Qwt User's Guide: QwtPlotDirectPainter Class Reference

Qwt User's Guide 6.0.1

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Public Types | Public Member Functions

# QwtPlotDirectPainter Class Reference

Painter object trying to paint incrementally. More...

`#include <qwt_plot_directpainter.h>`

List of all members.

## Public Types
enum | Attribute { AtomicPainter = 0x01, FullRepaint = 0x02, CopyBackingStore = 0x04 }
typedef QFlags< Attribute > | Attributes
## Public Member Functions
QRegion | clipRegion () const
void | drawSeries (QwtPlotAbstractSeriesItem *, int from, int to)
virtual bool | eventFilter (QObject *, QEvent *)
bool | hasClipping () const
| QwtPlotDirectPainter (QObject *parent=NULL)
void | reset ()
void | setAttribute (Attribute, bool on)
void | setClipping (bool)
void | setClipRegion (const QRegion &)
bool | testAttribute (Attribute) const
virtual | ~QwtPlotDirectPainter ()

## Detailed Description

Painter object trying to paint incrementally.

Often applications want to display samples while they are collected. When there are too many samples complete replots will be expensive to be processed in a collection cycle.

QwtPlotDirectPainter offers an API to paint subsets ( f.e all additions points ) without erasing/repainting the plot canvas.

On certain environments it might be important to calculate a proper clip region before painting. F.e. for Qt Embedded only the clipped part of the backing store will be copied to a ( maybe unaccelerated ) frame buffer.

Warning:
  Incremental painting will only help when no replot is triggered by another operation ( like changing scales ) and nothing needs to be erased.

## Member Typedef Documentation

typedef QFlags<Attribute> QwtPlotDirectPainter::Attributes

Paint attributes.

## Member Enumeration Documentation

enum QwtPlotDirectPainter::Attribute

Paint attributes.

See also:
  setAttribute(), testAttribute(), drawSeries()

Enumerator:

  AtomicPainter | Initializing a QPainter is an expensive operation. When AtomicPainter is set each call of drawSeries() opens/closes a temporary QPainter. Otherwise QwtPlotDirectPainter tries to use the same QPainter as long as possible.
  FullRepaint | When FullRepaint is set the plot canvas is explicitely repainted after the samples have been rendered.
  CopyBackingStore | When QwtPlotCanvas::BackingStore is enabled the painter has to paint to the backing store and the widget. In certain situations/environments it might be faster to paint to the backing store only and then copy the backingstore to the canvas. This flag can also be useful for settings, where Qt fills the the clip region with the widget background.

## Constructor & Destructor Documentation

QwtPlotDirectPainter::QwtPlotDirectPainter | ( | QObject * | parent = `NULL` | ) |

Constructor.

QwtPlotDirectPainter::~QwtPlotDirectPainter | ( |  | ) | `[virtual]`

Destructor.

## Member Function Documentation

QRegion QwtPlotDirectPainter::clipRegion | ( |  | ) | const

Returns:
  Currently set clip region.

See also:
  setClipRegion(), setClipping(), hasClipping()

void QwtPlotDirectPainter::drawSeries | ( | QwtPlotAbstractSeriesItem * | seriesItem,
|  | int | from,
|  | int | to
| ) |  |

Draw a set of points of a seriesItem.

When observing an measurement while it is running, new points have to be added to an existing seriesItem. drawSeries can be used to display them avoiding a complete redraw of the canvas.

Setting plot()->canvas()->setAttribute(Qt::WA_PaintOutsidePaintEvent, true); will result in faster painting, if the paint engine of the canvas widget supports this feature.

Parameters:

  seriesItem | Item to be painted
  from | Index of the first point to be painted
  to | Index of the last point to be painted. If to < 0 the series will be painted to its last point.

bool QwtPlotDirectPainter::eventFilter | ( | QObject * | ,
|  | QEvent * | event
| ) |  | `[virtual]`

Event filter.

bool QwtPlotDirectPainter::hasClipping | ( |  | ) | const

Returns:
  true, when clipping is enabled

See also:
  setClipping(), clipRegion(), setClipRegion()

void QwtPlotDirectPainter::reset | ( |  | ) |

Close the internal QPainter.

void QwtPlotDirectPainter::setAttribute | ( | Attribute | attribute,
|  | bool | on
| ) |  |

Change an attribute

Parameters:

  attribute | Attribute to change
  on | On/Off

See also:
  Attribute, testAttribute()

void QwtPlotDirectPainter::setClipping | ( | bool | enable | ) |

En/Disables clipping

Parameters:

  enable | Enables clipping is true, disable it otherwise

See also:
  hasClipping(), clipRegion(), setClipRegion()

void QwtPlotDirectPainter::setClipRegion | ( | const QRegion & | region | ) |

Assign a clip region and enable clipping.

Depending on the environment setting a proper clip region might improve the performance heavily. F.e. on Qt embedded only the clipped part of the backing store will be copied to a ( maybe unaccelerated ) frame buffer device.

Parameters:

  region | Clip region

See also:
  clipRegion(), hasClipping(), setClipping()

bool QwtPlotDirectPainter::testAttribute | ( | Attribute | attribute | ) | const

Check if a attribute is set.

Parameters:

  attribute | Attribute to be tested

See also:
  Attribute, setAttribute()