Support images with rounded corners (#3257)

* Add `Rect::ZERO`

* Add `Rounding::ZERO`

* Add `RectShape::new`

* Add `Image::rounding` to support images with rounded corners

examples/retained_image/src/main.rs

@@ -6,7 +6,7 @@ use egui_extras::RetainedImage;
 fn main() -> Result<(), eframe::Error> {
     env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).
     let options = eframe::NativeOptions {
-        initial_window_size: Some(egui::vec2(300.0, 900.0)),
+        initial_window_size: Some(egui::vec2(400.0, 1000.0)),
         ..Default::default()
     };
     eframe::run_native(
@@ -18,48 +18,66 @@ fn main() -> Result<(), eframe::Error> {
 
 struct MyApp {
     image: RetainedImage,
+    rounding: f32,
     tint: egui::Color32,
 }
 
 impl Default for MyApp {
     fn default() -> Self {
         Self {
-            image: RetainedImage::from_image_bytes(
-                "rust-logo-256x256.png",
-                include_bytes!("rust-logo-256x256.png"),
-            )
-            .unwrap(),
-            tint: egui::Color32::from_rgb(255, 0, 255),
+            // crab image is CC0, found on https://stocksnap.io/search/crab
+            image: RetainedImage::from_image_bytes("crab.png", include_bytes!("crab.png")).unwrap(),
+            rounding: 32.0,
+            tint: egui::Color32::from_rgb(100, 200, 200),
         }
     }
 }
 
 impl eframe::App for MyApp {
     fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        let Self {
+            image,
+            rounding,
+            tint,
+        } = self;
+
         egui::CentralPanel::default().show(ctx, |ui| {
             ui.heading("This is an image:");
-            self.image.show(ui);
+            image.show(ui);
 
-            ui.heading("This is a rotated image with a tint:");
+            ui.add_space(32.0);
+
+            ui.heading("This is a tinted image with rounded corners:");
             ui.add(
-                egui::Image::new(self.image.texture_id(ctx), self.image.size_vec2())
-                    .rotate(45.0_f32.to_radians(), egui::Vec2::splat(0.5))
-                    .tint(self.tint),
+                egui::Image::new(image.texture_id(ctx), image.size_vec2())
+                    .tint(*tint)
+                    .rounding(*rounding),
             );
 
             ui.horizontal(|ui| {
                 ui.label("Tint:");
                 egui::color_picker::color_edit_button_srgba(
                     ui,
-                    &mut self.tint,
+                    tint,
                     egui::color_picker::Alpha::BlendOrAdditive,
                 );
+
+                ui.add_space(16.0);
+
+                ui.label("Rounding:");
+                ui.add(
+                    egui::DragValue::new(rounding)
+                        .speed(1.0)
+                        .clamp_range(0.0..=0.5 * image.size_vec2().min_elem()),
+                );
             });
 
+            ui.add_space(32.0);
+
             ui.heading("This is an image you can click:");
             ui.add(egui::ImageButton::new(
-                self.image.texture_id(ctx),
-                self.image.size_vec2(),
+                image.texture_id(ctx),
+                image.size_vec2(),
             ));
         });
     }

examples/retained_image/src/rust-logo-license.txt

@@ -1 +0,0 @@
-Rust logo by Mozilla, from https://github.com/rust-lang/rust-artwork