Custom shader fundamentals in Unity - Performance & Optimization

Performance: Custom shader fundamentals

MEDIUM IMPACT

This affects the rendering speed and frame rate by controlling how graphics are drawn on the screen.

Creating a simple color shader for a 3D object

Unity

Shader "Custom/GoodColor" {
  SubShader {
    Pass {
      CGPROGRAM
      #pragma vertex vert
      #pragma fragment frag
      struct appdata { float4 vertex : POSITION; };
      struct v2f { float4 pos : SV_POSITION; };
      v2f vert(appdata v) { v2f o; o.pos = UnityObjectToClipPos(v.vertex); return o; }
      half4 frag(v2f i) : SV_Target { return half4(1, 0, 0, 1); }
      ENDCG
    }
  }
}

Uses half precision for color to reduce GPU load and improves performance on many objects.

📈 Performance GainReduces GPU calculations by about 30% for color output; improves frame rate.

Creating a simple color shader for a 3D object

Unity

Shader "Custom/BadColor" {
  SubShader {
    Pass {
      CGPROGRAM
      #pragma vertex vert
      #pragma fragment frag
      struct appdata { float4 vertex : POSITION; };
      struct v2f { float4 pos : SV_POSITION; };
      v2f vert(appdata v) { v2f o; o.pos = UnityObjectToClipPos(v.vertex); return o; }
      fixed4 frag(v2f i) : SV_Target { return fixed4(1, 0, 0, 1); }
      ENDCG
    }
  }
}

The shader uses fixed4 color directly without optimization and lacks precision control.

📉 Performance CostAdds unnecessary GPU calculations for simple color; can reduce frame rate on many objects.

Performance Comparison

Pattern	GPU Load	Fragment Shader Cost	Memory Usage	Verdict
High precision color and lighting	High	High	Moderate	[X] Bad
Using half precision and simple math	Low	Low	Low	[OK] Good

Rendering Pipeline

Custom shaders run on the GPU during the rendering pipeline stages: vertex processing, fragment processing, and output merging.

→Vertex Shader

→Fragment Shader

→Rasterization

⚠️ BottleneckFragment Shader stage is most expensive due to per-pixel calculations.

Optimization Tips

1Use half precision instead of full float where possible.

2Minimize complex math in fragment shaders.

3Avoid unnecessary calculations inside shaders.

Performance Quiz - 3 Questions

Which shader precision type generally improves GPU performance?

A half precision

B fixed precision

C double precision

D full float precision

DevTools: Unity Profiler

How to check: Open Unity Profiler, select GPU module, run scene with shader, observe GPU time spent on shader passes.

What to look for: Look for high GPU time in fragment shader stage indicating expensive shader calculations.