboard.
• Gamepad is only lightly tested. A gamepad cursor and buttons are built in, but they have not been played through every level.
• Installing the packages into another world is not proven. Installing the stress colour package (stressView) into a different world was refused in a player's test. Its install preview on ZeroMind shows no missing pieces, so the cause is not known yet. Each package was checked working on its own inside this world only.
• Long all-steel bridges sag. A long bridge built only of steel with 1 m panels sags under its own weight at the current physics accuracy; mix in other materials or shorter spans.

Built from six reusable packages

The game in game/ is a thin layer of settings (materials, levels), screens and glue over six packages: trussPhysics (truss simulation, bending, breaking, a generic wheeled vehicle body, settling once the load leaves), trussVehicles (truck, van, tanker), gridBuilder (build mode: grid, snapping, dragging, undo/redo, camera), stressView (the bridge drawing and stress colours: classic, thermal, colorblind), levelFlow (levels, budget, stars, saved progress) and canyonMaker (the canyon, five looks). Each package's README has a quick start and every option.

Performance

On a 226-piece bridge with a vehicle crossing, the game's own work is about 5 ms per frame (physics about 1.8 ms, view about 2.3 ms) and the GPU about 5 ms. Placing a piece costs under 0.1 ms however big the bridge is.