144 lines
9.3 KiB
Markdown
144 lines
9.3 KiB
Markdown
---
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uid: urp-how-to-custom-effect-render-objects
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---
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# Example: How to create a custom rendering effect using the Render Objects Renderer Feature
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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](renderer-feature-render-objects.md) lets you do such customizations by letting you draw objects on a certain layer, at a certain time, with specific overrides.
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The example on this page describes how to create a custom rendering effect with the Render Objects Renderer Feature.
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## Example overview
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The example on this page demonstrates how to implement the following effect:
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* There is a character in the scene.
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* When the character goes behind GameObjects, Unity draws the character silhouette with a different Material.
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## Prerequisites
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This example requires the following:
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* A Unity project with the URP package installed.
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* The **Scriptable Render Pipeline Settings** property refers to a URP asset (**Project Settings** > **Graphics** > **Scriptable Render Pipeline Settings**).
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## Create example Scene and GameObjects<a name="example-objects"></a>
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To follow the steps in this example, create a new scene with the following GameObjects:
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1. Create a Cube. Set its **Scale** values so that it looks like a wall.
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2. Create a Material and assign it the `Universal Render Pipeline/Lit` shader. Select the base color (for example, red). Call the Material `Character`.
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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.
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To make it easier to manipulate the character in the scene, add the three Capsules as child GameObjects under the Character GameObject.
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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`.
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Now you have the setup necessary to follow the steps in this example.
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## Example implementation
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This section assumes that you created a scene as described in section [Example scene and GameObjects](#example-objects).
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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.
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### Create a Renderer Feature to draw the character behind GameObjects
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Follow these steps to create a Renderer Feature to draw the character behind GameObjects.
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1. Select a URP Renderer.
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2. In the Inspector, click **Add Renderer Feature** and select **Render Objects**.
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Select the **Name** field and enter the name of the new Renderer Feature, for example, **DrawCharacterBehind**.
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3. This example uses Layers to filter the GameObjects to render. Create a new Layer and call it **Character**.
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4. Select the **Character** GameObject and assign it to the `Character` Layer. To do this, open the Layer drop down and select `Character`.
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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`.
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6. In **Overrides** > **Material**, select the `CharacterBehindObjects` Material.
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The Renderer Feature overrides the Material of a GameObject with the selected Material.
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7. The intended behavior is that the Renderer Feature renders the character with the `CharacterBehindObjects` Material only when the character is behind other GameObjects.
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To achieve this, select the **Depth** check box, and set the **Depth Test** property to **Greater**.
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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.
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### Create an extra Renderer Feature to avoid the self see-through effect
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The settings in the previous section result in the self see-through effect for the following reason:
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* 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.
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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.
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* 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.
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The following steps describe how to avoid such behavior and ensure that Unity draws all parts of the character with proper Materials.
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1. In the URP asset, in **Filtering** > **Opaque Layer Mask**, clear the check mark next to the `Character` Layer.
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Now Unity does not render the character unless it's behind a GameObject.
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2. Add a new Render Objects Renderer Feature, and call it `Character`.
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3. In the `Character` Renderer Feature, in **Filters** > **Layer Mask**, select the `Character` Layer.
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Now Unity renders the character with the `Character` Material even when the character is behind GameObjects.
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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.
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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.
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The example is complete. When the character goes behind GameObjects, Unity draws the character silhouette with the `CharacterBehindObjects` Material.
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With the extra `Character` Renderer Feature, Unity renders GameObjects as follows:
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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.
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2. The `DrawCharacterBehind` Renderer Feature draws parts of the character that are behind other GameObjects. This happens in the **AfterRenderingOpaques** event.
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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.
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