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Single-pass post-processing, URP Renderer Features, and mobile-safe screen effects for Unity
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| name | mobile-post-processing |
| description | Single-pass post-processing, URP Renderer Features, and mobile-safe screen effects for Unity |
Use this skill when the user wants to add, create, or optimize post-processing effects in Unity for mobile or WebGL targets. Triggers include: "post-processing", "bloom", "vignette", "color grading", "blur", "outline", "edge detection", "chromatic aberration", "Renderer Feature", "Full Screen Pass", "Blit", "post-process mobile", or any mention of screen-space effects on constrained hardware. Also trigger when the user reports post-processing is causing frame drops on mobile.
Every post-processing pass costs a full-screen blit — reading the entire framebuffer from main memory and writing it back. On tiled mobile GPUs, this flushes tile memory. Budget 0.5–2ms per pass on mid-range mobile.
Combine all effects into a single pass whenever possible. Unity's default post-processing stack runs each effect as a separate pass. On mobile, this alone can add 6ms+ (measured: vignette alone = 6ms on some devices). Use a single-pass approach instead.
Disable HDR unless you specifically need Bloom. HDR doubles framebuffer bandwidth (16-bit float vs 8-bit per channel). If you only need color grading, apply it in LDR.
Bloom is the most expensive default effect on mobile. It requires downsampling, blurring, and upsampling — multiple passes. If you need it, reduce iterations (2–3 max), use a half-resolution blur, and skip the high-quality prefilter.
Never use Motion Blur or Depth of Field on mobile. They require multiple texture samples per fragment across multiple passes.
Prefer Renderer Features over Volume-based post-processing for custom effects in URP. Renderer Features give you direct control over when and how the blit happens.
This approach combines vignette + color grading + simple bloom in one pass:
Shader "Mobile/PostProcess_SinglePass"
{
Properties
{
_MainTex ("Source", 2D) = "white" {}
_VignetteIntensity ("Vignette Intensity", Range(0, 1)) = 0.3
_VignetteRadius ("Vignette Radius", Range(0, 1)) = 0.7
_Contrast ("Contrast", Range(0.5, 1.5)) = 1.1
_Saturation ("Saturation", Range(0, 2)) = 1.1
_Brightness ("Brightness", Range(0.5, 1.5)) = 1.0
}
SubShader
{
Tags { "RenderPipeline" = "UniversalPipeline" }
Pass
{
ZTest Always ZWrite Off Cull Off
HLSLPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
CBUFFER_START(UnityPerMaterial)
half _VignetteIntensity;
half _VignetteRadius;
half _Contrast;
half _Saturation;
half _Brightness;
CBUFFER_END
TEXTURE2D(_MainTex); SAMPLER(sampler_MainTex);
struct Attributes { float4 positionOS : POSITION; float2 uv : TEXCOORD0; };
struct Varyings { float4 positionCS : SV_POSITION; float2 uv : TEXCOORD0; };
Varyings vert(Attributes v)
{
Varyings o;
o.positionCS = TransformObjectToHClip(v.positionOS.xyz);
o.uv = v.uv;
return o;
}
half4 frag(Varyings i) : SV_Target
{
half4 color = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.uv);
// --- Vignette (no extra texture sample) ---
half2 uvCentered = i.uv - 0.5h;
half vignette = 1.0h - saturate(
length(uvCentered) / _VignetteRadius
);
vignette = smoothstep(0.0h, 1.0h, vignette);
color.rgb *= lerp(1.0h, vignette, _VignetteIntensity);
// --- Brightness / Contrast ---
color.rgb *= _Brightness;
color.rgb = (color.rgb - 0.5h) * _Contrast + 0.5h;
// --- Saturation ---
half luminance = dot(color.rgb, half3(0.2126h, 0.7152h, 0.0722h));
color.rgb = lerp(luminance.xxx, color.rgb, _Saturation);
return saturate(color);
}
ENDHLSL
}
}
}
To inject the post-processing pass into URP:
using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Rendering.Universal;
public class MobilePostProcessFeature : ScriptableRendererFeature
{
[System.Serializable]
public class Settings
{
public Material material;
public RenderPassEvent renderPassEvent = RenderPassEvent.AfterRenderingPostProcessing;
}
public Settings settings = new Settings();
MobilePostProcessPass pass;
public override void Create()
{
pass = new MobilePostProcessPass(settings);
}
public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
{
if (settings.material == null) return;
renderer.EnqueuePass(pass);
}
class MobilePostProcessPass : ScriptableRenderPass
{
Settings settings;
RTHandle tempRT;
public MobilePostProcessPass(Settings settings)
{
this.settings = settings;
this.renderPassEvent = settings.renderPassEvent;
}
public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
{
var cmd = CommandBufferPool.Get("MobilePostProcess");
var source = renderingData.cameraData.renderer.cameraColorTargetHandle;
// Single blit with our combined shader
Blitter.BlitCameraTexture(cmd, source, source, settings.material, 0);
context.ExecuteCommandBuffer(cmd);
CommandBufferPool.Release(cmd);
}
}
}
| Effect | Cost | Mobile Verdict | Notes |
|---|---|---|---|
| Color grading (LDR) | ~0.1ms | SAFE | Pure math, no extra samples |
| Vignette | ~0.1ms | SAFE | UV distance calculation only |
| Film grain | ~0.2ms | SAFE | Noise from UV math, no texture |
| Simple outline (depth) | ~0.5ms | CAUTION | Requires depth texture + 4 neighbor samples |
| Bloom (2-iteration) | ~1-2ms | CAUTION | Use half-res, 2 iterations max |
| Chromatic aberration | ~0.3ms | CAUTION | 3 texture samples instead of 1 |
| Blur (single-pass box) | ~0.5ms | CAUTION | Use 4-tap box blur, never Gaussian |
| Motion blur | ~3-5ms | AVOID | Multiple samples along velocity |
| Depth of field | ~3-5ms | AVOID | CoC calculation + variable blur |
| Screen-space reflections | ~4-8ms | AVOID | Ray marching in screen space |
| Ambient occlusion (SSAO) | ~2-4ms | AVOID | Multiple depth samples per fragment |
| Repo | Purpose | Why It Matters |
|---|---|---|
| demonixis/FastPostProcessing | Single-pass mobile post-FX | Go-to for mobile. Everything in one pass. |
| TPiotr/SimpleMobilePostProcessing-Unity | Blur + vignette | Created because Unity's vignette cost 6ms alone |
| yahiaetman/URPCustomPostProcessingStack | URP Volume-compatible custom FX | 8 example effects with proper URP integration |
| QianMo/X-PostProcessing-Library | Dozens of effects (MIT) | Desktop-quality reference; adapt for mobile |
| GarrettGunnell/Post-Processing | Modular bloom/grade/edge | Notes on single-pass condensation |