[pixelpoet]

I'm in computer graphics, and find myself thinking "this dev really needs to better understand memory layout and computer architecture" all the time when I look at even basic code.

A perfect example of this is looping over some range of pixels, and many will just go ahead and do for (x) for (y) setPixel(x, y, f(x, y)). There's no logic error here but it's still terrible when dealing with images in the usual memory order idx = y * width + x.

It seems like many people have no idea how even basic abstractions (such as the aforementioned pixel indexing example) work, and have no performance expectations because they don't code in any systems languages.

People who are aware of such issues and still can structure large codebases well seem to be getting more rare to me, at least. In the 90s there were so many incredible demoscene programmers, and now... hmm...

(A related thing I wonder about is, where is the von Neumann or Newton of our times? There are more people around than ever, nutrition and medicine and poverty is globally better than ever, ...)

[QuestionPixel]

I'm currently studying EE and would like to get into embedded programming/semiconductor design, could you explain the optimal way to loop over the pixels if not with two nested for loops? Would it be something related to how in memory it's effectively a 1-D array?

[fyp]

It's a really deep problem actually! Doing y then x is better but it's far from "optimal".

These parallel programming course notes have an example of using z-order curves which is slightly better yet: http://ppc.cs.aalto.fi/ch2/v7/

And the best solution requires something like Halide https://halide-lang.org/ to find the best traversal order.

[jfim]

The loops should be inverted. It should be for y, then for x, which accesses the memory in a linear fashion instead of in stride.

This presentation (PDF) explains why: https://www.aristeia.com/TalkNotes/ACCU2011_CPUCaches.pdf

[kamih]

At the very least, the inner loop should be over X, since that is how the pixels are packed.

[RhysU]

It is precisely the linear ordering in memory. Whether X-then-Y or Y-then-X is best depends upon if the data is stored row- or column-major.

[papermachete]

>demoscene

Honestly, who has time these days?

[overgard]

People that care about their craft?

[papermachete]

Yeah buddy I get home tired from work and the commute, crack open a cold one, and surf late 2000s forum posts on installing gentoo on a PS3.

There are many healthy activities to take up rather than play with deprecated/obscure tech. Not to be judgemental of course, I draw my line at home repairs.

[zozbot234]

When it comes to computer graphics, "deprecated/obscure" tech is the tech that is comprehensively documented from the ground up. There is some documentation about internals of the Raspberry Pi SoC and GPU, but sadly not enough to make it a compelling demoscene target.

[overgard]

I'm not saying you should. Enjoy your free time. I just think it's weird to shame people that care more by implying they have too much time on their hands. Everyone has a level of caring that's appropriate for them.

There's a lot of things you can learn from writing demos that is still incredibly valuable. I wouldn't expect 99.9% of developers to know those things, but if I saw it on a resume? That'd totally jump off the charts to me and I'd definitely want to interview that person.

Don't shame expertise just because you choose to spend your time differently.

[dang]

I appreciate what you're writing about demoscene programming, but the GP comment does not seem to me to be shaming. It most likely was just about the commenter not having time themselves. HN has a guideline for cases like this:

"Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith."

https://news.ycombinator.com/newsguidelines.html

[overgard]

I agree with the rule, but I only accused him of shaming after he drew a broad insulting caracature of a community I'm involved in and actually understand (the demoscene) by suggesting that it just involves people "browsing early 2000 forums and installing gentoo on PS3s". I think if you said that to any demo coder they'd tell you to eat sand. It's not even remotely close to what that scene is about. If there's a criticism to be made here, perhaps it's about not making assumptions about groups you know nothing about?

I made no assumptions other than what he explicitly said, which was insulting and displayed ignorance of a community he clearly does not understand. My original comment was also only "People who care about their craft?", which was simply saying that people get into demo coding because they care about doing something worthwhile (getting the most out of their machines in an artistically satisfying and interesting way).

There's a common social anti-pattern in most tech forums of hand-waving away any complex domain knowledge that the person doesn't personally use as "useless". I have no regrets about stating the contrary.

I am amused that I am the one getting a warning about this though. I'm not the one that made a drive-by ambiguous comment that could easily be read as singling out a fun community as being a waste of time. I just pointed out that that's what he just did.

[papermachete]

I'm sorry it came off as shaming.