# EgdTextPanel [](https://hex.pm/packages/egd_text_panel) [](https://egd-text-panel.hexdocs.pm/EgdTextPanel.html) [](https://dl.circleci.com/status-badge/redirect/gh/fhunleth/egd_text_panel/tree/main) [](https://api.reuse.software/info/github.com/fhunleth/egd_text_panel) This is a simple text panel for use with the [EGD (Erlang Graphics Drawer)](https://github.com/erlang/egd) library.  This is being used to output text to an EInk display. EGD is not even close to supporting the feature set of other graphics libraries, but it's pure Erlang. It's also sufficient for lots of projects where I just want to show status or output diagnostics. ## Using The first step to using `EgdTextPanel` is to create one. This requires providing an `EgdTextPanel.Renderer` implementation that displays update to your display. This is a one-time setup device-specific step so see the next section for an example for the Nerves Starter Kit's display. ```elixir iex> {:ok, panel} = EgdTextPanel.start_link(...) {:ok, #PID<0.268.0>} iex> IO.puts(panel, "Hello, world!") :ok ``` You should see `"Hello, world!"` on your display now. Anything you can send to `IO.puts/2` goes to the display so you can pass around the `panel` reference and use it just like any other text output device. It's also possible to send a subset of ANSI commands to clear a line or clear the screen and start over. Use `IO.ANSI.format/1` to encode the ANSI control codes to clear the screen and put the cursor back at the top left. Set `panel` to `:stdio` to see what happens without `EgdTextPanel`. ```elixir iex> IO.puts(panel, IO.ANSI.format([:clear, :home, "A fresh start"])) :ok ``` You can also render horizontal animations by using `IO.write/2` to stay on a line: ```elixir iex> Enum.each(10..1//-1, fn n -> IO.write(panel, IO.ANSI.format([:clear_line, "\rT-#{n}"])); Process.sleep(1000) end);\ IO.puts(panel, IO.ANSI.format([:clear_line, "\rLift off!"])) ``` The parts to note are the use of `:clear_line` to erase the text on the line and the `\r` to move back to the start of the line. ## Example code This code snippet works on the Nerves Starter Kit. ```elixir defmodule Demo do @behaviour EgdTextPanel.Renderer def run() do {:ok, eink} = EInk.new(EInk.Driver.UC8179, dc_pin: "EPD_DC", reset_pin: "EPD_RESET", busy_pin: "EPD_BUSY", spi_device: "spidev0.0" ) {:ok, panel} = EgdTextPanel.start_link( renderer: __MODULE__, renderer_state: %{eink: eink, render_count: 0}, width: 648, height: 480 ) IO.puts(panel, "Hello, world!") panel end @impl EgdTextPanel.Renderer def draw_background(_image, state), do: state @impl EgdTextPanel.Renderer def render_image(image, state) do # Do a full refresh every 10 frames render_count = state.render_count refresh_type = if rem(render_count, 10) == 0, do: :full, else: :partial rgb = :egd.render(image, :raw_bitmap) data = pack_bits(rgb) EInk.draw(state.eink, data, refresh_type: refresh_type) %{state | render_count: render_count + 1} end defp pack_bits(binary) do # Convert 24-bit RGB to 1 bpp. This samples the high bit of the red # component. A more sophisticated conversion would convert to gray and # dither, but the example source image is black and white anyway. for <>, into: <<>> do <> end end end ``` ## Fonts EGD uses `.wingsfont` files. These appear to have originated with [Wings 3D](https://www.wings3d.com/) even though it hasn't used them in a long time. They're lightly processed BDF bitmap fonts that have been saved in Erlang term format to make them easy to load. At the moment, my [fork of EGD](https://github.com/fhunleth/egd/tree/fh-fixes) has the `.bdf` to `.wingsfont` conversion utility that used to be in the Wings 3D repository. Also be aware that EGD doesn't support Unicode characters. It's an easy fix that you can also find in my fork. Before converting a BDF font, you may want to use [BDF view](https://emurenmrz.github.io/bdf_view/) to view the glyphs.