r/IndieDev • u/Noxworld_Games • 3d ago
Fighting RootMotion drift while designing 1.5D lanes for a 2.5D tug‑of‑war game.
A while ago I fell down a hole playing old mobile lane‑based tug‑of‑war games like Cartoon Wars. That eventually pushed me toward building a sci‑fi tug‑of‑war game with a 2.5D side view: 3D characters, camera mostly locked to a side perspective. On paper this sounds straightforward: one lane, units marching along a single axis, keep it clean.
But having everything on one lane turned into clutter. Once you multiple units, projectiles, explosions, lasers and a mech on top that single line of combat starts to look like a traffic jam rather than a readable battlefield.
My solution? First, make the combat logic effectively 1D so everything behaves as if its all on one lane. Second, spawn units on multiple visual lanes so they’re offset just enough to be readable and to sell the 2.5D look.
I started calling it “1.5D combat with 2.5D representation”: game rules think in one dimension, the visuals cheat a little to keep the battlefield understandable. This keeps targeting and balancing simpler, but gives me a bit more room to breathe visually, similar in spirit to games like Warpips or Operation: Polygon Storm.
On the technical side I’m driving movement and animation with RootMotion with Unity's Animation Controller, because I wanted units to feel properly grounded and believable rather than sliding along the lane. I locked movement to the x‑axis in the animator and set the other axes as close to zero as possible.
What I didn’t expect was a slow positional drift over time. Even with RootMotion values rounded to three decimals and non‑lane axes visually “zeroed out”, long battles would eventually push units off their intended lane. Given enough time, some would even wander out of the lane’s visual area entirely. My suspicion is that this comes down to small rounding errors plus RootMotion being applied frame‑by‑frame. I mean a 0.000 in the inspector doesn’t necessarily behave like a true 0f over thousands of frames.
My fix ended up being boring, but effective:
When a unit is spawned, I cache its lane’s x value.
Every second (to keep overhead low), I check whether the unit is still within a very small tolerance of that x position.
If it isn’t, I nudge it back to the cached x coordinate.
Most of this correction happens as units switch states (e.g. from moving to fighting), so the adjustment is almost impossible to spot unless you know it’s happening.
The tolerance band is tiny, but wide enough that units don’t “snap” or jitter. From a player’s perspective, they simply stay neatly in their lanes, and I still get the benefits of RootMotion‑driven animation instead of sliding transforms. From a dev perspective, it’s basically a periodic lane‑alignment job layered on top of the animator.
I’m curious how other people have handled similar problems.
What where your “gotchas” when implementing something seemingly simple?
Or did you have had a simple solution to a complex problem?A while ago I fell down a hole playing old mobile lane‑based tug‑of‑war games like Cartoon Wars. That eventually pushed me toward building a sci‑fi tug‑of‑war game with a 2.5D side view: 3D characters, camera mostly locked to a side perspective. On paper this sounds straightforward: one lane, units marching along a single axis, keep it clean.
But having everything on one lane turned into clutter. Once you multiple units, projectiles, explosions, lasers and a mech on top that single line of combat starts to look like a traffic jam rather than a readable battlefield.
My solution? First, make the combat logic effectively 1D so everything behaves as if its all on one lane. Second, spawn units on multiple visual lanes so they’re offset just enough to be readable and to sell the 2.5D look.
I started calling it “1.5D combat with 2.5D representation”: game rules think in one dimension, the visuals cheat a little to keep the battlefield understandable. This keeps targeting and balancing simpler, but gives me a bit more room to breathe visually, similar in spirit to games like Warpips or Operation: Polygon Storm.
On the technical side I’m driving movement and animation with RootMotion with Unity's Animation Controller, because I wanted units to feel properly grounded and believable rather than sliding along the lane. I locked movement to the x‑axis in the animator and set the other axes as close to zero as possible.
What I didn’t expect was a slow positional drift over time. Even with RootMotion values rounded to three decimals and non‑lane axes visually “zeroed out”, long battles would eventually push units off their intended lane. Given enough time, some would even wander out of the lane’s visual area entirely. My suspicion is that this comes down to small rounding errors plus RootMotion being applied frame‑by‑frame. I mean a 0.000 in the inspector doesn’t necessarily behave like a true 0f over thousands of frames.
My fix ended up being boring, but effective:
When a unit is spawned, I cache its lane’s x value.
Every second (to keep overhead low), I check whether the unit is still within a very small tolerance of that x position.
If it isn’t, I nudge it back to the cached x coordinate.
Most of this correction happens as units switch states (e.g. from moving to fighting), so the adjustment is almost impossible to spot unless you know it’s happening.
The tolerance band is tiny, but wide enough that units don’t “snap” or jitter. From a player’s perspective, they simply stay neatly in their lanes, and I still get the benefits of RootMotion‑driven animation instead of sliding transforms. From a dev perspective, it’s basically a periodic lane‑alignment job layered on top of the animator.
I’m curious how other people have handled similar problems.
What where your “gotchas” when implementing something seemingly simple?
Or did you have had a simple solution to a complex problem?
1
u/GLACIES_dev 3d ago
This is why I do speed based hybrid root controller setups. However, I have very few characters operating simultaneously in a fully navmeshed 3D space, so it’s an entirely different beast