[fix] improve Windows taskbar icon clarity at small sizes

2026-10-17 09:23:10 +08:00 · 2026-09-16 23:19:12 +08:00
parent ce7a3c178e
commit 28de4cf938
4 changed files with 133 additions and 0 deletions
@@ -0,0 +1,100 @@
+#include "window_icons.h"
+
+#include <commctrl.h>
+
+#include <memory>
+#include <utility>
+
+namespace crossdesk {
+namespace {
+
+constexpr UINT_PTR kIconSubclassId = 1;
+
+struct WindowIcons {
+  HICON small_icon = nullptr;
+  HICON large_icon = nullptr;
+
+  ~WindowIcons() {
+    if (small_icon) DestroyIcon(small_icon);
+    if (large_icon) DestroyIcon(large_icon);
+  }
+
+  bool Load(UINT dpi) {
+    const HMODULE module = GetModuleHandleW(nullptr);
+    small_icon = static_cast<HICON>(LoadImageW(
+        module, L"IDI_ICON1", IMAGE_ICON,
+        GetSystemMetricsForDpi(SM_CXSMICON, dpi),
+        GetSystemMetricsForDpi(SM_CYSMICON, dpi), 0));
+    large_icon = static_cast<HICON>(LoadImageW(
+        module, L"IDI_ICON1", IMAGE_ICON,
+        GetSystemMetricsForDpi(SM_CXICON, dpi),
+        GetSystemMetricsForDpi(SM_CYICON, dpi), 0));
+    return small_icon && large_icon;
+  }
+
+  void Apply(HWND window) const {
+    // Do not destroy the replaced handles: Slint/winit owns those images.
+    SendMessageW(window, WM_SETICON, ICON_SMALL,
+                 reinterpret_cast<LPARAM>(small_icon));
+    SendMessageW(window, WM_SETICON, ICON_BIG,
+                 reinterpret_cast<LPARAM>(large_icon));
+  }
+};
+
+LRESULT CALLBACK IconSubclassProc(HWND window, UINT message, WPARAM wparam,
+                                  LPARAM lparam, UINT_PTR subclass_id,
+                                  DWORD_PTR reference_data) {
+  auto* icons = reinterpret_cast<WindowIcons*>(reference_data);
+  if (message == WM_SETICON) {
+    // Slint supplies the same PNG for both sizes, including during deferred
+    // window initialization. Keep using the matching frames from our ICO.
+    if (wparam == ICON_SMALL) {
+      lparam = reinterpret_cast<LPARAM>(icons->small_icon);
+    } else if (wparam == ICON_BIG) {
+      lparam = reinterpret_cast<LPARAM>(icons->large_icon);
+    }
+    return DefSubclassProc(window, message, wparam, lparam);
+  }
+  if (message == WM_DPICHANGED) {
+    WindowIcons next;
+    if (next.Load(HIWORD(wparam))) {
+      std::swap(icons->small_icon, next.small_icon);
+      std::swap(icons->large_icon, next.large_icon);
+      icons->Apply(window);
+      // 'next' releases the previous pair only after both were replaced.
+    }
+  }
+  if (message == WM_NCDESTROY) {
+    const LRESULT result = DefSubclassProc(window, message, wparam, lparam);
+    RemoveWindowSubclass(window, IconSubclassProc, subclass_id);
+    delete icons;
+    return result;
+  }
+  return DefSubclassProc(window, message, wparam, lparam);
+}
+
+}  // namespace
+
+bool ConfigureWindowsWindowIcons(HWND window) {
+  if (!window) {
+    return false;
+  }
+  DWORD_PTR existing = 0;
+  if (GetWindowSubclass(window, IconSubclassProc, kIconSubclassId, &existing)) {
+    return true;
+  }
+  auto icons = std::make_unique<WindowIcons>();
+  const UINT dpi = GetDpiForWindow(window);
+  if (!dpi || !icons->Load(dpi) ||
+      !SetWindowSubclass(window, IconSubclassProc, kIconSubclassId,
+                         reinterpret_cast<DWORD_PTR>(icons.get()))) {
+    return false;
+  }
+  // The subclass owns the pair until WM_NCDESTROY, even if Slint hides and
+  // recreates its native window while the component itself stays alive.
+  auto* installed = icons.release();
+  installed->Apply(window);
+  return true;
+}
+
+}  // namespace crossdesk