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Configuring Planar Reflection Probes - 2019.4 LTS

Planar Reflection Probes act as mirrors and give the user control over the accuracy of reflections in a Scene. They can also be used for special effects, such as magic mirrors. In this tutorial, we’ll explore Planar Reflection Probe settings and create a simple magic mirror using the default HDRP Scene.

This tutorial has been verified using Unity 2019 LTS

Configuring Planar Reflection Probes

1. Create or load a project that uses the HDRP framework.

3. In the default Scene, drag the Example Assets GameObject into 

4. Create a new Scene and drag an instance of the Example Assets Prefab into the Scene.

5. Move the Example Assets GameObject (included with the starting Scene in projects that use the HDRP template) to the origin, with no rotation, and scale it by 

6. Move the Workshop Set’s local position to (

7. Optionally, move the Props subobject (of Example Assets) into place (

8. Create an empty GameObject by selecting 

 and zero out the position and rotation of its Transform.

 at the bottom of the Inspector and add a Planar Reflection Probe component (

Setting the Scene

The Planar Reflection Probe Inspector is broken up into several sections: Realtime Mode, Projection Settings, Influence Volume, Capture Settings, and Custom Settings. 

Configuring the Planar Reflection Probe

) controls how often the Planar Reflection Probe refreshes its view.

, the default setting, enables real-time updates. Depending on the needs of your project and the specifications of target hardware, this may not be necessary.

 renders the Planar Reflection Probe when the GameObject is first enabled (or when the Scene starts if it’s already enabled).

 allows the user to control the refresh of the Planar Reflection Probe with scripting. For example, if we have a variable of type ReflectionProbe called reflectionProbe that stores a reference to our Planar Reflection Probe, we’d call reflectionProbe.RenderProbe() whenever we wanted to refresh its view. This option is especially useful in situations where you only need to update the Reflection Probe in certain conditions, or at a lower refresh rate than realtime. 

Realtime Mode

Depending on the relative location of the Reflection Probe to the GameObject that’s reflecting it, displacement — a visual mismatch between the position of the reflective surface(s) and the origin of the reflected image — can occur. This can be corrected by using a Reflection Probe Proxy Volume. You can either use the Influence Volume as the Reflection Probe Proxy Volume or create a dedicated Reflection Probe Proxy Volume.

If you use a dedicated Reflection Probe Proxy Volume, its shape (if not set to Infinite) must match that of the Influence Volume.

Projection Settings

1. Create an empty GameObject by selecting 

2. Using the Inspector, attach a Reflection Probe Proxy Volume component (

3. Use the Transform to adjust position and rotation (the offset/adjustment from the mirror’s position and rotation) and the Box Size or Sphere Radius settings to control the size of the Reflection Proxy Volume component (

4. We’ll leave this alone for now, but will use it later. For now, go back to the Planar Reflection Probe and check the box marked 

Creating a Reflection Probe Proxy Volume

), you can set the Reflection Probe mirror’s position and rotation relative to its Transform. Depending on your project, you may find it easier to position the GameObject at the origin and adjust the position and rotation of the mirror using these controls. A third option that we’ll explore a bit later is to use the Reflection Probe Proxy Volume to adjust the position and rotation of the mirror.

The Planar Reflection Probe’s Field Of View is calculated using the mirror position and the bounds of the Influence Volume. Check the box labeled 

 to override this with a value you specify.

Aside from the mirror and field of view adjustments, the controls in Capture Settings function identically to the stock Camera controls.

1. Set the mirror position to some value along Z. We’ll make our magic mirror a bit later in this tutorial, and the value will likely need adjusting, depending on your desired effect. Any value is fine for now. We’ve set this Scene up in such a way that we only need to adjust the position in the Z, but feel free to experiment with any of these steps to get a deeper understanding of how they work.

. Copy and paste the value from the Main Camera. 

Capture Settings

), you can increase the strength multiplier of the Probe’s reflection and/or its blending weight. It’s helpful to use a multiplier greater than 1 for the Planar Reflection Probe’s initial setup to make the reflection easier to see. 

Render Settings

We’re finally ready to create our magic mirror.

4. Using the Scene view camera, adjust the position of the Quad so that it obscures the Example Assets (

5. If you’d like to recreate our example exactly, select 

 in the Hierarchy and enter the following values for its Transform (

6. Align the Scene view camera to the Main Camera by selecting 

 and try moving it along the X and Y axes. Holding 

, click and drag in the Scene view to orbit the camera. Because the Planar Reflection Probe is on the opposite side of the Workshop as the Scene view camera, the Workshop’s reflection is rotated 180 degrees from the Scene view.

, making a note of the mirror Position and Rotation values. Zero these out.

9. In Projection Settings, uncheck the box marked 

12. Set the position and rotation of its Transform to match the values from Step 8. Whether or not you use a Proxy Volume (either the Influence Volume or a dedicated Proxy Volume) will depend on your settings.

13. Or, try adjusting the position of the Example Assets, then adjusting the Reflection Probe or Proxy Volume to match.

Making Magic 

Planar Reflection Probes are a powerful addition to Unity’s toolset. The most effective way to understand the probes is to dive in. Keeping your subject at the origin to start can help remove some of the variables as you develop your understanding. 

Unity Version 2019.4