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QwtPlotCanvas Class Reference

Canvas of a QwtPlot. More...

`#include <qwt_plot_canvas.h>`

Inheritance diagram for QwtPlotCanvas:

## Public Types

enum | PaintAttribute { BackingStore = 1 , Opaque = 2 , HackStyledBackground = 4 , ImmediatePaint = 8 }
| Paint attributes. More...
typedef QFlags< PaintAttribute > | PaintAttributes
Public Types inherited from QwtPlotAbstractCanvas
enum | FocusIndicator { NoFocusIndicator , CanvasFocusIndicator , ItemFocusIndicator }
| Focus indicator The default setting is NoFocusIndicator. More...

## Public Slots

void | replot ()

## Public Member Functions

| QwtPlotCanvas (QwtPlot *=NULL)
| Constructor.
virtual | ~QwtPlotCanvas ()
| Destructor.
void | setPaintAttribute (PaintAttribute, bool on=true)
| Changing the paint attributes.
bool | testPaintAttribute (PaintAttribute) const
const QPixmap * | backingStore () const
Q_INVOKABLE void | invalidateBackingStore ()
| Invalidate the internal backing store.
virtual bool | event (QEvent *) override
Q_INVOKABLE QPainterPath | borderPath (const QRect &) const
Public Member Functions inherited from QwtPlotAbstractCanvas
| QwtPlotAbstractCanvas (QWidget *canvasWidget)
| Constructor.
virtual | ~QwtPlotAbstractCanvas ()
| Destructor.
QwtPlot * | plot ()
| Return parent plot widget.
const QwtPlot * | plot () const
| Return parent plot widget.
void | setFocusIndicator (FocusIndicator)
FocusIndicator | focusIndicator () const
void | setBorderRadius (double)
double | borderRadius () const

## Protected Member Functions

virtual void | paintEvent (QPaintEvent *) override
virtual void | resizeEvent (QResizeEvent *) override
virtual void | drawBorder (QPainter *) override
Protected Member Functions inherited from QwtPlotAbstractCanvas
QWidget * | canvasWidget ()
const QWidget * | canvasWidget () const
virtual void | drawFocusIndicator (QPainter *)
virtual void | drawBackground (QPainter *)
| Helper function for the derived plot canvas.
void | fillBackground (QPainter *)
| Helper function for the derived plot canvas.
void | drawCanvas (QPainter *)
| Draw the plot to the canvas.
void | drawStyled (QPainter *, bool)
| Helper function for the derived plot canvas.
void | drawUnstyled (QPainter *)
| Helper function for the derived plot canvas.
QPainterPath | canvasBorderPath (const QRect &rect) const
void | updateStyleSheetInfo ()
| Update the cached information about the current style sheet.

## Detailed Description

Canvas of a QwtPlot.

Canvas is the widget where all plot items are displayed

See also
  QwtPlot::setCanvas(), QwtPlotGLCanvas, QwtPlotOpenGLCanvas

Definition at line 29 of file qwt_plot_canvas.h.

## Member Typedef Documentation

## PaintAttributes

typedef QFlags<PaintAttribute > QwtPlotCanvas::PaintAttributes

An ORed combination of PaintAttribute values.

Definition at line 102 of file qwt_plot_canvas.h.

## Member Enumeration Documentation

## PaintAttribute

enum QwtPlotCanvas::PaintAttribute

Paint attributes.

The default setting enables BackingStore and Opaque.

See also
  setPaintAttribute(), testPaintAttribute()

Enumerator

BackingStore

Paint double buffered reusing the content of the pixmap buffer when possible.

Using a backing store might improve the performance significantly, when working with widget overlays ( like rubber bands ). Disabling the cache might improve the performance for incremental paints (using QwtPlotDirectPainter ).

See also
  backingStore(), invalidateBackingStore()

Opaque

Try to fill the complete contents rectangle of the plot canvas.

When using styled backgrounds Qt assumes, that the canvas doesn't fill its area completely ( f.e because of rounded borders ) and fills the area below the canvas. When this is done with gradients it might result in a serious performance bottleneck - depending on the size.

When the Opaque attribute is enabled the canvas tries to identify the gaps with some heuristics and to fill those only.

Warning
  Will not work for semitransparent backgrounds

HackStyledBackground

Try to improve painting of styled backgrounds.

QwtPlotCanvas supports the box model attributes for customizing the layout with style sheets. Unfortunately the design of Qt style sheets has no concept how to handle backgrounds with rounded corners - beside of padding.

When HackStyledBackground is enabled the plot canvas tries to separate the background from the background border by reverse engineering to paint the background before and the border after the plot items. In this order the border gets perfectly antialiased and you can avoid some pixel artifacts in the corners.

ImmediatePaint

When ImmediatePaint is set replot() calls repaint() instead of update().

See also
  replot(), QWidget::repaint(), QWidget::update()

Definition at line 44 of file qwt_plot_canvas.h.

## Constructor & Destructor Documentation

## QwtPlotCanvas()

QwtPlotCanvas::QwtPlotCanvas | ( | QwtPlot * | plot = NULL | ) |

explicit

Constructor.

Parameters

  plot | Parent plot widget

See also
  QwtPlot::setCanvas()

Definition at line 41 of file qwt_plot_canvas.cpp.

## ~QwtPlotCanvas()

QwtPlotCanvas::~QwtPlotCanvas | ( |  | ) |

virtual

Destructor.

Definition at line 57 of file qwt_plot_canvas.cpp.

## Member Function Documentation

## backingStore()

const QPixmap * QwtPlotCanvas::backingStore | ( |  | ) | const

Returns
  Backing store, might be null

Definition at line 133 of file qwt_plot_canvas.cpp.

## borderPath()

QPainterPath QwtPlotCanvas::borderPath | ( | const QRect & | rect | ) | const

Calculate the painter path for a styled or rounded border

When the canvas has no styled background or rounded borders the painter path is empty.

Parameters

  rect | Bounding rectangle of the canvas

Returns
  Painter path, that can be used for clipping

Definition at line 320 of file qwt_plot_canvas.cpp.

## drawBorder()

void QwtPlotCanvas::drawBorder | ( | QPainter * | painter | ) |

override protected virtual

Draw the border of the plot canvas

Parameters

  painter | Painter

See also
  setBorderRadius()

Reimplemented from QwtPlotAbstractCanvas.

Definition at line 276 of file qwt_plot_canvas.cpp.

## event()

bool QwtPlotCanvas::event | ( | QEvent * | event | ) |

override virtual

Qt event handler for QEvent::PolishRequest and QEvent::StyleChange

Parameters

  event | Qt Event

Returns
  See QFrame::event()

Definition at line 151 of file qwt_plot_canvas.cpp.

## invalidateBackingStore()

void QwtPlotCanvas::invalidateBackingStore | ( |  | ) |

Invalidate the internal backing store.

Definition at line 139 of file qwt_plot_canvas.cpp.

## paintEvent()

void QwtPlotCanvas::paintEvent | ( | QPaintEvent * | event | ) |

override protected virtual

Paint event

Parameters

  event | Paint event

Definition at line 178 of file qwt_plot_canvas.cpp.

## replot

void QwtPlotCanvas::replot | ( |  | ) |

slot

Invalidate the paint cache and repaint the canvas

See also
  invalidatePaintCache()

Definition at line 301 of file qwt_plot_canvas.cpp.

## resizeEvent()

void QwtPlotCanvas::resizeEvent | ( | QResizeEvent * | event | ) |

override protected virtual

Resize event

Parameters

  event | Resize event

Definition at line 291 of file qwt_plot_canvas.cpp.

## setPaintAttribute()

void QwtPlotCanvas::setPaintAttribute | ( | PaintAttribute | attribute,
|  | bool | on = true )

Changing the paint attributes.

Parameters

  attribute | Paint attribute
  on | On/Off

See also
  testPaintAttribute(), backingStore()

Definition at line 70 of file qwt_plot_canvas.cpp.

## testPaintAttribute()

bool QwtPlotCanvas::testPaintAttribute | ( | PaintAttribute | attribute | ) | const

Test whether a paint attribute is enabled

Parameters

  attribute | Paint attribute

Returns
  true, when attribute is enabled

See also
  setPaintAttribute()

Definition at line 127 of file qwt_plot_canvas.cpp.