CircleWidget Class Reference

#include <circlewidget.h>

Inheritance diagram for CircleWidget:

[legend]Collaboration diagram for CircleWidget:

[legend]List of all members.

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Detailed Description

Definition at line 29 of file circlewidget.h.

Public Slots
void	nextAnimationFrame ()
Public Member Functions
	CircleWidget (QWidget *parent=0)
void	setFloatBased (bool floatBased)
void	setAntialiased (bool antialiased)
QSize	minimumSizeHint () const
QSize	sizeHint () const
Protected Member Functions
void	paintEvent (QPaintEvent *event)
Private Attributes
bool	floatBased
bool	antialiased
int	frameNo

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Constructor & Destructor Documentation

CircleWidget::CircleWidget

(

QWidget *

parent = 0

)

Definition at line 30 of file circlewidget.cpp.

References antialiased, QPalette::Base, QSizePolicy::Expanding, floatBased, frameNo, QWidget::setBackgroundRole(), and QWidget::setSizePolicy().

    : QWidget(parent)
{
    floatBased = false;
    antialiased = false;
    frameNo = 0;

    setBackgroundRole(QPalette::Base);
    setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
}

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Member Function Documentation

void CircleWidget::setFloatBased

(

bool

floatBased

)

Definition at line 41 of file circlewidget.cpp.

References QWidget::update().

{
    this->floatBased = floatBased;
    update();
}

void CircleWidget::setAntialiased

(

bool

antialiased

)

Definition at line 47 of file circlewidget.cpp.

References QWidget::update().

{
    this->antialiased = antialiased;
    update();
}

QSize CircleWidget::minimumSizeHint

(

)

const [virtual]

Reimplemented from QWidget.

Definition at line 53 of file circlewidget.cpp.

{
    return QSize(50, 50);
}

QSize CircleWidget::sizeHint

(

)

const [virtual]

Reimplemented from QWidget.

Definition at line 58 of file circlewidget.cpp.

{
    return QSize(180, 180);
}

void CircleWidget::nextAnimationFrame

(

)

[slot]

Definition at line 63 of file circlewidget.cpp.

References frameNo, and QWidget::update().

{
    ++frameNo;
    update();
}

void CircleWidget::paintEvent

(

QPaintEvent *

event

)

[protected, virtual]

This event handler can be reimplemented in a subclass to receive paint events which are passed in the event parameter.

A paint event is a request to repaint all or part of the widget. It can happen as a result of repaint() or update(), or because the widget was obscured and has now been uncovered, or for many other reasons.

Many widgets can simply repaint their entire surface when asked to, but some slow widgets need to optimize by painting only the requested region: QPaintEvent::region(). This speed optimization does not change the result, as painting is clipped to that region during event processing. QListView and QTableView do this, for example.

Qt also tries to speed up painting by merging multiple paint events into one. When update() is called several times or the window system sends several paint events, Qt merges these events into one event with a larger region (see QRegion::united()). repaint() does not permit this optimization, so we suggest using update() whenever possible.

When the paint event occurs, the update region has normally been erased, so that you're painting on the widget's background.

The background can be set using setBackgroundRole() and setPalette().

From Qt 4.0, QWidget automatically double-buffers its painting, so there's no need to write double-buffering code in paintEvent() to avoid flicker.

Note: Under X11 it is possible to toggle the global double buffering by calling qt_x11_set_global_double_buffer(). Example usage:

    ...
    extern void qt_x11_set_global_double_buffer(bool);
    qt_x11_set_global_double_buffer(false);
    ...

See also:

event(), repaint(), update(), QPainter, QPixmap, QPaintEvent, {Analog Clock Example}

Reimplemented from QWidget.

Definition at line 69 of file circlewidget.cpp.

References alpha, antialiased, QPainter::Antialiasing, QPainter::drawEllipse(), floatBased, frameNo, QWidget::height(), QPainter::setPen(), QPainter::setRenderHint(), QPainter::translate(), and QWidget::width().

{
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing, antialiased);
    painter.translate(width() / 2, height() / 2);

    for (int diameter = 0; diameter < 256; diameter += 9) {
        int delta = abs((frameNo % 128) - diameter / 2);
        int alpha = 255 - (delta * delta) / 4 - diameter;
        if (alpha > 0) {
            painter.setPen(QPen(QColor(0, diameter / 2, 127, alpha), 3));

            if (floatBased) {
                painter.drawEllipse(QRectF(-diameter / 2.0, -diameter / 2.0,
                                           diameter, diameter));
            } else {
                painter.drawEllipse(QRect(-diameter / 2, -diameter / 2,
                                          diameter, diameter));
            }
        }
    }
}

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Member Data Documentation

bool CircleWidget::floatBased [private]

Definition at line 49 of file circlewidget.h.

Referenced by CircleWidget(), and paintEvent().

bool CircleWidget::antialiased [private]

Definition at line 50 of file circlewidget.h.

Referenced by CircleWidget(), and paintEvent().

int CircleWidget::frameNo [private]

Definition at line 51 of file circlewidget.h.

Referenced by CircleWidget(), nextAnimationFrame(), and paintEvent().

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The documentation for this class was generated from the following files:

• examples/painting/concentriccircles/circlewidget.h
• examples/painting/concentriccircles/circlewidget.cpp

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