vendor

egui/examples/download_image/src/main.rs

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+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
+
+use eframe::egui;
+use egui_extras::RetainedImage;
+use poll_promise::Promise;
+
+fn main() -> Result<(), eframe::Error> {
+    let options = eframe::NativeOptions::default();
+    eframe::run_native(
+        "Download and show an image with eframe/egui",
+        options,
+        Box::new(|_cc| Box::new(MyApp::default())),
+    )
+}
+
+#[derive(Default)]
+struct MyApp {
+    /// `None` when download hasn't started yet.
+    promise: Option<Promise<ehttp::Result<RetainedImage>>>,
+}
+
+impl eframe::App for MyApp {
+    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        let promise = self.promise.get_or_insert_with(|| {
+            // Begin download.
+            // We download the image using `ehttp`, a library that works both in WASM and on native.
+            // We use the `poll-promise` library to communicate with the UI thread.
+            let ctx = ctx.clone();
+            let (sender, promise) = Promise::new();
+            let request = ehttp::Request::get("https://picsum.photos/seed/1.759706314/1024");
+            ehttp::fetch(request, move |response| {
+                let image = response.and_then(parse_response);
+                sender.send(image); // send the results back to the UI thread.
+                ctx.request_repaint(); // wake up UI thread
+            });
+            promise
+        });
+
+        egui::CentralPanel::default().show(ctx, |ui| match promise.ready() {
+            None => {
+                ui.spinner(); // still loading
+            }
+            Some(Err(err)) => {
+                ui.colored_label(ui.visuals().error_fg_color, err); // something went wrong
+            }
+            Some(Ok(image)) => {
+                image.show_max_size(ui, ui.available_size());
+            }
+        });
+    }
+}
+
+#[allow(clippy::needless_pass_by_value)]
+fn parse_response(response: ehttp::Response) -> Result<RetainedImage, String> {
+    let content_type = response.content_type().unwrap_or_default();
+    if content_type.starts_with("image/") {
+        RetainedImage::from_image_bytes(&response.url, &response.bytes)
+    } else {
+        Err(format!(
+            "Expected image, found content-type {:?}",
+            content_type
+        ))
+    }
+}