[HN Gopher] Lights and Shadows (2020)
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Lights and Shadows (2020)
Author : kg
Score : 215 points
Date : 2026-01-02 19:24 UTC (6 days ago)
(HTM) web link (ciechanow.ski)
(TXT) w3m dump (ciechanow.ski)
| fdeage wrote:
| Should add (2020) to the title.
| phailhaus wrote:
| Yeah I got real excited a new one dropped
| cies wrote:
| I love these interactive "text books". Usually I find out about
| them here on HN.
|
| Is there a collection of these somewhere?
| erikon wrote:
| You can start by looking at all his other entries:
| https://news.ycombinator.com/from?site=ciechanow.ski
| gyomu wrote:
| One term for them is "explorable explanations"
|
| https://en.wikipedia.org/wiki/Explorable_explanation
|
| https://explorabl.es/
| smusamashah wrote:
| https://samwho.dev/ (e.g. Reservoir sampling, Load balancing)
|
| https://imadr.me/pbr/ (physically based rendering)
| coolness wrote:
| damn, i was really excited to have a new article by this guy.
| Makes some of the best articles out there for sure
| isoprophlex wrote:
| bb wake up, new chichanow.ski just dropped
|
| oh wait, (2020) :(
|
| thankfully i don't remember much from this one, so was able to
| extract some dopamine from it still
| emilbratt wrote:
| I find it refreshing that a webpage can give such joy, to the
| point of having people talk about it in the same way you talk
| about books and movies. You know, being able to enjoy it for
| the first time and so and so.
| isoprophlex wrote:
| Absolutely agree, it's one of the modern internet's gems.
|
| I can't wait until one of my kids, who seems very
| interested in physics-adjacent topics, is old enough to go
| through these pages with me.
| throw0101d wrote:
| The inverse-square law can be non-intuitive:
|
| * https://en.wikipedia.org/wiki/Inverse-square_law
|
| I know a good number of photographers can struggle with it when
| they're getting into flash/strobe photography (even though may be
| good with f-stops generally, the moving of the flash stand
| appropriately takes some mental 'accounting').
|
| * https://www.youtube.com/watch?v=hySbIWzJAkM
|
| * https://www.youtube.com/watch?v=xO-J42VM448
| randlet wrote:
| In your first link the narrator says he "doesn't understand the
| physics of it" but there's really no physics involved (ignoring
| scatter). It's just a consequence of the math. It's relatively
| easy to understand if you think of it in terms of the surface
| of a sphere. There is a fixed amount of light coming from a
| point source, and as the light travels outward you can think of
| it as being spread over the surface of a sphere. Since the
| surface area of a sphere is 4 _pi_ r^2, if you double the
| radius the area quadruples, and therefore the light intensity
| at any point on the sphere drops by a factor of four.
|
| edit: And now after rtfm I see there's a nice demo of this!
| peterspath wrote:
| I love that the car animation has reversing lights on when
| reversing. The details are so good.
| prodigycorp wrote:
| 15 years ago I thought this type of thing would be the future of
| education. Is the educational system anything like this nowadays
| or are kids still more or less still stuck with static textbooks?
| pjmlp wrote:
| It seems most digital attempts aren't done properly, thus it
| tends to end back to books.
|
| A recent example,
|
| https://www.france24.com/en/tv-shows/focus/20260106-back-to-...
| SJMG wrote:
| Maybe someone with first-hand experience can weight in, but
| isn't this what alternative education platforms like
| "Brilliant" look like?
| segh wrote:
| School incentives are not really aligned around maximizing
| learning rate for every student. (E.g. that is why there is/was
| debate around teaching phonetics)
| GuB-42 wrote:
| This is edutainment. Kind of like YouTube channels like
| 3Blue1Brown, Veritasium or MinutePhysics. All good, it helps
| build intuition, and to better understand the world, but it is
| a bit lacking for actually using that knowledge.
|
| Notice how few equations there are in this page, it is a common
| feature of edutainment, they won't give you equations unless
| they can't get away without. No linear algebra here, just a
| cosine (actually a dot product in disguise) and the inverse
| square law (1/r2), two equations he considered too fundamental
| to skip. Also notable is the lack of exercises.
|
| But now that you have read this page, and played with the
| interactive elements, you probably have a good understanding of
| how lights and shadows work, but can you write a 3D engine or
| even just calculate exposure time without your camera helping
| you? Without prior knowledge, probably not. For that, you
| actually need to do the maths, with exercises and all that. And
| by the way, look at the source code (it is not obfuscated), all
| the linear algebra that is not present in the article is there!
|
| That, I think, explain the discrepancy between edutainment and
| textbooks. Textbooks are for you to do actual work, do the
| maths, solve problems, etc... not just give you an overview.
| That's also why is takes way longer and requires a lot more
| effort on the student part.
|
| Interactive content like this one is good, and maybe it should
| be given a bit more consideration by the traditional
| educational system. But I don't think it can replace textbooks,
| at least not for the "hard part".
| prodigycorp wrote:
| What you said makes sense. Thanks for your perspective.
| overtone1000 wrote:
| Comparing this site to Veritasium seems unfair to me. I don't
| see any evidence that this site generates direct revenue. I
| also think it's an excellent exercise in pedagogy. The best
| professors and brightest colleagues I remember from college -
| or, since you said "maths" I guess I should say "university"
| ;) - demonstrated extreme facility with the physical concepts
| and regarded their mathematical representations only as a
| useful tool to characterize them and communicate about them,
| not an end to themselves.
|
| Maybe this is just personal preference. I knew capable
| students who were wrote and prescriptive in their approach to
| the courses, but I was closer to those who played in the
| conceptual end of the pool.
|
| I once made a resource like this site for my own educational
| benefit when I was grappling with MR physics. You're right -
| I had to do the math(s)! - and came away with a much clearer
| understanding of the subject. Still, I received lots of
| correspondence from students and professors who found the
| visual aid helpful on their journey.
| GuB-42 wrote:
| > Comparing this site to Veritasium seems unfair to me. I
| don't see any evidence that this site generates direct
| revenue.
|
| He has a Patreon page, if you want to support
| https://www.patreon.com/ciechanowski
|
| All combined, he may get a few thousand dollars per
| article, which I admit is not much for what we get, and
| certainly not enough to make a living.
| snorwick wrote:
| There is the "tools for thought" space I came across where some
| work felt compelling for computer enabled teaching and
| learning.
|
| Bret Victor [0], Andy Matuschak [1], and Seymour Papert [2] to
| point to a few names.
|
| [0]https://www.youtube.com/watch?v=oUaOucZRlmE
|
| [1]https://quantum.country/
|
| [2]https://www.google.com/books/edition/Mindstorms/nDjRDwAAQBAJ
| ...
| mopsi wrote:
| Every time I see this site posted, I can't help but think this is
| what Wikipedia and other online sources could be. I loved Encarta
| for all the interactive things I could play with. Instead, for
| most things, we are stuck with Markdown and minimal formatting
| that is frustratingly neutered, even clickable image maps have
| become a rarity; can't remember when I last saw one in the wild.
| Really sad.
| sbondaryev wrote:
| I skimmed the source code (base.js, light.js) to see what he was
| using. It appears to be entirely custom, with no graphics
| libraries like Three.js. He even implements his own low-level
| math functions from scratch. It's impressive to see that kind of
| discipline.
| kubb wrote:
| The best programmers are cautious about dependencies. Taking
| something is easy. But you don't learn. And you give up
| control.
| typeint wrote:
| What are some good sources to learn this kind of graphics
| programming work?
| chrismorgan wrote:
| Honestly, if you're wanting to produce something as good as
| this, Three.js or other such things just aren't particularly
| helpful. It is _easier_ to just ignore all the libraries and do
| it all from scratch. Popular libraries are good at producing
| finished products in a particular shape. When you're wanting to
| demonstrate the implementation steps and allow intricate
| fiddling and have everything polished like _you_ want it,
| they're generally somewhere between painful and hopeless.
|
| You could still keep Three.js for bits like vector
| calculations, but it just doesn't feel worth it, it's easy
| enough to implement yourself--or copy and paste from some such
| library and modify as needed--and will be much lighter. And you
| build up the bits and pieces you need over time.
| bob1029 wrote:
| > With a small light source even a small change in position on
| the surface has big effects on the light's visibility - it
| quickly becomes fully visible or fully occluded. On the other
| hand, with a big light source that transition is much smoother -
| the distance on the floor surface between a completely exposed
| and completely invisible light source is much larger.
|
| This part of the demo illustrates the point vs area light issue
| really well. In designing practical 3d scenes and selecting
| tools, we would often prefer to use 2d area or 3d volumetric
| lights over point lights. Difficult problems like hard shadows
| and hotspots in reflection probes are magically resolved if we
| can afford to use these options. Unfortunately, in many realtime
| scenarios you cannot get access to high quality area or
| volumetric lighting without resorting to baking lightmaps (static
| objects only; lots of iteration delay) or nasty things like
| temporal antialiasing.
| cubefox wrote:
| There is a solution called Radiance Cascades [1] which doesn't
| require a denoiser for rendering real-time shadows for
| volumetric lights. Unfortunately the approach is relatively
| slow, so solutions based on denoising are still more efficient
| (though also expensive) in terms of the quality/performance
| tradeoff.
|
| One issue with modern ReSTIR path tracing is that currently the
| algorithm relies on white (random) noise, which contains low-
| frequency (large-scale) noise, which produces blotchy boiling
| artifacts at low sample counts. Optimally an algorithm should
| use some form of spatio-temporal blue noise with exponential
| decay to only get evenly distributed high frequency samples.
| But that's still an open research problem.
|
| 1: https://youtube.com/watch?v=rG2aok2SdbU
| seemaze wrote:
| ciechanow.ski has frequent submissions on HN, and is one of my
| favorite pages on the internet. Have a look through some other
| great submissions:
|
| https://news.ycombinator.com/from?site=ciechanow.ski
|
| https://ciechanow.ski/archives/
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(page generated 2026-01-08 23:00 UTC)