Unity URP custom render feature for UI Blur

readme.md

A simple render feature and a compute shader to grab the scene color after rendering and downscaling + blurring it for use in UI.

Uses canvas stacking in order for this to work. The canvas that uses the blurring effect needs a lower sorting order than the other canvases in the scene. If it doesnt have a lower sorting order it will simply overwrite the other canvases.

Downscaling the grabbed scene color texture before blurring it is recommended for performance, but reduces the quality somewhat. Even a 2x downscale is a huge increase in performance, but tweak both that and the blur iterations to find a good middleground.

It's currently not working great with scene view, and you'll probably need a different method of approach for this to work nicely. Other approaches uses camera stacking and render textures to work, but that does require a bit more setup.

How To

1. Add the "UIBlurFeature" to your renderer data
2. Add the "BlurEffect.compute" to the feature settings "Effect Compute"
3. A texture named "_UIBlurTexture" is now exposed to your shaders
4. Add a secondary canvas and set "Sort Order" to be lower than all your other canvases, if one of your canvases dissappear you need a lower sort order
5. Use the attached UIBlur shader on a RawImage in the new canvas you created
6. Anything in the scene under the RawImage should now be blurred, including transparent objects

Issues

• The effect will affect any Canvases in the "Screen Space - Camera/World" mode
• It doesnt work properly in scene view
• Requires a separate canvas for any blurring effect
• The texture wont work for objects in the scene, see https://gist.github.com/Refsa/54da34a9e2fc8e45472286572216ad17 for a workaround

MIT License

Copyright (c) 2020 Refsa

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

BlurEffect.compute

#pragma kernel Downscale
#pragma kernel GaussianBlurVertical
#pragma kernel GaussianBlurHorizontal
#pragma kernel BoxBlur

Texture2D<float4> _Source;
RWTexture2D<float4> _Dest;

float _Amount;
float2 _Size;

[numthreads(32,32,1)]
void Downscale(uint3 id : SV_DispatchThreadID)
{
    static const float samples = rcp(_Amount * _Amount);
    const int2 uv = id.xy * _Amount;

    float4 result = 0;
    for (int x = 0; x < _Amount; x++)
    {
        for (int y = 0; y < _Amount; y++)
        {
            result += _Source[uv + int2(x, y)];
        }
    }

    _Dest[id.xy] = result * samples;
}

static const float gaussian_offset[3] = {0.0, 1.3846153846, 3.2307692308};
static const float gaussian_weight[3] = {0.2270270270, 0.3162162162, 0.0702702703};

[numthreads(32,32,1)]
void GaussianBlurVertical(uint3 id : SV_DispatchThreadID)
{
    [branch] if (id.x >= _Size.x || id.y >= _Size.y) return;

    float4 result = _Dest[id.xy] * gaussian_weight[0];

    [unroll] for (int i = 1; i < 3; i++)
    {
        int2 uv = id.xy + int2(0, gaussian_offset[i]);
        if (uv.y < _Size.y)
        {
            result += _Dest[uv] * gaussian_weight[i];
        }
        else
        {
            result += _Dest[id.xy] * gaussian_weight[i];
        }

        uv = id.xy - int2(0, gaussian_offset[i]);
        if (uv.y > 0)
        {
            result += _Dest[uv] * gaussian_weight[i];
        }
        else
        {
            result += _Dest[id.xy] * gaussian_weight[i];
        }
    }

    _Dest[id.xy] = result;
}

[numthreads(32,32,1)]
void GaussianBlurHorizontal(uint3 id : SV_DispatchThreadID)
{
    [branch] if (id.x >= _Size.x || id.y >= _Size.y) return;

    float4 result = _Dest[id.xy] * gaussian_weight[0];

    [unroll] for (int i = 1; i < 3; i++)
    {
        int2 uv = id.xy + int2(gaussian_offset[i], 0);
        if (uv.x < _Size.x)
        {
            result += _Dest[uv] * gaussian_weight[i];
        }
        else
        {
            result += _Dest[id.xy] * gaussian_weight[i];
        }

        uv = id.xy - int2(gaussian_offset[i], 0);
        if (uv.x > 0)
        {
            result += _Dest[uv] * gaussian_weight[i];
        }
        else
        {
            result += _Dest[id.xy] * gaussian_weight[i];
        }
    }

    _Dest[id.xy] = result;
}

[numthreads(32,32,1)]
void BoxBlur(uint3 id : SV_DispatchThreadID)
{
    [branch] if (id.x >= _Size.x || id.y >= _Size.y) return;

    float4 result = 0;
    float count = 0;

    for (int x = -1; x <= 1; x++)
    {
        for (int y = -1; y <= 1; y++)
        {
            const int2 uv = id.xy + int2(x, y);
            if (uv.x < 0 || uv.y < 0 || uv.x >= _Size.x || uv.y >= _Size.y) continue;

            result += _Dest[uv];
            count++;
        }
    }

    _Dest[id.xy] = result * rcp(count);
}

UIBlur.shader

Shader "Unlit/UIBlur"
{
    Properties
    {
        _MainTex ("Main Tex", 2D) = "white" {}
        _Width ("Width of Blur", Range(0, 8)) = 4
    }
    SubShader
    {
        Tags
        {
            "RenderType"="Transparent"
        }
        Blend SrcAlpha OneMinusSrcAlpha
        Cull Off
        Lighting Off
        ZWrite Off
        ZTest On

        HLSLINCLUDE
        #include "UnityCG.cginc"

        struct appdata
        {
            float4 vertex : POSITION;
            float2 uv : TEXCOORD0;
        };

        struct v2f
        {
            float2 uv : TEXCOORD0;
            float4 vertex : SV_POSITION;
            float4 screenPos : TEXCOORD1;
        };

        float _Width;
        sampler2D _UIBlurTexture;
        float4 _UIBlurTexture_TexelSize;

        v2f vert(appdata v)
        {
            v2f o = (v2f)0;
            o.vertex = UnityObjectToClipPos(v.vertex);
            o.uv = v.uv;

            o.screenPos = ComputeScreenPos(o.vertex);
            return o;
        }

        // Note: This is a really inefficient way of blurring
        // We only use it to smooth out our downscaled texture
        float4 BoxFilter(float2 screenUV)
        {
            const int width = _Width;
            float4 result = 0;

            int count = 0;
            for (int x = -width; x <= width; x++)
            {
                for (int y = -width; y <= width; y++)
                {
                    result += tex2D(_UIBlurTexture, screenUV + float2(x, y) * _UIBlurTexture_TexelSize.xy);
                    count++;
                }
            }

            return result / count;
        }

        float4 frag(v2f i) : SV_Target
        {
            return BoxFilter(i.screenPos.xy / i.screenPos.w);
        }
        ENDHLSL

        Pass
        {
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            ENDHLSL
        }
    }
}

UIBlurFeature.cs

using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Rendering.Universal;

public class UIBlurFeature : ScriptableRendererFeature
{
    public enum BlurType
    {
        Gaussian,
        Box,
    }

    const string TextureName = "_UIBlurTexture";
    static int DownscaleKernelID = -1;
    static int GaussianBlurKernelID = -1;
    static int BoxBlurKernelID = -1;

    [System.Serializable]
    public class Settings
    {
        [Range(1, 16)] public int DownscaleAmount = 2;

        public BlurType BlurType;
        [Range(0, 16)] public int BlurIterations = 4;

        public ComputeShader EffectCompute;
    }

    class BlurSceneColorPass : ScriptableRenderPass
    {
        RenderTargetHandle tempColorTarget;
        Settings settings;

        RenderTargetIdentifier cameraTarget;

        Vector2Int scale;
        Vector2Int groupSizes;

        public BlurSceneColorPass(Settings s)
        {
            settings = s;
            renderPassEvent = RenderPassEvent.AfterRenderingPostProcessing;
            tempColorTarget.Init(TextureName);
        }

        public void Setup(RenderTargetIdentifier cameraTarget)
        {
            this.cameraTarget = cameraTarget;
        }

        public override void Configure(CommandBuffer cmd, RenderTextureDescriptor cameraTextureDescriptor)
        {
            var downscaleDesc = cameraTextureDescriptor;
            downscaleDesc.width = (int) ((float) downscaleDesc.width / (float) settings.DownscaleAmount);
            downscaleDesc.height = (int) ((float) downscaleDesc.height / (float) settings.DownscaleAmount);
            downscaleDesc.enableRandomWrite = true;

            scale = new Vector2Int(downscaleDesc.width, downscaleDesc.height);
            groupSizes = new Vector2Int(Mathf.CeilToInt(scale.x / 32f), Mathf.CeilToInt(scale.y / 32f));

            cmd.GetTemporaryRT(tempColorTarget.id, downscaleDesc);

            cmd.SetGlobalTexture(TextureName, tempColorTarget.Identifier());
        }

        public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
        {
            CommandBuffer cmd = CommandBufferPool.Get();
            context.ExecuteCommandBuffer(cmd);
            cmd.Clear();

            // Shared parameters between compute kernels
            cmd.SetComputeVectorParam(settings.EffectCompute, "_Size", new Vector2(scale.x, scale.y));
            cmd.SetComputeFloatParam(settings.EffectCompute, "_Amount", settings.DownscaleAmount);

            // Blit/Downscale scene color texture
            {
                cmd.SetComputeTextureParam(settings.EffectCompute, DownscaleKernelID, "_Source", cameraTarget);
                cmd.SetComputeTextureParam(settings.EffectCompute, DownscaleKernelID, "_Dest",
                    tempColorTarget.Identifier());
                cmd.DispatchCompute(settings.EffectCompute, DownscaleKernelID, groupSizes.x, groupSizes.y, 1);
            }

            // Apply iterative blur
            {
                int blurKernelID = settings.BlurType switch
                {
                    BlurType.Box => BoxBlurKernelID,
                    BlurType.Gaussian => GaussianBlurKernelID,
                };

                cmd.SetComputeTextureParam(settings.EffectCompute, blurKernelID, "_Dest", tempColorTarget.Identifier());
                cmd.SetComputeTextureParam(settings.EffectCompute, blurKernelID + 1, "_Dest", tempColorTarget.Identifier());
                
                for (int i = 0; i < settings.BlurIterations; i++)
                {
                    cmd.DispatchCompute(settings.EffectCompute, blurKernelID, groupSizes.x, groupSizes.y, 1);
                    if (settings.BlurType == BlurType.Gaussian)
                    {
                        cmd.DispatchCompute(settings.EffectCompute, blurKernelID + 1, groupSizes.x, groupSizes.y, 1);
                    }
                }
            }

            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release(cmd);
        }

        public override void FrameCleanup(CommandBuffer cmd)
        {
            cmd.ReleaseTemporaryRT(tempColorTarget.id);
        }
    }

    BlurSceneColorPass blurSceneColorPass;
    [SerializeField] Settings settings;

    public override void Create()
    {
        blurSceneColorPass = new BlurSceneColorPass(settings);

        FindKernels();
    }

    void FindKernels()
    {
        if (settings.EffectCompute != null)
        {
            DownscaleKernelID = settings.EffectCompute.FindKernel("Downscale");
            GaussianBlurKernelID = settings.EffectCompute.FindKernel("GaussianBlurVertical");
            BoxBlurKernelID = settings.EffectCompute.FindKernel("BoxBlur");
        }
    }

    public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
    {
        if (settings.EffectCompute == null)
        {
            return;
        }

        if (DownscaleKernelID == -1 || GaussianBlurKernelID == -1)
        {
            FindKernels();
        }

        blurSceneColorPass.Setup(renderer.cameraColorTarget);
        renderer.EnqueuePass(blurSceneColorPass);
    }
}