Comment by susam | Hacker News Reader

Comment by susam | Hacker News Reader

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An interesting excerpt from the section “3D Computer Graphics Primer”:

> The understanding of light and how we perceive it has evolved significantly over time. Ancient Greek philosophers posited that vision occurred through beams of light emitted from the eyes, interacting with the environment. Contrary to this, the Arab scholar Ibn al-Haytham (c. 965-1039) introduced a groundbreaking theory, explaining that vision results from light rays originating from luminous bodies like the sun, reflecting off objects and into our eyes, thereby forming visual images. This model marked a pivotal shift in the comprehension of light and vision, laying the groundwork for the modern scientific approach to studying light behavior.

Indeed! If you are interested in reading more about this, I recommend the article “Light Through the Ages: Ancient Greece to Maxwell”[1]. It is a very fascinating article written by J J O’Connor and E F Robertson in 2002 that takes us through a journey of how our understanding of light has evolved over the last few millennia.

[1] https://mathshistory.st-andrews.ac.uk/HistTopics/Light_1/

> "...vision occurred through beams of light emitted from the eyes, interacting with the environment"

How did they explain lanterns and torches in this theory?

What do you mean lanterns and torches?

On the macroscopic scale, light rays can be replaced with vision rays, and everything works out the same. That's how ray tracing works. People thought eyes were doing ray tracing.

That's how we still do (simulation of) ray tracing (Whitted).

What do you think he means? It's a good question.

I remember a guy who had a novel theory (mostly as a joke, I think) that light bulbs don't emit light, they simply suck away the darkness. He literally called lightbulbs "darksuckers."

Roger Wilcox, from the 1990s?

http://www.rogermwilcox.com/darksucker.html

It was someone I knew IRL but I guess that's where they got it from

That's why the lessons are online. You can read through them and everything is explained there. In ray-tracing light most often travels from the eyes to the surface and from the surface to the lights (direct illumination). Various laws (such as as the inverse square and lambert-cosine laws) are applied to simulate reality.

A far as I know, in raytracing, you bounce your ray from the surface's normal and if it hits a "light source" then it's brighter (by the inverse square distance to the source). Maybe they explained the same way, except they used a different name?

I think this is plausible. I guess they thought unlimited ray bounces were a thing.

Until you can observe that light doesn't travel instantaneously, it would be consistent to believe that a beam leaves your eyes, bounces off a surface, and informs you (as though it were a limb, perhaps) when it hits a light source.

Except that would never explain shadows. Why does my eye beam not let me see what is in shadow, if there is no such thing as light beams coming from a light source?

Because the beam coming from your eyes and hitting a shadow would never reach a light source (you could say it gets absorbed before it reaches a light source).

The more I think about it the weirder it gets.

It’s day time, the sun is up, it’s a cloudless day. Ambient light is bouncing all over, including into a south facing window (i.e. no direct sunlight.) How does the Eye Light Emitter do its job in this case?

Now, I don’t mean “this concept is impossible” because that’s clear. I’m genuinely curious how this would have been explained by someone at the time.

You should read scratchapixel really)

https://www.scratchapixel.com/lessons/3d-basic-rendering/int...

In the real world light travels from the light source to the eye. But this lesson xplains that simulating this with a computer is not efficient. A more efficient technique is to follow the path of light but in reverse, starting from the eye and waking back to the lights making up the scene. Again read the lesson(s) it's all explained and that's why the lessons are there in the first place.

Vision rays emanate from your retina, get refracted by the lens, exit the pupil, go outside the window, get scattered in the air, and - some of them - end up hitting the sun.

As far back as Aristotle, anyone who put a moment's though into it realized that eye beams were nonsense. They are like modern superstrings - any theory that includes them works works just as well if you remove them and keep the rest of the theory.

http://web.stanford.edu/class/history13/earlysciencelab/body...

I can't recommend that maths history site enough, I've read through basically all of it multiple times and sent in many corrections over the years :)

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