Example: How to create a custom rendering effect using the Render Objects Renderer Feature

URP draws objects in the DrawOpaqueObjects and DrawTransparentObjects passes. You might need to draw objects at a different point in the frame rendering, or interpret and write rendering data (like depth and stencil) in alternate ways. The Render Objects Renderer Feature lets you do such customizations by letting you draw objects on a certain layer, at a certain time, with specific overrides.

The example on this page describes how to create a custom rendering effect with the Render Objects Renderer Feature.

Example overview

The example on this page demonstrates how to implement the following effect:

  • There is a character in the Scene.

    Character

  • When the character goes behind GameObjects, Unity draws the character silhouette with a different Material.

    Character goes behind GameObjects

Prerequisites

This example requires the following:

  • A Unity project with the URP package installed.

  • The Scriptable Render Pipeline Settings property refers to a URP asset (Project Settings > Graphics > Scriptable Render Pipeline Settings).

Create example Scene and GameObjects

To follow the steps in this example, create a new Scene with the following GameObjects:

  1. Create a Cube. Set its Scale values so that it looks like a wall.

    Cube that represents a wall

  2. Create a Material and assign it the Universal Render Pipeline/Lit shader. Select the base color (for example, red). Call the Material Character.

  3. Create a basic character and assign it the Character Material. In this example, the character consists of three capsules: the big capsule in the center represents the body, and the two smaller capsules represent the hands.

    The character consisting of three capsules

    To make it easier to manipulate the character in the Scene, add the three Capsules as child GameObjects under the Character GameObject.

    Character objects in Hierarchy

  4. Create a Material and assign it the Universal Render Pipeline/Unlit shader. Select the base color that you would like the character to have when it's behind GameObjects (for example, blue). Call the Material CharacterBehindObjects.

Now you have the setup necessary to follow the steps in this example.

Example implementation

This section assumes that you created a Scene as described in section Example Scene and GameObjects.

The example implementation uses two Render Objects Renderer Features: one to draw parts of the character that are behind other GameObjects, and another one to draw the parts of the character that are in front of other GameObjects.

Create a Renderer Feature to draw the character behind GameObjects

Follow these steps to create a Renderer Feature to draw the character behind GameObjects.

  1. Select a URP Renderer.

    Select a URP Renderer

  2. In the Inspector, click Add Renderer Feature and select Render Objects.

    Add Render Object Renderer Feature

    Select the Name field and enter the name of the new Renderer Feature, for example, DrawCharacterBehind.

  3. This example uses Layers to filter the GameObjects to render. Create a new Layer and call it Character.

    Create new Layer called Character

  4. Select the Character GameObject and assign it to the Character Layer. To do this, open the Layer drop down and select Character. Assign Character GameObject to Character Layer

  5. In the DrawCharacterBehind Renderer Feature, in Filters > Layer Mask, select Character. With this setting, this Renderer Feature renders GameObjects only in the Layer Character.

  6. In Overrides > Material, select the CharacterBehindObjects Material.

    The Renderer Feature overrides the Material of a GameObject with the selected Material.

    Layer Mask, Material Override

  7. The intended behavior is that the Renderer Feature renders the character with the CharacterBehindObjects Material only when the character is behind other GameObjects.

    To achieve this, select the Depth check box, and set the Depth Test property to Greater.

    Set Depth Test to Greater

With these settings, Unity renders the character with the CharacterBehindObjects Material only when the character is behind another GameObject. However, Unity also renders parts of the character using the CharacterBehindObjects Material, because some parts of the character occlude the character itself.

Unity renders parts of the character using the `CharacterBehindObjects` Material

Create an extra Renderer Feature to avoid the self see-through effect

The settings in the previous section result in the self see-through effect for the following reason:

  • When performing the Opaque rendering pass of the URP Renderer, Unity renders all GameObjects belonging to the character with the Character Material and writes depth values to the Depth buffer. This happens before Unity starts executing the DrawCharacterBehind Renderer Feature, because, by default, new Render Objects Renderer Features have the value AfterRenderingOpaques in the Event property.

    The Event property defines the injection point where Unity injects Render Passes from the Render Objects Renderer Feature. The event when URP Renderer draws GameObjects in the Opaque Layer Mask is the BeforeRenderingOpaques event.

  • When executing the DrawCharacterBehind Renderer Feature, Unity performs the depth test using the condition specified in the Depth Test property. In the following screenshot, a bigger capsule occludes part of the smaller capsule, and the depth test passes for that part of the smaller capsule. The Renderer Feature overrides the Material for that part.

    Self see-through effect

The following steps describe how to avoid such behavior and ensure that Unity draws all parts of the character with proper Materials.

  1. In the URP asset, in Filtering > Opaque Layer Mask, clear the check mark next to the Character Layer.

    Clear the check mark next to the `Character` Layer

    Now Unity does not render the character unless it's behind a GameObject.

    Unity does not render the character unless it's behind an object

  2. Add a new Render Objects Renderer Feature, and call it Character.

  3. In the Character Renderer Feature, in Filters > Layer Mask, select the Character Layer.

    Set Layer Mask Filter to Character Layer

    Now Unity renders the character with the Character Material even when the character is behind GameObjects.

    This happens because the DrawCharacterBehind Renderer Feature writes values to the depth buffer. When Unity executes the Character Renderer Feature, the pixels on the character appear to be in front of the pixels that Unity has drawn previously, and Unity draws on top of those pixels.

  4. In the DrawCharacterBehind Renderer Feature, In Overrides > Depth, clear the Write Depth check box. With this setting, the DrawCharacterBehind Renderer Feature does not make changes to the depth buffer and the Character Renderer Feature does not draw the character when it's behind GameObjects.

    Clear Write Depth

The example is complete. When the character goes behind GameObjects, Unity draws the character silhouette with the CharacterBehindObjects Material.

Character goes behind objects

With the extra Character Renderer Feature, Unity renders GameObjects as follows:

  1. URP Renderer does not render the Character GameObject in the BeforeRenderingOpaques event, because the Character Layer is excluded from the Opaque Layer Mask list.

  2. The DrawCharacterBehind Renderer Feature draws parts of the character that are behind other GameObjects. This happens in the AfterRenderingOpaques event.

  3. The Character Renderer Feature draws parts of the character that are in front of other GameObjects. This happens in the AfterRenderingOpaques event, and after executing the DrawCharacterBehind Renderer Feature.

To see another use case of the Render Objects Renderer Feature, refer to the Object Occlusion Scene in the Universal Rendering Examples project.