- Qt 6.9
- Qt GUI
- C++ Classes
- QPainterStateGuard
- Qt 6.9.2 Reference Documentation

# 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.