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Use Depth in your AR Foundation Android app

The Depth API helps a device’s camera to understand the size and shape of the real objects in a scene. It uses the camera to create depth images, or depth maps, thereby adding a layer of AR realism into your apps. You can use the information provided by a depth image to make virtual objects accurately appear in front of or behind real world objects, enabling immersive and realistic user experiences.

Depth information is calculated from motion and may be combined with information from a hardware depth sensor, such as a time-of-flight (ToF) sensor, if available. A device does not need a ToF sensor to support the Depth API.

Prerequisites

Make sure that you understand fundamental AR concepts and how to configure an ARCore session before proceeding.

Restrict access to Depth-supported devices

If your app requires Depth API support, either because a core part of the AR experience relies on depth, or because there's no graceful fallback for the parts of the app that use depth, you may choose to restrict distribution of your app in the Google Play Store to devices that support the Depth API by adding the following line to your AndroidManifest.xml:

<uses-feature android:name="com.google.ar.core.depth" />

Enable Depth

To save resources, ARCore does not enable the Depth API by default. To take advantage of depth on supported devices, you must manually add the AROcclusionManager component to the AR Camera game object with the Camera and ARCameraBackground component. See Automatic occlusion in the Unity documentation for more information.

In a new ARCore session, check whether a user's device supports depth and the Depth API, as follows:

// Reference to AROcclusionManager that should be added to the AR Camera
// game object that contains the Camera and ARCameraBackground components.
var occlusionManager = …

// Check whether the user's device supports the Depth API.
if (occlusionManager.descriptor?.supportsEnvironmentDepthImage)
{
    // If depth mode is available on the user's device, perform
    // the steps you want here.
}

Acquire depth images

Get the latest environment depth image from the AROcclusionManager.

// Reference to AROcclusionManager that should be added to the AR Camera
// game object that contains the Camera and ARCameraBackground components.
var occlusionManager = …

if (occlusionManager.TryAcquireEnvironmentDepthCpuImage(out XRCpuImage image))
{
    using (image)
    {
        // Use the texture.
    }
}

You can convert the raw CPU image into a RawImage for greater flexibility. An example for how to do this can be found in Unity's ARFoundation samples.

Understand depth values

Given point A on the observed real-world geometry and a 2D point a representing the same point in the depth image, the value given by the Depth API at a is equal to the length of CA projected onto the principal axis. This can also be referred as the z-coordinate of A relative to the camera origin C. When working with the Depth API, it is important to understand that the depth values are not the length of the ray CA itself, but the projection of it.

Occlude virtual objects and visualize depth data

Check out Unity's blog post for a high-level overview of depth data and how it can be used to occlude virtual images. Additionally, Unity's ARFoundation samples demonstrate occluding virtual images and visualizing depth data.

You can render occlusion using two-pass rendering or per-object, forward-pass rendering. The efficiency of each approach depends on the complexity of the scene and other app-specific considerations.

Per-object, forward-pass rendering

Per-object, forward-pass rendering determines the occlusion of each pixel of the object in its material shader. If the pixels are not visible, they are clipped, typically via alpha blending, thus simulating occlusion on the user’s device.

Two-pass rendering

With two-pass rendering, the first pass renders all of the virtual content into an intermediary buffer. The second pass blends the virtual scene onto the background based on the difference between the real-world depth with the virtual scene depth. This approach requires no additional object-specific shader work and generally produces more uniform-looking results than the forward-pass method.

Extract distance from a depth image

To use the Depth API for purposes other than occluding virtual objects or visualizing depth data, extract information from the depth image.

Texture2D _depthTexture;
short[] _depthArray;

void UpdateEnvironmentDepthImage()
{
  if (_occlusionManager &&
        _occlusionManager.TryAcquireEnvironmentDepthCpuImage(out XRCpuImage image))
    {
        using (image)
        {
            UpdateRawImage(ref _depthTexture, image, TextureFormat.R16);
            _depthWidth = image.width;
            _depthHeight = image.height;
        }
    }
  var byteBuffer = _depthTexture.GetRawTextureData();
  Buffer.BlockCopy(byteBuffer, 0, _depthArray, 0, byteBuffer.Length);
}

// Obtain the depth value in meters at a normalized screen point.
public static float GetDepthFromUV(Vector2 uv, short[] depthArray)
{
    int depthX = (int)(uv.x * (DepthWidth - 1));
    int depthY = (int)(uv.y * (DepthHeight - 1));

    return GetDepthFromXY(depthX, depthY, depthArray);
}

// Obtain the depth value in meters at the specified x, y location.
public static float GetDepthFromXY(int x, int y, short[] depthArray)
{
    if (!Initialized)
    {
        return InvalidDepthValue;
    }

    if (x >= DepthWidth || x < 0 || y >= DepthHeight || y < 0)
    {
        return InvalidDepthValue;
    }

    var depthIndex = (y * DepthWidth) + x;
    var depthInShort = depthArray[depthIndex];
    var depthInMeters = depthInShort * MillimeterToMeter;
    return depthInMeters;
}

What’s next