Developer experiences from the trenches

Developer experiences from the trenches

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Ninja Build for Asset Baking

Sun 22 January 2023 by Michael Labbe
tags code 

Ninja Build is typically used as a low-level source builder for CMake, Meson or GENie, but it is incredibly good at building game asset files, too.

Frogtoss Tech 3, the current-gen Frogtoss engine, uses Ninja to bake all assets (lighting, texture compression, etc). This has proven to be an extremely reliable and high performing choice. In terms of effort-for-results, it was a clear win for me.

Ninja tracks which files need updating on re-run, builds a DAG and executes all of the commands using your available cores. It supports incremental builds with great reliability and can be integrated to bake a source asset tree in a matter of hours from the start of experimentation.

The rest of this article makes the case for exploring using Ninja for baking assets.

Many developers have used Ninja to build source through CMake, or otherwise. It’s billed by the official website as supporting the low-level parts of building:

Where other build systems are high-level languages Ninja aims to be an assembler.

Many high level tools with incredible flexibility such as Meson generate Ninja files. Once Meson, GENie or CMake does this initial project scan, the Ninja file is generated and the project can be efficiently rebuilt.

Today, I am inviting you to look at Ninja quite differently than how it is advertised. In my view, Ninja is good for two things that aren’t frequently mentioned:

  1. Ninja files are straightforward to write by hand. Sure, you wouldn’t want to do it all the time, but you can learn it quite quickly.

  2. Ninja’s executable is easily distributable to your co-developers. It’s a much smaller dependency than Make/Bash to inflict on your Windows developers — just a single 600kB executable per platform.

For these reasons, I use Ninja even when its performance benefits are not necessary.

The official manual on writing your own ninja files is fairly short, but if you’re building assets and not source, you can cherry pick three things to get started:

Hand-writing your first experimental Ninja build file that can build a few of your assets is an exercise that should take less than half an hour.

From there, it is pretty clear to see how one could write a script to walk their asset tree and create a ninja build file. Many source asset trees are built from convention: a certain extension in a certain directory tells you everything you need to know to produce the output asset for a specific platform.

If you write your own Ninja Build generator that consists of rules and statements, I would encourage you to not be constrained by languages that include libraries that help you build Ninja files. In my case, this was achieved in about 200 lines of Rust with no third party crates.

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