QPainterStateGuard Class
The QPainterStateGuard is a RAII convenience class for balanced QPainter::save() and QPainter::restore() calls. More...
| Header: | #include <QPainterStateGuard> |
| CMake: | find_package(Qt6 REQUIRED COMPONENTS Gui)target_link_libraries(mytarget PRIVATE Qt6::Gui) |
| qmake: | QT += gui |
| Since: | Qt 6.9 |
- List of all members, including inherited members
- QPainterStateGuard is part of Painting Classes.
Note: All functions in this class are reentrant.
Public Functions
| QPainterStateGuard(QPainter *painter, QPainterStateGuard::InitialState state = InitialState::Save) | |
| QPainterStateGuard(QPainterStateGuard &&other) | |
| ~QPainterStateGuard() | |
| void | restore() |
| void | save() |
| void | swap(QPainterStateGuard &other) |
| QPainterStateGuard & | operator=(QPainterStateGuard &&other) |
Detailed Description
QPainterStateGuard should be used everywhere as a replacement for QPainter::save() to make sure that the corresponding QPainter::restore() is called upon finishing of the painting routine to avoid unbalanced calls between those two functions.
Example with QPainter::save()/QPainter::restore():
void MyWidget::paintEvent(QPaintEvent *) { QPainter painter(this); painter.setPen(Qt::red); if (drawText) { painter.save(); painter.setPen(Qt::blue); painter.setFont(QFont("Arial", 30)); painter.drawText(rect(), Qt::AlignCenter, "Qt"); painter.restore(); // don't forget to restore previous painter state } painter.drawLine(line); }
Example with QPainterStateGuard:
void MyGuardWidget::paintEvent(QPaintEvent *) { QPainter painter(this); painter.setPen(Qt::red); if (drawText) { QPainterStateGuard guard(&painter) painter.setPen(Qt::blue); painter.setFont(QFont("Arial", 30)); painter.drawText(rect(), Qt::AlignCenter, "Qt"); } painter.drawLine(line); }
See also QPainter.
Member Function Documentation
[explicit] QPainterStateGuard::QPainterStateGuard(QPainter *painter, QPainterStateGuard::InitialState state = InitialState::Save)
Constructs a QPainterStateGuard and calls save() on painter if state is InitialState::Save (which is the default). When QPainterStateGuard is destroyed, restore() is called as often as save() was called to restore the QPainter's state.
[noexcept] QPainterStateGuard::QPainterStateGuard(QPainterStateGuard &&other)
Move-constructs a painter state guard from other.
[noexcept] QPainterStateGuard::~QPainterStateGuard()
Destroys the QPainterStateGuard instance and calls restore() as often as save() was called to restore the QPainter's state.
void QPainterStateGuard::restore()
Calls QPainter::restore() if the internal save/restore counter is greater than zero.
Note: This function asserts in debug builds if the counter has already reached zero.
void QPainterStateGuard::save()
Calls QPainter::save() and increases the internal save/restore counter by one.
[noexcept] void QPainterStateGuard::swap(QPainterStateGuard &other)
Swaps the other with this painter state guard. This operation is very fast and never fails.
[noexcept] QPainterStateGuard &QPainterStateGuard::operator=(QPainterStateGuard &&other)
Move-assigns other to this painter state guard.