Fix: Unity Shader Graph Procedural Grid Aliasing

A procedural grid floor shader. Close up: crisp lines. Mid-distance: looks fine. Far distance: shimmer everywhere as the camera moves. Classic aliasing of sub-pixel features.

The Math Behind It

A pixel at far distance covers ~10 units of world space. With grid lines every 0.5 unit, the pixel spans ~20 lines. Whichever UV value the pixel happens to sample determines whether the pixel reads “line” or “empty”. Sub-pixel jitter causes flicker.

The Fix: Derivative-Based Width

// Pseudo-HLSL from Shader Graph Custom Function
float GridAA(float2 uv, float lineWidth) {
    float2 coord = frac(uv);
    float2 distToLine = min(coord, 1.0 - coord);
    float2 screenWidth = fwidth(uv);
    float line = min(
        smoothstep(0.0, screenWidth.x, distToLine.x),
        smoothstep(0.0, screenWidth.y, distToLine.y)
    );
    return 1.0 - line;
}

fwidth scales the smoothstep edge by screen-space pixel width. Lines stay ~1 pixel regardless of distance.

In Shader Graph

Wire this as a Custom Function node, or replicate the math with Subtraction, Fract, Min, fwidth (DDX+DDY), and Smoothstep nodes. The fwidth equivalent is length(ddxy).

Distance Fade

Combine with a distance-based fade to reduce grid contrast at far distance. Reduces the visual impact of any residual aliasing:

float distanceFade = saturate(1.0 - distance / fadeRange);
gridColor *= distanceFade;

The grid fades into the floor color at distance. Even imperfect AA is hidden by reduced contrast.

Alternative: Texture-Based

For static grids, bake to a power-of-two texture with mipmaps and aniso. GPU filtering handles distance for free. Less flexible (can’t change spacing at runtime) but zero aliasing concerns.

Verifying

Move the camera away from the grid. With AA, lines stay clean at distance, neither shimmering nor disappearing. Without, you see distinct flicker patterns. Compare side by side to confirm.

Understanding the issue

Shader bugs manifest visually but trace to invisible state. Triage requires understanding the runtime context as much as the source.

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

There's almost always a less obvious case where the same problem applies. The reported case is the one a player hit; the related cases hide because they're rarer or affect fewer players. After fixing the reported case, search the codebase for the pattern - one fix often unlocks several.

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

For shipping titles with a long support window, watch for this issue resurfacing after dependency updates. Engine upgrades, driver updates, OS releases - each one can resurface a bug class you thought you'd fixed because the underlying behavior changed slightly. Regression tests catch the obvious ones; player reports catch the rest.

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

Modern engine versions ship better tooling for this kind of issue than older versions. If you're on an older release, the diagnostic step may take significantly longer because the tools you'd want don't exist yet. Sometimes the right answer is upgrading rather than fighting through limited tooling.

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

Edge cases for this class of issue often involve specific timing: the first frame after a state change, the last frame before a transition, frames where multiple subsystems update simultaneously. Reproducing these reliably is part of what makes the bug class hard to test.

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.

“Procedural patterns need derivative-based AA. fwidth tells you how much UV space a pixel covers; size lines accordingly.”

The same fwidth pattern works for hex grids, brick patterns, line art — any procedural sharp-edge shader.