wasm: Handle theme colors

Changing color themes did not work since the results from
qt_fusionPalette is cached by default.

The solution is to track changes and call qt_fusionPalette
when necessary.

Fixes: QTBUG-129399
Pick-to: 6.8
Change-Id: I77824098349be5e5264fa9e230a949e3ccd6f14f
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/plugins/platforms/wasm/qwasmtheme.cpp

@@ -5,6 +5,18 @@
 #include <QtCore/qvariant.h>
 #include <QFontDatabase>
 #include <QList>
+#include <qpa/qwindowsysteminterface.h>
+
+#include <private/qstdweb_p.h>
+
+#include <emscripten.h>
+#include <emscripten/bind.h>
+#include <emscripten/val.h>
+
+Q_GUI_EXPORT QPalette qt_fusionPalette();
+
+Qt::ColorScheme QWasmTheme::s_autoColorScheme = Qt::ColorScheme::Unknown;
+bool QWasmTheme::s_autoPaletteIsDirty = false;
 
 QT_BEGIN_NAMESPACE
 
@@ -12,9 +24,29 @@ using namespace Qt::StringLiterals;
 
 QWasmTheme::QWasmTheme()
 {
+    if (emscripten::val::global("window").call<emscripten::val>(
+        "matchMedia",
+        std::string("(prefers-color-scheme:dark)"))["matches"].as<bool>())
+        s_autoColorScheme = Qt::ColorScheme::Dark;
+    else
+        s_autoColorScheme = Qt::ColorScheme::Light;
+
     for (auto family : QFontDatabase::families())
         if (QFontDatabase::isFixedPitch(family))
             fixedFont = new QFont(family);
+
+    m_palette = std::make_unique<QPalette>();
+    m_paletteIsDirty = true; // Force update later
+
+    const auto callback = [=](emscripten::val event) { QWasmTheme::onColorSchemeChange(event); };
+    const emscripten::val window = emscripten::val::global("window");
+    if (!window.isUndefined()) {
+        const emscripten::val matchMedia = window.call<emscripten::val>("matchMedia", emscripten::val("(prefers-color-scheme: dark)"));
+        if (!matchMedia.isUndefined()) {
+            static auto changeEvent =
+                std::make_unique<qstdweb::EventCallback>(matchMedia, "change", callback);
+        }
+    }
 }
 
 QWasmTheme::~QWasmTheme()
@@ -23,6 +55,35 @@ QWasmTheme::~QWasmTheme()
         delete fixedFont;
 }
 
+const QPalette *QWasmTheme::palette(Palette type) const
+{
+    if (type == SystemPalette) {
+        if (m_paletteIsDirty || s_autoPaletteIsDirty) {
+            m_paletteIsDirty = false;
+            s_autoPaletteIsDirty = false;
+            *m_palette = qt_fusionPalette();
+        }
+        return m_palette.get();
+    }
+    return nullptr;
+}
+
+Qt::ColorScheme QWasmTheme::colorScheme() const
+{
+    if (m_colorScheme != Qt::ColorScheme::Unknown)
+        return m_colorScheme;
+    return s_autoColorScheme;
+}
+
+void QWasmTheme::requestColorScheme(Qt::ColorScheme scheme)
+{
+    if (m_colorScheme != scheme) {
+        m_paletteIsDirty = true;
+        m_colorScheme = scheme;
+        QWindowSystemInterface::handleThemeChange<QWindowSystemInterface::SynchronousDelivery>();
+    }
+}
+
 QVariant QWasmTheme::themeHint(ThemeHint hint) const
 {
     if (hint == QPlatformTheme::StyleNames)
@@ -40,4 +101,22 @@ const QFont *QWasmTheme::font(Font type) const
     return nullptr;
 }
 
+void QWasmTheme::onColorSchemeChange(emscripten::val event)
+{
+    const emscripten::val matches = event["matches"];
+    if (!matches.isUndefined()) {
+        const auto oldAutoColorScheme = s_autoColorScheme;
+        if (matches.as<int>())
+            s_autoColorScheme = Qt::ColorScheme::Dark;
+        else
+            s_autoColorScheme = Qt::ColorScheme::Light;
+
+        if (oldAutoColorScheme != s_autoColorScheme) {
+            s_autoPaletteIsDirty = true;
+            QWindowSystemInterface::handleThemeChange<QWindowSystemInterface::SynchronousDelivery>();
+        }
+    }
+}
+
+
 QT_END_NAMESPACE

src/plugins/platforms/wasm/qwasmtheme.h

@@ -23,9 +23,22 @@ public:
     QWasmTheme();
     ~QWasmTheme();
 
+    const QPalette *palette(Palette type = SystemPalette) const override;
+    Qt::ColorScheme colorScheme() const override;
+    void requestColorScheme(Qt::ColorScheme scheme) override;
     QVariant themeHint(ThemeHint hint) const override;
     const QFont *font(Font type) const override;
     QFont *fixedFont = nullptr;
+
+    static void onColorSchemeChange(emscripten::val event);
+
+private:
+    Qt::ColorScheme m_colorScheme = Qt::ColorScheme::Unknown;
+    std::unique_ptr<QPalette> m_palette;
+    mutable bool m_paletteIsDirty = false;
+
+    static Qt::ColorScheme s_autoColorScheme;
+    static bool s_autoPaletteIsDirty;
 };
 
 QT_END_NAMESPACE