What causes uneven speed along a Bezier curve in Unity?

Advancing the curve parameter t at a constant rate does not map to constant distance, because a Bezier covers more arc length per unit t where control points spread the curve out.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix Bezier Movement Having Uneven Speed in Unity

Quick answer: Build an arc-length lookup table that maps distance traveled to the t value, then sample by distance instead of by raw t for constant-speed motion.

An object following a Bezier path that races through the straight sections and crawls through the curves is sampling by t, not by distance. Reparameterizing by arc length gives constant speed. Here is how.

How to fix it

1. Build an arc-length table

Sample the curve at many t values, accumulate the segment lengths, and store pairs of (distance, t). This table maps any traveled distance back to the t that produces it.

2. Sample by distance

Each frame advance a distance speed * Time.deltaTime, look up the corresponding t in the table (interpolating between entries), and evaluate the curve at that t.

3. Refine the table resolution

If speed still wobbles, increase the number of samples so the distance-to-t mapping is finer, especially around tight curvature where t and distance diverge most.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every Unity error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

The bug you can't reproduce isn't gone — it's just invisible until you capture it from the player's device.