{"id":49788,"date":"2020-04-21T06:00:05","date_gmt":"2020-04-21T10:00:05","guid":{"rendered":"https:\/\/www.shamusyoung.com\/twentysidedtale\/?p=49788"},"modified":"2020-04-21T13:14:15","modified_gmt":"2020-04-21T17:14:15","slug":"adventures-in-raytracing","status":"publish","type":"post","link":"https:\/\/www.shamusyoung.com\/twentysidedtale\/?p=49788","title":{"rendered":"Adventures in Raytracing"},"content":{"rendered":"

In the previous entry I ended with an abrupt half-joke where I said I got raytracing working. The idea was that I spent days struggling to get simple old technology working properly, but then casually mastered cutting-edge tech in a single sentence. Sadly, it’s not totally true. I got access to raytracing, but I think it’s a stretch to say it’s “working”.<\/p>\n

When I left off, I presented you with an image that looked more or less like this:<\/p>\n

I've fiddled with the lighting \/ textures \/ render settings since the last entry, which is why this looks different than it did a few days ago. This is still the same room \/ viewing angle we've been looking at all along.<\/div>
I've fiddled with the lighting \/ textures \/ render settings since the last entry, which is why this looks different than it did a few days ago. This is still the same room \/ viewing angle we've been looking at all along.<\/div><\/p>\n

That’s what the program looks like when you leave it alone, but if you move the camera even slightly then it looks something like this: <\/p>\n

I know this looks bad in still frame, but trust me: It's actually way worse in motion.<\/div>
I know this looks bad in still frame, but trust me: It's actually way worse in motion.<\/div><\/p>\n

To a certain extent, this is expected. This is what you get with raytracing \/ path tracing. Even on the cutting-edge magic hardware we have these days, you still don’t get more than a few thousand rays per frame. We get around this with two techniques:<\/p>\n

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  1. We take the little bit of data available and spread it out. I’m not sure of the exact algorithm used, but it’s probably something like “if you’re rendering a spot that hasn’t been hit with ANY rays, then use the nearest available one”. So those existing pixels of light would get smeared out to fill the gaps. This means that the lighting starts out “blurry”. The walls and textures remain crisp, but the patterns of light and dark are initially vague. This gives the images a kind of “dreamy” quality.<\/li>\n
  2. We accumulate rays over multiple frames. Each frame adds a few more rays to the scene, gradually filling things in and sharpening up the lighting. This means the room is initially dark if the whole thing enters the frame abruptly. The room starts out dim, and then gradually lightens as more light rays are added. You’d think this would look wrong, but it ends up feeling like your eyes adjusting when you enter a dark room. This works even if the previous room and this new one are supposed to be the same level of brightness. You can run back and forth between the two rooms, and it will always feel like you’re moving from a brighter room to a dimmer one. It seems to be one of those tricks that your brain just ignores.<\/li>\n<\/ol>\n

    As far as I can tell, these features are collectively called “denoising”. In the Quake 2 RTX demo<\/a>, there’s a console command to turn denoising off and allow you to see the raw images with low ray counts, like my image above. The problem I’m having in Unity is that I can’t find either of these features. There are a few possibilities:<\/p>\n

      \n
    1. Denoising hasn’t been implemented. I’m using a preview version of Unity for this projectUnity is REALLY graceful about letting you have several different versions installed simultaneously, and it keeps track of which projects belong with which versions. It’s pretty great.<\/span> and it’s possible that denoising is still on someone’s to-do list.<\/li>\n
    2. The denoising in the Quake 2 demo is an implementation of a very NVIDIA-specific feature. Maybe the Unity team wants to avoid manufacturer-specific gimmicks like that and aim for generalized solutions. Therefore, this is as good as it’s going to get until NVIDIA and AMD embrace some sort of standard. That will probably take months or years.<\/li>\n
    3. The denoising feature exists, but it’s not documented and so I have no way of knowing where to find it or how to use it.<\/li>\n<\/ol>\n

      Normally I’m hard on the Unity team for the state of their documentationParticularly this ludicrous habit of documenting important things inside of hour-long video presentations. Arg. My rage is boundless.<\/span>, but in this case I’m obliged to cut them some slack. It’s called a “preview” version for a reason, and documentation is usually the last step. It’s annoying to have to fumble around in the dark like this, but that comes with the territory if you’re messing around with beta software.<\/p>\n

      Soon, or Never?<\/h3>\n