QwtPlotCanvas - Man Page

Canvas of a QwtPlot.

Synopsis

#include <qwt_plot_canvas.h>

Inherits QFrame, and QwtPlotAbstractCanvas.

Public Types

enum PaintAttribute { BackingStore = 1, Opaque = 2, HackStyledBackground = 4, ImmediatePaint = 8 }
Paint attributes.
typedef QFlags< PaintAttribute > PaintAttributes

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

Protected Member Functions

virtual void paintEvent (QPaintEvent *) override
virtual void resizeEvent (QResizeEvent *) override
virtual void drawBorder (QPainter *) override

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

typedef QFlags<PaintAttribute > QwtPlotCanvas::PaintAttributes

An ORed combination of PaintAttribute values.

Definition at line 102 of file qwt_plot_canvas.h.

Member Enumeration Documentation

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.