Unity-DualCameraOverlay

This is a Unity project that demonstrates a dual-camera overlay rendering system.
It composites the rendered outputs of two Virtual Cameras with alpha blending, and outputs the final result to the Main Camera.

This project is useful for applications such as:

• multi-perspective VR/AR visualization
• mixed overlay UI + world rendering
• experimental multi-camera composition pipelines

Overview

This Unity project implements a dual-camera overlay system that composites two independent camera outputs into a single final view.

In this project, two environments (Env1 and Env2) are rendered separately by two Virtual Cameras.
Their outputs are then alpha-blended (transparent overlay composition) and displayed through the Main Camera.

This allows two different scenes (or layers) to be visually merged in real time.

Rendering Flow

↓ Alpha-blended composition (Dual Camera Overlay) ↓

The transparency of each camera layer can be adjusted dynamically, enabling smooth blending and flexible visualization of multiple camera perspectives.

Environment

This project was developed and tested with the following environment:

• Unity: 2022.3.28f1
• Render Pipeline: Built-in Render Pipeline
• XR Interaction Toolkit: 2.5.4
• XR Plugin Management: 4.5.4
• OpenXR Plugin: 1.10.0
• Stereo Rendering Mode: Multi Pass (Single Pass is NOT supported)

Quick Start

Follow the steps below to run the Dual Camera Overlay system.

1. Add the DualCameraCompositor script

Add the DualCameraCompositor component to your Main Camera.

2. Create two Virtual Cameras

Under the following hierarchy:

XR Origin (XR Rig)
├── Camera Offset
│   ├── Main Camera
│   ├── Virtual Camera 1
│   └── Virtual Camera 2

Create two standard Unity Camera objects:

• Virtual Camera 1
• Virtual Camera 2

3. Assign Virtual Cameras

In the DualCameraCompositor inspector, assign:

• Virtual Camera Env 1 → Virtual Camera 1
• Virtual Camera Env 2 → Virtual Camera 2

4. Configure Layer Settings

Assign your scene objects to Unity Layers (e.g., Env 1 and Env 2), then set the Layer Masks:

• Layer Mask Camera Env 1
• Layer Mask Camera Env 2

This determines which objects are rendered by each Virtual Camera.

5. Press Play

Press the Unity Play button to run the system.
The outputs of the two Virtual Cameras will be alpha-blended and displayed through the Main Camera.

Configuration (Layer & Alpha Settings)

This project allows you to configure which objects are rendered by each Virtual Camera using Unity Layers.

In the Dual Camera Compositor component, you can specify:

• Layer Mask Camera Env L: the Layer rendered by Virtual Camera 1 (Env 1)
• Layer Mask Camera Env R: the Layer rendered by Virtual Camera 2 (Env 2)

This makes it possible to separate two environments (or two object groups) into independent camera outputs.

In addition, you can control the transparency of each camera output individually:

• Alpha Env L: transparency of Env 1 output
• Alpha Env R: transparency of Env 2 output

By adjusting these alpha values, the two camera views can be blended smoothly in real time.

Inspector Parameters

Below is a summary of the parameters available in the DualCameraCompositor component.

Category	Parameter	Description
Virtual Cameras	Virtual Camera Env 1	Camera used to render Env 1 (left layer).
Virtual Cameras	Virtual Camera Env 2	Camera used to render Env 2 (right layer).
Layer Settings	Layer Mask Camera Env 1	LayerMask used by Virtual Camera Env 1. Only objects in this layer will be rendered.
Layer Settings	Layer Mask Camera Env 2	LayerMask used by Virtual Camera Env 2. Only objects in this layer will be rendered.
Main Camera Clipping Planes	Main Camera Near Clip	Near clipping plane value for the Main Camera.
Main Camera Clipping Planes	Main Camera Far Clip	Far clipping plane value for the Main Camera.
Alpha Settings	Alpha Env L	Alpha blending weight for Env 1 output. (0 = invisible, 1 = fully visible)
Alpha Settings	Alpha Env R	Alpha blending weight for Env 2 output. (0 = invisible, 1 = fully visible)
Render Textures	Render Texture Width	Width of the internal RenderTexture used for each Virtual Camera.
Render Textures	Render Texture Height	Height of the internal RenderTexture used for each Virtual Camera.
Render Textures	Depth Buffer	Depth buffer bit depth used for the RenderTextures (e.g., 24).