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Excellent response by Carmack. "Ray Tracing" has always been an overhyped or misunderstood technology, at least in my experience. Because of the impressive lig

Excellent response by Carmack. "Ray Tracing" has always been an overhyped or misunderstood technology, at least in my experience. Because of the impressive lighting effects it's famous for producing, people view it as some "holy grail" of superior computer graphics technology that we just need to optimize a bit for use in games. As Carmack described, those highly realistic ray traced renders come at a price: billions of ray calculations. You don't get all that pixel-perfect refraction, etc. for free (and probably never will - at least not with ray tracing.) He also explains that for most people, this (e.g. pixel perfect refraction) really doesn't matter, when rasterization techniques exist that achieve extremely high quality approximations at a fraction of the computational cost. Conversely though, ray tracing and related concepts (ray casting) are not at all without value. Many modern video games today actually use a sort of hybrid rasterization / ray casting approach. Macrostructure objects are rasterized the normal way, while smaller high resolution detail patterns (like a brick wall, or stones in the ground) are "added" to surfaces via per-pixel displacement mapping, which is ray casting at its core. This is one of the few cases where you can take advantage of the "log2" efficiency Carmack mentioned -- in a highly specialized implementation without a huge time constant.

ChuckMcM 14y ago
Pretty much agree, the only thing that we might disagree on is the 'billions' number, while I expect good ray tracing to trace billions of rays, if transistors are cheap enough this becomes more interesting. The typical HDMI 1080p display is 2 megapixels (or megatexels) if you have a rendering engine with 2,073,600 cores each of which is looking at a billion ray 'view' based on where it sits in the scene, its easier to set up the scene and light it. That presumes that you can do those cores like DRAM instead of like current processors of course. My point is that cheap transistors keep amazing me and whenever I say "Oh that will never happen" some fool goes and shows me I'm wrong. I'm trying to imagine how complex a 'core' would be that computed the incident rays on a single pixel. Then figuring out how big that is in a 18nm process technology and then trying to see if I can fit 2M on a reasonable size die. My head exploded sadly.
- yk 14y ago
  Throwing more ( or finer etched) silicon at an algorithm will not help the algorithm, compared to a superior algorithm. For almost all scenes you get better results with rasterization, the two exceptions I can think of is scenes where the geometry of light rays is not flat, so for example involving lenses or black holes, or where there is a lot more optical complexity than you can reasonably use. ( A forest where each of the leafs is an object, you will never be able to notice that the advantage of this over an forest where the trees in the background are just textures.)
  - Osmium 14y ago
    e.g. mirrors?
    - yk 14y ago
      Yes, but it perhaps more instructive to think of a curved mirror. In case of a raster engine, you need to calculate a texture for every triangle of the mirror. ( Which is essentially the same as rendering the scene in the first place.) On the other hand for a ray tracing engine you just need to reflect one ray on the mirror surface for every pixel the mirror occupies in the final rendering. So compared to the same scene with a window instead of the mirror, you just need to calculate one additional reflection instead of running the entire rendering pipeline again.
      - willvarfar 14y ago
        I think John says not just one ray per pixel?
        yk 14y ago
        Yes, I was essentially using one ray per pixel as shorthand for constant amount of rays per pixel. (As in 'I did not think about that point.') One needs more than one to avoid creating artifacts like aliasing ( see [1] for a very nice example), or depending on how 'naive' or complex the algorithm is for stuff like shadows or caustics. But for nice scenes (which do not create artifacts) with mirrors and lenses, one ray per pixel would work fine. [1] https://en.wikipedia.org/wiki/Aliasing https://en.wikipedia.org/wiki/Aliasing
yk 14y ago
I think people rather think of ray-tracing as much better motivated by physics ( and intuition) compared to all the complicated matrices in raster engines. Instead of thinking it is superior because of some demos.
- InclinedPlane 14y ago
  An even more physics based rendering method is called radiosity, but it's also hugely computationally intensive.
  - Tloewald 14y ago
    Physically Based Rendering - often GPU accelerated - is the new thing -- check out Octane Renderer, Lux-Render, Indigo, the Cycles renderer in Blender. These renderers start at the light source and stochastically generate and follow photons. Like a digital camera they suffer from noise :-)
    - raverbashing 14y ago
      "These renderers start at the light source and stochastically generate and follow photons." Yes, that's similar to ray tracing, but going 'backwards' Rasterizing is certainly faster, requiring more work in the 'intelligence' of scene assembly. With raytracing (or physics rendering) you have lights, objects 'naturally interacting' with each other so shadows, reflection, radiosity comes ""automatically"" (still hard to do) With rasterizing you have triangles with different colors, and it's up to you to paint them accordingly.

ChuckMcM 14y ago

Pretty much agree, the only thing that we might disagree on is the 'billions' number, while I expect good ray tracing to trace billions of rays, if transistors are cheap enough this becomes more interesting. The typical HDMI 1080p display is 2 megapixels (or megatexels) if you have a rendering engine with 2,073,600 cores each of which is looking at a billion ray 'view' based on where it sits in the scene, its easier to set up the scene and light it. That presumes that you can do those cores like DRAM instead of like current processors of course. My point is that cheap transistors keep amazing me and whenever I say "Oh that will never happen" some fool goes and shows me I'm wrong. I'm trying to imagine how complex a 'core' would be that computed the incident rays on a single pixel. Then figuring out how big that is in a 18nm process technology and then trying to see if I can fit 2M on a reasonable size die. My head exploded sadly.

yk 14y ago
Throwing more ( or finer etched) silicon at an algorithm will not help the algorithm, compared to a superior algorithm. For almost all scenes you get better results with rasterization, the two exceptions I can think of is scenes where the geometry of light rays is not flat, so for example involving lenses or black holes, or where there is a lot more optical complexity than you can reasonably use. ( A forest where each of the leafs is an object, you will never be able to notice that the advantage of this over an forest where the trees in the background are just textures.)
- Osmium 14y ago
  e.g. mirrors?
  - yk 14y ago
    Yes, but it perhaps more instructive to think of a curved mirror. In case of a raster engine, you need to calculate a texture for every triangle of the mirror. ( Which is essentially the same as rendering the scene in the first place.) On the other hand for a ray tracing engine you just need to reflect one ray on the mirror surface for every pixel the mirror occupies in the final rendering. So compared to the same scene with a window instead of the mirror, you just need to calculate one additional reflection instead of running the entire rendering pipeline again.
    - willvarfar 14y ago
      I think John says not just one ray per pixel?
      - yk 14y ago
        Yes, I was essentially using one ray per pixel as shorthand for constant amount of rays per pixel. (As in 'I did not think about that point.') One needs more than one to avoid creating artifacts like aliasing ( see [1] for a very nice example), or depending on how 'naive' or complex the algorithm is for stuff like shadows or caustics. But for nice scenes (which do not create artifacts) with mirrors and lenses, one ray per pixel would work fine. [1] https://en.wikipedia.org/wiki/Aliasing https://en.wikipedia.org/wiki/Aliasing

yk 14y ago

I think people rather think of ray-tracing as much better motivated by physics ( and intuition) compared to all the complicated matrices in raster engines. Instead of thinking it is superior because of some demos.

InclinedPlane 14y ago
An even more physics based rendering method is called radiosity, but it's also hugely computationally intensive.
- Tloewald 14y ago
  Physically Based Rendering - often GPU accelerated - is the new thing -- check out Octane Renderer, Lux-Render, Indigo, the Cycles renderer in Blender. These renderers start at the light source and stochastically generate and follow photons. Like a digital camera they suffer from noise :-)
  - raverbashing 14y ago
    "These renderers start at the light source and stochastically generate and follow photons." Yes, that's similar to ray tracing, but going 'backwards' Rasterizing is certainly faster, requiring more work in the 'intelligence' of scene assembly. With raytracing (or physics rendering) you have lights, objects 'naturally interacting' with each other so shadows, reflection, radiosity comes ""automatically"" (still hard to do) With rasterizing you have triangles with different colors, and it's up to you to paint them accordingly.