Add QWindowsWindowClassDescription class

Replace loose parameter set with a small value type to clarify call
sites and allow future extension (cursor/menu/extra bytes) without API
churn.

Change-Id: I84303ab62f22778338a5950557117db7cc2edb77
Reviewed-by: Volker Hilsheimer <[email protected]>

7 files changed, 152 insertions, 80 deletions

diff --git a/src/plugins/platforms/direct2d/CMakeLists.txt b/src/plugins/platforms/direct2d/CMakeLists.txt
index 0b3ecf33967..38d7e4160a5 100644
--- a/src/plugins/platforms/direct2d/CMakeLists.txt
+++ b/src/plugins/platforms/direct2d/CMakeLists.txt
@@ -33,6 +33,7 @@ qt_internal_add_plugin(QWindowsDirect2DIntegrationPlugin
         ../windows/qwindowstheme.cpp ../windows/qwindowstheme.h
         ../windows/qwindowsthreadpoolrunner.h
         ../windows/qwindowswindow.cpp ../windows/qwindowswindow.h
+        ../windows/qwindowswindowclassdescription.cpp ../windows/qwindowswindowclassdescription.h
         ../windows/qwindowswindowclassregistry.cpp ../windows/qwindowswindowclassregistry.h
         qwindowsdirect2dbackingstore.cpp qwindowsdirect2dbackingstore.h
         qwindowsdirect2dbitmap.cpp qwindowsdirect2dbitmap.h
diff --git a/src/plugins/platforms/windows/CMakeLists.txt b/src/plugins/platforms/windows/CMakeLists.txt
index c7563c72979..40f173c8c82 100644
--- a/src/plugins/platforms/windows/CMakeLists.txt
+++ b/src/plugins/platforms/windows/CMakeLists.txt
@@ -38,6 +38,7 @@ qt_internal_add_plugin(QWindowsIntegrationPlugin
         qwindowstheme.cpp qwindowstheme.h
         qwindowsthreadpoolrunner.h
         qwindowswindow.cpp qwindowswindow.h
+        qwindowswindowclassdescription.cpp qwindowswindowclassdescription.h
         qwindowswindowclassregistry.cpp qwindowswindowclassregistry.h
     NO_UNITY_BUILD_SOURCES
         qwindowspointerhandler.cpp
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index c49ddbb3247..26d0f907b92 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -23,6 +23,7 @@
 #ifdef QT_NO_CURSOR
 #  include "qwindowscursor.h"
 #endif
+#include "qwindowswindowclassdescription.h"
 #include "qwindowswindowclassregistry.h"
 
 #include <QtGui/qguiapplication.h>
@@ -886,7 +887,9 @@ QWindowsWindowData
     const auto appinst = reinterpret_cast<HINSTANCE>(GetModuleHandle(nullptr));
 
     const QString windowClassName = QWindowsWindowClassRegistry::instance()->registerWindowClass(w);
-    const QString windowTitlebarName = QWindowsWindowClassRegistry::instance()->registerWindowClass(QStringLiteral("_q_titlebar"), DefWindowProc, CS_VREDRAW|CS_HREDRAW, nullptr, false);
+    const QString windowTitlebarName = QWindowsWindowClassRegistry::instance()->registerWindowClass({
+        QStringLiteral("_q_titlebar"), DefWindowProc, CS_VREDRAW | CS_HREDRAW
+    });
 
     const QScreen *screen{};
     const QRect rect = QPlatformWindow::initialGeometry(w, data.geometry,
diff --git a/src/plugins/platforms/windows/qwindowswindowclassdescription.cpp b/src/plugins/platforms/windows/qwindowswindowclassdescription.cpp
new file mode 100644
index 00000000000..cb862bba47c
--- /dev/null
+++ b/src/plugins/platforms/windows/qwindowswindowclassdescription.cpp
@@ -0,0 +1,79 @@
+// Copyright (C) 2025 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include "qwindowswindowclassdescription.h"
+
+#include <QtGui/qwindow.h>
+
+#include "qwindowswindowclassregistry.h"
+
+QT_BEGIN_NAMESPACE
+
+using namespace Qt::StringLiterals;
+
+QWindowsWindowClassDescription QWindowsWindowClassDescription::fromName(QString name, WNDPROC procedure)
+{
+    return { std::move(name), procedure };
+}
+
+QWindowsWindowClassDescription QWindowsWindowClassDescription::fromWindow(const QWindow *window, WNDPROC procedure)
+{
+    Q_ASSERT(window);
+
+    QWindowsWindowClassDescription description;
+    description.procedure = procedure;
+
+    const Qt::WindowFlags flags = window->flags();
+    const Qt::WindowFlags type = flags & Qt::WindowType_Mask;
+    // Determine style and icon.
+    description.style = CS_DBLCLKS;
+    description.hasIcon = true;
+    // The following will not set CS_OWNDC for any widget window, even if it contains a
+    // QOpenGLWidget or QQuickWidget later on. That cannot be detected at this stage.
+    if (window->surfaceType() == QSurface::OpenGLSurface || (flags & Qt::MSWindowsOwnDC))
+        description.style |= CS_OWNDC;
+    if (!(flags & Qt::NoDropShadowWindowHint)
+        && (type == Qt::Popup || window->property("_q_windowsDropShadow").toBool())) {
+        description.style |= CS_DROPSHADOW;
+    }
+    switch (type) {
+        case Qt::Tool:
+        case Qt::ToolTip:
+        case Qt::Popup:
+            description.style |= CS_SAVEBITS; // Save/restore background
+            description.hasIcon = false;
+            break;
+        case Qt::Dialog:
+            if (!(flags & Qt::WindowSystemMenuHint))
+                description.hasIcon = false; // QTBUG-2027, dialogs without system menu.
+            break;
+    }
+    // Create a unique name for the flag combination
+    description.name = QWindowsWindowClassRegistry::classNamePrefix();
+    description.name += "QWindow"_L1;
+    switch (type) {
+        case Qt::Tool:
+            description.name += "Tool"_L1;
+            break;
+        case Qt::ToolTip:
+            description.name += "ToolTip"_L1;
+            break;
+        case Qt::Popup:
+            description.name += "Popup"_L1;
+            break;
+        default:
+            break;
+    }
+    if (description.style & CS_DROPSHADOW)
+        description.name += "DropShadow"_L1;
+    if (description.style & CS_SAVEBITS)
+        description.name += "SaveBits"_L1;
+    if (description.style & CS_OWNDC)
+        description.name += "OwnDC"_L1;
+    if (description.hasIcon)
+        description.name += "Icon"_L1;
+
+    return description;
+}
+
+QT_END_NAMESPACE
diff --git a/src/plugins/platforms/windows/qwindowswindowclassdescription.h b/src/plugins/platforms/windows/qwindowswindowclassdescription.h
new file mode 100644
index 00000000000..ece48e4343c
--- /dev/null
+++ b/src/plugins/platforms/windows/qwindowswindowclassdescription.h
@@ -0,0 +1,29 @@
+// Copyright (C) 2025 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef QWINDOWSWINDOWCLASSDESCRIPTION_H
+#define QWINDOWSWINDOWCLASSDESCRIPTION_H
+
+#include "qtwindowsglobal.h"
+
+#include <QtCore/qstring.h>
+
+QT_BEGIN_NAMESPACE
+
+class QWindow;
+
+struct QWindowsWindowClassDescription
+{
+    static QWindowsWindowClassDescription fromName(QString name, WNDPROC procedure);
+    static QWindowsWindowClassDescription fromWindow(const QWindow *window, WNDPROC procedure);
+
+    QString name;
+    WNDPROC procedure{ DefWindowProc };
+    unsigned int style{ 0 };
+    HBRUSH brush{ nullptr };
+    bool hasIcon{ false };
+};
+
+QT_END_NAMESPACE
+
+#endif // QWINDOWSWINDOWCLASSDESCRIPTION_H
diff --git a/src/plugins/platforms/windows/qwindowswindowclassregistry.cpp b/src/plugins/platforms/windows/qwindowswindowclassregistry.cpp
index 0d405dc419a..e367350d55e 100644
--- a/src/plugins/platforms/windows/qwindowswindowclassregistry.cpp
+++ b/src/plugins/platforms/windows/qwindowswindowclassregistry.cpp
@@ -6,9 +6,9 @@
 
 #include <QtCore/qlibraryinfo.h>
 #include <QtCore/quuid.h>
-#include <QtGui/qwindow.h>
 
 #include "qwindowscontext.h"
+#include "qwindowswindowclassdescription.h"
 
 QT_BEGIN_NAMESPACE
 
@@ -55,64 +55,10 @@ QString QWindowsWindowClassRegistry::classNamePrefix()
     return result;
 }
 
-QString QWindowsWindowClassRegistry::registerWindowClass(const QWindow *w)
+QString QWindowsWindowClassRegistry::registerWindowClass(const QWindowsWindowClassDescription &description)
 {
-    Q_ASSERT(w);
-    const Qt::WindowFlags flags = w->flags();
-    const Qt::WindowFlags type = flags & Qt::WindowType_Mask;
-    // Determine style and icon.
-    uint style = CS_DBLCLKS;
-    bool icon = true;
-    // The following will not set CS_OWNDC for any widget window, even if it contains a
-    // QOpenGLWidget or QQuickWidget later on. That cannot be detected at this stage.
-    if (w->surfaceType() == QSurface::OpenGLSurface || (flags & Qt::MSWindowsOwnDC))
-        style |= CS_OWNDC;
-    if (!(flags & Qt::NoDropShadowWindowHint)
-        && (type == Qt::Popup || w->property("_q_windowsDropShadow").toBool())) {
-        style |= CS_DROPSHADOW;
-    }
-    switch (type) {
-        case Qt::Tool:
-        case Qt::ToolTip:
-        case Qt::Popup:
-            style |= CS_SAVEBITS; // Save/restore background
-            icon = false;
-            break;
-        case Qt::Dialog:
-            if (!(flags & Qt::WindowSystemMenuHint))
-                icon = false; // QTBUG-2027, dialogs without system menu.
-            break;
-    }
-    // Create a unique name for the flag combination
-    QString cname = classNamePrefix();
-    cname += "QWindow"_L1;
-    switch (type) {
-        case Qt::Tool:
-            cname += "Tool"_L1;
-            break;
-        case Qt::ToolTip:
-            cname += "ToolTip"_L1;
-            break;
-        case Qt::Popup:
-            cname += "Popup"_L1;
-            break;
-        default:
-            break;
-    }
-    if (style & CS_DROPSHADOW)
-        cname += "DropShadow"_L1;
-    if (style & CS_SAVEBITS)
-        cname += "SaveBits"_L1;
-    if (style & CS_OWNDC)
-        cname += "OwnDC"_L1;
-    if (icon)
-        cname += "Icon"_L1;
-
-    return registerWindowClass(cname, m_proc, style, nullptr, icon);
-}
+    QString className = description.name;
 
-QString QWindowsWindowClassRegistry::registerWindowClass(QString cname, WNDPROC proc, unsigned style, HBRUSH brush, bool icon)
-{
     // since multiple Qt versions can be used in one process
     // each one has to have window class names with a unique name
     // The first instance gets the unmodified name; if the class
@@ -122,52 +68,63 @@ QString QWindowsWindowClassRegistry::registerWindowClass(QString cname, WNDPROC
     // Note: GetClassInfo() returns != 0 when a class exists.
     const auto appInstance = static_cast<HINSTANCE>(GetModuleHandle(nullptr));
     WNDCLASS wcinfo;
-    const bool classExists = GetClassInfo(appInstance, reinterpret_cast<LPCWSTR>(cname.utf16()), &wcinfo) != FALSE
-        && wcinfo.lpfnWndProc != proc;
+    const bool classExists = GetClassInfo(appInstance, reinterpret_cast<LPCWSTR>(className.utf16()), &wcinfo) != FALSE
+        && wcinfo.lpfnWndProc != description.procedure;
 
     if (classExists)
-        cname += QUuid::createUuid().toString();
+        className += QUuid::createUuid().toString();
 
-    if (m_registeredWindowClassNames.contains(cname))        // already registered in our list
-        return cname;
+    if (m_registeredWindowClassNames.contains(className))        // already registered in our list
+        return className;
 
     WNDCLASSEX wc;
     wc.cbSize = sizeof(WNDCLASSEX);
-    wc.style = style;
-    wc.lpfnWndProc = proc;
+    wc.style = description.style;
+    wc.lpfnWndProc = description.procedure;
     wc.cbClsExtra = 0;
     wc.cbWndExtra = 0;
     wc.hInstance = appInstance;
     wc.hCursor = nullptr;
-    wc.hbrBackground = brush;
-    if (icon) {
+    wc.hbrBackground = description.brush;
+    if (description.hasIcon) {
         wc.hIcon = static_cast<HICON>(LoadImage(appInstance, L"IDI_ICON1", IMAGE_ICON, 0, 0, LR_DEFAULTSIZE));
         if (wc.hIcon) {
             int sw = GetSystemMetrics(SM_CXSMICON);
             int sh = GetSystemMetrics(SM_CYSMICON);
             wc.hIconSm = static_cast<HICON>(LoadImage(appInstance, L"IDI_ICON1", IMAGE_ICON, sw, sh, 0));
-        } else {
+        }
+        else {
             wc.hIcon = static_cast<HICON>(LoadImage(nullptr, IDI_APPLICATION, IMAGE_ICON, 0, 0, LR_DEFAULTSIZE | LR_SHARED));
             wc.hIconSm = nullptr;
         }
-    } else {
+    }
+    else {
         wc.hIcon = nullptr;
         wc.hIconSm = nullptr;
     }
 
     wc.lpszMenuName = nullptr;
-    wc.lpszClassName = reinterpret_cast<LPCWSTR>(cname.utf16());
+    wc.lpszClassName = reinterpret_cast<LPCWSTR>(className.utf16());
     ATOM atom = RegisterClassEx(&wc);
-    if (!atom) {
+    if (!atom)
         qErrnoWarning("QApplication::regClass: Registering window class '%s' failed.",
-                      qPrintable(cname));
-    }
+            qPrintable(className));
+
+    m_registeredWindowClassNames.insert(className);
+    qCDebug(lcQpaWindowClass).nospace() << __FUNCTION__ << ' ' << className
+        << " style=0x" << Qt::hex << description.style << Qt::dec
+        << " brush=" << description.brush << " icon=" << description.hasIcon << " atom=" << atom;
+    return className;
+}
 
-    m_registeredWindowClassNames.insert(cname);
-    qCDebug(lcQpaWindowClass).nospace() << __FUNCTION__ << ' ' << cname
-        << " style=0x" << Qt::hex << style << Qt::dec
-        << " brush=" << brush << " icon=" << icon << " atom=" << atom;
-    return cname;
+QString QWindowsWindowClassRegistry::registerWindowClass(const QWindow *window)
+{
+    return registerWindowClass(QWindowsWindowClassDescription::fromWindow(window, m_proc));
+}
+
+QString QWindowsWindowClassRegistry::registerWindowClass(QString name, WNDPROC procedure)
+{
+    return registerWindowClass(QWindowsWindowClassDescription::fromName(name, procedure));
 }
 
 void QWindowsWindowClassRegistry::unregisterWindowClasses()
diff --git a/src/plugins/platforms/windows/qwindowswindowclassregistry.h b/src/plugins/platforms/windows/qwindowswindowclassregistry.h
index d599497abd0..d1f10310dc8 100644
--- a/src/plugins/platforms/windows/qwindowswindowclassregistry.h
+++ b/src/plugins/platforms/windows/qwindowswindowclassregistry.h
@@ -16,6 +16,7 @@ QT_BEGIN_NAMESPACE
 Q_DECLARE_LOGGING_CATEGORY(lcQpaWindowClass)
 
 class QWindow;
+struct QWindowsWindowClassDescription;
 
 class QWindowsWindowClassRegistry
 {
@@ -28,8 +29,9 @@ public:
 
     static QString classNamePrefix();
 
-    QString registerWindowClass(const QWindow *w);
-    QString registerWindowClass(QString cname, WNDPROC proc, unsigned style = 0, HBRUSH brush = nullptr, bool icon = false);
+    QString registerWindowClass(const QWindowsWindowClassDescription &description);
+    QString registerWindowClass(const QWindow *window);
+    QString registerWindowClass(QString name, WNDPROC procedure);
 
 private:
     void unregisterWindowClasses();