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To replace the QGraphicsScene, we need the possibility of showing and hiding items. Turns out, the QSG API is completely insane. Whether an item should be shown is queried by the virtual function isSubtreeBlocked(), which is supposed to be overriden by the derived classes. However, the common nodes for rectangles and pixmaps are supposed to be created by QQuickWindow, for hardware optimization. This gives nodes that cannot be derived from and therefore whether the item is shown or not cannot be controlled. There are therefore two distinct cases to consider: The node is allocated by the code directly or indirectly by QQuickWindow. In the latter case, we use a proxy node with the only purpose of having a "visible" flag and add the obtained node as a child. This madness is performed with template trickery to get unified code. Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
104 lines
3.2 KiB
C++
104 lines
3.2 KiB
C++
// SPDX-License-Identifier: GPL-2.0
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// Helper functions to render the stats. Currently only
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// contains a small template to create scene-items. This
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// is for historical reasons to ease transition from QtCharts
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// and might be removed.
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#ifndef STATSHELPER_H
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#define STATSHELPER_H
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#include <memory>
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#include <QGraphicsScene>
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#include <QSGNode>
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template <typename T, class... Args>
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T *createItem(QGraphicsScene *scene, Args&&... args)
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{
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T *res = new T(std::forward<Args>(args)...);
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scene->addItem(res);
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return res;
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}
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template <typename T, class... Args>
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std::unique_ptr<T> createItemPtr(QGraphicsScene *scene, Args&&... args)
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{
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return std::unique_ptr<T>(createItem<T>(scene, std::forward<Args>(args)...));
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}
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// In general, we want chart items to be hideable. For example to show/hide
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// labels on demand. Very sadly, the QSG API is absolutely terrible with
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// respect to temporarily disabling. Instead of simply having a flag,
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// a QSGNode is queried using the "isSubtreeBlocked()" virtual function(!).
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//
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// Not only is this a slow operation performed on every single node, it
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// also is often not possible to override this function: For improved
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// performance, the documentation recommends to create QSG nodes via
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// QQuickWindow. This provides nodes optimized for the actual hardware.
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// However, this obviously means that these nodes cannot be derived from!
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//
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// In that case, there are two possibilities: Add a proxy node with an
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// overridden "isSubtreeBlocked()" function or remove the node from the
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// scene. The former was chosen here, because it is less complex.
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//
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// The following slightly cryptic templates are used to unify the two
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// cases: The QSGNode is generated by our own code or the QSGNode is
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// obtained from QQuickWindow.
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//
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// The "HideableQSGNode<Node>" template augments the QSGNode "Node"
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// by a "setVisible()" function and overrides "isSubtreeBlocked()"
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//
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// The "QSGProxyNode<Node>" template is a QSGNode with a single
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// child of type "Node".
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//
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// Thus, if the node can be created, use:
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// HideableQSGNode<NodeTypeThatCanBeCreated> node
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// and if the node can only be obtained from QQuickWindow, use:
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// HideableQSGNode<QSGProxyNode<NodeThatCantBeCreated>> node
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// The latter should obviously be typedef-ed.
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//
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// Yes, that's all horrible, but if nothing else it teaches us about
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// composition.
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template <typename Node>
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class HideableQSGNode : public Node {
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bool hidden;
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bool isSubtreeBlocked() const override final;
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public:
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template<class... Args>
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HideableQSGNode(bool visible, Args&&... args);
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void setVisible(bool visible);
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};
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template <typename Node>
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class QSGProxyNode : public QSGNode {
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public:
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std::unique_ptr<Node> node;
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QSGProxyNode(Node *node);
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};
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// Implementation detail of templates - move to serparate header file
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template <typename Node>
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QSGProxyNode<Node>::QSGProxyNode(Node *node) : node(node)
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{
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appendChildNode(node);
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}
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template <typename Node>
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bool HideableQSGNode<Node>::isSubtreeBlocked() const
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{
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return hidden;
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}
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template <typename Node>
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template<class... Args>
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HideableQSGNode<Node>::HideableQSGNode(bool visible, Args&&... args) :
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Node(std::forward<Args>(args)...),
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hidden(!visible)
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{
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}
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template <typename Node>
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void HideableQSGNode<Node>::setVisible(bool visible)
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{
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hidden = !visible;
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}
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#endif
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