A render loop is the term for all of the rendering operations that take place in a single frame. This page contains information on creating a simple render loop in a custom render pipeline that is based on Unity’s Scriptable Render Pipeline.
The code examples on this page demonstrate the basic principles of using the Scriptable Render Pipeline. You can use this information to build your own custom Scriptable Render Pipeline, or to understand how Unity’s prebuilt Scriptable Render Pipelines work.
Before you begin writing the code for your render loop, you must prepare your project.
The steps are as follows:
In the Scriptable Render Pipeline, you use the LightMode Pass tag in a Unity shader to determine how to draw geometry. For more information on assigning Pass tags to Unity shaders, see ShaderLab: assigning tags to a Pass.
This task shows you how to create a very simple unlit Unity shader with a LightMode Pass tag value of ExampleLightModeTag.
// This is a simple unlit Unity shader that is compatible with a custom Scriptable Render Pipeline.
// It applies a hardcoded color, and demonstrates the use of the LightMode Pass tag.
// It is not compatible with SRP Batcher.
Shader "Examples/SimpleUnlitColor"
{
SubShader
{
Pass
{
// The value of the LightMode Pass tag must match the ShaderTagId in ScriptableRenderContext.DrawRenderers
Tags { "LightMode" = "ExampleLightModeTag"}
HLSLPROGRAM
#pragma vertex vert
#pragma fragment frag
float4x4 unity_MatrixVP;
float4x4 unity_ObjectToWorld;
struct Attributes
{
float4 positionOS : POSITION;
};
struct Varyings
{
float4 positionCS : SV_POSITION;
};
Varyings vert (Attributes IN)
{
Varyings OUT;
float4 worldPos = mul(unity_ObjectToWorld, IN.positionOS);
OUT.positionCS = mul(unity_MatrixVP, worldPos);
return OUT;
}
float4 frag (Varyings IN) : SV_TARGET
{
return float4(0.5,1,0.5,1);
}
ENDHLSL
}
}
}
In order to test that your render loop works, you must create something to render. This task shows you how to put GameObjects in your scene that use the SRP-compatible Unity shader that you created in the previous task.
The final stage of preparation is to create the basic source files needed for your custom SRP, and tell Unity to begin rendering using the custom SRP.
RenderPipeline and a compatible Render Pipeline Asset, following the instructions in Creating a Render Pipeline Instance and Render Pipeline Asset
In a simple render loop, the basic operations are:
Clearing means removing the things that were drawn during the last frame. The render target is usually the screen; however, you can also render to textures to create a “picture in picture” effect. These examples demonstrate how to render to the screen, which is Unity’s default behavior.
To clear the render target in the Scriptable Render Pipeline, you do the following:
CommandBuffer with a Clear command.CommandBuffer to the queue of commands on the ScriptableRenderContext; to do this, call ScriptableRenderContext.ExecuteCommandBuffer.ScriptableRenderContext; to do this, call ScriptableRenderContext.Submit.As with all Scriptable Render Pipeline operations, you use the RenderPipeline.Render method as the entry point for this code. This example code demonstrates how to do this:
/*
This is a simplified example of a custom Scriptable Render Pipeline.
It demonstrates how a basic render loop works.
It shows the clearest workflow, rather than the most efficient runtime performance.
*/
using UnityEngine;
using UnityEngine.Rendering;
public class ExampleRenderPipeline : RenderPipeline {
public ExampleRenderPipeline() {
}
protected override void Render (ScriptableRenderContext context, Camera[] cameras) {
// Create and schedule a command to clear the current render target
var cmd = new CommandBuffer();
cmd.ClearRenderTarget(true, true, Color.black);
context.ExecuteCommandBuffer(cmd);
cmd.Release();
// Instruct the graphics API to perform all scheduled commands
context.Submit();
}
}
Culling is the process of filtering out geometry that is not visible to a Camera.
To cull in the Scriptable Render Pipeline, you do the following:
ScriptableCullingParameters struct.CullingResults struct.This example code extends the example above, and demonstrates how to clear the render target and then perform a culling operation:
/*
This is a simplified example of a custom Scriptable Render Pipeline.
It demonstrates how a basic render loop works.
It shows the clearest workflow, rather than the most efficient runtime performance.
*/
using UnityEngine;
using UnityEngine.Rendering;
public class ExampleRenderPipeline : RenderPipeline {
public ExampleRenderPipeline() {
}
protected override void Render (ScriptableRenderContext context, Camera[] cameras) {
// Create and schedule a command to clear the current render target
var cmd = new CommandBuffer();
cmd.ClearRenderTarget(true, true, Color.black);
context.ExecuteCommandBuffer(cmd);
cmd.Release();
// Iterate over all Cameras
foreach (Camera camera in cameras)
{
// Get the culling parameters from the current Camera
camera.TryGetCullingParameters(out var cullingParameters);
// Use the culling parameters to perform a cull operation, and store the results
var cullingResults = context.Cull(ref cullingParameters);
}
// Instruct the graphics API to perform all scheduled commands
context.Submit();
}
}
Drawing is the process of instructing the graphics API to draw a given set of geometry with given settings.
To draw in SRP, you do the following:
CullingResults struct.This example code builds on the examples above, and demonstrates how to clear the render target, perform a culling operation, and draw the resulting geometry:
/*
This is a simplified example of a custom Scriptable Render Pipeline.
It demonstrates how a basic render loop works.
It shows the clearest workflow, rather than the most efficient runtime performance.
*/
using UnityEngine;
using UnityEngine.Rendering;
public class ExampleRenderPipeline : RenderPipeline {
public ExampleRenderPipeline() {
}
protected override void Render (ScriptableRenderContext context, Camera[] cameras) {
// Create and schedule a command to clear the current render target
var cmd = new CommandBuffer();
cmd.ClearRenderTarget(true, true, Color.black);
context.ExecuteCommandBuffer(cmd);
cmd.Release();
// Iterate over all Cameras
foreach (Camera camera in cameras)
{
// Get the culling parameters from the current Camera
camera.TryGetCullingParameters(out var cullingParameters);
// Use the culling parameters to perform a cull operation, and store the results
var cullingResults = context.Cull(ref cullingParameters);
// Update the value of built-in shader variables, based on the current Camera
context.SetupCameraProperties(camera);
// Tell Unity which geometry to draw, based on its LightMode Pass tag value
ShaderTagId shaderTagId = new ShaderTagId("ExampleLightModeTag");
// Tell Unity how to sort the geometry, based on the current Camera
var sortingSettings = new SortingSettings(camera);
// Create a DrawingSettings struct that describes which geometry to draw and how to draw it
DrawingSettings drawingSettings = new DrawingSettings(shaderTagId, sortingSettings);
// Tell Unity how to filter the culling results, to further specify which geometry to draw
// Use FilteringSettings.defaultValue to specify no filtering
FilteringSettings filteringSettings = FilteringSettings.defaultValue;
// Schedule a command to draw the geometry, based on the settings you have defined
context.DrawRenderers(cullingResults, ref drawingSettings, ref filteringSettings);
// Schedule a command to draw the Skybox if required
if (camera.clearFlags == CameraClearFlags.Skybox && RenderSettings.skybox != null)
{
context.DrawSkybox(camera);
}
// Instruct the graphics API to perform all scheduled commands
context.Submit();
}
}
}