wasm: Add support for contrastPreference detection to WASM theme

Task-number: QTBUG-133596
Change-Id: I4482fe5a3457579867bd870cb2c8d371dd08e1a0
Reviewed-by: Oliver Eftevaag <oliver.eftevaag@qt.io>

src/plugins/platforms/wasm/qwasmtheme.cpp

@@ -5,32 +5,55 @@
 #include <QtCore/qvariant.h>
 #include <QFontDatabase>
 #include <QList>
+#include <qloggingcategory.h>
 #include <qpa/qwindowsysteminterface.h>
 #include <qpalette.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
 
+Q_STATIC_LOGGING_CATEGORY(lcQpaThemeWasm, "qt.qpa.theme.wasm")
+
+namespace {
+bool matchMedia(std::string mediaQueryString)
+{
+    return emscripten::val::global("window")
+            .call<emscripten::val>("matchMedia", mediaQueryString)["matches"]
+            .as<bool>();
+}
+
+Qt::ColorScheme getColorSchemeFromMedia()
+{
+    if (matchMedia(colorSchemePreferenceDark)) {
+        return Qt::ColorScheme::Dark;
+    } else {
+        return Qt::ColorScheme::Light;
+    }
+}
+
+Qt::ContrastPreference getContrastPreferenceFromMedia()
+{
+    if (matchMedia(contrastPreferenceMore)) {
+        return Qt::ContrastPreference::HighContrast;
+    } else {
+        return Qt::ContrastPreference::NoPreference;
+    }
+}
+} // namespace
+
 using namespace Qt::StringLiterals;
 
 QWasmTheme::QWasmTheme()
 {
-    if (emscripten::val::global("window").call<emscripten::val>(
+    m_colorScheme = getColorSchemeFromMedia();
-        "matchMedia",
+    qCDebug(lcQpaThemeWasm) << "Initializing Wasm theme. Color scheme: " << m_colorScheme;
-        std::string("(prefers-color-scheme:dark)"))["matches"].as<bool>())
+    m_contrastPreference = getContrastPreferenceFromMedia();
-        s_autoColorScheme = Qt::ColorScheme::Dark;
+    qCDebug(lcQpaThemeWasm) << "Initializing Wasm theme. Contrast preference: " << m_contrastPreference;
-    else
-        s_autoColorScheme = Qt::ColorScheme::Light;
 
     for (auto family : QFontDatabase::families())
         if (QFontDatabase::isFixedPitch(family))
@@ -39,15 +62,15 @@ QWasmTheme::QWasmTheme()
     m_palette = std::make_unique<QPalette>();
     m_paletteIsDirty = true; // Force update later
 
-    const auto callback = [=](emscripten::val event) { QWasmTheme::onColorSchemeChange(event); };
+    registerCallbacks(
-    const emscripten::val window = emscripten::val::global("window");
+            { colorSchemePreferenceDark },
-    if (!window.isUndefined()) {
+            [this](emscripten::val) { QWasmTheme::onColorSchemeChange(); },
-        const emscripten::val matchMedia = window.call<emscripten::val>("matchMedia", emscripten::val("(prefers-color-scheme: dark)"));
+            m_colorSchemeChangeCallback);
-        if (!matchMedia.isUndefined()) {
+    registerCallbacks(
-            static auto changeEvent =
+            { contrastPreferenceNoPreference, contrastPreferenceMore, contrastPreferenceLess,
-                std::make_unique<qstdweb::EventCallback>(matchMedia, "change", callback);
+              contrastPreferenceCustom },
-        }
+            [this](emscripten::val) { QWasmTheme::onContrastPreferenceChange(); },
-    }
+            m_contrastPreferenceChangeCallbacks);
 }
 
 QWasmTheme::~QWasmTheme()
@@ -59,9 +82,8 @@ QWasmTheme::~QWasmTheme()
 const QPalette *QWasmTheme::palette(Palette type) const
 {
     if (type == SystemPalette) {
-        if (m_paletteIsDirty || s_autoPaletteIsDirty) {
+        if (m_paletteIsDirty) {
             m_paletteIsDirty = false;
-            s_autoPaletteIsDirty = false;
             *m_palette = qt_fusionPalette();
         }
         return m_palette.get();
@@ -71,9 +93,7 @@ const QPalette *QWasmTheme::palette(Palette type) const
 
 Qt::ColorScheme QWasmTheme::colorScheme() const
 {
-    if (m_colorScheme != Qt::ColorScheme::Unknown)
+    return m_colorScheme;
-        return m_colorScheme;
-    return s_autoColorScheme;
 }
 
 void QWasmTheme::requestColorScheme(Qt::ColorScheme scheme)
@@ -85,6 +105,11 @@ void QWasmTheme::requestColorScheme(Qt::ColorScheme scheme)
     }
 }
 
+Qt::ContrastPreference QWasmTheme::contrastPreference() const
+{
+    return m_contrastPreference;
+}
+
 QVariant QWasmTheme::themeHint(ThemeHint hint) const
 {
     if (hint == QPlatformTheme::StyleNames)
@@ -102,20 +127,25 @@ const QFont *QWasmTheme::font(Font type) const
     return nullptr;
 }
 
-void QWasmTheme::onColorSchemeChange(emscripten::val event)
+void QWasmTheme::onColorSchemeChange()
 {
-    const emscripten::val matches = event["matches"];
+    auto colorScheme = getColorSchemeFromMedia();
-    if (!matches.isUndefined()) {
+    if (m_colorScheme != colorScheme) {
-        const auto oldAutoColorScheme = s_autoColorScheme;
+        qCDebug(lcQpaThemeWasm) << "Color scheme changed to " << colorScheme;
-        if (matches.as<int>())
+        m_colorScheme = colorScheme;
-            s_autoColorScheme = Qt::ColorScheme::Dark;
+        m_paletteIsDirty = true;
-        else
+        QWindowSystemInterface::handleThemeChange<QWindowSystemInterface::SynchronousDelivery>();
-            s_autoColorScheme = Qt::ColorScheme::Light;
+    }
+}
 
-        if (oldAutoColorScheme != s_autoColorScheme) {
+void QWasmTheme::onContrastPreferenceChange()
-            s_autoPaletteIsDirty = true;
+{
-            QWindowSystemInterface::handleThemeChange<QWindowSystemInterface::SynchronousDelivery>();
+    auto contrastPreference = getContrastPreferenceFromMedia();
-        }
+    if (m_contrastPreference != contrastPreference) {
+        qCDebug(lcQpaThemeWasm) << "Contrast preference changed to " << contrastPreference;
+        m_contrastPreference = contrastPreference;
+        m_paletteIsDirty = true;
+        QWindowSystemInterface::handleThemeChange<QWindowSystemInterface::SynchronousDelivery>();
     }
 }
 

src/plugins/platforms/wasm/qwasmtheme.h

@@ -7,6 +7,10 @@
 #include <qpa/qplatformtheme.h>
 #include <QtGui/QFont>
 
+#include <memory>
+
+#include <private/qstdweb_p.h>
+
 QT_BEGIN_NAMESPACE
 
 class QWasmEventTranslator;
@@ -17,6 +21,30 @@ class QWasmScreen;
 class QWasmCompositor;
 class QWasmBackingStore;
 
+// this reflects @media/prefers-contrast
+constexpr auto colorSchemePreferenceDark =  "(prefers-color-scheme: dark)";
+constexpr auto contrastPreferenceNoPreference =  "(prefers-contrast: no-preference)";
+constexpr auto contrastPreferenceMore =  "(prefers-contrast: more)";
+constexpr auto contrastPreferenceLess =  "(prefers-contrast: less)";
+constexpr auto contrastPreferenceCustom =  "(prefers-contrast: custom)";
+
+template <typename MediaName, typename CallbackFn, typename Container>
+void registerCallbacks(std::initializer_list<MediaName> mediaNames, CallbackFn callback, Container &callbacksContainer)
+{
+    emscripten::val window = emscripten::val::global("window");
+    if (!window.isUndefined()) {
+        for (auto &&mediaName : mediaNames) {
+            auto media = window.call<emscripten::val>("matchMedia", emscripten::val(mediaName));
+            if constexpr (std::is_same_v<Container, std::vector<QWasmEventHandler>>) {
+                callbacksContainer.emplace_back(media, "change", callback);
+            } else {
+                Q_ASSERT(mediaNames.size() == 1);
+                callbacksContainer = QWasmEventHandler(media, "change", callback);
+            }
+        }
+    }
+}
+
 class QWasmTheme : public QPlatformTheme
 {
 public:
@@ -26,19 +54,21 @@ public:
     const QPalette *palette(Palette type = SystemPalette) const override;
     Qt::ColorScheme colorScheme() const override;
     void requestColorScheme(Qt::ColorScheme scheme) override;
+    Qt::ContrastPreference contrastPreference() const override;
     QVariant themeHint(ThemeHint hint) const override;
     const QFont *font(Font type) const override;
     QFont *fixedFont = nullptr;
 
-    static void onColorSchemeChange(emscripten::val event);
+    void onColorSchemeChange();
+    void onContrastPreferenceChange();
 
 private:
     Qt::ColorScheme m_colorScheme = Qt::ColorScheme::Unknown;
+    QWasmEventHandler m_colorSchemeChangeCallback;
     std::unique_ptr<QPalette> m_palette;
     mutable bool m_paletteIsDirty = false;
-
+    Qt::ContrastPreference m_contrastPreference;
-    static Qt::ColorScheme s_autoColorScheme;
+    std::vector<QWasmEventHandler> m_contrastPreferenceChangeCallbacks;
-    static bool s_autoPaletteIsDirty;
 };
 
 QT_END_NAMESPACE