Use custom application icon on Windows, if present.

On Windows, if the executable contains an icon resource with id 1,
this icon will be used in the Taskbar and in the titlebar of Druid windows.
If there is no such icon resource, the default application icon IDI_APPLICATION
will be used (as before this change).

Adding a custom icon: one way is to use the [winres crate](https://crates.io/crates/winres)
and follow the guide in its README; `winres::WindowsResource::set_icon()` adds
an icon with id 1.

Non-Windows back-ends are not modified.

Author: tay64

CHANGELOG.md

@@ -251,6 +251,7 @@ values and their textual representations. ([#1377])
 - All Image formats are now optional, reducing compile time and binary size by default ([#1340] by [@JAicewizard])
 - The `Cursor` API has changed to a stateful one ([#1433] by [@jneem])
 - Part of the `SAVE_FILE` command is now `SAVE_FILE_AS` ([#1463] by [@jneem])
+- Windows: Use custom application icon, if present ([#????] by [@tay64])
 
 ### Deprecated
 - Parse widget (replaced with `Formatter` trait) ([#1377] by [@cmyr])

druid-shell/src/backend/windows/application.rs

@@ -26,13 +26,14 @@ use winapi::shared::ntdef::LPCWSTR;
 use winapi::shared::windef::{DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2, HCURSOR, HWND};
 use winapi::shared::winerror::HRESULT_FROM_WIN32;
 use winapi::um::errhandlingapi::GetLastError;
+use winapi::um::libloaderapi::GetModuleHandleW;
 use winapi::um::shellscalingapi::PROCESS_PER_MONITOR_DPI_AWARE;
 use winapi::um::winnls::GetUserDefaultLocaleName;
 use winapi::um::winnt::LOCALE_NAME_MAX_LENGTH;
 use winapi::um::winuser::{
     DispatchMessageW, GetAncestor, GetMessageW, LoadIconW, PeekMessageW, PostMessageW,
     PostQuitMessage, RegisterClassW, TranslateAcceleratorW, TranslateMessage, GA_ROOT,
-    IDI_APPLICATION, MSG, PM_NOREMOVE, WM_TIMER, WNDCLASSW,
+    MAKEINTRESOURCEW, MSG, PM_NOREMOVE, WM_TIMER, WNDCLASSW,
 };
 
 use piet_common::D2DLoadedFonts;
@@ -90,7 +91,7 @@ impl Application {
             .is_ok()
         {
             let class_name = CLASS_NAME.to_wide();
-            let icon = unsafe { LoadIconW(0 as HINSTANCE, IDI_APPLICATION) };
+            let icon = unsafe { LoadIconW(GetModuleHandleW(0 as LPCWSTR), MAKEINTRESOURCEW(1)) };
             let wnd = WNDCLASSW {
                 style: 0,
                 lpfnWndProc: Some(window::win_proc_dispatch),