How to make HoloLens2's eyes display different content

To make the HoloLens 2 display different content in each eye, you can use a technique called **stereo rendering**. This involves rendering two separate images, one for each eye, creating a sense of depth and 3D perception. Here's how to implement this in a Unity application with the Mixed Reality Toolkit (MRTK):

### 1. Set Up Your Project
- **Install Unity**: Ensure you have Unity installed with the Mixed Reality Toolkit.
- **Configure Your Project**: Create a new project and set it up for HoloLens development:
- Go to `File > Build Settings`, select `Universal Windows Platform`, and set your target device to `HoloLens`.
- Enable `XR Settings` in the project settings and configure the XR plugin management for the Mixed Reality Toolkit.

### 2. Create a Custom Shader
- To render different content for each eye, you will typically need to write a custom shader. The shader will adjust the texture coordinates based on the eye being rendered.

```hlsl
Shader "Custom/StereoContentShader"
{
Properties
{
_MainTex ("Texture", 2D) = "white" {}
}
SubShader
{
Tags { "RenderType"="Opaque" }
LOD 200

Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag

#include "UnityCG.cginc"

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

struct v2f
{
float2 uv : TEXCOORD0;
float4 vertex : SV_POSITION;
UNITY_FOG_COORDS(1)
};

sampler2D _MainTex;
float4 _MainTex_ST;

v2f vert (appdata_t v)
{
v2f o;
o.vertex = UnityObjectToClipPos(v.vertex);
o.uv = TRANSFORM_TEX(v.uv, _MainTex);
UNITY_TRANSFER_FOG(o,o.vertex);
return o;
}

fixed4 frag (v2f i) : SV_Target
{
// Use a different texture or adjust based on the eye index
fixed4 col = tex2D(_MainTex, i.uv);
// Logic to determine which eye is rendering and modify the content accordingly
return col;
}
ENDCG
}
}
}
```

### 3. Modify Content for Each Eye
- In your Unity script, check which eye is being rendered and load different content accordingly.

```csharp
using UnityEngine;
using UnityEngine.XR;

public class EyeContentSwitcher : MonoBehaviour
{
public Texture leftEyeTexture;
public Texture rightEyeTexture;

private Material material;

void Start()
{
material = GetComponent<Renderer>().material;
}

void Update()
{
if (XRSettings.eyeTextureDesc.vrUsage == VRTextureUsage.TwoEyes)
{
if (XRSettings.eyeTextureDesc.eye == XRNode.LeftEye)
{
material.mainTexture = leftEyeTexture;
}
else
{
material.mainTexture = rightEyeTexture;
}
}
}
}
```

### 4. Test on HoloLens 2
- Build and deploy your application to the HoloLens 2.
- Ensure that the stereo rendering is working, with different content displayed in each eye.

### Additional Considerations
- **Performance**: Rendering different content in each eye can impact performance. Optimize your assets and shaders as needed.
- **User Experience**: Consider how different content might affect user experience and ensure it adds value to the application.

By following these steps, you can create an engaging experience on HoloLens 2 that takes advantage of its mixed reality capabilities!