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TOPIC: Ray Tracing with Reshade - Unofficial Guide

Ray Tracing with Reshade - Unofficial Guide 3 weeks 1 day ago #1



I just designed the graphics, which is just temporary by the way, but I don't remember who provided me the screenshots.
If you're the one who gave me the screens, give me a shout.


Since Ray Tracing is now on everyone's lips, I thought it was a good time to make a dedicated Guide on ReShade's official forum to help all those people (and not only) who are discovering or rediscovering ReShade thanks to this shader.


So, I read a lot of people having confused ideas on the internet about Marty McFly's GI shader and Ray Tracing in general.
"This is not real ray tracing" | "Just a large radius ambient occlusion" | "Fake cause it works in screen space, unlike Nvidia's RTX"
With this guide I hope to shed some light on this.

For Newcomers: I suggest you to take a look at ReShade guide for newcomers, that can help you to get over the first steps.


What is PTGL?
PTGL stands for Path Traced Global Illumination. Developed by Marty McFly, qUINT-RT it is an upcoming shader which make use of this technique to bring real time path traced global illumination to almost every games through ReShade.
Ray Tracing is a rendering technique that aims to produce more physically correct images compared to rasterizzation, the method known for its ability to render 3d scenes in a very fast way.
For that reason this last one is used in the overwhelming majority of the games.

What we are witnessing are the first games featuring hybrid rendering: Games are still rendered with the fastest rasterization technique, except for some graphics elements which are ray traced, like shadows, reflections or global illumination.


How does it work?
In real life a light source emits several rays. These rays travel until they reach an object, where, depending on its scattering properties, they bounce from till our eyes catch them.
Ray Tracing works more or less in the opposite way: Rays are traced starting from the digital camera, and, once they meet an intersection point, they send new rays to every light sources.
Path Tracing work in a similar way, but, when rays reach an intersection point, they act more in a life-like way: They keep bouncing through objects getting, consequently, more precise informations till they reach light sources..

Ray Tracing Scheme                                                                                                    Path Tracing Scheme

source: docplayer.net


Please Note: qUINT-RT is currently in its alpha build. Consider this guide in alpha state, too, and expect changes in the future.
Last Edit: 2 weeks 4 days ago by Duran.te.
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RT Guidebook - A ray traced Guide to Ray Tracing 3 weeks 1 day ago #2

Which games are supported by this shader?
The shader is not restricted to a limited amount of games.
Every game ReShade can inject into (and get depth buffer) is supported.
That's the power of generic post processing!


Requirements
First, you need the game to be API-compatible with ReShade.
Vulkan only games, for example, are excluded, as ReShade can't inject into them.

You also need depth buffer access, since qUINT-RT, like every depth based shaders, requires it to work properly.
Check Daodan's display depth guide for more information about how depth works in ReShade.


Is this real Ray Tracing?
This question probably comes from the comparison people are making with Nvidia Ray Tracing.
Nvidia's method takes advantage of out of screen information to calculate light, shadows or reflection, depending on the game. Marty's shader can just use screen space information provided by ReShade, such as color and depth buffer, but the rendering method used to calculate, in this case, global illumination is the same.

So yes, this is real ray tracing, working in screen space, but still not fake.


Nvidia RTX graphics cards related questions
  -Do I need an Nvidia RTX card to make it work?
No, you will be able to use this with any cards, for the delight of GTX / AMD owners.

  -Will I get benefits in terms of performance with an RTX card?
No, qUINT-RT does not uses RT cores from newest Nvidia GPUs to make it run better.


How can I try it?
Right now, the shader is in alpha state and it's not available for the public yet.
Once it'll reach its final build, it will likely be available to everyone for free.

The alpha version of this shader is avaiable to all Pascal "Marty McFly" Gilcher's patreons.
Since right now the shader is still in alpha build, you'll need to join the $20 Tier, as shown on Pascal's page.
Pascal Gilcher Patreon page: www.patreon.com/mcflypg


About Performance
Real time path tracing rendering is an exhausting work for hardware. This inevitably leads to a huge impact of performance.
Not much can be done about it for now, except for some minor tweaking.
Ray Amount and Ray Step Amount are the general parameters for path tracing quality, but they're also the responsible for performance decrease.

You can think at Ray Amount as a parameter responsible of precision. If you wanna trade as less quality as possible in favour of performance, this is the first one you should think to decrease.
Seems like  ♫ 3 is the magic number ♫  for most of qUINT-RT users.

Ray Step Amount also helps getting some performance boost when decreased, but it also causes the most quality lost.
Values under 6 are not recommended.

Just like MXAO, this new shader comes with adjustable mip levels for both Ambient Occlusion and Indirect Lighting textures. You can check these informations in your shader file. The lower the values are, the better quality you get: raise up these parameters to get a little bit of extra performance. Click on Edit Global Preprocessor Definitions and type there your interested values to edit them.


About Noise
  - Why I'm getting the screen noisy when qUINT-RT is enabled?
This is caused by the random sampling nature of path tracing algorithm.
It's a side effect you always come up against while dealing with this rendering method.
The reason you don't see this in Nvidia's Ray Tracing is 'cause it uses a proprietary denoise filter based on AI.

  - What can I do?
The higher the Ray Amount you have, the less noise you get.
However it won't solve noise completely, especially in motion, plus you'll get a notable decrease in performance.

A common way being used to deal with the problem is to apply FXAA anti aliasing after GI shader is rendered: just drag FXAA below qUINT-RT and play with its values at the point you reduce noise without loosing too many details in the overall image.
You can use a denoise shader in addition to reduce noise further, as well.
Last Edit: 2 weeks 3 days ago by Duran.te.
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RT Guidebook - A ray traced Guide to Ray Tracing 3 weeks 1 day ago #3

I would add that you can also play around with the miplevel for both the AO and IL in the shader file for very noticeable performance benefits. The "infinite bounces" parameter is pretty interesting as well, but very demanding.
Last Edit: 3 weeks 1 day ago by Riadon.
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RT Guidebook - A ray traced Guide to Ray Tracing 3 weeks 16 hours ago #4

Thanks for the advice!
I'll provide to add these information also, as detailed as possible, as soon as I can.

Unfortunately, being a student and not being able to afford economic support to Pascal's work, doesn't help me in making this guide. :lol:
I'll keep searching online infos about it.
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RT Guidebook - A ray traced Guide to Ray Tracing 2 weeks 6 days ago #5

Great guide. I'd clarify that it's currently only available to alpha backers in the 20$ tier. Though that's already implied by mentioning the shader being in alpha state the line "The alpha version of this shader is avaiable to all Pascal "Marty McFly" Gilcher's patreons" sounds like someone might think 1$ is enough. Deffo not available to "all" patrons.
Also because I just noticed "The more ray amount you have, the less noise you get." should be "The higher the ray amount [...]". But keep up the good work.
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RT Guidebook - A ray traced Guide to Ray Tracing 2 weeks 6 days ago #6

Thanks, Uncle Crassius!
Patreon information was added, as well as the "ray amount" line was corrected.
Riadon's performance advice are now included.
Last Edit: 2 weeks 3 days ago by Duran.te.
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