Applying post processing effect after UI ignores linear color space

Unity Engine
1

Hello girls and boys!

I found a way to apply a post processing effect after the screenspace-overlay ui, which made me pretty proud. Here is the somewhat hackish code:

// --------------------------------------------------------------------------------------------------------------------
// <copyright file="PostProcessCompleteImage.cs" company="Supyrb">
//   Copyright (c) 2017 Supyrb. All rights reserved.
// </copyright>
// <author>
//   Johannes Deml
//   send@johannesdeml.com
// </author>
// --------------------------------------------------------------------------------------------------------------------

using System;
using System.Collections;
using UnityEngine;

namespace Supyrb
{
    [ExecuteInEditMode]
    [RequireComponent(typeof(Camera))]
    public class PostProcessCompleteImage : MonoBehaviour
    {
        [SerializeField]
        private RenderTextureReadWrite renderTextureReadWrite = RenderTextureReadWrite.Linear;

        [SerializeField]
        private RenderTextureFormat renderTextureFormat = RenderTextureFormat.DefaultHDR;

        [SerializeField]
        private Camera cam = null;

        private RenderTexture tempRt;
        private WaitForEndOfFrame waitForEndOfFrame;
        private bool running;

        void Awake()
        {
            waitForEndOfFrame = new WaitForEndOfFrame();
        }

        void OnEnable()
        {
            running = true;
            StartCoroutine(ApplyEffectAtEndOfFrame());
        }

        void OnDisable()
        {
            running = false;
            StopAllCoroutines();
        }

        void OnPreRender()
        {
            tempRt = RenderTexture.GetTemporary(Screen.width, Screen.height, 24, renderTextureFormat, renderTextureReadWrite);
            cam.targetTexture = tempRt;
        }

        private IEnumerator ApplyEffectAtEndOfFrame()
        {
            while (running)
            {
                yield return waitForEndOfFrame;

                cam.targetTexture = null; //null means framebuffer
                Graphics.Blit(tempRt, null as RenderTexture);
                RenderTexture.ReleaseTemporary(tempRt);
            }
        }


#if UNITY_EDITOR

        void Reset()
        {
            if (cam == null)
            {
                cam = GetComponent<Camera>();
            }
        }

#endif
    }
}

Sadly I found a problem: When using linear color space + UI the color will be quite dark:
Without effect:

3255783--250818--upload_2017-10-16_22-5-58.png
3255783--250818--upload_2017-10-16_22-5-58.png660×1126 39.5 KB

With effect:
3255783--250817--upload_2017-10-16_22-5-33.png
3255783--250817--upload_2017-10-16_22-5-33.png660×1126 44.5 KB

This does not happen when using gamma color space and also when not using any ui. Is there anything I can change to make the effect work? And is it a really bad idea to run an image effect after WaitForEndOfFrame or is that kind of okay? Feels like a bad idea, but somehow works.
If that is not possible that way, should I take a look at the ScriptableRenderLoop? Or are there any other possibilities? :slight_smile:

2

I dont understand why is there this song and dance with coroutine and separate render texture? You dont need that. As far as other possibilties go, you can try command buffers.

3

Thanks for the answer! I never used command buffers before and I wanted to see if it is possible to apply an effect similar to OnRenderImage.

Anyways, that’s good to know. I thought I might have to try the ScriptableRenderLoop, which I really don’t want to do. I will take a look at command buffers :slight_smile: