Why do joint anchors drift during pause?

Box2D’s solver continues to apply position correction during paused frames if the world step still ticks but with zero dt. Better: explicitly stop world simulation with the Physics behavior’s Stop simulation action, not just set time scale to 0.

How do I pause physics cleanly in Construct?

Use System Set time scale to 0 for everything, OR Physics behavior’s Stop simulation for just physics. The second prevents Box2D’s solver from running at all during pause, eliminating drift.

Can I recreate joints after pause?

Yes — Physics Destroy joint, then Physics Create joint with current positions as anchors. Restores the joint to its current pose without accumulated drift.

Fix: Construct 3 Physics Joint Anchor Drift After Pause

Quick answer: Use the Physics behavior’s Stop simulation action instead of setting time scale to 0. Stops Box2D’s solver entirely; no drift can occur.

A physics puzzle uses revolute joints. Pausing via Time Scale = 0, resuming, then waiting a moment — the jointed bodies have slightly separated from their anchors. Each pause cycle adds drift. Eventually visible misalignment.

Why Time Scale Zero Drifts

Setting time scale to 0 makes dt = 0 for the Box2D step. The solver still runs each tick, just with no time elapsed. Some solver passes still apply position correction (Baumgarte stabilization, for example) even at dt=0, accumulating tiny corrections per tick that show as drift.

The Fix

// On pause
System Set global variable IsPaused to true
System Set time scale to 0
PhysicsWorld Stop simulation   // the key step

// On resume
PhysicsWorld Resume simulation
System Set time scale to 1
System Set IsPaused false

Stop simulation halts all Box2D internal step calls. The solver doesn’t run; corrections aren’t applied; no drift. Resume restarts cleanly.

Rebuild Joints if Drifted Already

If your project already has accumulated drift, rebuild joints on resume:

On resume:
    Sprite(joint A) Physics Destroy joint "swing"
    Sprite(joint A) Physics Create revolute joint "swing" to SpriteB at currentX, currentY

The new joint anchors at current positions; the visual state is preserved while the solver gets a fresh start.

Physics Time Step vs Game Time

Physics behavior has its own internal time step (Project Settings → Physics → Step Size). For deterministic physics, set Stepping Mode = Fixed and pick a step appropriate for your game (1/60s is common). Variable stepping can also contribute to drift.

Verifying

Pause and resume 50 times in a stress test. Anchor positions should stay identical to before pausing. Print global positions of jointed bodies before and after each pause; diff should be zero.

“Time scale 0 isn’t a real pause for Box2D — the solver still nudges. Stop simulation is the clean pause.”

For any game using physics joints, build a centralized pause routine that Stops physics and Resumes — never scatter time scale tweaks.