Kivy Headless Renderer for Raspberry Pi

This project demonstrates the use of the Kivy framework to create a headless renderer for a Raspberry Pi. The renderer is specifically designed for and tested with the ST7789 SPI display, but it should work with other SPI displays as well. The code utilizes the Adafruit RGB Display library to communicate with the display. The renderer is optimized to not update the LCD if nothing has changed in the frame.

⚡️ Requirements

• Raspberry Pi 4
• SPI Display (tested with ST7789 module)
• SDL2 with kmsdrm backend

You need to compile and install SDL2 from source with kmsdrm backend. Please follow the instructions provided here

📦 Installation

You can install it using this handle: headless-kivy-pi@git+https://github.com/ubopod/headless-kivy-pi.git

pip install headless-kivy-pi

To work on a non-RPi environment, run this:

# pip:
pip install headless-kivy-pi[dev]
# poetry:
poetry --group dev headless-kivy-pi

🚀 Usage

1. Call setup_headless() before inheriting the HeadlessWidget class for the root widget of your application, and provide the optional parameters as needed. For example (these are all default values, you only need to provide the ones you want to change):

   setup_headless(
       min_fps=1,
       max_fps=30,
       width=240,
       height=240,
       baudrate=60000000,
       debug_mode=False,
       display_class=ST7789,
       double_buffering=True,
       synchronous_clock=True,
   )
   

2. Inherit the HeadlessWidget class for the root widget of your Kivy application. For example:

   class FboFloatLayout(FloatLayout, HeadlessWidget):
       pass
   

3. Run the Kivy app as you normally would.

Checkout Ubo App to see a sample implementation.

⚙️ Parameters

These parameters can be set to control the behavior of headless kivy pi:

min_fps

Minimum frames per second for when the Kivy application is idle.

max_fps

Maximum frames per second for the Kivy application.

width

The width of the display in pixels.

height

The height of the display in pixels.

baudrate

The baud rate for the display connection.

debug_mode

If set to True, the application will print debug information, including FPS.

display_class

The display class to use (default is ST7789).

double_buffering

Is set to True, it will let Kivy generate the next frame while sending the last frame to the display.

synchronous_clock

If set to True, Kivy will wait for the LCD before rendering next frames. This will cause Headless to skip frames if they are rendered before the LCD has finished displaying the previous frames. If set to False, frames will be rendered asynchronously, letting Kivy render frames regardless of display being able to catch up or not at the expense of possible frame skipping.

⚒️ Contribution

You need to have Poetry installed on your machine.

To install poetry in Raspbian you need to follow these instructions to install rust compiler, this is temporary until this issue is resolved:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
sudo apt-get install pkg-config libssl-dev
curl -sSL https://install.python-poetry.org | python3 -

After having poetry, to install the required dependencies, run the following command:

poetry install

Also be aware of this issue and until it is resolved you can manually disable keyring by prefixing your poetry commands like this:

PYTHON_KEYRING_BACKEND=keyring.backends.null.Keyring poetry install

⚠️ Important Note

This project has only been tested with the ST7789 SPI display module. Other display modules might not be compatible or may require changing the parameters or even modifications to the code.

📜 License

This project is released under the Apache-2.0 License.