feat: usage info on start

src/main.rs

@@ -1,13 +1,11 @@
 use std::{env, ffi::OsStr, fs};
 
 use iced::{
-    Color, Element, Length, Renderer, Subscription, Task, Theme, color, event,
+    Alignment, Color, Element, Length, Renderer, Subscription, Task, Theme, color, event,
     keyboard::{self, Key, key},
     theme, widget, window,
 };
-use image::{
-    EncodableLayout, ImageReader, Pixel, Rgba, RgbaImage, codecs::webp::WebPEncoder, imageops,
-};
+use image::{EncodableLayout, ImageReader, RgbaImage, codecs::webp::WebPEncoder, imageops};
 use rfd::FileDialog;
 
 #[derive(Clone, Debug)]
@@ -19,32 +17,22 @@ enum Message {
 
 #[derive(Clone, Debug)]
 struct State {
-    image: RgbaImage,
+    image: Option<RgbaImage>,
     image_display: Option<widget::image::Allocation>,
 }
 impl State {
     fn new() -> (Self, Task<Message>) {
-        let image = if let Some(path) = env::args().nth(1) {
-            ImageReader::open(path)
-                .unwrap()
-                .decode()
-                .unwrap()
-                .into_rgba8()
-        } else {
-            let mut image = RgbaImage::new(100, 100);
-
-            imageops::horizontal_gradient(
-                &mut image,
-                Rgba::from_slice(&[0, 0, 0, 0]),
-                Rgba::from_slice(&[255, 255, 255, 255]),
-            );
-
-            image
-        };
-
         let state = State {
             image_display: None,
-            image,
+            image: env::args().nth(1).and_then(|path| {
+                Some(
+                    ImageReader::open(path)
+                        .unwrap()
+                        .decode()
+                        .unwrap()
+                        .into_rgba8(),
+                )
+            }),
         };
         let allocate_image = state.allocate_image();
 
@@ -57,7 +45,12 @@ impl State {
                 .height(Length::Fill)
                 .into()
         } else {
-            widget::space().into()
+            widget::container(widget::text(include_str!("usage.txt")))
+                .height(Length::Fill)
+                .width(Length::Fill)
+                .align_x(Alignment::Center)
+                .align_y(Alignment::Center)
+                .into()
         }
     }
     fn update(&mut self, message: Message) -> Task<Message> {
@@ -80,17 +73,6 @@ impl State {
                     }
                 }
 
-                Key::Character("q") => return window::latest().and_then(window::close),
-
-                Key::Character("r") => {
-                    self.image = imageops::rotate90(&self.image);
-                    return self.allocate_image();
-                }
-                Key::Character("i") => {
-                    imageops::invert(&mut self.image);
-                    return self.allocate_image();
-                }
-
                 Key::Character("o") => {
                     let Some(path) = FileDialog::new()
                         .add_filter(
@@ -106,15 +88,40 @@ impl State {
                         return Task::none();
                     };
 
-                    self.image = ImageReader::open(path)
-                        .unwrap()
-                        .decode()
-                        .unwrap()
-                        .into_rgba8();
+                    self.image = Some(
+                        ImageReader::open(path)
+                            .unwrap()
+                            .decode()
+                            .unwrap()
+                            .into_rgba8(),
+                    );
 
                     return self.allocate_image();
                 }
+
+                Key::Character("r") => {
+                    let Some(image) = self.image.as_ref() else {
+                        eprintln!("no image to rotate");
+                        return Task::none();
+                    };
+                    self.image = Some(imageops::rotate90(image));
+                    return self.allocate_image();
+                }
+                Key::Character("i") => {
+                    let Some(image) = self.image.as_mut() else {
+                        eprintln!("no image to invert");
+                        return Task::none();
+                    };
+                    imageops::invert(image);
+                    return self.allocate_image();
+                }
+
                 Key::Character("s") => {
+                    let Some(image) = self.image.as_ref() else {
+                        eprintln!("no image to save");
+                        return Task::none();
+                    };
+
                     let Some(path) = FileDialog::new().save_file() else {
                         eprintln!("no path to save provided");
                         return Task::none();
@@ -134,15 +141,17 @@ impl State {
                         };
 
                     let result = if let Some(encoder) = maybe_encoder {
-                        self.image.write_with_encoder(encoder)
+                        image.write_with_encoder(encoder)
                     } else {
-                        self.image.save(path)
+                        image.save(path)
                     };
 
                     #[allow(unused_must_use)]
                     result.inspect_err(|e| eprintln!("failed to save image: {e}"));
                 }
 
+                Key::Character("q") => return window::latest().and_then(window::close),
+
                 // ignore unused keys
                 _ => {}
             },
@@ -155,10 +164,15 @@ impl State {
     }
 
     fn allocate_image(&self) -> Task<Message> {
+        let Some(image) = self.image.as_ref() else {
+            eprintln!("no image to allocate");
+            return Task::none();
+        };
+
         widget::image::allocate(widget::image::Handle::from_rgba(
-            self.image.width(),
-            self.image.height(),
-            unsafe { std::mem::transmute::<_, &'static [u8]>(self.image.as_bytes()) },
+            image.width(),
+            image.height(),
+            unsafe { std::mem::transmute::<_, &'static [u8]>(image.as_bytes()) },
         ))
         .map(Message::ImageDisplayReady)
     }

src/usage.txt

@@ -0,0 +1,5 @@
+"o" to open a new image
+"r" to rotate
+"i" to invert colors
+"s" to save the image
+"q" to quit