Writing a small ray tracer in Rust and Zig(nelari.us)
nelari.us
Writing a small ray tracer in Rust and Zig
https://nelari.us/post/raytracer_with_rust_and_zig/
97 comments
> I’m convinced that there’s a proper mathy / lighting-y word for each component in that expression.
Sometimes yes, but often no. Frequently this kind of expression is the result of solving an equation, so it’s just an expression.
Graphics people often use two approaches for sub-expressions:
- You can name them with the same letters that are in the expression, just with the punctuation & operators removed, for example:
It might be worth reflecting on what the goals are with your naming, and whether it matters what they’re named. As software engineers, our biases lean toward making choices that improve readability and maintainability. But for a specific equation that will never change once it works correctly, our preconceived notions about good software design and best practices might not actually apply to this situation. It might be more important to document the source of the equation than to make the implementation readable.
Sometimes yes, but often no. Frequently this kind of expression is the result of solving an equation, so it’s just an expression.
Graphics people often use two approaches for sub-expressions:
- You can name them with the same letters that are in the expression, just with the punctuation & operators removed, for example:
const uvMinusNTimesDt = uv.sub(n.mul(dt))
const q = uv.sub(n.mul(dt))
It might be worth reflecting on what the goals are with your naming, and whether it matters what they’re named. As software engineers, our biases lean toward making choices that improve readability and maintainability. But for a specific equation that will never change once it works correctly, our preconceived notions about good software design and best practices might not actually apply to this situation. It might be more important to document the source of the equation than to make the implementation readable.
People say “the two hardest problems in computer science are cache invalidation, naming and off-by-one errors” and we often design systems so that we don’t have to think about cache invalidation and off by one errors (e.g. list.map rather than a for loop). I often wonder if we should think about minimizing how often we name things as well.
Excel is the most popular functional programming language in the world. Its killer feature is that you don’t have to name your values before you can use them.
I'd argue that its killer feature is that everything is inherently reactive.
Well, it just has a cartesian namespace
Point free form? Ditch your variable names.
> It is very common for functional programmers to write functions as a composition of other functions, never mentioning the actual arguments they will be applied to.
https://wiki.haskell.org/Pointfree
> We are going to use named variables to keep track of the arguments, then write a definition without them.
http://joypy.osdn.io/notebooks/Quadratic.html
> It is very common for functional programmers to write functions as a composition of other functions, never mentioning the actual arguments they will be applied to.
https://wiki.haskell.org/Pointfree
> We are going to use named variables to keep track of the arguments, then write a definition without them.
http://joypy.osdn.io/notebooks/Quadratic.html
> I often wonder if we should think about minimizing how often we name things as well.
Personally, I think that depends, so I like to challenge my own assumptions and examine things case by case. The implementation of a math equation, especially one that is the result of solving a different equation, and so went through a symbolic/algebraic transformation, that is one place where adding more names might not clarify the implementation.
In general, though, my personal experience has been one of not seeing things named enough. Specifically, feature creep in software tends to try to add code with a light touch without disturbing too much of the surrounding code, but with new concepts that deserve more naming than they get. This can and does lead to code that is difficult to maintain, and I think I’ve seen more of that mistake than of naming things too much, and I suspect it’s much easier to not just shoot yourself in the foot, but cut your leg off, by under-naming rather than by over-naming.
Personally, I think that depends, so I like to challenge my own assumptions and examine things case by case. The implementation of a math equation, especially one that is the result of solving a different equation, and so went through a symbolic/algebraic transformation, that is one place where adding more names might not clarify the implementation.
In general, though, my personal experience has been one of not seeing things named enough. Specifically, feature creep in software tends to try to add code with a light touch without disturbing too much of the surrounding code, but with new concepts that deserve more naming than they get. This can and does lead to code that is difficult to maintain, and I think I’ve seen more of that mistake than of naming things too much, and I suspect it’s much easier to not just shoot yourself in the foot, but cut your leg off, by under-naming rather than by over-naming.
Aren’t features like if-expressions just that?
> Frequently this kind of expression is the result of solving an equation
Some time ago I’ve stopped solving equations, using software for that. Nowadays, when I need them solved, I sometimes don’t even write code, here’s an example: https://stackoverflow.com/questions/1351746/find-a-tangent-p...
Symbolic math software does more “optimizations” than even offline compilers. For example, I have never saw an optimizer which is aware that sin(x)^2 + cos(x)^2 = 1.
Some time ago I’ve stopped solving equations, using software for that. Nowadays, when I need them solved, I sometimes don’t even write code, here’s an example: https://stackoverflow.com/questions/1351746/find-a-tangent-p...
Symbolic math software does more “optimizations” than even offline compilers. For example, I have never saw an optimizer which is aware that sin(x)^2 + cos(x)^2 = 1.
In my experience writing math code the intermediary values get quite goofy Ex: orthogonal-vector-to-plane-bisecting-input-vector-and-first-column-vector
But I rather use crazy descriptive names than hiding it away. Otherwise it gets quite incomprehensible when you reread it 3 months later
Anyone else hit this problem? I suspect most people just reference a paper or book and use the letters to match the source ( x/y/n/m/etc. )
But I rather use crazy descriptive names than hiding it away. Otherwise it gets quite incomprehensible when you reread it 3 months later
Anyone else hit this problem? I suspect most people just reference a paper or book and use the letters to match the source ( x/y/n/m/etc. )
I think people's brains must work different, because for me this would be a terrible way to do it. I simply cannot read and comprehend math with very long descriptive variable names.
Whenever I see people do that, I have to write down the equation with single letters, and then look at it.
I am more of a literate programming type of person. I prefer writing longer explanations of code. But usually as a header. I like keeping the core of the code as clean and noise free as possible.
So I write code more like a math or physics book I guess. The equations are kept simple and clutter free, and then there is a body of text above or below explaining how to think about it. I tend to prefer using a lot of unicode, because following conventions helps me a lot. If I see a t₀, t and Δt variable e.g. I immediately get a sense of what sort of variables this is and how they are related. If instead it said start_time_of_incident, current_time and time_difference_between_events I could not quickly parse and internalize that.
Whenever I see people do that, I have to write down the equation with single letters, and then look at it.
I am more of a literate programming type of person. I prefer writing longer explanations of code. But usually as a header. I like keeping the core of the code as clean and noise free as possible.
So I write code more like a math or physics book I guess. The equations are kept simple and clutter free, and then there is a body of text above or below explaining how to think about it. I tend to prefer using a lot of unicode, because following conventions helps me a lot. If I see a t₀, t and Δt variable e.g. I immediately get a sense of what sort of variables this is and how they are related. If instead it said start_time_of_incident, current_time and time_difference_between_events I could not quickly parse and internalize that.
Yeah, I feel you on that and I started out writing in a similar style b/c it's terse and easy to digest. To be clear, this is mostly a hobby things for me so I'm not speaking from a position of authority, but in my limited experience once the problem gets bigger and you worry about performance/caching/recursion/etc. the math and equation start to diverge from the code substantially.
For instance over the last few months I've been playing with BLAS and the BLAS operators just don't really map cleanly to equations - and the way you structure efficient solutions just ends up being more nuanced and complicated than the simple clean "theoretical" on-paper solution. All the nuances need to be captured in the variable names to have any chance of making the code understandable
For instance over the last few months I've been playing with BLAS and the BLAS operators just don't really map cleanly to equations - and the way you structure efficient solutions just ends up being more nuanced and complicated than the simple clean "theoretical" on-paper solution. All the nuances need to be captured in the variable names to have any chance of making the code understandable
the distance between BLAS and mathematics is quite big.
Have you had a look at, for example, the Eigen library?
Although it's still more verbose than math notation, it stays much closer and, in my experience, does allow for nearly all the optimization-wiggle-room one could want.
Although it's still more verbose than math notation, it stays much closer and, in my experience, does allow for nearly all the optimization-wiggle-room one could want.
I suspect most people just reference a paper or book and use the letters to match the source ( x/y/n/m/etc. )
If you do this (and I'll certainly admit that I do this as well) make sure you link to the paper in question somewhere in either comments or the documentation so that future developers can find the canonical reference to what the variables mean.
If you do this (and I'll certainly admit that I do this as well) make sure you link to the paper in question somewhere in either comments or the documentation so that future developers can find the canonical reference to what the variables mean.
That assumes there is a geometrically meaningful description. A lot of times a computation has no intrinsic meaning. Algebra is going to rearrange and cancel terms into nonsense.
A long name can tell you _what_ a value is. But it’s of zero use in explaining _why_ it’s being used.
The only solution is a lengthy comment explaining the process. Here some ballistic trajectory code I wrote awhile back. Good luck making sense of any single term!
https://github.com/forrestthewoods/lib_fts/blob/26a0d115eb44...
A long name can tell you _what_ a value is. But it’s of zero use in explaining _why_ it’s being used.
The only solution is a lengthy comment explaining the process. Here some ballistic trajectory code I wrote awhile back. Good luck making sense of any single term!
https://github.com/forrestthewoods/lib_fts/blob/26a0d115eb44...
Yep, agree! I think extremely long variable names (when used locally), if necessary, are wildly underrated. I mean, we all know horror stories like SimpleBeanFactoryAwareAspectInstanceFactory, but they are really design problems much more than naming problems. They gave long variables a bad rep, undeservedly so. Inside an expression, names like that truly do wonders.
So why not just write the original formula into the comment above the code? Maybe it's not the purest approach, but it sure would help parsing the code in this case.
Yep. If the code doesn't clearly show the original intent, document your intent in a comment next to the code so future you or others can double check. Esp in gfx engines where some blocks are just math translated one to one to code.
Why not one step further, and let the original formula be the code? Directly compilable Latex:
\vec r = \frac {n_{1}}{n_{2}} \cdot (\vec v - dot(\vec v, \vec n) \cdot \vec N) - \sqrt{1 - \frac {n_{1}^2}{n_{2}^2} \cdot (1 - dot(\vec v, \vec n))} \cdot \vec N
Julia (a language focused on science/math) does it partially. For example in the editor or REPL you can just type \sqrt [tab] \alpha [tab] and it will generate √α which is valid code. Most math symbols in unicode are supported and overloadable. And you can also write matrix like a table, such as
[1 2 3
4 5 6
7 8 9].
And you can transform Julia expressions to LaTeX:
https://github.com/korsbo/Latexify.jl
But even they didn't go as far as being able to parse full LaTeX expressions (though you technically could with reader macros plus editor support).
[1 2 3
4 5 6
7 8 9].
And you can transform Julia expressions to LaTeX:
https://github.com/korsbo/Latexify.jl
But even they didn't go as far as being able to parse full LaTeX expressions (though you technically could with reader macros plus editor support).
You could probably do it that way in Julia.
The most principled approach there, I think, would be to build a little Expression data-structure, and then feed it to an evaluation routine, trusting the optimizer to compile the whole thing down to something efficient. If Rust didn't have operator overloading anyway, you could do the job with procedural macros.
In practice, if I had to write that quasi-monstrosity in something like C, I'd probably just comment it as clearly and liberally as possible, to the point where I manage to reassure the reader that the final expression is correct; and then add a // See above: Please DO NOT edit this expression directly!// comment as an extra caution.
In practice, if I had to write that quasi-monstrosity in something like C, I'd probably just comment it as clearly and liberally as possible, to the point where I manage to reassure the reader that the final expression is correct; and then add a // See above: Please DO NOT edit this expression directly!// comment as an extra caution.
Why would you need to do that with small vectors? The compiler is going to do that anyway. Eigen originally took this approach because it could avoid heap allocating temporary variable before C++ had move operations. This isn't applicable here.
The fruity method should be preferred: Any compiler worth using will immediately eliminate/register-allocate the variables and now you don't have undebuggable spaghetti code
This is how I've been helping my daughter understand some maths problems at school. Break it down and name everything, then write the sum with the names in and it makes sense.
> But rendering in separate threads turned out to be (unsurprisingly) harder than the way I would do it in C++...It was a bit frustrating to figure out how to accomplish this. Googling yielded a few stack overflow posts with similar questions, and were answered by people basically saying use my crate!
Based on some discussion in r/rust (https://www.reddit.com/r/rust/comments/c7t5za/writing_a_smal...) I went ahead and added a Rayon-based answer to that SO question (https://stackoverflow.com/a/56840441/823869). That's been the de facto standard for data parallelism in Rust for the last few years. But the article highlights that discovering the de facto standards is still a challenge for new Rust users -- does anyone know of a well-maintained list of the 10-20 most critical crates that new users should familiarize themselves with after reading The Book? Things like Rayon and lazy_static. The ranked search results at https://crates.io/crates?sort=recent-downloads are almost good enough, but they include a lot of transitive dependencies that new users shouldn't care about. (I.e. `regex` is a very important crate, but `aho-corasick` is usually only downloaded as a dependency of `regex`.)
Based on some discussion in r/rust (https://www.reddit.com/r/rust/comments/c7t5za/writing_a_smal...) I went ahead and added a Rayon-based answer to that SO question (https://stackoverflow.com/a/56840441/823869). That's been the de facto standard for data parallelism in Rust for the last few years. But the article highlights that discovering the de facto standards is still a challenge for new Rust users -- does anyone know of a well-maintained list of the 10-20 most critical crates that new users should familiarize themselves with after reading The Book? Things like Rayon and lazy_static. The ranked search results at https://crates.io/crates?sort=recent-downloads are almost good enough, but they include a lot of transitive dependencies that new users shouldn't care about. (I.e. `regex` is a very important crate, but `aho-corasick` is usually only downloaded as a dependency of `regex`.)
> But the article highlights that discovering the de facto standards is still a challenge for new Rust users -- does anyone know of a well-maintained list of the 10-20 most critical crates that new users should familiarize themselves with after reading The Book?
I came across this exact thing recently: https://github.com/brson/stdx
I came across this exact thing recently: https://github.com/brson/stdx
That seems old, especially as error-chain is no longer maintained so I wouldn't recommend it.
[0]: https://users.rust-lang.org/t/error-chain-is-no-longer-maint...
[0]: https://users.rust-lang.org/t/error-chain-is-no-longer-maint...
I'm new to Rust, so I wasn't aware. Thanks!
I still don't understand why Rayon is not part of the Rust standard library.
Rust was created to have easy and safe multithreading on the CPU, and Rayon is the clear winner in this space, for me it feels like something that should be part of Rust.
Rust was created to have easy and safe multithreading on the CPU, and Rayon is the clear winner in this space, for me it feels like something that should be part of Rust.
If Rayon were in the standard library, we would never be able to make breaking changes, whereas in a crate we can possibly release a Rayon 2.0. For instance, we might want to make some low-level changes in the way iterators split their workload, per current experiments in rayon-adaptive: https://github.com/rayon-rs/rayon/issues/616
As somebody else wrote, what's really important is to stabilize a high level parallel iterator API that would probably be common even between Rayon 1 and 2. Of course I see some new APIs, like setting the task splitting policy, but some things, like parallel iteration over a vector and mapping through it should still work.
Java had to change the collection API when it added generics, but it showed that it's possible to split the API contract while improving on the underlying implementation over time. The low level Rayon primitives of course shouldn't be in the standard library name space.
Java had to change the collection API when it added generics, but it showed that it's possible to split the API contract while improving on the underlying implementation over time. The low level Rayon primitives of course shouldn't be in the standard library name space.
The Rust stdlib is specifically intended to be as lightweight as possible (while still providing those idiomatic abstractions that might be needed throughout the ecosystem, e.g. std.future) in order to avoid the Python "dead batteries" problem.
What the Rust ecosystem is still lacking is a quasi-standard "Rust Platform" of best-practice library components where the community can freely deprecate something when a clearly better replacement comes along. There are a few "community" websites that try to provide guidance wrt. some parts of the Rust ecosystem, but nothing that feels even close to official or consensus-driven.
What the Rust ecosystem is still lacking is a quasi-standard "Rust Platform" of best-practice library components where the community can freely deprecate something when a clearly better replacement comes along. There are a few "community" websites that try to provide guidance wrt. some parts of the Rust ecosystem, but nothing that feels even close to official or consensus-driven.
When I search for the Python dead batteries problem, the main issue is that the Rust developers don't want to maintain a growing list of libraries forever, especially that some of them will be depreciated over time.
This is totally understandable position, but it is still important to have sensible defaults for common tasks for end users.
One example that I can point to is Haskell, which I tried to learn from Haskell books, and it took me years to realize that it's not the language that's extremely inefficient, but the default libraries that use lists instead of arrays for most of the tasks.
I'm writing about Rayon because I see it as a reoccuring discoverability problem for people who are new to Rust.
There are many possible solutions, but one would be to have a default list of dependencies created in Cargo.toml that can of course be modified by the Rust users. Also that list can of course be changed over time by Rust developers.
This is totally understandable position, but it is still important to have sensible defaults for common tasks for end users.
One example that I can point to is Haskell, which I tried to learn from Haskell books, and it took me years to realize that it's not the language that's extremely inefficient, but the default libraries that use lists instead of arrays for most of the tasks.
I'm writing about Rayon because I see it as a reoccuring discoverability problem for people who are new to Rust.
There are many possible solutions, but one would be to have a default list of dependencies created in Cargo.toml that can of course be modified by the Rust users. Also that list can of course be changed over time by Rust developers.
Rust needs something like Rust dev blessed "extension packs", in my opinion.
Sort of like VS Code has extension packs.
Basically have some metapackages for common development areas, that pull in community vetted, high quality libraries for certain areas.
Sort of like VS Code has extension packs.
Basically have some metapackages for common development areas, that pull in community vetted, high quality libraries for certain areas.
We have tried to suggest this, but the community has overwhelmingly rejected it, both as an explicit plan, and when people provided such a thing.
That's unfortunate. Whenever I talk about rust with my coworkers, getting crates through IT comes up as a major deal breaker. I imagine cooperate approved "packs" would make it much easier for us rust hobbyists to get some projects started at work in rust.
See python: my workplace (and I'm sure many others) is stuck with what's in anaconda for better or worse. The situation is certainly better than pure std.
See python: my workplace (and I'm sure many others) is stuck with what's in anaconda for better or worse. The situation is certainly better than pure std.
why do they need to be dev blessed? You could do something like conda that's basically a distribution.
In my opionion the stdlib is a bit too conservative.
It is easy to end up with 200+ dependencies on more complex projects.
Some things should definitely be moved into std over the long term.
BUT: the time is not now. The language is still evolving rapidly. Upcoming features like specialization and a form of higher kinded types have the potential to impact API design a lot. I also really want named function arguments.
No-one wants to end up with a outdated and arcane standard library.
It is easy to end up with 200+ dependencies on more complex projects.
Some things should definitely be moved into std over the long term.
BUT: the time is not now. The language is still evolving rapidly. Upcoming features like specialization and a form of higher kinded types have the potential to impact API design a lot. I also really want named function arguments.
No-one wants to end up with a outdated and arcane standard library.
The main problem is that you cannot version the standard library (well, there are "editions" but that's a bit of a workaround for other language changes).
Go has the exact same problem, and has also historically made similar mistakes to Rust in their stdlib (the "syscall" module is strongly recommended against -- instead you should use "golang.org/x/sys"). And it should be noted that Go is even more bare-bones than Rust -- the lack of generics means you have to use "containers" which is very limited (I also have a feeling it's used by effectively nobody, because of the bad ergonomics).
I think the best solution for this problem might be some form of "meta-crate" concept which would allow you to pull in all of the well-vetted and stable libraries that most people want, without having to curate ~20 libraries yourself.
Go has the exact same problem, and has also historically made similar mistakes to Rust in their stdlib (the "syscall" module is strongly recommended against -- instead you should use "golang.org/x/sys"). And it should be noted that Go is even more bare-bones than Rust -- the lack of generics means you have to use "containers" which is very limited (I also have a feeling it's used by effectively nobody, because of the bad ergonomics).
I think the best solution for this problem might be some form of "meta-crate" concept which would allow you to pull in all of the well-vetted and stable libraries that most people want, without having to curate ~20 libraries yourself.
> And it should be noted that Go is even more bare-bones than Rust
In certain ways Go is more bare bones, but Go also comes with common hashes, some crypto primitives, encodings like JSON, compression/archives, logging, date/time utilities, Regex, a templating engine, an http client and server, regex, .... All of which requires a dependency with Rust.
I do remember an effort of a meta package like you mentioned. I think it was driven by brson and on Github, but I can't find it now, and it was abandoned anyway.
In certain ways Go is more bare bones, but Go also comes with common hashes, some crypto primitives, encodings like JSON, compression/archives, logging, date/time utilities, Regex, a templating engine, an http client and server, regex, .... All of which requires a dependency with Rust.
I do remember an effort of a meta package like you mentioned. I think it was driven by brson and on Github, but I can't find it now, and it was abandoned anyway.
The problem is that several of those standard library components are no longer recommended for general usage:
* As with "syscall", users are strongly suggested to use "golang.org/x/crypto" for crypto primitives like AEAD. All of the crypto bits in the standard library are probably still "okay" but there are better interfaces and more efficient implementations in "golang.org/x/crypto".
* The "flags" package is basically useless for large projects (everyone uses "cobra" or "spf13/cli" to create CLI interfaces now). It also has the really weird Go-ism of "-flag" arguments.
* For logging, most people use "logrus" or similar. "log" isn't necessarily bad, but it's not full-featured enough that most people end up not using it.
* As for HTTP servers, at the very least you'll use "gorilla" to deal with routes -- if not completely switch to a different HTTP server implementation.
* Not to mention some of the other weird bits and bobs which are useful, but are strange to include in such a small stdlib, like "mime". Or some of the more fruity stuff like "database".
This is the downside of the batteries-included model. Especially when a lot of the bits in the Go stdlib were included early in the language's life and then quickly became a clearly bad idea but it was too late to remove them.
* As with "syscall", users are strongly suggested to use "golang.org/x/crypto" for crypto primitives like AEAD. All of the crypto bits in the standard library are probably still "okay" but there are better interfaces and more efficient implementations in "golang.org/x/crypto".
* The "flags" package is basically useless for large projects (everyone uses "cobra" or "spf13/cli" to create CLI interfaces now). It also has the really weird Go-ism of "-flag" arguments.
* For logging, most people use "logrus" or similar. "log" isn't necessarily bad, but it's not full-featured enough that most people end up not using it.
* As for HTTP servers, at the very least you'll use "gorilla" to deal with routes -- if not completely switch to a different HTTP server implementation.
* Not to mention some of the other weird bits and bobs which are useful, but are strange to include in such a small stdlib, like "mime". Or some of the more fruity stuff like "database".
This is the downside of the batteries-included model. Especially when a lot of the bits in the Go stdlib were included early in the language's life and then quickly became a clearly bad idea but it was too late to remove them.
I agree and I'm not advocating for Rust's std to gain things like http clients or template engines.
But some parts of the ecosystem end up in a lot of projects. Conservatively extending std would be good for the language, IMO. To set a standard, reduce compile times, and ease the burden for companies that have hard review requirements for each dependency.
Some things I'd like to see in std in a few years:
* `serde`
* `rand`
* `log`, but probably without a backend, or a simple default
* a subset of `chrono`
* some parts of `rayon`
But some parts of the ecosystem end up in a lot of projects. Conservatively extending std would be good for the language, IMO. To set a standard, reduce compile times, and ease the burden for companies that have hard review requirements for each dependency.
Some things I'd like to see in std in a few years:
* `serde`
* `rand`
* `log`, but probably without a backend, or a simple default
* a subset of `chrono`
* some parts of `rayon`
I think we could strike a balance. Don't put this stuff in the standard library, but have a category for crates that are officially blessed (or even maintained by) the core team, such that if you trust the Rust stdlib then you should be comfortable trusting these crates. Then provide binary distributions for the built crates for all tier 1 platforms at least (ideally for any platform where a binary distribution of the stdlib is available) and teach cargo how to download those. This way we maintain the ability to version these crates and have breaking changes, but without the overhead of having to recompile these crates.
What about a set of "blessed" crates (that can only depend on other "blessed" crates) that are maintained by the language developers? Seems like the best of both worlds to me.
Ah, I found the meta approach I mentioned: https://github.com/brson/stdx
There was also https://aturon.github.io/blog/2016/07/27/rust-platform/
Both failed to gain any traction.
Both failed to gain any traction.
To be clear here, yes, editions cannot change the standard library, as it must be the same across all editions.
Also, https://www.arewewebyet.org/ is somehow trying to provide a little bit of this but fails to actually recommend the best option.
What is the best option, in your opinion?
I find lib.rs mentioned in the article a good tool. Here on concurrency: https://lib.rs/concurrency
https://rust-lang-nursery.github.io/rust-cookbook/ is sorta kinda this, sorta
I will say, the one example they have there which is sort-of analogous to "render each pixel of this image in parallel" is the "draw a julia set" one [0], and it's a very bad way of convincing a C/C++ programmer that Rust is good at this sort of thing. Even if the "loop over all rows in the main thread, adding to the pool a lambda that loops over each column" is somehow optimized in a good data-parallel way (I doubt it compares favorably performance-wise with "#pragma omp parallel for"), the lambdas then push each finished pixel into a channel along with their coordinates. The main thread then has to literally loop through every pixel and read from the channel for each and every one.
The natural way to do that in C/C++ is to just write the pixel to the bitmap in each thread. There are no race conditions here (everything is embarassingly parallel), just write the resulting pixel to the bitmap and be done with it. The only reason to have that channel with all that overhead (and that final synchronization on the main thread) is to satisfy the borrow checker, which is just silly in this case. It adds a tremendous amount of overhead just to make it idiomatic Rust.
It's true that you can do it the "C++ way" in Rust using unsafe and raw pointers (and there's probably crates that can do the "parallel for" in a way that compares well with OpenMP), but as a graphics programmer who's done a lot of this sort of thing, that piece of code made a very bad first impression of Rust as a high-performance language.
EDIT: also, the description is wrong. It says: "ThreadPool::execute receives each pixel as a separate job". No it doesn't, it receives each scanline as a separate job. It might be better if the pool had each pixel as a separate job, but that's not what the code is doing.
[0]: https://rust-lang-nursery.github.io/rust-cookbook/concurrenc...
The natural way to do that in C/C++ is to just write the pixel to the bitmap in each thread. There are no race conditions here (everything is embarassingly parallel), just write the resulting pixel to the bitmap and be done with it. The only reason to have that channel with all that overhead (and that final synchronization on the main thread) is to satisfy the borrow checker, which is just silly in this case. It adds a tremendous amount of overhead just to make it idiomatic Rust.
It's true that you can do it the "C++ way" in Rust using unsafe and raw pointers (and there's probably crates that can do the "parallel for" in a way that compares well with OpenMP), but as a graphics programmer who's done a lot of this sort of thing, that piece of code made a very bad first impression of Rust as a high-performance language.
EDIT: also, the description is wrong. It says: "ThreadPool::execute receives each pixel as a separate job". No it doesn't, it receives each scanline as a separate job. It might be better if the pool had each pixel as a separate job, but that's not what the code is doing.
[0]: https://rust-lang-nursery.github.io/rust-cookbook/concurrenc...
To me, this somehow says that most truely interesting problems can only be solved efficiently in Rust using unsafe. Granted, my definition of interesting may be a bit limited, but my initial takeaway here is that Rusts safety story is much more limited than its proponents claim.
> To me, this somehow says that most truely interesting problems can only be solved efficiently in Rust using unsafe.
Even Vec is implemented with unsafe code under the hood. Rust isn't about not using unsafe code anywhere: it's about encapsulating that unsafe code in reusable abstractions that can be easily audited. This is how essentially all languages work to begin with: unless you're using CompCert, the compiler itself is not proven correct, and so the compiler's code generator is "unsafe".
Here's an example of how rav1e, an AV1 encoder in Rust, builds safe abstractions out of unsafe primitives in order to solve a similar problem: https://blog.rom1v.com/2019/04/implementing-tile-encoding-in...
Even Vec is implemented with unsafe code under the hood. Rust isn't about not using unsafe code anywhere: it's about encapsulating that unsafe code in reusable abstractions that can be easily audited. This is how essentially all languages work to begin with: unless you're using CompCert, the compiler itself is not proven correct, and so the compiler's code generator is "unsafe".
Here's an example of how rav1e, an AV1 encoder in Rust, builds safe abstractions out of unsafe primitives in order to solve a similar problem: https://blog.rom1v.com/2019/04/implementing-tile-encoding-in...
Wait, so how exactly is Rust better than C++ again? If I need to bring my own unsafe code to the party, where is the gain? Especially, if - in your words - "This is how essentially all languages work to begin with". I can build "safe" abstractions in any other language, too, can I not?
No, you can't build safe abstractions in C++. The language lacks the ability to enforce memory safety. Every abstraction you can come up with will have some way to subvert it. In Rust, the abstractions can't be broken without using unsafe, which application logic should never use.
This isn't just a theoretical distinction. Empirically, Rust programs have far fewer memory safety problems than C++ programs do.
This isn't just a theoretical distinction. Empirically, Rust programs have far fewer memory safety problems than C++ programs do.
In other languages, nothing ensures that those safe abstractions are actually used in safe ways. You can keep a dangling reference to a C++ vector, but Rust will make sure your references are valid, and you can only escape that with raw pointers in an unsafe block.
C++ doesn't have the tool to do so. Just like you can build abstraction for raw data in any language, but only the compiler in static typed language will scream at you at compile time if you use it the wrong way and dynamic language will just believe you will do the right thing.
In general you don't need to bring your own unsafe code to the party. The standard library contains most of the unsafe code you'll need to use in your normal code, and a handful of well-supported crates (like rayon) provide the more advanced utilities that the standard library doesn't. In most cases you're only writing `unsafe` if you're interacting with C.
And when you do decide you need to use `unsafe` for a non-FFI purpose, Rust provides the tooling to explicitly define the abstraction barrier such that clients of your code don't have to care (or even know) that you're using unsafe internally.
And when you do decide you need to use `unsafe` for a non-FFI purpose, Rust provides the tooling to explicitly define the abstraction barrier such that clients of your code don't have to care (or even know) that you're using unsafe internally.
To reply to both you and your parent at once, yes, the reason this is in the nursery is that it's not a complete resource yet. I agree that this particular example is bad; it's showing the right pattern for the wrong example.
The right way is to use rayon, which is similar to OpenMP in this sense. Each thread would get a pointer to the chunk of the buffer it's operating on. You don't need to write any unsafe code to do this.
The right way is to use rayon, which is similar to OpenMP in this sense. Each thread would get a pointer to the chunk of the buffer it's operating on. You don't need to write any unsafe code to do this.
It's good to hear that there's an idiomatic Rust way of doing this that doesn't require unsafe but is still performant. I figured there was, but to an outsider it was not obvious how.
This is not actually the first time I've seen this example code. I was wondering how Rust solved this issue (parallel rendering into a single framebuffer) in a way that satisfied the borrow checker, and came across this example. It was a bit disheartening. Rust seems like an excellent language with boundless potential, but as I said, this particular example makes for a very bad first impression. It is also not obvious at all that this is part of the "nursery" and is not an official Rust document (the "Rust Cookbook" makes it seem more polished than maybe it is).
This is not actually the first time I've seen this example code. I was wondering how Rust solved this issue (parallel rendering into a single framebuffer) in a way that satisfied the borrow checker, and came across this example. It was a bit disheartening. Rust seems like an excellent language with boundless potential, but as I said, this particular example makes for a very bad first impression. It is also not obvious at all that this is part of the "nursery" and is not an official Rust document (the "Rust Cookbook" makes it seem more polished than maybe it is).
> It's good to hear that there's an idiomatic Rust way of doing this that doesn't require unsafe but is still performant. I figured there was, but to an outsider it was not obvious how.
Yeah, I mean, the reddit thread way up this comment chain talks about how Rayon should have been used, but the discoverability issue is real.
> It is also not obvious at all that this is part of the "nursery" and is not an official Rust document (the "Rust Cookbook" makes it seem more polished than maybe it is).
Yep; it's in the URL but not everyone will see that. Like most things, this is basically an accident of history; there was a push to clean this project up and make it an official resource, but before that work was finished, all the contributors had life stuff happen and had to go do something else. So it's in this weird quasi-state where there's a ton of good in there, but also some bad. We'll get to it...
Yeah, I mean, the reddit thread way up this comment chain talks about how Rayon should have been used, but the discoverability issue is real.
> It is also not obvious at all that this is part of the "nursery" and is not an official Rust document (the "Rust Cookbook" makes it seem more polished than maybe it is).
Yep; it's in the URL but not everyone will see that. Like most things, this is basically an accident of history; there was a push to clean this project up and make it an official resource, but before that work was finished, all the contributors had life stuff happen and had to go do something else. So it's in this weird quasi-state where there's a ton of good in there, but also some bad. We'll get to it...
Oh, someone on Reddit posted the rayon using code https://www.reddit.com/r/programming/comments/c7sgvw/writing...
Here's an article explaining how rav1e, an AV1 encoder aiming for production quality, solves this problem: https://blog.rom1v.com/2019/04/implementing-tile-encoding-in...
Oh nice.
What a delightful post. Author wrote a very nice description of things they learned from a little weekend project. No preaching or ranting or opinionating. Just “I did a thing and here’s what I learned”. That’s easily my favorite type of blog post.
Thanks for sharing! ️
Thanks for sharing! ️
> I wrapped my objects in atomic reference counters, and wrapped my pixel buffer in a mutex
Rust people, is there a way to tell the compiler that each thread gets its own elements? Do you really have to either (unnecessarily) add a lock or reach for unsafe?
Rust people, is there a way to tell the compiler that each thread gets its own elements? Do you really have to either (unnecessarily) add a lock or reach for unsafe?
It's a library, so only half an answer to your question, but there's a fantastic library called rayon[1] created by one of the core contributors the the Rust language itself, Niko Matsakis. It lets you use Rust's iterator API to do extremely easy parallelism:
list.iter().map(<some_fn>)
list.par_iter().map(<some_fn>)
let rendered = buffers.par_iter().map(<rendering>).collect();
for buffer in rendered.iter() {
// The copy from the article
}
Yes, there's `chunks_mut` [0] in the standard library that separate the slice to multiple non-overlapped chunks.
[0]: https://doc.rust-lang.org/std/primitive.slice.html#method.ch...
[0]: https://doc.rust-lang.org/std/primitive.slice.html#method.ch...
If you want to use completely safe Rust, you could probably get the Vec<u32> as a `&mut [u32]`, then use `.split_at()` on the slice to chop up the buffer into multiple contiguous sub-pieces for each thread. Collect up those pieces behind a struct for easier usage. It would cost you an extra pointer + length for each subpiece, but that's the price for guaranteeing that no thread reaches outside the contiguous intervals assigned to it.
EDIT: As mentioned by a sibling, `chunks_mut` is probably closer to what you want in this instance. If you have to get chunks of various sizes -- for instance, if the number of threads doesn't evenly divide the buffer into nice uniform tiles -- you'd need to drop down to the `split_at` level anyway.
EDIT: As mentioned by a sibling, `chunks_mut` is probably closer to what you want in this instance. If you have to get chunks of various sizes -- for instance, if the number of threads doesn't evenly divide the buffer into nice uniform tiles -- you'd need to drop down to the `split_at` level anyway.
> Rust people, is there a way to tell the compiler that each thread gets its own elements?
That's what `local_pixels` does in the post. Where things get trickier is when you want to share write access to a single shared buffer in a non-overlapping way (e.g. `buffer` in the post.) To do this you need to either resort to unsafe, or to prove to the compiler that the writes aren't overlapping. One way to do the latter this is to get a slice (which Vec is convertable into), and then split up that slice (which the standard library has plenty of methods for: https://doc.rust-lang.org/std/slice/index.html ), and then give each thread those non-overlapping slices.
That's what `local_pixels` does in the post. Where things get trickier is when you want to share write access to a single shared buffer in a non-overlapping way (e.g. `buffer` in the post.) To do this you need to either resort to unsafe, or to prove to the compiler that the writes aren't overlapping. One way to do the latter this is to get a slice (which Vec is convertable into), and then split up that slice (which the standard library has plenty of methods for: https://doc.rust-lang.org/std/slice/index.html ), and then give each thread those non-overlapping slices.
Yes. Instead of having a single slice of pixels, split it into n slices, one for each thread.
I wonder if there’s a way to borrow noncontiguous slices.
Yes, the standard library has many methods for splitting up a single mutable slice into multiple non-overlapping mutable slices. There's split_at_mut() which just splits at an index, or split_mut() which splits using a predicate, or chunks() which gives you an iterator over non-overlapping subslices of a given length, and more.
unsafe is the tool u are looking for.
No, there are plenty of safe ways to achieve this in the standard library. The chunks and split families of functions on slices are all designed to do pretty much exactly this.
My comment really upset folks, https://doc.rust-lang.org/src/core/slice/mod.rs.html#991-100...
unsafe is the mechanism that GP needs to use to get multiple contiguous mutable borrows.
There is nothing wrong with unsafe, it is used to build all of the safe abstractions in Rust.
unsafe is the mechanism that GP needs to use to get multiple contiguous mutable borrows.
There is nothing wrong with unsafe, it is used to build all of the safe abstractions in Rust.
Everyone here is aware that split\* and chunks\* are built using unsafe. However, reaching for unsafe yourself in this situation is explicitly the wrong thing to do.
The entire point of rust's safety system is that it is possible to build safe things on unsafe foundations because the unsafety can be encapsulated into functions and types that can only be used safely. The safety of these functions then depends on them being bug-free, and the best way this is achieved is by minimizing the total amount of unsafe code in the ecosystem, and sharing it in widely used libraries so that there are enough users and testing to find the bugs.
So no, unsafe is not the mechanism GP needs to, or should use, because the split\* and chunks\* families of functions already exist and do exactly what he wants.
The entire point of rust's safety system is that it is possible to build safe things on unsafe foundations because the unsafety can be encapsulated into functions and types that can only be used safely. The safety of these functions then depends on them being bug-free, and the best way this is achieved is by minimizing the total amount of unsafe code in the ecosystem, and sharing it in widely used libraries so that there are enough users and testing to find the bugs.
So no, unsafe is not the mechanism GP needs to, or should use, because the split\* and chunks\* families of functions already exist and do exactly what he wants.
In fairness to GP, they are implemented using unsafe (which is unsurprising since they take one &mut and return two to the same borrowed data).
If you go by that definition, I think you’ll eventually find out that everything depends on unsafe, and thus nothing is actually safe
Which isn’t a very useful distinction
Which isn’t a very useful distinction
:(
All of Rust's safe abstractions are on top of unsafe. It isn't a bad thing, it just need to be used with rigor.
Splitting a single slice into two mutable slices is done via https://doc.rust-lang.org/std/primitive.slice.html#method.sp... if you want more than that, you will need to roll your own.
I think it would be a great exercise to implement what you are asking for, the docs link directly to the source.
https://doc.rust-lang.org/src/core/slice/mod.rs.html#991-100...
Splitting a single slice into two mutable slices is done via https://doc.rust-lang.org/std/primitive.slice.html#method.sp... if you want more than that, you will need to roll your own.
I think it would be a great exercise to implement what you are asking for, the docs link directly to the source.
https://doc.rust-lang.org/src/core/slice/mod.rs.html#991-100...
Zig is worth supporting on Patreon: https://www.patreon.com/andrewrk
I didn't quite grok this bit:
> The ability to return values from if expressions and blocks is awesome and I don’t know how I’ve managed to live up until now without it. Instead of conditionally assigning to a bunch of variables it is better to return them from an if expression instead.
The example shown (aside from the fact it's assigning a tuple, which is a different point) would naturally be a ternary in C/C++. Does the awesomeness kick in for more complicated examples where you want intermediate vars etc in the two branches?
> The ability to return values from if expressions and blocks is awesome and I don’t know how I’ve managed to live up until now without it. Instead of conditionally assigning to a bunch of variables it is better to return them from an if expression instead.
The example shown (aside from the fact it's assigning a tuple, which is a different point) would naturally be a ternary in C/C++. Does the awesomeness kick in for more complicated examples where you want intermediate vars etc in the two branches?
There are lots of little nice things:
* you can more easily handle more than 2 options
* you can more easily have a bunch of code in each case
* you don't have a new syntax for the compiler or programmer to have to know about, everything is just consistently an expression
It is nice, and those of us who say that are usually aware of various alternative workarounds with ternaries etc.
* you can more easily handle more than 2 options
* you can more easily have a bunch of code in each case
* you don't have a new syntax for the compiler or programmer to have to know about, everything is just consistently an expression
It is nice, and those of us who say that are usually aware of various alternative workarounds with ternaries etc.
Yes, anything which is more complex than a very simple if-else. The advantage is even more obvious with switch-expressions, e.g.:
https://ziglang.org/documentation/master/#switch
https://doc.rust-lang.org/reference/expressions/match-expr.h...
https://ziglang.org/documentation/master/#switch
https://doc.rust-lang.org/reference/expressions/match-expr.h...
Really cool post. I always dreamed of writing a small realtime, raytraced game, with lights etc. Basically a roguelike in 3D. I never managed to finish it, and this project reminds me of it.
I really don't think these languages should be set opposite to one another as much as they do. I mean, I get why they are. They take up almost the same position and have quite different ways to view security and lang design. And they both try to grow and compete.
But still. I think there are some space for them both.
I would really think it would be cool to spend my working hours programming Rust for safety and switching to Zig whenever I have to code an unsafe block (all of it compiling to webasm :o )
In my mind/opinion, Rust is a potential replacement for C++, while Zig is a potential replacement for C, and both have their place in the world.
Rust feels more restrictive, but that may be the right approach for building large software projects with big, "diverse" (in terms of skill level) teams.
Zig is smaller and feels more nimble, and might be better suited for smaller teams working on smaller projects, and for getting results faster, while avoiding most of C's darker corners.
Rust feels more restrictive, but that may be the right approach for building large software projects with big, "diverse" (in terms of skill level) teams.
Zig is smaller and feels more nimble, and might be better suited for smaller teams working on smaller projects, and for getting results faster, while avoiding most of C's darker corners.
That was a really fun read... Now if the author could do it in nim and v-lang...
At the risk of shedding it to bikes, one point that the author makes is that Zig's lack of operator overloading makes him write vector math like this:
He signs off with:
> How do C programmers manage?
The answer is simple: we assign names to intermediate results. Now, I have absolutely no idea what that expression computes, because I suck at graphics programming and math in general. Please pretend that these are proper mathy terms:
I'm convinced that there's a proper mathy/lighting-y word for each component in that expression. Of course this approach totally breaks down if you're copying expressions from papers or articles without understanding why they are correct (which is how I do all my graphics programming). I do find that naming variables is often a great way to force myself to grok what's going on.