What It Means & How to Fix It in UE5

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🧠 Why You’re Seeing This Error

This error means your shader is using more samplers (texture samplers) than the hardware or shader model allows.

In HLSL/UE5, a sampler is an object that lets you sample textures. Most platforms and shader models have strict limits on how many samplers you can bind in a single shader.

SM5 and most desktop GPUs allow up to 16 samplers. Exceeding this limit causes X4509.

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💥 Example Error Message

error X4509: maximum number of samplers exceeded (16)

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🛠️ Common Shader Scenarios That Cause This

❌ Too Many Texture Samplers

Texture2D Texture0;
SamplerState Sampler0;
...
Texture2D Texture16;
SamplerState Sampler16;

float4 color = Texture16.Sample(Sampler16, uv); // ❌ Sampler16 is the 17th — exceeds limit

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❌ Material Graphs with Too Many Unique Texture Samples

In Material Editor:

• Using more than 16 unique Texture Sample nodes in a single shader path (like Base Color) will trigger this
• Each unique sample with a different sampler counts against the limit

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❌ Sampler Redundancy

// Reusing the same texture but with different samplers still adds to the count
MyTexture.Sample(SamplerA, uv);
MyTexture.Sample(SamplerB, uv); // ❌ counts as 2 samplers

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✅ How to Fix X4509 in UE5 – Step-by-Step

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✔️ 1. Reduce the Number of Unique Samplers

Use fewer Texture2D + SamplerState pairs:

// ✅ Preferred
Texture2D MyTexture;
SamplerState SharedSampler;

float4 a = MyTexture.Sample(SharedSampler, uv1);
float4 b = MyTexture.Sample(SharedSampler, uv2);

This only uses one sampler.

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✔️ 2. Use Shared Samplers Where Possible

When sampling the same texture, reuse the sampler:

float4 a = Tex.Sample(SamplerLinear, uv1);
float4 b = Tex.Sample(SamplerLinear, uv2); // ✅ still only one sampler used

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✔️ 3. Merge Multiple Textures Into an Atlas (Advanced)

If you’re sampling multiple textures with separate samplers:

• Combine them into a texture atlas
• Use UV offsets and scales to simulate multiple textures with a single sampler

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✔️ 4. Optimize Materials (if error occurs in Material Editor)

• Reduce the number of Texture Sample nodes in each material path
• Share the same texture across roughness, specular, metallic channels (packed maps)
• Disable unused shader paths (e.g., disable tessellation or other features you’re not using)

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✅ Summary: How to Fix “error X4509: maximum number of samplers exceeded” in UE5

Cause	Fix
More than 16 samplers used	Reduce number of Texture2D + SamplerState pairs
Same texture sampled with different samplers	Reuse the same sampler across all samples
Too many textures in material	Use texture atlases or combine packed maps
Excessive Texture Sample nodes	Simplify material graph and remove unused sample paths