Windows: load PNG icons for window/taskbar

docs/status/windows.md

@@ -26,7 +26,7 @@ Release asset: `DesktopWebView-windows-x64.exe` (GitHub Releases; not Hex `priv/
 | Tray / status item | done | `Shell_NotifyIcon`; E2E tray create |
 | Apple menu | n/a | Successful no-op |
 | Notifications | done | Balloon via tray when present; E2E |
-| Icons from path / PNG | partial | Path/ICO via `LoadImage`; PNG→HICON deferred |
+| Icons from path / PNG | done | ICO via `LoadImage`; PNG/JPEG via GDI+ `Bitmap::GetHICON`; class/default from exe |
 | OS events (reopen, open url/file) | partial | `system.open_url` done; OS reopen/file events not wired |
 | Locale / os_description | done | E2E |
 | Permission policy hybrid | done | E2E simulate + policy |

native/windows/CMakeLists.txt

@@ -60,6 +60,7 @@ target_link_libraries(DesktopWebView PRIVATE
   shell32
   user32
   gdi32
+  gdiplus
   comctl32
   advapi32
   shlwapi

native/windows/src/host_controller.cpp

@@ -661,7 +661,8 @@ jsonutil::Json HostController::menu_update(const jsonutil::Json& params) {
 }
 
 void HostController::update_tray_icon(TrayEntry& tray) {
-  HICON icon = LoadIconW(nullptr, IDI_APPLICATION);
+  HICON icon = extract_module_icon();
+  if (!icon) icon = LoadIconW(nullptr, IDI_APPLICATION);
   if (!tray.icon_id.empty()) {
     auto it = icons_.find(tray.icon_id);
     if (it != icons_.end() && it->second.icon) icon = it->second.icon;
@@ -694,10 +695,13 @@ jsonutil::Json HostController::icon_create(const jsonutil::Json& params) {
   auto id = next_id("icon");
   IconEntry icon;
   if (auto path = jsonutil::get_string(params, "path")) {
-    icon.icon = static_cast<HICON>(LoadImageW(nullptr, utf8_to_wide(*path).c_str(), IMAGE_ICON, 0, 0,
-                                              LR_LOADFROMFILE | LR_DEFAULTSIZE));
+    // Prefer ICO via LoadImage; fall back to GDI+ for PNG/JPEG (diode.png etc.).
+    icon.icon = load_hicon_from_file(utf8_to_wide(*path));
+  } else {
+    // Default / missing path: use the host executable's embedded icon.
+    icon.icon = extract_module_icon();
   }
-  // png_base64 accepted for protocol compatibility; decoding deferred (status: partial).
+  // png_base64 still deferred; callers should pass a filesystem path for now.
   icons_[id] = std::move(icon);
   return jsonutil::Json{{"icon_id", id}};
 }

native/windows/src/web_window.cpp

@@ -22,6 +22,10 @@ void WebWindow::register_class() {
   wc.hCursor = LoadCursorW(nullptr, IDC_ARROW);
   wc.hbrBackground = reinterpret_cast<HBRUSH>(COLOR_WINDOW + 1);
   wc.lpszClassName = kClassName;
+  // Title-bar/taskbar icons come from the class (or WM_SETICON). Without these,
+  // Windows shows a blank default even when the .exe has an embedded icon.
+  wc.hIcon = extract_module_icon();
+  wc.hIconSm = extract_module_icon();
   RegisterClassExW(&wc);
   g_class_registered = true;
 }

native/windows/src/win_util.hpp

@@ -2,7 +2,11 @@
 
 #include "win_prefix.hpp"
 
+#include <gdiplus.h>
+
 #include <cctype>
+#include <cwchar>
+#include <cwctype>
 #include <optional>
 #include <string>
 
@@ -45,3 +49,54 @@ inline bool is_absolute_path(const std::string& p) {
   if (p.size() >= 2 && std::isalpha(static_cast<unsigned char>(p[0])) && p[1] == ':') return true;
   return p.size() >= 2 && p[0] == '\\' && p[1] == '\\';
 }
+
+inline bool ends_with_ignore_case(const std::wstring& s, const wchar_t* suffix) {
+  const size_t n = wcslen(suffix);
+  if (s.size() < n) return false;
+  for (size_t i = 0; i < n; i++) {
+    wchar_t a = towlower(s[s.size() - n + i]);
+    wchar_t b = towlower(suffix[i]);
+    if (a != b) return false;
+  }
+  return true;
+}
+
+// LoadImage(IMAGE_ICON) only accepts .ico. App icons are often PNG (e.g. diode.png);
+// use GDI+ so window/taskbar icons are not left blank.
+inline HICON load_hicon_from_file(const std::wstring& path) {
+  if (path.empty()) return nullptr;
+
+  HICON icon = static_cast<HICON>(
+      LoadImageW(nullptr, path.c_str(), IMAGE_ICON, 0, 0, LR_LOADFROMFILE | LR_DEFAULTSIZE));
+  if (icon) return icon;
+
+  if (!ends_with_ignore_case(path, L".png") && !ends_with_ignore_case(path, L".jpg") &&
+      !ends_with_ignore_case(path, L".jpeg") && !ends_with_ignore_case(path, L".bmp") &&
+      !ends_with_ignore_case(path, L".gif")) {
+    return nullptr;
+  }
+
+  static ULONG_PTR gdiplus_token = 0;
+  static bool gdiplus_ready = false;
+  if (!gdiplus_ready) {
+    Gdiplus::GdiplusStartupInput input;
+    gdiplus_ready = Gdiplus::GdiplusStartup(&gdiplus_token, &input, nullptr) == Gdiplus::Ok;
+  }
+  if (!gdiplus_ready) return nullptr;
+
+  Gdiplus::Bitmap bitmap(path.c_str());
+  if (bitmap.GetLastStatus() != Gdiplus::Ok) return nullptr;
+  HICON from_png = nullptr;
+  if (bitmap.GetHICON(&from_png) != Gdiplus::Ok) return nullptr;
+  return from_png;
+}
+
+inline HICON extract_module_icon() {
+  wchar_t module[MAX_PATH]{};
+  HINSTANCE inst = GetModuleHandleW(nullptr);
+  if (!GetModuleFileNameW(inst, module, MAX_PATH)) return nullptr;
+  HICON icon = ExtractIconW(inst, module, 0);
+  // ExtractIcon returns 1 when the file has no icons.
+  if (!icon || icon == reinterpret_cast<HICON>(static_cast<uintptr_t>(1))) return nullptr;
+  return icon;
+}