Support dark theme in Windows candidate window

src/bazel/win32/BUILD.bazel

@@ -65,6 +65,10 @@ bzl_library(
     deps = ["//:build_defs_bzl"],
 )
 
+mozc_win32_lib(
+    name = "advapi32",
+)
+
 mozc_win32_lib(
     name = "aux_ulib",
 )

src/renderer/win32/BUILD.bazel

@@ -107,6 +107,7 @@ mozc_cc_library(
     tags = MOZC_TAGS.WIN_ONLY,
     target_compatible_with = ["@platforms//os:windows"],
     deps = [
+        "//bazel/win32:advapi32",
         "//bazel/win32:shcore",
         "//bazel/win32:user32",
         "//protocol:renderer_cc_proto",

src/renderer/win32/candidate_window.cc

@@ -39,6 +39,7 @@
 #include <memory>
 #include <sstream>
 #include <string>
+#include <string_view>
 
 #include "absl/log/check.h"
 #include "absl/log/log.h"
@@ -424,7 +425,14 @@ void CandidateWindow::DoPaint(HDC dc) {
   DrawFrame(dc);
 }
 
-void CandidateWindow::OnSettingChange(UINT uFlags, LPCTSTR /*lpszSection*/) {
+void CandidateWindow::OnSettingChange(UINT uFlags, LPCTSTR lpszSection) {
+  // Windows broadcasts "ImmersiveColorSet" when the light/dark mode changes.
+  if (lpszSection != nullptr &&
+      std::wstring_view(lpszSection) == L"ImmersiveColorSet") {
+    UpdateDpiDependentResources();
+    metrics_changed_ = true;
+    return;
+  }
   // Since TextRenderer uses dialog font to render,
   // we monitor font-related parameters to know when the font style is changed.
   switch (uFlags) {

src/renderer/win32/infolist_window.cc

@@ -37,6 +37,7 @@
 
 #include <cstdint>
 #include <string>
+#include <string_view>
 
 #include "base/coordinates.h"
 #include "base/vlog.h"
@@ -250,6 +251,12 @@ Size InfolistWindow::DoPaintRow(HDC dc, int row, int ypos) {
       ypos + title_rect.size.height + infostyle.row_rect_padding() +
           desc_rect.size.height + infostyle.row_rect_padding());
 
+  // Use the candidate background so that the dark theme is applied too.
+  const RendererStyle::RGBAColor& background =
+      style_->candidate_style().background_color();
+  const COLORREF default_background_color =
+      RGB(background.r(), background.g(), background.b());
+
   if (usages.has_focused_index() && (row == usages.focused_index())) {
     const CRect selected_rect(
         infostyle.window_border(), ypos,
@@ -272,15 +279,15 @@ Size InfolistWindow::DoPaintRow(HDC dc, int row, int ypos) {
                         title_style.background_color().g(),
                         title_style.background_color().b()));
     } else {
-      FillSolidRect(dc, &title_back_crect, RGB(255, 255, 255));
+      FillSolidRect(dc, &title_back_crect, default_background_color);
     }
     if (desc_style.has_background_color()) {
       FillSolidRect(dc, &desc_back_crect,
                     RGB(title_style.background_color().r(),
                         title_style.background_color().g(),
                         title_style.background_color().b()));
     } else {
-      FillSolidRect(dc, &desc_back_crect, RGB(255, 255, 255));
+      FillSolidRect(dc, &desc_back_crect, default_background_color);
     }
   }
 
@@ -291,7 +298,14 @@ Size InfolistWindow::DoPaintRow(HDC dc, int row, int ypos) {
   return Size(0, row_height);
 }
 
-void InfolistWindow::OnSettingChange(UINT uFlags, LPCTSTR /*lpszSection*/) {
+void InfolistWindow::OnSettingChange(UINT uFlags, LPCTSTR lpszSection) {
+  // Windows broadcasts "ImmersiveColorSet" when the light/dark mode changes.
+  if (lpszSection != nullptr &&
+      std::wstring_view(lpszSection) == L"ImmersiveColorSet") {
+    *style_ = GetScaledRendererStyle(dpi_);
+    metrics_changed_ = true;
+    return;
+  }
   // Since TextRenderer uses dialog font to render,
   // we monitor font-related parameters to know when the font style is changed.
   switch (uFlags) {

src/renderer/win32/win32_dpi_util.cc

@@ -48,6 +48,22 @@ void ScaleTextStyle(RendererStyle::TextStyle* text_style, double scale_factor) {
   text_style->set_right_padding(text_style->right_padding() * scale_factor);
 }
 
+RendererStyleHandler::ColorTheme GetSystemColorTheme() {
+  // Windows exposes the "app mode" (light/dark) setting in this registry value.
+  // 0 means dark mode. The value may be missing on older Windows.
+  DWORD apps_use_light_theme = 1;
+  DWORD size = sizeof(apps_use_light_theme);
+  const LSTATUS result = ::RegGetValueW(
+      HKEY_CURRENT_USER,
+      L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+      L"AppsUseLightTheme", RRF_RT_REG_DWORD, nullptr, &apps_use_light_theme,
+      &size);
+  if (result == ERROR_SUCCESS && apps_use_light_theme == 0) {
+    return RendererStyleHandler::ColorTheme::kDark;
+  }
+  return RendererStyleHandler::ColorTheme::kLight;
+}
+
 }  // namespace
 
 double GetDPIScalingFactor(uint32_t dpi) {
@@ -68,7 +84,8 @@ uint32_t GetDpiForPoint(int x, int y) {
 ::mozc::renderer::RendererStyle GetScaledRendererStyle(uint32_t dpi) {
   const double scale_factor = GetDPIScalingFactor(dpi);
 
-  RendererStyle style = RendererStyleHandler::GetRendererStyle();
+  RendererStyle style =
+      RendererStyleHandler::GetRendererStyle(GetSystemColorTheme());
 
   // style.window_border is non-scalable.
   style.set_scrollbar_width(style.scrollbar_width() * scale_factor);