Support for esp32

[haikyuu]

I am planning to build an ebook reader and so I ordered a LILYGO® E-ink Display
I am still looking for a convenient way to build the UI and this project seems like the most developer friendly one.

How hard is it to add support for this?

[ogoffart]

It all depends on the Rust support for it.
From my understanding after a quick search, rust should be supported without much problem on such devices.

The MCU port is still work in progress, but basically, to support a custom board, you have to implement a trait providing capabilities such as sending pixels to the screen and listening to the touchscreen.

This is the current trait (but it may change in the future):

slint/internal/backends/mcu/lib.rs

Lines 38 to 48 in eb9092b

	pub trait Devices {
	fn screen_size(&self) -> PhysicalSize;
	fn fill_region(&mut self, region: PhysicalRect, pixels: &[TargetPixel]);
	fn read_touch_event(&mut self) -> Option<i_slint_core::input::MouseEvent> {
	None
	}
	fn debug(&mut self, _: &str);
	fn time(&self) -> core::time::Duration {
	core::time::Duration::ZERO
	}
	}

So for example, this file implements the support for the RaspberryPi Pico https://github.com/slint-ui/slint/blob/eb9092ba15f212dc35f92b2bceae07b851cef6d2/internal/backends/mcu/pico_st7789.rs
It contains all the code to configure the pins, the touch driver (which arguably should be in a different crate), a panic handler, and the implementation of the Devices trait.

(We will also expose that from other programming languages when we support that.)