Fix: Unity Shader Graph SRP Batcher Incompatible

URP, Shader Graph, three properties. Material inspector says “SRP Batcher: not compatible.” Frame Debugger shows your draw calls broken into one per renderer. The Shader Graph default of throwing color/scalar overrides into a global CBUFFER kills batching.

The Symptom

Material inspector states “SRP Batcher: not compatible.” Reason listed underneath. Frame Debugger shows separate draw calls per material instance even though the material is identical across renderers.

What Causes This

SRP Batcher requires every per-material constant to live in a single CBUFFER named UnityPerMaterial, with a known layout the batcher can patch quickly between draws. Properties declared as Global, or types Shader Graph doesn’t put in the CBUFFER, break the contract.

The Fix

Step 1: Read the inspector reason. The Material inspector explicitly states why batching failed. Common reasons:

• “Material property X is missing from CBUFFER” — property is global.
• “Material property X has unsupported type” — rare.
• “Shader uses a sampler in CBUFFER” — samplers aren’t allowed inline.

Step 2: Per-material properties stay in UnityPerMaterial. In Shader Graph, click each property. Inspector pane → Override Property Declaration → UnityPerMaterial (or leave default Hybrid Per Instance for DOTS).

Float, Vector, Color, Matrix — all fine in CBUFFER. Texture references stay outside (textures are sampler binds, not constants).

Step 3: Globals stay global. If a property is set globally via Shader.SetGlobalFloat (wind speed, time-of-day, world fog), set Override Property Declaration to Global on it. The batcher then ignores it for per-material packing.

Inspecting the Generated CBUFFER

In Shader Graph, right-click the master node → Show Generated Code. Search for CBUFFER_START(UnityPerMaterial). Every per-material property should appear inside; globals outside.

DOTS / Hybrid Renderer

For Entities Graphics, properties marked Hybrid Per Instance are exposed to the BatchRendererGroup. Use this for properties that vary per entity but you still want batched. Same idea, different bucket.

Verifying

Inspector now reads “SRP Batcher: compatible.” Frame Debugger collapses many draw calls into one batched draw. Stats overlay shows lower SetPass calls.

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

This bug class disproportionately affects late-stage development. The work to surface it is interactive testing in realistic conditions, which only really happens after the gameplay is in place and assets are populated. Catching it early requires deliberate testing of conditions that look unimportant.

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

After applying the fix, the verification step has three parts: confirm the original repro is resolved, confirm no obvious regressions in adjacent functionality, and (for shipping titles) deploy to a small player cohort first and watch the crash and report rates. Each step catches something the others miss.

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

If this issue manifests under high load (many actors, many particles, many network connections), profile the post-fix code path with realistic counts. The original cost was a bug; the new cost is real work, and real work has a budget.

Diagnostic approach

The diagnostic tools available depend on your engine and platform. Use the engine's native profilers and debug overlays before reaching for external tools. The native tools have context that external tools lack - they know which subsystem owns the code, which assets are loaded, and what state the engine is in.

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.

“Per-material in UnityPerMaterial. Globals declared global. Batcher loves you.”

Related Issues

For shaders not updating in build, see build shader updates. For Time node frozen, see Time node.

CBUFFER right. Batcher batches.