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https://github.com/sassanh/headless-kivy

Headless renderer for Kivy framework
https://github.com/sassanh/headless-kivy

drm headless kivy pytest raspberry-pi-4 sdl sdl2 snapshot-testing spi-display

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Headless renderer for Kivy framework

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# Headless Kivy



Provides utilities to render Kivy applications headlessly. It calls a callback whenever something has changed in the framebuffer in a locality.



It can be used to render the Kivy application on a custom display like an SPI display, it provides tools for local updates, limiting the bandwidth and limiting the fps based on the spec of the display.



It can also be used in test environments with it tools for snapshot testing.



You can control the orientation of the display and flipping the display horizontally and vertically.



The renderer is optimized to not schedule a render when nothing has changed since the last rendered frame, by default it divides the screen into tiles and checks each tile for changes separately.



It can be configured to use double buffering, so that the next frame is generated while the last frame is being transmitted to the display.



You can have multiple instances of the headless renderer in the same application, each works as a portal to your display (or multiple different displays).



## 📦 Installation



```sh

pip install headless-kivy

```



To use its test tools, you can install it with the following command:



```sh

pip install headless-kivy[test]

```



## 🛠 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):



   ```python

   setup_headless(

       width=240,

       height=240,

       bandwidth_limit=1000000, # number of pixels per second

       bandwidth_limit_window=.1, # allow bandwidth_limit x bandwidth_limit_window pixels to be transmitted in bandwidth_limit_window seconds

       bandwidth_limit_overhead=1000, # each draw command, regardless of the size, has equivalent of this many pixels of cost in bandwidth

       is_debug_mode=False,

       rotation=1, # gets multiplied by 90 degrees

       flip_horizontal=True,

       double_buffering=True, # let headless kivy generate the next frame while the previous callback is still running

   )

   ```



1. Inherit the `HeadlessWidget` class for the root widget of your Kivy application.

   For example:



   ```python

   class FboFloatLayout(FloatLayout, HeadlessWidget):

       pass

   ```



1. Run the Kivy app as you normally would.



Checkout [Ubo App](https://github.com/ubopod/ubo-app) to see a sample implementation.



### ⚙️ Parameters



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



#### `callback`



A callback function that will be called when the screen data changes. It should

have this signature:



```python

def render(

    *,

    rectangle: tuple[int, int, int, int],

    data: NDArray[np.uint8],

    data_hash: int,

    last_render_thread: Thread,

) -> None: ...

```



`rectangle` is a tuple with the coordinates and size of the changed area in the

`(x, y, width, height)` format.



`data` is a numpy array with the screen RGB data in the `uint8` format. So its

dimensions are `(width, height, 3)`.



`data_hash` is probably not very useful for most cases, it is mostly for logging

and debugging purposes.



It always runs in a new thread, the previous thread is provided so that it can call

its `join` if desired.



#### `bandwidth_limit`



Maximum bandwidth usage in pixels per second, no limit if set to 0.



#### `bandwidth_limit_window`



Length of the time window in seconds to check the bandwidth limit.



#### `bandwidth_limit_overhead`



The overhead of each draw command in pixels, regardless of its size.



#### `width`



The width of the display in pixels.



#### `height`



The height of the display in pixels.



#### `is_debug_mode`



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



#### `double_buffering`



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

frame to the display.



#### `rotation`



The rotation of the display. It will be multiplied by 90 degrees.



#### `flip_horizontal`



If set to `True`, it will flip the display horizontally.



#### `flip_vertical`



If set to `True`, it will flip the display vertically.



## 🤝 Contributing



You need to have [uv](https://github.com/astral-sh/uv) installed on your machine.



To install the required dependencies, run the following command in the root directory of the project:



```sh

uv sync

```



## ⚠️ 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. See the [LICENSE](./LICENSE)

file for more details.