QPen Class

Qt 3.0.5

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QPen Class Reference

The QPen class defines how a QPainter should draw lines and outlines of shapes. More...

#include <qpen.h>

Inherits Qt.

List of all member functions.

Public Members

QPen ()
QPen ( PenStyle style )
QPen ( const QColor & color, uint width = 0, PenStyle style = SolidLine )
QPen ( const QColor & cl, uint w, PenStyle s, PenCapStyle c, PenJoinStyle j )
QPen ( const QPen & p )
~QPen ()
QPen & operator= ( const QPen & p )
PenStyle style () const
void setStyle ( PenStyle s )
uint width () const
void setWidth ( uint w )
const QColor & color () const
void setColor ( const QColor & c )
PenCapStyle capStyle () const
void setCapStyle ( PenCapStyle c )
PenJoinStyle joinStyle () const
void setJoinStyle ( PenJoinStyle j )
bool operator== ( const QPen & p ) const
bool operator!= ( const QPen & p ) const

Related Functions

QDataStream & operator<< ( QDataStream & s, const QPen & p )
QDataStream & operator>> ( QDataStream & s, QPen & p )

Detailed Description

The QPen class defines how a QPainter should draw lines and outlines of shapes.

A pen has a style, width, color, cap style and join style.

The pen style defines the line type. The default pen style is Qt::SolidLine. Setting the style to NoPen tells the painter to not draw lines or outlines.

When drawing 1 pixel wide diagonal lines you can either use a very fast algorithm (specified by a line width of 0, which is the default), or a slower but more accurate algorithm (specified by a line width of 1). For horizontal and vertical lines a line width of 0 is the same as a line width of 1. The cap and join style have no effect on 0-width lines.

The pen color defines the color of lines and text. The default line color is black. The QColor documentation lists predefined colors.

The cap style defines how the end points of lines are drawn. The join style defines how the joins between two lines are drawn when multiple connected lines are drawn (QPainter::drawPolyLine() etc.). The cap and join styles only apply to wide lines, i.e. when the width is 1 or greater.

Use the QBrush class to specify fill styles.

Example:

    QPainter painter;
    QPen     pen( red, 2 );             // red solid line, 2 pixels wide
    painter.begin( &anyPaintDevice );   // paint something
    painter.setPen( pen );              // set the red, wide pen
    painter.drawRect( 40,30, 200,100 ); // draw a rectangle
    painter.setPen( blue );             // set blue pen, 0 pixel width
    painter.drawLine( 40,30, 240,130 ); // draw a diagonal in rectangle
    painter.end();                      // painting done

See the Qt::PenStyle enum type for a complete list of pen styles.

With reference to the end points of lines, for wide (non-0-width) pens it depends on the cap style whether the end point is drawn or not. QPainter will try to make sure that the end point is drawn for 0-width pens, but this cannot be absolutely guaranteed because the underlying drawing engine is free to use any (typically accelerated) algorithm for drawing 0-width lines. On all tested systems, however, the end point of at least all non-diagonal lines are drawn.

A pen's color(), width(), style(), capStyle() and joinStyle() can be set in the constructor or later with setColor(), setWidth(), setStyle(), setCapStyle() and setJoinStyle(). Pens may also be compared and streamed.

Member Function Documentation

QPen::QPen ()

Constructs a default black solid line pen with 0 width, which renders lines 1 pixel wide (fast diagonals).

QPen::QPen ( PenStyle style )

Constructs a black pen with 0 width (fast diagonals) and style style.

QPen::QPen ( const QColor & color, uint width = 0, PenStyle style = SolidLine )

Constructs a pen with the specified color, width and style.

See also setWidth(), setStyle() and setColor().

QPen::QPen ( const QColor & cl, uint w, PenStyle s, PenCapStyle c, PenJoinStyle j )

Constructs a pen with the specified color cl and width w. The pen style is set to s, the pen cap style to c and the pen join style to j.

A line width of 0 will produce a 1 pixel wide line using a fast algorithm for diagonals. A line width of 1 will also produce a 1 pixel wide line, but uses a slower more accurate algorithm for diagonals. For horizontal and vertical lines a line width of 0 is the same as a line width of 1. The cap and join style have no effect on 0-width lines.

See also setWidth(), setStyle() and setColor().

QPen::QPen ( const QPen & p )

Constructs a pen that is a copy of p.

QPen::~QPen ()

Destroys the pen.

PenCapStyle QPen::capStyle () const

Returns the pen's cap style.

const QColor & QPen::color () const

Returns the pen color.

PenJoinStyle QPen::joinStyle () const

Returns the pen's join style.

bool QPen::operator!= ( const QPen & p ) const

Returns TRUE if the pen is different from p; otherwise returns FALSE.

Two pens are different if they have different styles, widths or colors.

QPen & QPen::operator= ( const QPen & p )

Assigns p to this pen and returns a reference to this pen.

bool QPen::operator== ( const QPen & p ) const

Returns TRUE if the pen is equal to p; otherwise returns FALSE.

Two pens are equal if they have equal styles, widths and colors.

void QPen::setCapStyle ( PenCapStyle c )

Sets the pen's cap style to c.

The default value is FlatCap. The cap style has no effect on 0-width pens.

Warning: On Windows 95/98 and Macintosh, the cap style setting has no effect. Wide lines are rendered as if the cap style was SquareCap.

void QPen::setColor ( const QColor & c )

Sets the pen color to c.

void QPen::setJoinStyle ( PenJoinStyle j )

Sets the pen's join style to j.

The default value is MiterJoin. The join style has no effect on 0-width pens.

Warning: On Windows 95/98 and Macintosh, the join style setting has no effect. Wide lines are rendered as if the join style was BevelJoin.

void QPen::setStyle ( PenStyle s )

Sets the pen style to s.

See the Qt::PenStyle documentation for a list of all the styles.

Warning: On Windows 95/98 and Macintosh, the style setting (other than NoPen and SolidLine) has no effect for lines with width greater than 1.

void QPen::setWidth ( uint w )

Sets the pen width to w.

PenStyle QPen::style () const

Returns the pen style.

uint QPen::width () const

Returns the pen width.

Related Functions

QDataStream & operator<< ( QDataStream & s, const QPen & p )

Writes the pen p to the stream s and returns a reference to the stream.

QDataStream & operator>> ( QDataStream & s, QPen & p )

Reads a pen from the stream s into p and returns a reference to the stream.

Trademarks

Qt version 3.0.5

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