Of course in PoE2 it's used in full 3d.
The benefit of this approach is that you get global illumination with a constant cost for the entire scene and because it doesn't use any temporal acculation, it has zero latency as well.
This means you can rely on it as the lighting for fast effects. For example: https://www.youtube.com/watch?v=p1SvodIDz6E
There is no traditional "lighting" added to these two effects. The light on the nearby surfaces is indirect light from the GI solution that you get for free by just spawning the particles. That means all effects just naturally emit light with no extra work from artists.
On my GPU (which is admittedly a 4090) the GI solution runs in 0.8ms for a 4k scene in "High" quality. This is exactly what it will always cost, no matter what scene you choose.
Definitely an area that could use more research!
You can gather data in other ways.
Also the article this post links says this is diffuse only.. kinda not so impressive as specular is also very important.
I assume this means they are using a diffuse model that is view direction independent so Lambert.. which is a rather crummy diffuse model.. the better diffuse models are view dependent..
Is the key idea the fact that light intensity and shadowing require more resolution near the light source and lower resolution far from it?
So you have higher probe density nearby the light source and then relax it as distance increases minimising the number of radiance collection points?
Also using interpolation eliminates a lot of the calculations.
Does this make any sense? I'm sure there's a lot more detail, but I was looking for a bird's eye understanding that I can keep in the back of my mind.
There's ambient occlusion that computes light intensity with high spatial resolution, but completely handwaves the direction the light is coming from. OTOH there are environment maps that are rendered from a single location, so they have no spatial resolution, but have precise light intensity for every angle. Cascade Radiance observes that these two techniques are two extremes of spatial vs angular resolution trade-off, and it's possible to render any spatial vs angular trade-off in between.
Getting information about light from all angles at all points would cost (all sample points × all angles), but Radiance Cascades computes and combines (very few sample points × all angles) + (some sample points × some angles) + (all sample points × very few angles), which works out to be much cheaper, and is still sufficient to render shadows accurately if the light sources are not too small.
https://graphicscodex.com/app/app.html
and
https://mini.gmshaders.com/p/radiance-cascades
so I could have a basic grasp of classical rendering theory.
I made some assumptions:
1. There's an isometric top-down virtual camera just above the player
2. The Radiance Cascades stack on top of each other, incresing probe density as they get closer to the objects and players
I suspect part of the increased algorithm efficiency results from:
1. The downsampling of radiance measuring at some of the levels
2. At higher probe density levels, ray tracing to collect radiance measurements involves less computation than classic long path ray tracing
But I'm still confused about what exactly in the "virtual 3D world" is being downsampled and what the penumbra theory has to do with all thus.
I've gained a huge respect for game developers though - this is not eady stuff to grasp.
RC is different, at least in 2D and screen-space 3D. It brute-force traces fixed sets of rays in regular grids, regardless of what is in the scene. There is no attempt to be clever about picking the best locations and best rays. It just traces the exact same set of rays every frame.
Full 3D RC is still too expensive beyond voxels with Minecraft's chunkiness. There's SPWI RC that is more like other real-time raytracing techniques: traces rays in the 3D world, but not exhaustively, only from positions visible on screen (known as Froxels and Surfels elsewhere).
Penumbra hypothesis is an observation that hard shadows require high resolution to avoid looking pixelated, but soft shadows can be approximated with bilinear interpolation of low-res data.
RC adjusts its sampling resolution to be the worst resolution it can get away with, so that edges of soft shadows that are going from dark to light are all done by interpolation of just two samples.
IIUC basically you have a quad/oct-tree of probes throughout the area of screen space (or volume of view frustum?). The fine level uses faster measurements, and the broad level uses more intensive measurements. The number of levels/fineness determines resolution.
I guess for comparison:
- Radiance cascades: complexity based on resolution + view volume; can have leakage and other artifacts
- Ray tracing: complexity based on number of light sources, screen resolution, and noise reduction; has noise
- RTX: ??
- Radiosity: complexity based on surface area of scene
Also not sure, but I guess ray tracing + radiosity are harder to do in GPU?
Depending on your approach the geometry of the scene is completely irrelevant. (Fixed step / DDA truly, JFA + DF has some dependence due to circle marching, but largely independent)
(I recently discovered his channel, and I like his calm down-to-earth explanations of game dev techniques).
An equation given to you will be one of 2 forms usually; the raw equation that may come from optics, in which case expect an ass load of calculus and diff equations with arcane terms not seen outside of Maxwell’s equations. Or, in the likely case, the presenter is a PhD ubermensch nerd who has already pulled the terms out, rewritten them, is presenting them, and you need to be really paying close attention to every single word during their talk to figure it out. It’s at your discretion to determine which of the two forms is easier for you to deal with.
Can someone who's more knowledgeable than myself offer any explanation on why it took so long to discover a method like this? I remember hearing about rt-GI from over 25 years ago.
However, the technique has been used to speed up astrophysics calculations:
I WANT TO GO BAAACK!
Flashbacks to sitting the GRE