Pre luminance-1.0.0 and random thoughts

luminance, imposter-syndrom
Fri Apr 26 22:30:00 2019 UTC, by Dimitri Sabadie — feed

Random thoughts on making luminance-1.0.0

Hello people. It’s been weeks I have started to work on luminance-1.0.0. For a brief recap, luminance is a graphics crate that I originally created in Haskell, when I ripped it off from a demoscene engine called quaazar in order to make and maintain tiner packages. The Rust port was my first Rust project and it became quickly the default language I would develop graphics applications in.

So if you’re interested, yes, luminance in Haskell still exists but I maintain it for strictly minimal support (i.e. support compiler bumps, for instance). The default and official language to use, if you’re interested by luminance, is Rust.

Another important thing I have to explain is the current feature list of luminance and what it’s going to be soon. Currently, luminance’s goals are (according to the documentation):

  • Making the unsafe and stateful OpenGL API safe and stateless.
    • Unsafe means that OpenGL performs operations by relying on the fact you know what you’re doing: pointer arithmetic, memory alignment, etc. Lots of situations in which you can literally RIP in pepperonis.
    • Stateful means that lots of OpenGL functions expect a context to be in a special state for a correct behavior. For instance, when uploading texels to the GPU’s VRAM, the texture that must receive the texels must be bound to a texture unit. If you forget to do that, you get a weird behavior that is seen at runtime and not always correctly interpreted. It is sometimes hard to know why and what something has gone wrong. It makes also a pain in the @!#=$ as soon as you want to share work on several threads.
  • Providing a simple and easy interface; that is, exposing core concepts without anything extra – just the bare stuff.
    • Most low-level graphics library are hard for newcomers to grasp knowledge about. gfx-hal is an excellent graphics crate (so far, I think it’s the one everyone is recommending everyone in the Rust gamedev community) but it is hard to play with it when you don’t know either OpenGL 4.5 or Vulkan — and all the required concepts might be a bit overwhelming at first.
    • Even though luminance is still a pretty low-level API (you have renderbuffers, framebuffers, shader stages, etc.), the interface is opinionated and — in my opinion — easier to work with. Because it is my idea and my design, the experience might be slightly different from e.g. gfx-hal. It’s neither bad or good, just different. That also responds to the folks who don’t understand why I’m still maintaining luminance: because I want to do graphics code my way, and more choices is always a good sign to me. Yes, we could talk about community efforts, but OH LOOK A BIRD!
  • Easy to read with a good documentation and set of tutorials, so that newcomers don’t have to learn a lot of new concepts to get their feet wet.
  • Need-driven: every piece of code added in the project must come from a real use case. If you feel something is missing, feel free to open an issue or even contribute!
    • This is an important aspect to me. I don’t write code for the sake of writing code (even libraries). I have a problem and write code to solve it. So, on the surface, luminance might seem a bit less complete that, again, e.g. gfx-hal. And that would be likely right. However, if someone likes the API and wants something in, I accept both issues and PRs. There are several examples of people asking for features and having me implement them. There’s also some folks who actually wrote the code and it’s now in luminance!
    • Head over to if you want to start discussing the feature set.

That’s the current situaton. A very important other aspect is that luminance was designed, in the first place, to be backend agnostic. I quickly decided not to go this way and stick to a simpler design with OpenGL only.

A comparison between luminance and other famous crates is available here.

However, I have — again! — changed my mind. Today, I want to have a system of backend in luminance. Maybe not something as complex and complete as the gfx-rs project, but something that will allow those backends:

  • Any OpenGL version: missing features from older versions will be implemented (if not too much work is needed) by luminance software patches.
  • At least one WebGL implementation and it must be WASM compatible.
  • Vulkan.

I really do not target Metal, DirectX12 nor any other graphics backend you might have in mind. However, if you think it’s possible to do so, then we should discuss about it. Nevertheless, as I said above, luminance is need-driven: as I don’t need DirectX12, I will not work on it unless someone REALLY needs it and provides a PR (or at least enough for me to work on it… including beers).

What to expect

luminance-1.0.0 will ship… as soon as possible. The current feature set is huge, though:

  • Add the "std" feature-gate. This will help use luminance with specific contexts, especially for demoscene or size-limited devices. Currently, the work on no_std has been saved for later as I had hit a bug last time I checked.
  • Change the Tess interface. Now, a TessBuilder must be used. This allows for three major enhancements:
    • Vertex instancing.
    • Deinterleaved memory.
    • Builder pattern.
  • Enhance the quality and variety of examples.
  • Introduce the luminance-derive crate. This crate provides several proc-macros used to implement various unsafe traits easily, without writing any unsafe code. Among those:
    • The Vertex trait, used to create vertex types.
    • The Semantics trait, used to create vertex semantics types.
    • The UniformInterface trait, used to create shader uniform interfaces.
    • All the previous macro_rules are removed.
  • Support a new dynamic way to get uniforms. Sometimes, you don’t know in advance the uniforms your shader is going to use. When such a case arise, you might be tempted to have a minimal uniform interface — if none. Dynamic uniform lookups allow you to query uniforms on the fly. That has obviously a runtime cost but it can be handy for lots of situations (GUI editors, scripting, etc.).
  • Update framebuffer code so that color slots and depth slots are easier to use.
  • Introduce the concept of drivers. Drivers allow code to be parametered by a type which represents a given implementation to use for the graphics code. You can have a GL33 driver for OpenGL 3.3, a GL40, GL44, GL45 etc., but you can also have WebGL and VK10.
  • Add vertex instancing. Vertex instancing allows to instantiate objects by providing instance data directly in a Tess — instead of using the current method with GPU Buffer<_>. This was asked by several people and I just couldn’t ignore such an interesting and useful feature!
  • Support for deinterleaved memory. Deinterleaved memory allows for more granularity on how data is fetched GPU-side. With the legacy luminance situation, data is completely interleaved, which means that a vertex’s attributes all follow each other in a GPU buffer. This is both nice and bad: if you need to access all attributes of a vertex, this is pretty good, since cache-locality will be in your advantage. However, if you’re only interested in positions, for instance, you will waste your cache lines with attributes you will never read from! Deinterleaved memory stores each attributes in a different GPU memory region, allowing for a way better memory scheme for such uses. People using the ECS pattern might be used to deinterleaved memory.
  • Add vertex primitive restart. This allows to use tessellation indexing modes such as TriangleFan or LineStrip and “cut” a primitive if an index is equal to a given value. This is very useful for implementing terrains, quadrics or a lot of other nice things.
  • Introduce vertex semantics. This is one of the sexiest and most exciting feature of this next release. I got the idea by thinking about the fact luminance should be low-level but provide very quick access to building high-level blocks. I got the idea with vertex semantics via my spectra crate. The idea is simple: currently, we must define a Vertex type and the order in which the fields appear in the struct defines the bindings the GPU will present to shaders… but it’s the user responsibility to tell how the shader will fetch those attributes. This can lead to very wrong situations in which, for instance, the GPU present the normal attribute as having the index 4 but the shader tries to fetch them on index 2. Vertex semantics fix this situation by adding an intermediate layer both the user and the GPU (i.e. via luminance) must speak: semantics. Semantics are user-defined and none is hardcoded in luminance. As soon as a type uses vertex semantics, all the type system knows how to forward that information to shaders and what shaders should do to fetch them. The other bonus, ultra cool thing is that shaders and memory buffers now compose way better: since vertex semantics define a sort of namespace, you will never have two shaders using the same index for different semantics (unless you use completely different vertex semantics type). A very cool feature I’m proud of and that I will detail in a future article / luminance tutorial.
  • And lots of other doc fixes, enhancements, etc.

One word about the feature set and spare-time

You might be wondering “Woah, this is such a big feature set. A lot of things are coming! Why not having split the feature set into several releases?”, and that’s a good question.

Lately, I’ve been feeling on-and-off about everything I do on my spare-time on the FOSS level. I have several crates I care about and sometimes people show up and start asking for features and/or bug fixes. This takes some time and after a long day of work, I sometimes feel that I just want to hack on things I like, play my electric guitar, go to swim or wakeboard or just spend time with people I care about and love.

Currently, luminance — even though it has an unexpected amount of downloads! — is not a famous crate. People nowadays talk about crates living in a higher-level stack, such as ggez, gfx, amethyst, piston, etc. I don’t communicate a lot about luminance because of, mostly, two things:

  1. Imposter syndrom.
  2. Avoid success at all cost.

I guess Haskellers will get the second point. ;)

My own philosophy about software and especially my own software is that it should have a top-tier quality, both in terms of API design, elegance, type safety, performance and documentation. The front documentation of warmy is a good example of something I continuously seek, because good documentation helps my future myself to read the code and public interface but also for onboarding people. Lots of projects — especially in professional industries — suffer from knowledge bubbles, in which just a bunch (often only one!) of people know about A and B and when someone joins in, they’re lost and have to ask questions. As an engineer, I always write everything I know in whatever source-of-truth the company I’m in can offer (it can be a Confluence server; a git repository; a wiki; whatever) because sharing knowledge and writing processes is key in engineering — also, pro tip: I highly value that when interviewing candidates!

But the more I advance and grow up, the more things I learn and the more things I master. And as I master new things, I tend to get used to them. And the “mental effort” it requires tends to slowly disappear. I remember when I tried (hard!) to wrap my finger around what a profunctor is, or what free monads or even natural transformations are and how to use them. It was hard. As a friend of mine (@lucasdicciocio) perfectly summarized it some times ago, when we learn something as a beginner, we struggle. But people who master those concepts struggle even harder when trying to learn the next concepts at hand. And I’m not an exception. Today, free monads are something I know (even though I don’t use them; it’s a myth! it’s a trap! :D) and I feel like I’m not legitimate to talk about them because they feel easy — and it’s normal, since I’ve learned them. But I see new things to learn, new hard things that I know I’ll be struggling with for a while. And now it feeds the imposter syndrom. You know, when you’re 20, you feel like you know a lot of things (and you likely do) and that you’re pretty confident with your skill base. Today, I’m 27, and I feel like I will always be a rookie, because there is always something I don’t know to struggle with. And I find that very exciting. Of course, I don’t project that on others, which is soooo paradoxal: I don’t expect a newcomer to tell me what a fundep is or know lifetime elision rules in Rust. But I guess I have a very very strict way to judge my knowledge. I still haven’t figured out if it’s a good thing or if it’s not.

I’ve been told that talking about what I do, what I think, what I know and my engineering philosophy should help with this kind of questioning. So I decided to use that blog article to share some thoughts about the next release of luminance that took me so much of my spare-time (but happily!) and to talk a bit about myself. I know a lot of people in the Rust and Haskell community don’t know me, but I also know lots of other folks do know me, in both communities. I hope my little vent will give people some relief — maybe you too have a similar experience? Please share your comments on the Reddit thread this article is post in.

As always, stick doing awesome things and spend your spare-time wisely. Spend time with the ones you love and do the things you hecking love too!

Keep the vibes!