#791 Try to fix second Windows 7/8 compatibility issue

main/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "realearn"
-version = "2.14.2"
+version = "2.14.3"
 authors = ["Benjamin Klum <[email protected]>"]
 edition = "2021"
 build = "build.rs"

swell-ui/Cargo.toml

@@ -15,6 +15,7 @@ raw-window-handle = "0.4.2"
 [target.'cfg(windows)'.dependencies]
 winapi = { version = "0.3", features = ["winuser", "uxtheme"] }
 palette = "0.5"
+libloading = "0.7"
 
 [target.'cfg(target_os = "macos")'.dependencies]
 objc2 = "0.3.0-beta.3"

swell-ui/src/lib.rs

@@ -23,3 +23,6 @@ pub mod menu_tree;
 
 #[cfg(target_os = "macos")]
 mod macos;
+
+#[cfg(target_os = "windows")]
+mod win;

swell-ui/src/win.rs

@@ -0,0 +1,29 @@
+use libloading::{Library, Symbol};
+use winapi::shared::minwindef::UINT;
+use winapi::shared::windef::HWND;
+
+/// Provides access to some Win32 API functions that are not available in older Windows versions.
+///
+/// This is better than eagerly linking to these functions because then the resulting binary
+/// wouldn't work *at all* in the older Windows versions, whereas with this approach, we can
+/// fall back to alternative logic or alternative values on a case-by-case basis.  
+pub struct DynamicWinApi {
+    user32_library: Library,
+}
+
+impl DynamicWinApi {
+    pub fn load() -> Self {
+        unsafe {
+            Self {
+                user32_library: Library::new("user32.dll").unwrap(),
+            }
+        }
+    }
+
+    /// Should be available from Windows 10 onwards.
+    pub fn get_dpi_for_window(&self) -> Option<Symbol<GetDpiForWindow>> {
+        unsafe { self.user32_library.get(b"GetDpiForWindow").ok() }
+    }
+}
+
+type GetDpiForWindow = extern "stdcall" fn(hwnd: HWND) -> UINT;

swell-ui/src/window.rs

@@ -606,7 +606,12 @@ impl Window {
     pub fn dpi(&self) -> u32 {
         #[cfg(target_family = "windows")]
         {
-            unsafe { winapi::um::winuser::GetDpiForWindow(self.raw as _) }
+            let dynamic_win_api = crate::win::DynamicWinApi::load();
+            if let Some(f) = dynamic_win_api.get_dpi_for_window() {
+                f(self.raw as _)
+            } else {
+                96
+            }
         }
         #[cfg(target_family = "unix")]
         96