Linux: default to XWayland for file drag-and-drop on Wayland desktops (#165)

* Linux: default to XWayland for file drag-and-drop on Wayland desktops

* Ignore an empty DISPLAY before forcing X11

Cargo.lock

@@ -1885,6 +1885,7 @@ dependencies = [
  "pollster 1.0.1",
  "rfd",
  "serde_json",
+ "winit",
  "winresource",
 ]
 

apps/gridcraft/Cargo.toml

@@ -24,6 +24,9 @@ chrono = { workspace = true }
 # Icon + VERSIONINFO for gridcraft.exe; build.rs only uses it when the target is Windows.
 winresource = "0.1"
 
+[target.'cfg(all(unix, not(target_os = "macos")))'.dependencies]
+winit = { version = "0.30", default-features = false, features = ["x11"] }
+
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 craft-print = { git = "https://github.com/storytold/craft-libs", rev = "25da1314d443171b4adeaad2cd9454b273f35c6f" }
 craft-update = { workspace = true }

apps/gridcraft/src/main.rs

@@ -336,6 +336,18 @@ fn main() -> eframe::Result<()> {
         viewport = viewport.with_icon(i);
     }
     let options = eframe::NativeOptions { viewport, ..Default::default() };
+    #[cfg(all(unix, not(target_os = "macos")))]
+    let mut options = options;
+    // winit has no file drag-and-drop on Wayland (only on X11), so dropping files from the file
+    // manager showed a "no" cursor. Run through XWayland when it's there; GRIDCRAFT_WAYLAND=1
+    // keeps the native Wayland backend.
+    #[cfg(all(unix, not(target_os = "macos")))]
+    if std::env::var_os("DISPLAY").is_some_and(|d| !d.is_empty()) && std::env::var_os("GRIDCRAFT_WAYLAND").is_none() {
+        options.event_loop_builder = Some(Box::new(|b| {
+            use winit::platform::x11::EventLoopBuilderExtX11;
+            b.with_x11();
+        }));
+    }
     // Before eframe creates the wgpu instance: Windows starts on DirectX 12, or OpenGL when
     // DirectX 12 has no GPU driver, and never touches Vulkan unless asked (see graphics.rs).
     #[cfg(target_os = "windows")]