Add support for binding directly to QProperty instances

Avoid going through externally managed bindings and instead allocate a
more lightweight property binding. It's basically a
QQmlJavaScriptExpression and one pointer plus the overhead of
QPropertyBindingPrivate.

Change-Id: I1530330926d351b61f2b3bbad39301c628a8bef1
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 101 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlpropertybinding.cpp b/src/qml/qml/qqmlpropertybinding.cpp
new file mode 100644
index 0000000000..ca64cf412a
--- /dev/null
+++ b/src/qml/qml/qqmlpropertybinding.cpp
@@ -0,0 +1,101 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQml module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qqmlpropertybinding_p.h"
+
+#include <private/qpropertybinding_p.h>
+
+QT_BEGIN_NAMESPACE
+
+QUntypedPropertyBinding QQmlPropertyBinding::create(const QQmlPropertyData *pd, QV4::Function *function,
+                                                    QObject *obj, const QQmlRefPointer<QQmlContextData> &ctxt,
+                                                    QV4::ExecutionContext *scope)
+{
+    auto binding = new QQmlPropertyBinding(QMetaType(pd->propType()));
+    binding->setNotifyOnValueChanged(true);
+    binding->setContext(ctxt);
+    binding->setScopeObject(obj);
+    binding->setupFunction(scope, function);
+    return QUntypedPropertyBinding(QPropertyBindingPrivatePtr(binding));
+}
+
+void QQmlPropertyBinding::expressionChanged()
+{
+    setDirty(true);
+}
+
+QQmlPropertyBinding::QQmlPropertyBinding(const QMetaType &mt)
+    : QPropertyBindingPrivate(mt,
+                              [this](const QMetaType &metaType, void *dataPtr) -> QUntypedPropertyBinding::BindingEvaluationResult {
+                                  return evaluateAndReturnTrueIfChanged(metaType, dataPtr);
+                              }, QPropertyBindingSourceLocation())
+{
+}
+
+QUntypedPropertyBinding::BindingEvaluationResult QQmlPropertyBinding::evaluateAndReturnTrueIfChanged(const QMetaType &metaType, void *dataPtr)
+{
+    QQmlEngine *engine = context()->engine();
+    QQmlEnginePrivate *ep = QQmlEnginePrivate::get(engine);
+    ep->referenceScarceResources();
+
+    bool isUndefined = false;
+
+    QV4::Scope scope(engine->handle());
+    QV4::ScopedValue result(scope, QQmlJavaScriptExpression::evaluate(&isUndefined));
+
+    ep->dereferenceScarceResources();
+
+    if (hasError()) {
+        QPropertyBindingError error(QPropertyBindingError::UnknownError);
+        error.setDescription(delayedError()->error().description());
+        return error;
+    }
+
+    QVariant resultVariant(scope.engine->toVariant(result, metaType.id()));
+
+    int compareResult = 0;
+    if (QMetaType::compare(dataPtr, resultVariant.constData(), metaType.id(), &compareResult)
+        && compareResult == 0)
+        return false;
+    QMetaType::destruct(metaType.id(), dataPtr);
+    QMetaType::construct(metaType.id(), dataPtr, resultVariant.constData());
+    return true;
+}
+
+QT_END_NAMESPACE