# Build Scripts

This folder holds common build scripts accessed via the various `npm run` commands.
Codegen is executed when calling `npm install` in order to generate all artifacts needed for the build to pass

## Bundeling all the code

The bundling process can be split into several steps:

`npm run build-css`
This command will compile the css code and create the css file.

`npm run build-prod` and `npm run build-dev`
These commands will use rollup to bundle the code. This is where the magic happens and uses some files in this folder.

`banner.ts` is used to create a banner at the beginning of the output file

`rollup_plugins.ts` is used to define common plugins for rollup configurations

`rollup_plugin_minify_style_spec.ts` is used to specify the plugin used in style spec bundeling

In the `rollup` folder there are some files that are used as linking files as they link to other files for rollup to pick when bundling.

Rollup is generating 3 files throughout the process of bundling:

`index.ts` a file containing all the code that will run in the main thread.

`shared.ts` a file containing all the code shared between the main and worker code.

`worker.ts` a file containing all the code the will run in the worker threads.

These 3 files are then referenced and used by the `bundle_prelude.js` file. It allows loading the web worker code automatically in web workers without any extra effort from someone who would like to use the library, i.e. it simply works.

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### `npm run codegen`

The `codegen` command runs the following three scripts, to update the corresponding code files based on the `v8.json` style source, and other data files. Contributors should run this command manually when the underlying style data is modified. The generated code files are then committed to the repo.

#### generate-struct-arrays.ts

Generates `data/array_types.ts`, which consists of:

 - `StructArrayLayout_*` subclasses, one for each underlying memory layout
 - Named exports mapping each conceptual array type (e.g., `CircleLayoutArray`) to its corresponding `StructArrayLayout` class
 - Specific named `StructArray` subclasses, when type-specific struct accessors are needed (e.g., `CollisionBoxArray`)

#### generate-style-code.ts

Generates the various `style/style_layer/[layer type]_style_layer_properties.ts` code files based on the content of `v8.json`. These files provide the type signatures for the paint and layout properties for each type of style layer.

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