3 ms·

Is this ray tracing or path tracing? I'd think that real-time path tracing would still be hard/impossible in real-time considering the number of samples, but I'

Is this ray tracing or path tracing? I'd think that real-time path tracing would still be hard/impossible in real-time considering the number of samples, but I'm not sure. People throw around these terms interchangeably which complicates the discussion, though the algorithms have notable departures from each other.

crote 8y ago
0:36 in the video, "all based on path tracing". Easy tell: the soft shadows, volumetric lighting, indirect lighting, complex shaders. Some of it could probably be faked, but it's trivial with path tracing. About speed: it's still very hard to do real-time, but it seems like denoising algorithms are getting good enough that it's getting doable. Keep in mind that it is a game, so small graphical glitches aren't that big of a deal.
seanalltogether 8y ago
I thought path tracing was just ray tracing with additional random scatters traced, is it not?
- dahart 8y ago
  Depends on who you ask, the term is overloaded now. These days, it does tend to mean doing global illumination using ray tracing. Originally, the term “path tracing” was used to refer to taking a single random scatter at every step along a path of connected segments, as opposed to the idea of taking multiple random scatters at a point and averaging them, recursively. It’s a way of thinking of Monte Carlo rendering as taking one sample in a very high dimensional space - where a chain of ray segments, or “path” is a single sample - rather than thinking of each ray segment separately as a sample. Ray tracing, FWIW, can sometimes refer to situations where you’re not even rendering. It has a more general meaning of doing line based visibility queries, which you can use for lots of things.
  - hellofunk 8y ago
    If I’m not mistaken, for your last paragraph, general visibility tests for lines that does not otherwise involve actual rendering is typically just called ray casting.
    - dahart 8y ago
      You’re not mistaken, ray casting would be more common, but ray tracing is also used. This is especially true among people that design path tracing renderers where we consider “ray tracing” to be a visibility primitive. “Trace a ray” and “cast a ray” are synonymous. I also think using “ray tracing” for visibility might start become more popular now with RTX hardware since the “ray tracing” hardware only provides the visibility test, not a renderer.
- kuzehanka 8y ago
  In the realtime graphics world, Ray tracing = initiate rays from light sources, bounce them around, accumulate them on camera. This is accurate but incredibly inefficient. This is how pre-baked light mapping and GI works. Path tracing = initiate rays from camera, induce bounce rays toward light sources. Not quite as accurate but orders of magnitude mode efficient in terms of producing an acceptable image.
  - hellofunk 8y ago
    This is confusing and not true. The RTX is specifically referred to as "ray tracing" but no one does forward ray tracing which is what you are referring to. Both general Ray Tracing and Path Tracing involve "backwards ray tracing", starting from the camera. The distinction is not where the ray originates, its the algorithm for generating and following those rays.
    - kuzehanka 8y ago
      This guy is right. I have been inadvertently perpetuating a misconception for the last 5 years.

crote 8y ago

0:36 in the video, "all based on path tracing". Easy tell: the soft shadows, volumetric lighting, indirect lighting, complex shaders. Some of it could probably be faked, but it's trivial with path tracing. About speed: it's still very hard to do real-time, but it seems like denoising algorithms are getting good enough that it's getting doable. Keep in mind that it is a game, so small graphical glitches aren't that big of a deal.

seanalltogether 8y ago

I thought path tracing was just ray tracing with additional random scatters traced, is it not?

dahart 8y ago
Depends on who you ask, the term is overloaded now. These days, it does tend to mean doing global illumination using ray tracing. Originally, the term “path tracing” was used to refer to taking a single random scatter at every step along a path of connected segments, as opposed to the idea of taking multiple random scatters at a point and averaging them, recursively. It’s a way of thinking of Monte Carlo rendering as taking one sample in a very high dimensional space - where a chain of ray segments, or “path” is a single sample - rather than thinking of each ray segment separately as a sample. Ray tracing, FWIW, can sometimes refer to situations where you’re not even rendering. It has a more general meaning of doing line based visibility queries, which you can use for lots of things.
- hellofunk 8y ago
  If I’m not mistaken, for your last paragraph, general visibility tests for lines that does not otherwise involve actual rendering is typically just called ray casting.
  - dahart 8y ago
    You’re not mistaken, ray casting would be more common, but ray tracing is also used. This is especially true among people that design path tracing renderers where we consider “ray tracing” to be a visibility primitive. “Trace a ray” and “cast a ray” are synonymous. I also think using “ray tracing” for visibility might start become more popular now with RTX hardware since the “ray tracing” hardware only provides the visibility test, not a renderer.
kuzehanka 8y ago
In the realtime graphics world, Ray tracing = initiate rays from light sources, bounce them around, accumulate them on camera. This is accurate but incredibly inefficient. This is how pre-baked light mapping and GI works. Path tracing = initiate rays from camera, induce bounce rays toward light sources. Not quite as accurate but orders of magnitude mode efficient in terms of producing an acceptable image.
- hellofunk 8y ago
  This is confusing and not true. The RTX is specifically referred to as "ray tracing" but no one does forward ray tracing which is what you are referring to. Both general Ray Tracing and Path Tracing involve "backwards ray tracing", starting from the camera. The distinction is not where the ray originates, its the algorithm for generating and following those rays.
  - kuzehanka 8y ago
    This guy is right. I have been inadvertently perpetuating a misconception for the last 5 years.