fix: image flickering

src/main.rs

@@ -9,16 +9,18 @@ use image::{EncodableLayout, ImageReader, RgbaImage, imageops};
 
 #[derive(Clone, Debug)]
 enum Message {
+    ImageDisplayReady(Result<widget::image::Allocation, widget::image::Error>),
+
     Event(iced::Event),
 }
 
 #[derive(Clone, Debug)]
 struct State {
     image: RgbaImage,
-    image_handle: widget::image::Handle,
+    image_display: Option<widget::image::Allocation>,
 }
 impl State {
-    fn new() -> Self {
+    fn new() -> (Self, Task<Message>) {
         let image = if let Some(path) = env::args().nth(1) {
             ImageReader::open(path)
                 .unwrap()
@@ -29,18 +31,34 @@ impl State {
             RgbaImage::new(100, 100)
         };
 
+        let allocate_image = widget::image::allocate(widget::image::Handle::from_rgba(
+            image.width(),
+            image.height(),
+            unsafe { std::mem::transmute::<_, &'static [u8]>(image.as_bytes()) },
+        ))
+        .map(Message::ImageDisplayReady);
+
+        (
             State {
-            image_handle: widget::image::Handle::from_rgba(image.width(), image.height(), unsafe {
-                std::mem::transmute::<_, &'static [u8]>(image.as_bytes())
-            }),
+                image_display: None,
                 image,
-        }
+            },
+            allocate_image,
+        )
     }
     fn view(&self) -> Element<'_, Message, Theme, Renderer> {
-        widget::image(&self.image_handle).expand(true).into()
+        if let Some(allocation) = self.image_display.as_ref() {
+            widget::image(allocation.handle()).expand(true).into()
+        } else {
+            widget::space().into()
+        }
     }
     fn update(&mut self, message: Message) -> Task<Message> {
         match message {
+            Message::ImageDisplayReady(result) => {
+                self.image_display = Some(result.unwrap());
+            }
+
             Message::Event(iced::Event::Keyboard(keyboard::Event::KeyPressed {
                 key,
                 modifiers,
@@ -59,11 +77,12 @@ impl State {
 
                 Key::Character("r") => {
                     self.image = imageops::rotate90(&self.image);
-                    self.image_handle = widget::image::Handle::from_rgba(
+                    return widget::image::allocate(widget::image::Handle::from_rgba(
                         self.image.width(),
                         self.image.height(),
                         unsafe { std::mem::transmute::<_, &'static [u8]>(self.image.as_bytes()) },
-                    )
+                    ))
+                    .map(Message::ImageDisplayReady);
                 }
 
                 // ignore unused keys