4 ms·

Shadows are too sharp, so I don't think they use raytracing.

by olavgg 6y ago

_bxg1 6y ago
It certainly isn't completely raytraced, because current hardware can't support that. If they use the new hardware, they're using it in some kind of mixed mode. Whether that means only for certain materials, or whether they're able to use it to do "fat rays" that approximate only the general direction for indirect light, or whatever else. But direct, hard shadows are quite cheap (comparatively) on today's regular, rasterization-based rendering systems, so that part isn't surprising.
- skohan 6y ago
  It certainly isn't fully path traced, but the result does look to me like they are using ray-traced GI. You can tell by some of the details, like colored bounce lighting which I am not sure can be achieved with this level of detail using other methods. The current standard for getting real-time performance for ray tracing is to limit the number of rays and bounces, and stabilize the results temporally. I.e. to get a "physically accurate" result you would have to send hundreds, or thousands of rays per pixel, and bounce them up dozens or hundreds of times. With this method, instead you send maybe even one or two rays per pixel, which gives you a noisy result. But you store the result, and accumulate it over a number of frames, and apply de-noising, and over time you end up with a high-quality result. I believe that is why when the light moves, the GI lags for a fraction of a second in this demo.
  - longtom 6y ago
    Another trick is in stead of tracing multiple bounces per ray at once, to compute one indirect bounce every n-th frame using intermediate results from the previous (not the current) frame and then spatio-temporally smooth the results, possibly with on-screen bilateral filtering of the past few frames. I think one can see they do this when they move the light source. It takes a while for the indirect bounces to fade out. Perhaps they use screen space ray tracing for this (meaning no indirect bounces for occluded geometry).
skohan 6y ago
Why would sharp shadows rule out raytracing? And how would they achieve this quality of GI without it?
- longtom 6y ago
  Because softer shadows add to the realism, so they would have used them if they had invented a new efficient ray tracing method! Look at 5:12 in the video. The shadows are way too sharp. It's probably good old shadow mapping for the first bounce and then screen space(?) global illumination.

Shadows are too sharp, so I don't think they use raytracing.

by olavgg 6y ago

Shadows are too sharp, so I don't think they use raytracing.

It certainly isn't completely raytraced, because current hardware can't support that. If they use the new hardware, they're using it in some kind of mixed mode. Whether that means only for certain materials, or whether they're able to use it to do "fat rays" that approximate only the general direction for indirect light, or whatever else. But direct, hard shadows are quite cheap (comparatively) on today's regular, rasterization-based rendering systems, so that part isn't surprising.

skohan 6y ago
It certainly isn't fully path traced, but the result does look to me like they are using ray-traced GI. You can tell by some of the details, like colored bounce lighting which I am not sure can be achieved with this level of detail using other methods. The current standard for getting real-time performance for ray tracing is to limit the number of rays and bounces, and stabilize the results temporally. I.e. to get a "physically accurate" result you would have to send hundreds, or thousands of rays per pixel, and bounce them up dozens or hundreds of times. With this method, instead you send maybe even one or two rays per pixel, which gives you a noisy result. But you store the result, and accumulate it over a number of frames, and apply de-noising, and over time you end up with a high-quality result. I believe that is why when the light moves, the GI lags for a fraction of a second in this demo.
- longtom 6y ago
  Another trick is in stead of tracing multiple bounces per ray at once, to compute one indirect bounce every n-th frame using intermediate results from the previous (not the current) frame and then spatio-temporally smooth the results, possibly with on-screen bilateral filtering of the past few frames. I think one can see they do this when they move the light source. It takes a while for the indirect bounces to fade out. Perhaps they use screen space ray tracing for this (meaning no indirect bounces for occluded geometry).

skohan 6y ago

Why would sharp shadows rule out raytracing? And how would they achieve this quality of GI without it?

longtom 6y ago
Because softer shadows add to the realism, so they would have used them if they had invented a new efficient ray tracing method! Look at 5:12 in the video. The shadows are way too sharp. It's probably good old shadow mapping for the first bounce and then screen space(?) global illumination.