Question: How to randomize a background image

[cd25643]

Very new to both Unity, and the perception package. I followed the entire tutorial, and am now building my own scene with custom randomizers/objects/etc. I was wondering how I would go about randomizing a background image for a scene? What I have in mind, is having a folder of multiple HDRIs and each frame it randomly picks one of those. How would I go about doing something like this?

[esgnn]

One approach could be (I'm not sure if it is a performant one)

1. Read HDRI's at the start of the simulation -
2. Pick one at the start of each frame
3. Assign it to VolumeProfile. It is a little bit trickier. An example code is below

void ChangeSky(VolumeProfile vp, Cubemap hdri)
{
	HDRISky hs;
	vp.TryGet<HDRISky>(out hs);
	hs.hdriSky.value = hdri;
}

[RuiyuZ]

@esgnn thank you so much for helping out!
@cd25643 I think you are on the right track, and I will just add a little bit on @esgnn's answer
The steps would be:

1. add a "Volume" component to your sky object
2. on the "Profile" box, create a new Volume profile
3. click into that Volume profile and "add override" -> sky -> HDRI sky
4. check the checkbox "Hdri Sky"
5. on the same sky object, create a SkyRandomizerTag class that reads in the HDRISky that can be getting from the Volume we just created on the same object,

public class SkyboxRandomizerTag: RandomizerTag
{
    HDRISky m_Sky;
    public HDRISky sky
    {
        get
            {
                if (m_Sky == null) 
                    GetComponent<Volume>().profile.TryGet(out m_Sky);
                return m_Sky;
            }
    }
}

6. create a randomizer script

[Serializable]
[AddRandomizerMenu("Perception/My sky Randomizer")]
public class MySkyRandomizer : Randomizer
{
    public CubemapCategoricalParameter skyboxes = new CubemapCategoricalParameter();
    protected override void OnIterationStart()
    {
        var tags = tagManager.Query<SkyboxRandomizerTag>();
        foreach (var tag in tags)
             tag.sky.hdriSky.Override(skyboxes.Sample());
    }
}

7. Add MySkyRandomizer to the list of Randomizers in SimulationScenario.
8. click "add folder" to add the folder of HDRIs

[cd25643]

@RuiyuZ Thanks a lot for your detailed response. That is very helpful! However, I can't seem to find the "sky" or "HDRI sky" option in the Volume Profile override box? (see pic below) What am I missing here? I only see "post-processing" and in that sub-menu, there is no sky or HDRI sky option...

[RuiyuZ]

Hi @cd25643, my mistake, please ignore steps 1, 2, 3 &4, you should be able to create a "Sky and Fog Volume" Scene Settings GameObject by going to Menu: GameObject > Volumes> Sky and Fog Volume. and then attaching the SkyRandomizerTag script to it.
See the image below for reference:

[cd25643]

@RuiyuZ When I go to create a new gameobject, I do not see the "Sky and Fog Volume" option within the Volume category. I instead tried to create a Global Volume, when adding a component I also don't see the option to add a "Visual Environment" or "HDRI Sky"...

[RuiyuZ]

Hi @cd25643, you can find it here

[esgnn]

I might be wrong, @cd25643 are you using Universal Render Pipeline? If so, I am not experienced in URP, but couldn’t find any reference to HDRI at volume documentation. If so, there seems to be a skybox shader

[cd25643]

@esgnn I am using a URP, thanks for the link...

@RuiyuZ I am looking in the exact same spot, but don't see the same menu options. Are you running the 0.9.0-preview.2 release? I see you are working in a HDRP, perhaps this option isn't available in URP (which is what I am using).

[RuiyuZ]

@cd25643 Oh.. that's right, this option is not available in URP, only in HDRP, do you think you can switch to HDRP?

[cd25643]

@RuiyuZ Switched over to HDRP... Got everything set up again. I created the Sky Randomizer Tag and the Sky Randomizer. I keep running into this error...

Looks like "HDRISky" is not a "type" that can be used in the script. This feels like I'm missing a directive/assembly reference?

Having a similar issue with the "CubeCategorcalParameter" variable...

Here is all of the current references I am using in my scripts...

[RuiyuZ]

@cd25643 yes, I think
using UnityEngine.Rendering.HighDefinition;
is missing

[cd25643]

@RuiyuZ That fixed the HDRISky and Sky issues... but it looks like I'm still missing referneces for "CubemapCategoricalParamter" and "Volume".

I haven't worked with a HDRP before, so I am likely just missing common references. Here are all my current references:

[cd25643]

I actually fixed the "Volume" issue by adding this reference: using UnityEngine.Rendering;

But I still have the CubemapCategoricalParameter issue

[mkamalza]

Hi @cd25643 , apologies for the missing piece. This is actually a class that you need to add to your project. Just create a new C# class file and name it CubemapCategoricalParameter.cs and paste the following into it:

using System;
using UnityEngine;
using UnityEngine.Perception.Randomization.Parameters;

/// <summary>
/// A categorical parameter for generating cubemap samples
/// </summary>
[Serializable]
public class CubemapCategoricalParameter : CategoricalParameter<Cubemap>
{
}

[cd25643]

That was the missing piece! Thanks for the assistance on this @mkamalza and @RuiyuZ !