The new luminance is there

luminance, opengl, webgl, sdl2, backend

2020-07-16 18:49:00 UTC, by Dimitri Sabadie — feed

Today is the day luminance-0.40 got released. This is a massive update. Like never before in the luminance ecosystem.

(Short) story of what happened

A huge amount of features, bug fixes, usability / comfort enhancement, new crates and architecture redesign are gathered in that update. First, let’s talk about the new most important feature: the redesign.

The backend (re)design

Before 0.40, luminance was an OpenGL 3.3 crate. If you’re not into graphics APIs, OpenGL is a graphics normalized specification, built by an open group (Khronos) that has been around for decades. Because it’s an open specification, lots of vendors can implement and provide drivers to have OpenGL support, but also Free and OpenSource projects. The 3.3 version was old enough to support a wide variety of devices, even old ones, while still having interesting features allowing to do lots of useful things.

However, as time passes, new devices and technologies emerge. WebGL 1.0, which appeared in 2011, is to the Web what OpenGL is to desktop and console graphics programming. It is an open API browsers can implement to provide support for accelerated 2D/3D rendering in your browser.

WebGL 2.0, which appeared more recently, in 2017 (partial support in some browsers), provide an API almost identical to what you find in OpenGL 3.3 (with some tricky caveats).

I’ve been wanting to have a way to write “luminance code”, and have it compile for other platforms than desktops, like Web and mobile (Android and iOS). With the previous architecture, since luminance was bound to OpenGL 3.3, it was not possible. Here comes the new archicture.

Backends… backends? backends!

The whole luminance crate was rewritten so that its public-facing interface is completely agnostic of what executing GPU code is about. No OpenGL anymore. Instead, it depends on a type variable, referred as B in luminance’s types, which must satisfy a set of conditions to be considered a backend.

A backend is an implementation of the expectations made on the public-facing interface. For instance, you can set a GPU buffer by providing an index and a value. That’s the public facing part. However, what happens on the GPU is left to the backend implementation.

This new way of doing split the luminance crate into several ones:

Added to this, because of how generic and abstract luminance now is, people might get issues when trying to write code that will work whatever the backend. When using the set functions on a buffer, it is required that the type implements a trait from luminanceluminance::backend::buffer::Buffer. So it’s likely the user will have to constrain types and it might get boring. For this reason, a new crate was created: luminance-front.

luminance-front allows people to write code using types from luminance that got their B type variable replaced by a backend type at compile-time. This is done by inspecting the compilation target, and features you enable. You are then free to write your code without worrying about whether traits are implemented, since luminance-front takes care of that for you. The re-exported types are simple aliases to luminance’s types, so your generic code — if you write any — will be compatible.

Changelog, migration guide

The changelog is quite massive for a single update. I wish I had the opportunity to split it into several updates, but the redesign meant a lot of changes, and I got several very interesting PRs and feature requests. Among very new stuff:

A huge thanks to all the people who contributed. It means a lot to me! The list of changes is big, so I’ll leave you with the changelog here.

Disclaimer: this is the luminance changelog, but all the crates have their own, too.

Because that update is massive and has some breaking changes, I have also decided to include a migration guide. The migration guide is a section in luminance’s changelog to explain all the things you need to do to migrate from luminance-0.39 to luminance-0.40. Please: if you find something that is missing or you’re struggling with, please open an issue, a PR, or ping me on whatever platform you like.

What’s next to read

The Tess type now supports slicing deinterleaved memory in very, very elegant ways, checked at compile-type and type-driven. The whole new Tess type design is so new that a blog article is on its way about that topic, as I find it very interesting.

While testing the redesign and new features, I have implemented a Conway’s Game of Life for fun — no code available yet. I plan to remake it from scratch and record the whole experience on video. That will be a new format and I want to hear from people and know whether they like the format.

Finally, the book was also updated. The three chapters have been updated and some features have been added — like aspect ratio in chapter 3; I don’t understand why I haven’t talked about that earlier!

The next steps for luminance and myself, besides the blog articles and video, are… getting some rest. I plan to get back to demoscene production, and I’m 100% sure there’s already a lot to do with that current release of luminance. I plan to experiment with new backends as well, such as an OpenGL 2.0 backend (if possible), to support really old hardware; an OpenGL 4.6 backend for modern hardware (easy), as I already know that API pretty well; an OpenGL ES backend for mobile development, and later, a Vulkan and, perhaps, a WebGPU backends.

Stay tuned for the Tess article, the Game of Life video… and keep making super fun video games, animation and toys with luminance!

And keep the vibes!