In these slides, you will learn the basics to help you get started with ray tracing in Unity 2019.3. Speakers: Soner Sen - Unity Kate McFadden - Unity Dany Ayoub - Unity

2. Getting Started with Ray
Tracing in Unity 2019.3
Dany Ayoub - Technical Artist
Kate McFadden - Senior Demo Artist
Soner Sen - Desktop Graphics Lead

3. Overview
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— Technical details
– DXR
– Acceleration Structure
– Ray tracing shaders
– HDRP integration
— Demo and Samples
— We’re done!

4. How Ray Tracing Works
in Unity 2019.3
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5. DXR Overview
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API designed to leverage hardware-accelerated ray
tracing
Why trace rays?
— Off-screen rendering (reflection, refraction)
— Algorithms that calls for raycasting
Two major concepts to be concerned with:
— Ray Tracing Acceleration Structures:
What are we drawing?
— Ray Tracing Shaders:
How should we draw things?

6. Acceleration Structure
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— Bottom-Level AS: only geometry
— BVH: construction done by driver
— Top-Level AS: Materials,
transforms, hierarchy

7. Acceleration Structure
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— New Unity class: RayTracingAccelerationStructure
— Manually or automatically managed
– Manual: AddInstance(), UpdateInstanceTransform()
— Specify layer masks to filter GameObjects to be added
— Call BuildRayTracingAccelerationStructure once a frame

8. — New Renderer setting: RayTracingMode
— In the order of least to most expensive
– Off
– Static
– DynamicTransform
– DynamicGeometry (WIP)
Acceleration Structure
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9. Ray Tracing Shaders
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— Raytrace shaders
– Raygeneration: First shader executed during dispatch
– Miss: Executes only if ray fails to intersect any object
— Surface shaders
– ClosestHit: Executes for the intersection nearest to ray
origin
– AnyHit: Executes for every intersection
— Callable Shaders

10. Ray Tracing Shaders
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11. — New shader type: RayTracingShader
– Extension is .raytrace
— CommandBuffer API additions
– CommandBuffer.SetRayTracingShaderPass
– CommandBuffer.SetRayTracingAccelerationStructure
– CommandBuffer.SetRayTracing*Param
– e.g. SetRayTracingMatrixParam, SetRayTracingIntParam, etc.
– CommandBuffer.DispatchRays
– Analogous bindings also available from RayTracingShader class
itself, for immediate execution
Ray Tracing Shader API
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12. Ray Tracing Shader Authoring
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// Dispatch shader: Defines at minimum a ray generation shader, often also a miss shader.
// This is the shader that is dispatched, as one would a compute shader,
// for a given ray traced pass.
struct RayPayload { float4 color; uint2 launchIdx; }; // User-defined
[shader(“raygeneration”)]
void FullResRayGen()
{
uint2 launchIdx = DispatchRaysIndex().xy; // DXR callback
uint2 launchDim = DispatchRaysDimensions().xy; // DXR callback
float2 ndcCoords = (launchIdx / float2(launchDim.x - 1, launchDim.y - 1)) * 2 - float2(1, 1);
float3 viewDirection = normalize(float3(ndcCoords.x * aspectRatio, ndcCoords.y, -1);
RayDesc ray; // DXR defined
ray.Origin = float3(camera_IV[0][3], camera_IV[1][3], camera_IV[2][3]);
ray.Direction = normalize(mul(camera_IV, viewDirection));
ray.TMin = 0;
ray.TMax = 1e20f;
RayPayLoad payload;
payload.color = float4(0, 0, 0, 0);
TraceRay(accelerationStructure, 0, 0xFF, 0, 1, 0, ray, payload); // DXR callback
}
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13. Ray Tracing Shader Authoring
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[shader(“miss”)]
void SampleSkybox(inout RayPayload payload : SV_RayPayload)
{
rayDirection = WorldRayDirection();
float4 skyboxColor = skyboxTex.SampleLevel(linearRepeatSampler, rayDirection, 0);
payload.color = skyboxColor;
}
// These slides have a good introduction to built-in DXR callbacks:
// http://intro-to-dxr.cwyman.org/presentations/IntroDXR_RaytracingShaders.pdf
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14. Surface Shader Authoring for Ray Tracing
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// Material/Surface shader: Hit shaders should be defined as a pass in a shader used for a
// material in the scene.
Shader “FlatColor”
{
SubShader { Pass { CGPROGRAM
#pragma vertex vert
#pragma fragment frag
v2f vert (appdata v) { return UnityObjectToClipPos(v.vertex); }
fixed4 frag (v2f i) : SV_Target { return albedo; }
ENDCG
} }
SubShader { Pass Name "DefaultRTPass" { HLSLPROGRAM // Pass name must match that specified
by SetShaderPass()
#pragma raytracing
struct AttributeData { float2 barycentrics; }; // User-defined
[shader(“closesthit”)]
void FullResRayGen(inout RayPayload payload : SV_RayPayload,
AttributeData attribs : SV_IntersectionAttributes)
{ // A trivial hit shader that populates a bound RT with albedo of hit object
payload.color = albedo;
outputRT[payload.launchIdx] = albedo;
} ENDHLSL
} }
}
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15. — Windows 10 v1809+
— Unity 2019.3b1+
— DXR capable graphics card with
latest drivers
Requirements for Ray Tracing
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Unity > Edit > Project Settings > Player:
— Select DX12 as Windows Graphics
API

16. State of Ray Tracing in Unity
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— Ray tracing API is pipeline-agnostic
– Officially supported for only HDRP
– HDRP is the only pipeline that actually implements features using ray
tracing
– Users can still use the public C# API to build their own features!
— Unsupported in 19.3:
– Intersection shaders
– Animated meshes
– Procedural geometry

17. HDRP Ray Tracing Architecture
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— Primary rays for most effects are computed from depth/normal buffers
— Cluster-based lighting added to HDRP for ray tracing
— Render graph here is simplified and omits many HDRP stages

18. TransparencyShadowsIndirect Lighting
Ray Traced Effects on HDRP
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19. Thank You!
Any Questions?
dany@unity3d.com
katem@unity3d.com
soner@unity3d.com

20. Want to learn more?
Project:
Unity Lighting Fundamentals
Tutorial:
Post-Processing Effects
(2018.x+)
Tutorial:
HDRP Material Properties
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