Fix: Unity LineRenderer UV Stretching on Curves

Here is how to fix Unity LineRenderer textures that stretch grotesquely on curved or long lines. A trail-render or rope effect looks fine on a short straight line but smears comically on bends. The cause is the default Texture Mode, which maps the entire texture from line start to line end without regard for length or curvature.

The Symptom

A LineRenderer with a striped or patterned texture renders the pattern stretched across the whole line. On a curve, the stretch is even more pronounced. Short straight lines look fine.

What Causes This

Stretch mode default. The line’s UV V coordinate goes 0–1 across all segments combined, ignoring distance.

Few line points on curves. A curve approximated by 3 points has only 3 segments; UVs distribute crudely. More points yield finer UV distribution.

Wrong tile factor. Tile mode needs a matching tile multiplier; default 1 may not match your desired world-space density.

The Fix

Step 1: Switch to Tile mode.

line.textureMode = LineTextureMode.Tile;
line.material.mainTextureScale = new Vector2(2f, 1f);  // 2x repeats per length unit

Tile maps the V coordinate to world distance, so the texture repeats consistently regardless of total line length.

Step 2: Increase line subdivisions. If you generate a curved line in code, sample more points:

int samples = 64;
line.positionCount = samples;
for (int i = 0; i < samples; i++)
{
    float t = (float)i / (samples - 1);
    line.SetPosition(i, SampleCurve(t));
}

More positions = smoother visual curve and finer-grained UVs.

Step 3: Use a seamless tileable texture. Authored textures with edges that tile horizontally avoid visible seams when Tile repeats. Test by laying the texture next to itself and looking for the join.

Step 4: Match Use World Space to art expectations. If Use World Space is enabled, line points are in world coordinates and the texture density reflects world units. If disabled, density is in local units. Choose the one that gives consistent appearance regardless of parent scale.

Step 5: For per-segment art, use Distribute Per Segment.

line.textureMode = LineTextureMode.DistributePerSegment;

The full texture maps to each segment independently. Useful for chain-link art where each segment is a discrete chain icon.

Mode Comparison

Stretch:               0-1 UV across whole line
Tile:                  UV repeats per world unit
Repeat Per Segment:    UV repeats per segment, with edge sharing
Distribute Per Segment: full UV per segment, no sharing

Pick based on what your art is meant to show. Trails of dust: Tile with seamless dust. Chains: Distribute with chain link. Lasers: Stretch with a single laser texture is often fine because the line is short.

Understanding the issue

Render pipelines have ordering: which pass runs when, what state is bound, which targets are written. Bugs at this layer are often invisible in code review and only manifest at runtime.

The specific bug described above is the kind that surfaces during integration rather than unit testing. It depends on a combination of factors: the asset configuration, the runtime state, the platform's specific behavior. In isolation, each piece looks correct; in combination, the bug emerges. This is why thorough integration testing - playing the actual game in realistic conditions - catches things that automated tests miss.

Why this happens

The triage path for this kind of bug is long. The symptom appears in gameplay, but the cause is in a different system. The reporter describes the gameplay effect; the engineer has to translate that into a hypothesis about the underlying cause. Misdirection is common.

At the engine level, the behavior comes from a deliberate design decision in Unity. The engine team chose a particular trade-off - usually performance versus convenience, or generality versus specificity - and that trade-off has consequences when you push against it. Understanding the trade-off is what turns 'this bug is mysterious' into 'this bug is the expected consequence of this design'.

Verifying the fix

For shipping games, the safest verification is a staged rollout. Apply the fix to 1% of players for 24 hours; watch the affected metric; expand if green. Skipping the staged rollout means the verification is the entire player base, which is too high a stakes for most fixes.

Reproducibility is the prerequisite for verification. If you can't reliably reproduce the bug pre-fix, you can't reliably verify it post-fix. Spend time getting a clean reproduction before you write any fix code. The fix is fast once you understand the reproduction; the reproduction is the slow part.

Variations to watch for

Related bug classes often share the same root cause. If you find yourself fixing this issue, look for cousins: similar symptoms in adjacent systems, the same data flow but a different value, or the same fix pattern in another module. The catalog of 'we've seen this before' becomes valuable institutional knowledge.

Adjacent bugs often share a root cause. After fixing the case you've found, spend an hour searching the codebase for similar patterns. What's the same call with different arguments? The same data flow with a different entity type? The same lifecycle issue in a sibling system? Each match is a candidate for the same fix, or a related fix that prevents future bugs of the same class.

In production

Live games surface this bug class at scale. What's a rare edge case in development becomes a daily occurrence once you have a few thousand concurrent players. The class isn't 'this player has a unique setup'; it's 'one in N thousand sessions will trigger this exact combination'.

When triaging a similar issue in production, prioritize gathering data over hypothesizing causes. A player report describes a symptom; what you need is a build SHA, a session timestamp, and ideally a screen recording or session replay. With those, the bug becomes tractable. Without them, you're guessing at hypothetical reproductions that may not match what the player actually hit.

Performance considerations

Performance implications matter when this bug class scales with player count or asset count. A bug that fires once per session is annoying; a bug that fires once per frame compounds. After fixing, profile the affected code path under realistic load. The fix that's correct for one entity may be too slow for ten thousand.

Diagnostic approach

Before applying any fix, gather enough context to be confident you're addressing the actual cause and not a similar-looking symptom. The cheapest diagnostic step is reproducing the bug deterministically - if you can't get the same failure twice in a row, your fix attempts will be hard to evaluate. Lock down the reproduction first.

For Unity-specific diagnostics, the editor's profiler is the canonical starting point. Capture a representative frame with the symptom present; compare against a frame without the symptom; the diff often points directly at the cause. If the symptom is non-deterministic, capture multiple frames and look for the pattern - the cause is usually a state transition or a specific input value rather than a continuous effect.

Tooling and ecosystem

Third-party plugins often provide better diagnostics for their own behavior than the engine does. If the affected code is in a plugin, check the plugin's documentation for debug modes, verbose logging, or inspector tools - these can save hours of investigation when they exist.

Within Unity, the relevant diagnostic surfaces include the standard frame debugger, memory profiler, and engine-specific debug overlays. Each one shows a different facet of what's happening. The frame debugger reveals draw call ordering and state transitions; the memory profiler shows allocation patterns; the debug overlay reveals per-system state. Bugs that resist one tool usually surrender to another - the trick is knowing which tool to reach for first.

Edge cases and pitfalls

Boundary conditions deserve specific testing attention. What happens when the input is zero, maximum, negative, or NaN? What happens at the start of a session vs hours in? What happens at the boundary between two systems handling the same data? These are where bugs hide and where regression tests are most valuable.

When writing a regression test for this fix, focus on the boundary conditions that surfaced the original bug. Tests that exercise the happy path catch obvious regressions; tests that exercise the boundary catch the subtler regressions that look like new bugs but are really the original returning. The latter are the tests that earn their keep over the long life of the project.

Team communication

When this bug class affects multiple teams (often the case for cross-system issues), early communication prevents duplicate work. The team that owns the symptom may not own the cause. A 15-minute conversation at the start of triage often saves hours of independent investigation.

If this fix touches a system several engineers work in, a short writeup in the team's engineering channel helps. Not a full design doc - a paragraph explaining what was wrong, what's fixed, and what to watch for. Future engineers encountering similar symptoms will search for the fix; making it findable is a small investment that pays back later.

“Stretch mode is for short lines. Tile is for long lines. Per Segment is for repeating discrete art.”

Related Issues

For LineRenderer not visible in URP, see LineRenderer Not Visible URP. For trail issues, see Particle Trail Through Walls.

Tile mode. Match world scale. Seamless texture. Lines stop stretching.