Window icons (#497)

examples/window_icon.rs

@@ -0,0 +1,95 @@
+// Heads up: you need to compile this example with `--features icon_loading`.
+// `Icon::from_path` won't be available otherwise, though for your own applications, you could use
+// `Icon::from_rgba` if you don't want to depend on the `image` crate.
+
+extern crate winit;
+#[cfg(feature = "icon_loading")]
+extern crate image;
+
+use winit::Icon;
+
+#[cfg(feature = "icon_loading")]
+fn main() {
+    // You'll have to choose an icon size at your own discretion. On X11, the desired size varies
+    // by WM, and on Windows, you still have to account for screen scaling. Here we use 32px,
+    // since it seems to work well enough in most cases. Be careful about going too high, or
+    // you'll be bitten by the low-quality downscaling built into the WM.
+    let path = concat!(env!("CARGO_MANIFEST_DIR"), "/examples/icon.png");
+    // While `Icon::from_path` is the most straightforward, you have a few other options. If you
+    // want to use the `include_bytes` macro, then pass the result to `Icon::from_bytes`. See the
+    // docs for the full list of options (you'll have to generate the docs with the `icon_loading`
+    // feature enabled).
+    let icon = Icon::from_path(path).expect("Failed to open icon");
+
+    let mut events_loop = winit::EventsLoop::new();
+
+    let window = winit::WindowBuilder::new()
+        .with_title("An iconic window!")
+        // At present, this only does anything on Windows and X11, so if you want to save load
+        // time, you can put icon loading behind a function that returns `None` on other platforms.
+        .with_window_icon(Some(icon))
+        .build(&events_loop)
+        .unwrap();
+
+    events_loop.run_forever(|event| {
+        if let winit::Event::WindowEvent { event, .. } = event {
+            use winit::WindowEvent::*;
+            match event {
+                CloseRequested => return winit::ControlFlow::Break,
+                DroppedFile(path) => {
+                    use image::GenericImage;
+
+                    let icon_image = image::open(path).expect("Failed to open window icon");
+
+                    let (width, height) = icon_image.dimensions();
+                    const DESIRED_SIZE: u32 = 32;
+                    let (new_width, new_height) = if width == height {
+                        (DESIRED_SIZE, DESIRED_SIZE)
+                    } else {
+                        // Note that this will never divide by zero, due to the previous condition.
+                        let aspect_adjustment = DESIRED_SIZE as f64
+                            / std::cmp::max(width, height) as f64;
+                        (
+                            (width as f64 * aspect_adjustment) as u32,
+                            (height as f64 * aspect_adjustment) as u32,
+                        )
+                    };
+
+                    // By scaling the icon ourselves, we get higher-quality filtering and save
+                    // some memory.
+                    let icon = image::imageops::resize(
+                        &icon_image,
+                        new_width,
+                        new_height,
+                        image::FilterType::Lanczos3,
+                    );
+
+                    let (offset_x, offset_y) = (
+                        (DESIRED_SIZE - new_width) / 2,
+                        (DESIRED_SIZE - new_height) / 2,
+                    );
+
+                    let mut canvas = image::ImageBuffer::new(DESIRED_SIZE, DESIRED_SIZE);
+                    image::imageops::replace(
+                        &mut canvas,
+                        &icon,
+                        offset_x,
+                        offset_y,
+                    );
+
+                    window.set_window_icon(Some(canvas.into()));
+                },
+                _ => (),
+            }
+        }
+        winit::ControlFlow::Continue
+    });
+}
+
+#[cfg(not(feature = "icon_loading"))]
+fn main() {
+    print!(
+r#"This example requires the `icon_loading` feature:
+    cargo run --example window_icon --features icon_loading
+"#);
+}