Improve the frame around ImageButton

Helps https://github.com/emilk/egui/issues/721

eframe/examples/image.rs

@@ -2,7 +2,7 @@ use eframe::{egui, epi};
 
 #[derive(Default)]
 struct MyApp {
-    texture: Option<egui::TextureId>,
+    texture: Option<(egui::Vec2, egui::TextureId)>,
 }
 
 impl epi::App for MyApp {
@@ -13,7 +13,7 @@ impl epi::App for MyApp {
     fn update(&mut self, ctx: &egui::CtxRef, frame: &mut epi::Frame<'_>) {
         if self.texture.is_none() {
             // Load the image:
-            let image_data = include_bytes!("rust-logo-512x512.png");
+            let image_data = include_bytes!("rust-logo-256x256.png");
             use image::GenericImageView;
             let image = image::load_from_memory(image_data).expect("Failed to load image");
             let image_buffer = image.to_rgba8();
@@ -29,13 +29,17 @@ impl epi::App for MyApp {
             let texture = frame
                 .tex_allocator()
                 .alloc_srgba_premultiplied(size, &pixels);
-            self.texture = Some(texture);
+            let size = egui::Vec2::new(size.0 as f32, size.1 as f32);
+            self.texture = Some((size, texture));
         }
 
         egui::CentralPanel::default().show(ctx, |ui| {
-            ui.heading("Here is an image for you:");
-            if let Some(texture) = self.texture {
-                ui.image(texture, egui::Vec2::splat(256.0));
+            if let Some((size, texture)) = self.texture {
+                ui.heading("This is an image:");
+                ui.image(texture, size);
+
+                ui.heading("This is an image you can click:");
+                ui.add(egui::ImageButton::new(texture, size));
             }
         });
     }