Drag and drop files into egui_glium and egui_web (#637)

* Implement file drag-and-drop for egui_glium

* Implement file drag-and-drop into egui_web

* Cleanup

egui/src/data/input.rs

@@ -57,6 +57,12 @@ pub struct RawInput {
     /// but you can check if egui is using the keyboard with [`crate::Context::wants_keyboard_input`]
     /// and/or the pointer (mouse/touch) with [`crate::Context::is_using_pointer`].
     pub events: Vec<Event>,
+
+    /// Dragged files hovering over egui.
+    pub hovered_files: Vec<HoveredFile>,
+
+    /// Dragged files dropped into egui.
+    pub dropped_files: Vec<DroppedFile>,
 }
 
 impl Default for RawInput {
@@ -72,12 +78,17 @@ impl Default for RawInput {
             predicted_dt: 1.0 / 60.0,
             modifiers: Modifiers::default(),
             events: vec![],
+            hovered_files: Default::default(),
+            dropped_files: Default::default(),
         }
     }
 }
 
 impl RawInput {
-    /// Helper: move volatile (deltas and events), clone the rest
+    /// Helper: move volatile (deltas and events), clone the rest.
+    ///
+    /// * [`Self::hovered_files`] is cloned.
+    /// * [`Self::dropped_files`] is moved.
     pub fn take(&mut self) -> RawInput {
         #![allow(deprecated)] // for screen_size
         let zoom = self.zoom_delta;
@@ -92,10 +103,34 @@ impl RawInput {
             predicted_dt: self.predicted_dt,
             modifiers: self.modifiers,
             events: std::mem::take(&mut self.events),
+            hovered_files: self.hovered_files.clone(),
+            dropped_files: std::mem::take(&mut self.dropped_files),
         }
     }
 }
 
+/// A file about to be dropped into egui.
+#[derive(Clone, Debug, Default)]
+pub struct HoveredFile {
+    /// Set by the `egui_glium` backend.
+    pub path: Option<std::path::PathBuf>,
+    /// With the `egui_web` backend, this is set to the mime-type of the file (if available).
+    pub mime: String,
+}
+
+/// A file dropped into egui.
+#[derive(Clone, Debug, Default)]
+pub struct DroppedFile {
+    /// Set by the `egui_glium` backend.
+    pub path: Option<std::path::PathBuf>,
+    /// Name of the file. Set by the `egui_web` backend.
+    pub name: String,
+    /// Set by the `egui_web` backend.
+    pub last_modified: Option<std::time::SystemTime>,
+    /// Set by the `egui_web` backend.
+    pub bytes: Option<std::sync::Arc<[u8]>>,
+}
+
 /// An input event generated by the integration.
 ///
 /// This only covers events that egui cares about.
@@ -295,6 +330,8 @@ impl RawInput {
             predicted_dt,
             modifiers,
             events,
+            hovered_files,
+            dropped_files,
         } = self;
 
         ui.label(format!("scroll_delta: {:?} points", scroll_delta));
@@ -313,6 +350,8 @@ impl RawInput {
         ui.label(format!("modifiers: {:#?}", modifiers));
         ui.label(format!("events: {:?}", events))
             .on_hover_text("key presses etc");
+        ui.label(format!("hovered_files: {}", hovered_files.len()));
+        ui.label(format!("dropped_files: {}", dropped_files.len()));
     }
 }