How To Access and Display Depth Information

This how-to covers accessing the depth buffer and provides a use case for that information. In this example, a shader takes in depth information and displays it on-screen as a color filter.

This how-to covers:

1. Accessing the depth buffer and displaying it on screen using a shader.
2. Getting the display transform from the camera to set rotation and aspect ratio.
3. Passing the raw depth texture and the matrix to a shader.
4. Calculating the correct sampling points on the depth texture using the display matrix.
5. Converting the texture to a color scale mathematically as an example of what to do with depth information.

Prerequisites

You will need a Unity project with ARDK installed and a set-up basic AR scene. For more information, see Installing ARDK 3 and Setting up an AR Scene.

Adding the AR Occlusion Manager

To help display the depth information using Lightship's AR Occlusion Manager:

1. Add an AROcclusionManager to your Main Camera GameObject:
   1. In the Hierarchy, expand the XROrigin and Camera Offset, then select the Main Camera object. Then, in the Inspector, click Add Component and add an AROcclusionManager.

Adding a Raw Image

To add the raw image that will display depth information:

1. Add a Raw Image to the Hierarchy under the AR scene:

   1. Right-click in the Hierarchy under the main scene, then mouse over UI and select Raw Image.

2. Using the image transform tools, center the Raw Image and stretch it across the screen to make it visible later (see image below).

   1. Set all parameters (Left, Top, Z, Right, Bottom) to 0.
   

Adding a Material and Shader

To create a material and shader:

1. In the Assets window, right-click, then mouse over Create and select Material. Name it DepthMaterial.
2. Repeat this process, but mouse over Shader and select Standard Surface Shader. Name it DisplayDepth.
3. Drag the shader onto the material to connect them.
4. Add the code from DisplayDepth Shader Code to the DisplayDepth shader.

DisplayDepth Shader Code

Click here to reveal the DisplayDepth code

Shader "Unlit/DisplayDepth"
{
    Properties
    {
        _MainTex ("_MainTex", 2D) = "white" {}
        _DepthTex ("_DepthTex", 2D) = "green" {}
    }
    SubShader
    {
        Tags {"Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent"}
        Blend SrcAlpha OneMinusSrcAlpha
        // No culling or depth
        Cull Off ZWrite Off ZTest Always
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

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

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

            };

            float4x4 _DisplayMat;

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

                #if !UNITY_UV_STARTS_AT_TOP
                o.uv.y = 1-o.uv.y;
                #endif

                //we need to adjust our image to the correct rotation and aspect.
                o.texcoord = mul(float3(o.uv, 1.0f), _DisplayMat).xy;
                return o;
            }

            sampler2D _MainTex;
            sampler2D _DepthTex;

            fixed4 frag (v2f i) : SV_Target
            {
                float depth = tex2D(_DepthTex, i.texcoord).r;

                const float MAX_VIEW_DISP = 4.0f;
                const float scaledDisparity = 1.0f / depth;
                const float normDisparity = scaledDisparity / MAX_VIEW_DISP;

                return float4(normDisparity,normDisparity,normDisparity,1.0f);
            }
            ENDCG
        }
    }
}

Creating a Script to Get Depth Data

1. Create a C# Script file in the Assets window.
2. Name it Depth_HowTo.
3. Open Depth_HowTo in a file editor, then add the code from Depth Script Code.

Depth Script Code

using System;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.XR.ARFoundation;
using UnityEngine.XR.ARSubsystems;

public class Depth_HowTo : MonoBehaviour
{
    public ARCameraManager _cameraManager;

    public AROcclusionManager _occlusionManager;

    public RawImage _rawImage;

    public Material _material;

    private Matrix4x4 _displayMat = Matrix4x4.identity;

    void OnEnable()
    {
        _cameraManager.frameReceived += OnCameraFrameUpdate;
    }

    private void OnDisable()
    {
        _cameraManager.frameReceived -= OnCameraFrameUpdate;
    }

    void Update()
    {
        if (!_occlusionManager.subsystem.running)
        {
            return;
        }

        //add our material to the raw image
        _rawImage.material = _material;

        //set our variables in our shader
        //NOTE: Updating the depth texture needs to happen in the Update() function
        _rawImage.material.SetTexture("_DepthTex", _occlusionManager.environmentDepthTexture);
        _rawImage.material.SetMatrix("_DisplayMat",_displayMat);
    }

    private void OnCameraFrameUpdate(ARCameraFrameEventArgs args)
    {
        if (!_occlusionManager.subsystem.running)
        {
            return;
        }

        //get the display matrix
        _displayMat = args.displayMatrix?? Matrix4x4.identity;

        #if UNITY_ANDROID && !UNITY_EDITOR
            _displayMat = _displayMat.transpose;
        #endif
    }
}

Putting It All Together

To connect all the pieces and test it out:

1. Create an Empty GameObject.
2. Drag the Depth_HowTo Script to the Empty GameObject.
3. In the Inspector:
   1. Drag the main camera to the script under Camera Manager.
   2. Drag the main camera to the script under Occlusion Manager.
   3. Drag the material to the script under Material.
   4. Pass the raw image to the script under Raw Image.
4. Open Build Settings and build the scene to a device to try it out.

Output

Depending on modifications to the shader, your sample scene may not look the same!