neiam /gitgud

defmodule GitGud.Badges.Native do
  @moduledoc """
  The `native/gitgud_badge` Rustler NIF: B612 Mono glyph outlines and
  SVG-to-PNG rendering.

  Badge lettering is drawn as paths instead of `<text>`. An SVG that
  another site loads through `<img>` can't fetch a web font, so `<text>`
  would render in whatever monospace the reader happens to have, and
  the PNG renderer would need a font stack of its own. As outlines, the
  SVG and the PNG are the same drawing everywhere. The font (SIL OFL
  1.1) is compiled into the NIF; `resvg` is built without its text
  features, so neither image needs fontconfig or any other system
  library.
  """

  use Rustler, otp_app: :git_gud, crate: "gitgud_badge"

  @doc "One B612 Mono character's advance as a fraction of the font size."
  @spec advance_em() :: float()
  def advance_em, do: :erlang.nif_error(:nif_not_loaded)

  @doc """
  How wide `text` draws at `size` px. B612 Mono is monospaced, but the
  emoji it falls back to for what it lacks aren't.
  """
  @spec text_width(String.t(), boolean(), float()) :: float()
  def text_width(_text, _bold, _size), do: :erlang.nif_error(:nif_not_loaded)

  @doc """
  `text` as an SVG path `d`, at `size` px, starting at `x` on `baseline`.
  All three numbers must be floats.
  """
  @spec text_path(String.t(), boolean(), float(), float(), float()) :: String.t()
  def text_path(_text, _bold, _size, _x, _baseline), do: :erlang.nif_error(:nif_not_loaded)

  @doc "PNG bytes for `svg`, rendered at `zoom` times its own size."
  @spec rasterize(String.t(), float()) :: {:ok, binary()} | {:error, String.t()}
  def rasterize(_svg, _zoom), do: :erlang.nif_error(:nif_not_loaded)
end