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Comment by woodrowbarlow | Hacker News Reader

can someone help me understand what "ray tracing" means in this case?

i've read a few technical articles about ray-tracing, but they mostly describe it as a rudimentary (largely outdated) way of achieving 3d effects with relatively little code, and with severe limitations (walls must be orthonormal, changes in elevation require extra work, etc.). i understand ray-tracing at this level (break the view into columns, set the fill height of the column according to the distance of the ray).

then i see marketing-style articles like this one that use the same term to describe advanced lighting effects, material reflections, etc. and i don't understand the technological jump. what am i missing?

edit: i was thinking of "ray casting", not "ray tracing". thank you for the corrections below.

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What you are describing sounds more like ray casting than ray tracing.

Ray casting is the old Wolfenstein 3D look: https://en.wikipedia.org/wiki/Ray_casting

Ray tracing is what Pixar uses for Toy Story, Monsters Inc, etc... https://en.wikipedia.org/wiki/Ray_tracing_(graphics)

And then the new hotness for offline rendering is Path Tracing, which is a form really good but really hard to accelerate form of ray tracing: https://en.wikipedia.org/wiki/Path_tracing

And yes fundamentally all of these are "shoot rays out from the camera", hence the very specific terminology used for each to disambiguate which approach to shooting out rays from the camera is being used and what happens when rays hit a thing.

I'm pretty sure toy story 1 didn't use ray tracing. Iirc cars was the first that did.

The technique you are talking about, used for Wolfenstein 3D in the '92, is more commonly called "ray-casting." You cast one ray per screen X (or fewer) and see what object it hits, and then draw a slice of that object. https://en.wikipedia.org/wiki/Ray_casting

Ray tracing as used here means simulating light rays bouncing off of objects - it's a high fidelity technique generally not used in games in the past, because it is so slow. https://en.wikipedia.org/wiki/Ray_tracing_(graphics)

Sounds like the first thing you are describing is closer to ray casting. Ray tracing doesn't have the limitations you mention.

Roughly speaking, ray tra in techniques are variations on the concept of tracing a ray from the camera back into the screen and seeing where is ends up. The different variations distinguish themselves by what happens at a ray intersection. Classical ray tracing will spawn a shadow ray towards light source. Path tracing will stochastically sample some distribution of ray directions (usually based on a combination of light locations and material properties) in order to do Monte Carlo integration of the rendering equation. There are other variations.

Ray tracing (w/ only shadow rays) doesn't give you global illumination. Path tracing (this work) does.

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