MCU backend: build with no_std

sixtyfps_runtime/rendering_backends/default/lib.rs

@@ -25,6 +25,13 @@ In order for the crate to be available at runtime, they need to be added as feat
 
 */
 #![doc(html_logo_url = "https://sixtyfps.io/resources/logo.drawio.svg")]
+#![cfg_attr(
+    not(any(
+        feature = "sixtyfps-rendering-backend-qt",
+        feature = "sixtyfps-rendering-backend-gl"
+    )),
+    no_std
+)]
 
 cfg_if::cfg_if! {
     if #[cfg(feature = "sixtyfps-rendering-backend-qt")] {

sixtyfps_runtime/rendering_backends/mcu/lib.rs

@@ -18,13 +18,18 @@ only be used with `version = "=x.y.z"` in Cargo.toml.
 
 */
 #![doc(html_logo_url = "https://sixtyfps.io/resources/logo.drawio.svg")]
+#![cfg_attr(not(feature = "simulator"), no_std)]
 
+extern crate alloc;
+
+use alloc::boxed::Box;
+use alloc::rc::Rc;
+use alloc::string::String;
 use sixtyfps_corelib::{
     graphics::{Image, Size},
     window::Window,
     ImageInner,
 };
-use std::rc::Rc;
 
 #[cfg(feature = "simulator")]
 mod simulator;
@@ -33,7 +38,6 @@ mod simulator;
 use simulator::*;
 
 mod renderer;
-
 pub struct Backend;
 
 impl sixtyfps_corelib::backend::Backend for Backend {
@@ -101,5 +105,5 @@ pub const HAS_NATIVE_STYLE: bool = false;
 pub const IS_AVAILABLE: bool = true;
 
 pub fn init() {
-    sixtyfps_corelib::backend::instance_or_init(|| Box::new(Backend));
+    sixtyfps_corelib::backend::instance_or_init(|| alloc::boxed::Box::new(Backend));
 }

sixtyfps_runtime/rendering_backends/mcu/renderer.rs

@@ -8,9 +8,10 @@
     Please contact info@sixtyfps.io for more information.
 LICENSE END */
 
+use alloc::collections::VecDeque;
+use alloc::rc::Rc;
+use alloc::{vec, vec::Vec};
 use core::pin::Pin;
-use std::collections::VecDeque;
-use std::rc::Rc;
 
 use embedded_graphics::pixelcolor::Rgb888;
 use embedded_graphics::prelude::*;
@@ -25,7 +26,7 @@ pub fn render_window_frame<T: DrawTarget<Color = Rgb888>>(
     background: Rgb888,
     display: &mut T,
 ) where
-    T::Error: std::fmt::Debug,
+    T::Error: core::fmt::Debug,
 {
     let size = display.bounding_box().size;
     let mut scene = prepare_scene(runtime_window, SizeF::new(size.width as _, size.height as _));
@@ -244,7 +245,7 @@ struct LineCommand {
     spans: Vec<SceneItem>,
 }
 
-fn compare_scene_item(a: &SceneItem, b: &SceneItem) -> std::cmp::Ordering {
+fn compare_scene_item(a: &SceneItem, b: &SceneItem) -> core::cmp::Ordering {
     // First, order by line (top to bottom)
     match a.y.partial_cmp(&b.y) {
         None | Some(core::cmp::Ordering::Equal) => {}