If you like what I do and want to support me and this project(as this takes a LOT of my time), consider becoming a Github Sponsor!

Notes:
Currently working on:

Volumetric voxels, looking for ways to make it faster or be able to precompute individual light contributions
Looking desperately for optimizations(let me know if you have any ideas)

Currently needs to be done but havent implemented fully:

Volumetric Clouds(struggling, they look garbage)

Currently want to do but havent started:

Need More Ideas

Compute Shader Based Unity PathTracer

A passion projects that has been going on for awhile with the goal of bringing at least interactive pathtracing to everyone in unity, regardless of their hardware

Features:

Fast Compute Shader based path tracing
Diffuse, Diffuse Transmission, Emissive, Plastic, and Disney BSDF materials
Ability to move, add, and remove objects during play
Ability to update material properties on the fly during play
ASVGF and SVGF Denoiser
Compressed Wide Bounding Volume Hierarchy as the Acceleration Structure (See Ylitie et al. 2017 below)
PBR Texture Support
Next Event Estimation with Multiple Importance Sampling for Explicit Light Sampling
Support for default unity lights which interact via NEE(Supports Directional, Point Spot, and Area lights)
Bloom
No specific GPU vendor needed(this will run on integrated graphics if you so wish it, aka no RTX cores)
MagicaVoxel support
Ability to pathtrace voxels and triangle scenes at the same time
Depth of Field
AutoExposure
Temporal Anti-Aliasing
ReSTIR for better sampling of many lights
Precomputed Multiple Atmospheric Scattering for dynamic and realtime sky(from ebruneton below)
Object Instancing
ReSTIR GI for faster convergence in complex scenes and more complete images in scenes with changing lighting

Ylitie et al
ebruneton

If you have any questions, or suggestions, etc. let me know either through github issues or my twitter or my discord! I am always looking for more stuff to add, and more ways to make it more user friendly or appealing for others to use

You can contact me easiest through my discord: Pjbomb2#6129, or my Twitter: https://twitter.com/Pjbomb2

Notes:

Let me know if you use this for anything, I would be excited to see any use of this! Just please give some credit somewhere if you use it, thank you!

Requires Unity 2021 or higher

Instructions:

Required Settings Changes:

Set the Color Space to Linear through Edit Tab(Top Left) -> Project Settings -> Player -> Other Settings -> Color Space, and change from Gamma to Linear
Enable Unsafe Code(Its for memory management) through Edit -> Project Settings -> Player -> Other Settings -> "Allow 'unsafe' Code" (near the bottom)
Change the Graphics Api for Windows to DirectX12 through Edit Tab(Top Left) -> Project Settings -> Player -> Other Settings -> Untoggle "Auto Graphics API For Windows", then click the little + that appears, select "Direct3D12(Experimental)", and drag that to the top. A restart of the editor is required

General Setup

Download and import the UnityPackage provided and open the new Pathtracer Settings at the top of the screen(This WILL re-arrange your hierarchy a bit)
Whenever you add a new object(or tree of objects), you need to add it to under the gameobject named Scene, and its reccomended you press quickstart to automatically assign the needed scripts to it
I highly reccomend you use 1920x1080 or higher, dont use free resolution

Basic script structure breakdown:

Top Level is a gameobject called Scene with an AssetManager script attatched
Second Level: Parent Object Script - Attatch this to all objects that will have children with meshes you want to raytrace(can be a child to any gameobject as long as its eventual parent is the AssetManager script)
Third Level: RayTracingObject Script - This defines what meshes get raytraced, must either be a direct child of a gameobject with the ParentObject Script, or in the same gameobject as the ParentObject Script
Misc Level: Unity Lights - Must have a RayTracingLight script attatched to be considered(and UseNEE needs to be on), can be ANYWHERE in the hierarchy, only supports Point, Spotlight, and 1 Directional

General Use/Notes

The green/red rectangle shows when the acceleration structure is done building, and thus ready to render, red means that its not done, and green means its done building
Objects can be added and removed at will simply by toggling the associated gameobject with a ParentObject script on/off in the hierarchy(clicking on parent objects with complex objects for children will lag), but they will take time to appear as the acceleration structure needs to be rebuilt for them
If you change the emissiveness of an object, you need to disable and re-enable its parent(basically reloading it) if you want to take advantage of NEE correctly sampling it(Does not need to be reloaded for Naive tracing)
If you use normal maps, they need to be in unity normal map format
To set up PBR with the default material, all textures go into their proper names, but Roughness goes into the Occlusion texture(Since path tracing gets ambient occlusion by default)
If you are using blendshapes to change geometry of a skinned mesh, you may need to go to the import settings of it(in the inspector), turn off Legacy Blendshape Normals, and make sure all normals are imported, not calculated, otherwise the normals for blendshapes might be wrong

MagicaVoxel Usage

Before anything, the files need to be in .txt format, to do this, go to the file in file explorer, and rename the .vox to .txt and change the format
Firstly, you still need to have a gameobject under the scene gameobject to attatch your voxel model to
Second, you need to attatch a VoxelObject to that gameobject(Located under Assets->Resources->BVH->VoxelObject)
Next you need to attatch the voxel model to this script, by dragging your voxel model asset in the project tab to the VoxelRef space in the VoxelObject script

Using Instancing

First, there needs to be a gameobject called InstancedStorage in the scene with the InstanceManager attatched to it as a sibling object of the Scene gameobject(this is automatically created on initial start of the scene and pathtracing settings)
Second, all objects that will be the source of instanced objects will need to go under the InstancedStorage and can be arranged like normal objects(with regards to the layout of parentobject to raytracingobjects)
Finally, to instance the objects, you just need gameobjects with the InstanceObject script attatched to them under the Scene gameobject, and then drag the desired object instance from the hierarchy to the Instance Parent slot in the InstanceObject script(all of this is displayed in the demoscene)

Linking your own Materials

So this isnt how to use your own materials, this is how to take your material, and have the textures assign properly
Firstly, all material links are defined under Resources -> Utility -> MaterialMappings; On the first time running with a new material, a basic definition for it will be created at the bottom of this file
Secondly, all data that you need for this is gotten from clicking on the material you want to add support for in unity, going to the inspector, pressing the 3 dots in the top right, and then Select Shader
Then, you need to expand the arrow called "Properties", and the names on the left side will be the names you need to enter into the MaterialMappings file
From here, you need to look at the names on the right side of the list under the properties dropdown, and match what the variable is doing to the texture/range name on the left
For example, for the Standard Shader/Material, if on the right theres an entry called "Metallic (Range)", you know this is the metallic float variable, so you take the name on the left of this, which in this case is "_Metallic". Copy the "_Metallic", go to the MaterialMappings xml file, find your material by its shader name, find the corropsponding variable (in this case we are looking for MetallicRange), and replace the "null" with "_Metallic"
Doing this will indicate that the slider property "Metallic" in the materials UI(the slider you directly interact in unity if you click the material) is actually the Metallic property in my own material, and should be set to the same value

Controls:

Camera Controls: WASD, Mouse, and press T to freeze/unfreeze the camera(Camera starts frozen), and shift increases speed

Editor Window Guide

BVH Options Description -

Build Aggregated BVH(Recommended to do any time you change objects in edit mode)- Allows you to pre-build objects BVH's before running so you dont have to wait every time you go into play mode for it to build.
Clear Parent Data - Clears the data stored in parent gameobjects, allowing you to actually click them without lagging(but will then require the BVH to be rebuilt)
Take Screenshot - Requires a folder called Screenshots under the asset folder, takes a screenshot
QuickStart - Assigns all required scripts to all objects under the Scene gameobject, best way to add objects
Make All Static - Utility button that takes all objects in the scene and puts them under one parent object, not reccomended for general use
Force Instances - Looks at all meshes in the scene, sees what objects have the same meshes, and makes them into instances, keep in mind instances use the same material and textures
Remaining Objects - Objects still being processed
Max Bounces - Sets the maximum number of bounces a ray can achieve
Render Scale - Render scale in comparison to gameview size, turn to below 1 while in edit mode to decrease rendered resolution(to then be upscaled)
Atlas Size - Maximum size of the texture atlas used(All textures are packed into atlas's so I can send them to the GPU)
Use Russian Roulette - Highly reccomended to leave this on, kills rays that may not contribute much early, and thus greatly increases performance
Enable Object Moving - Allows objects to be moved during play, and allows for added objects to spawn in when they are done building
Allow Image Accumulation - Allows the image to accumulate while the camera is not moving
Use Next Event Estimation - Enables shadow rays/NEE for direct light sampling
Allow Mesh Skinning - Turns on the ability for skinned meshes to be animated or deformed with respect to their armeture
Allow Bloom - Turns on or off Bloom
Enable DoF - Turns on or off Depth of Field, and its associated settings
Enable Auto/Manual Exposure - Turns on or off Auto Exposure(impacts a lot more than I thought it would)
Use ReSTIR - Enables the much better sampling for lots of lights
Allow ReSTIR Sample Regeneration - Applies if Precomputed Sampling is on, Regenerates the light samples every frame
Allow ReSTIR Precomputed Sampling - Samples lights in a more efficient way but introduces artifacts due to sample correlation
Allow ReSTIR Temporal - Enables the Temporal pass of ReSTIR(allows samples to travel across time
Allow ReSTIR Spatial - Enables the Spatial pass of ReSTIR(Allows pixels to choose to use the neighboring pixels sample instead)
ReSTIR Spatial M-Cap - Tuneable parameter, increase this if you have lots of lights(standard values would be between 32 and 640 for reference, but going higher or lower is needed at times)
Use ReSTIR GI - Enables ReSTIR GI which is usually much higher quality
Do Sample Connection Validation - Confirms that two samples are mutually visable and throws it away if they are not
Update Rate - How many pixels per frame get re-traced to ensure they are still valid paths
Enable Temporal - Enables the Temporal pass of ReSTIR GI(allows samples to travel across time
Temporal M Cap - How long a sample may live for, lower means lighting updates faster(until 0 which is the opposite) but more noise(reccomended either 0 or around 12, but can be played with)
Permute Temporal Samples - Turns on permutation sampling, can lead to much higher quality much faster, but a lower M cap is reccomended(around 3-12)
Enable Spatial - Enables the Spatial pass of ReSTIR GI(Allows pixels to choose to use the neighboring pixels sample instead)
Spatial Sample Count - How many neighboring pixels are looked at
Enable Spatial Stabalizer - Rarely useful, but turns spatial into spatiotemporal
Use Temporal Antialiasing - Enables Temporal Antialiasing(TAA)
Use SVGF Denoiser - Turns on the SVGF denoiser
(If SVGF Denosier is on)Atrous Kernel Size - The amount of times the SVGF denoiser runs through the Atrous kernel
Use ASVGF Denoiser - Turns on the ASVGF denoiser
(If ASVGF Denoiser is on)ASVGF Atrous Kernel Size - The amount of iterations the final ASVGF atrous goes through, limited to 4, 5, and 6
Enable Tonemapping - Turns on Uchimura Tonemapping
Enable TAAU - Use TAAU for upscaling(if off, you use my semi custom upscaler instead)
Atmospheric Scatter Samples - Lower this to 1 if you keep crashing on entering play mode(controls how many atmospheric samples are precomputed)
Current Samples - Shows how many samples have currently been accumulated

Materials(RayTracingObject script)

Selected Material - Selects which material you want to edit on the mesh
Material Type - Select your type of material you want(You usually want Disney, its the most versatile)
Base Color - If theres no Albedo Texture, this is the color the object will be
Emission - The emittance of an object(how much light it gives off)
Emission Color - Changes the color of emissive objects, most useful when you have an emission mask on an object
Roughness - Roughness of the object

Disney BSDF Only Properties

IOR - Index of Refraction of an object. Affects only Disney BSDF
Metallic - How metallic an object is. Affects only Disney BSDF
Specular - Adds specular reflection to an object, use in conjunction with Roughness and IOR. Affects only Disney BSDF
Specular Tint - Weights color more towards the objects color for specular reflections. Affects only Disney BSDF
Sheen - Adds Sheen to objects. Affects only Disney BSDF
SheenTint - Allows you to choose if an objects sheen is white or is that objects base color. Affects only Disney BSDF
ClearCoat - Adds a Clearcoat effect to the object. Affects only Disney BSDF
ClearCoatGloss - Influences the Clearcoat. Affects only Disney BSDF
Anisotropic - Makes the material(mostly metallic and specular) anisotropic. Affects only Disney BSDF
Specular Transmission - Makes an object more or less like glass. Affects only Disney BSDF(Play with the IOR for this)
Diffuse Transmission - Makes an object Diffuse but Transmissive(transluscent). Affects only Disney BSDF
Transmission Color - Doesnt do anything for now, used for volumetric disney bsdf(which is not yet implemented)
Flatness - Affects Thin objects. Affects only Disney BSDF
Thin - Marks an object as thing so it can be better handled by the BSDF. Affects only Disney BSDF, can be either 0 or 1

Known Bugs:

Error that RayTracingShader is using too many UAV's. This isnt really a bug, but happens because you cant disable DX11 which doesnt allow more than 8(whereas DX12, which is actually used, allows a lot more), so it yells at you for a non-issue

Sample Images(Taken from various stages of development)

Credits(will continue to expand when I have time)

Biggest thanks to Zuen who helped me a huge amount with the new BVH and traversal, thanks to them I got to where I am now, and I am very thankful to them for their help and patience
https://github.com/jan-van-bergen

Scenes From:

Disney BSDF from: https://schuttejoe.github.io/post/disneybsdf/ Rectangle packer for faster atlas creation from here: https://github.com/ThomasMiz/RectpackSharp/tree/main/RectpackSharp

Ideas/Reminders for later

Reduce memory consumption, work on adding back in Mitsuba scene support

Pjbomb2 / Realtime-Compute-Shader-Unity-PathTracer