QwtPlotDirectPainter man page

QwtPlotDirectPainter — Painter object trying to paint incrementally.  


#include <qwt_plot_directpainter.h>

Inherits QObject.

Public Types

enum Attribute { AtomicPainter = 0x01, FullRepaint = 0x02, CopyBackingStore = 0x04 } Paint attributes. "
typedef QFlags< Attribute > Attributes
Paint attributes.

Public Member Functions

QwtPlotDirectPainter (QObject *parent=NULL)
virtual ~QwtPlotDirectPainter ()
void setAttribute (Attribute, bool on)
bool testAttribute (Attribute) const
void setClipping (bool)
bool hasClipping () const
void setClipRegion (const QRegion &)
Assign a clip region and enable clipping.
QRegion clipRegion () const
void drawSeries (QwtPlotSeriesItem *, int from, int to)
Draw a set of points of a seriesItem.
void reset ()
Close the internal QPainter.
virtual bool eventFilter (QObject *, QEvent *)
Event filter.

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.


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

Member Enumeration Documentation

enum QwtPlotDirectPainter::Attribute

Paint attributes.

See also:

setAttribute(), testAttribute(), drawSeries()



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.


When FullRepaint is set the plot canvas is explicitly repainted after the samples have been rendered.


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 backing store to the canvas. This flag can also be useful for settings, where Qt fills the the clip region with the widget background.

Member Function Documentation

QRegion QwtPlotDirectPainter::clipRegion () const


Currently set clip region.

See also:

setClipRegion(), setClipping(), hasClipping()

void QwtPlotDirectPainter::drawSeries (QwtPlotSeriesItem * 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.


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::hasClipping () const


true, when clipping is enabled

See also:

setClipping(), clipRegion(), setClipRegion()

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

Change an attribute


attribute Attribute to change
on On/Off

See also:

Attribute, testAttribute()

void QwtPlotDirectPainter::setClipping (bool enable)

En/Disables clipping


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.


region Clip region

See also:

clipRegion(), hasClipping(), setClipping()

bool QwtPlotDirectPainter::testAttribute (Attribute attribute) const


True, when attribute is enabled


attribute Attribute to be tested

See also:

Attribute, setAttribute()


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Mon Jun 13 2016 Version 6.1.3 Qwt User's Guide