Q3Painter Class Reference
[Qt3Support module]

The Q3Painter class is a Qt 3 compatibility wrapper for QPainter. More...

 #include <Q3Painter>

This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See Porting to Qt 4 for more information.

Inherits QPainter.

List of all members, including inherited members

Public Functions

	Q3Painter ()
	Q3Painter ( QPaintDevice * pdev )
void	drawArc ( const QRect & r, int a, int alen )
void	drawArc ( int x, int y, int w, int h, int startAngle, int spanAngle )
void	drawChord ( const QRect & r, int a, int alen )
void	drawChord ( int x, int y, int w, int h, int startAngle, int spanAngle )
void	drawEllipse ( const QRect & r )
void	drawEllipse ( int x, int y, int width, int height )
void	drawPie ( const QRect & r, int a, int alen )
void	drawPie ( int x, int y, int w, int h, int startAngle, int spanAngle )
void	drawRect ( const QRect & r )
void	drawRect ( int x, int y, int w, int h )
void	drawRoundRect ( const QRect & r, int xrnd = 25, int yrnd = 25 )
void	drawRoundRect ( int x, int y, int w, int h, int xrnd = 25, int yrnd = 25 )

182 public functions inherited from QPainter

Detailed Description

The Q3Painter class is a Qt 3 compatibility wrapper for QPainter.

Prior to Qt 4, QPainter specialized the pen drawing for rectangle based functions (in particular: drawRect, drawEllipse, drawRoundRect, drawArc, drawChord and drawPie). When stroking a rectangle of width 10, the pen would draw a rectangle of width 10. Drawing a polygon defined by the corner points of the same rectangle the stroke would have a width of 11.

The reason for this is best explained using the picture below:

As we can see, stroking the rectangle so it gets a width of 10, means the pen is drawn on a rectangle on width 9. The polygon, however follows a consistent model.

In Qt 4, all rectangle based functions have changed to follow the polygon approach, which means that the rectangle defines the size of the fill, and the pen follows the edges of the shape. For pen widths of 0 and 1 this means that the stroke will be inside the shape on the left and the top and outside on the bottom and right.

The reason for the change in Qt 4 is so that we provide consistency for all drawing functions even with complex transformations.

Member Function Documentation

Q3Painter::Q3Painter ()

Constructs a Q3Painter.

Q3Painter::Q3Painter ( QPaintDevice * pdev )

Constructs a Q3Painter that operates on device pdev.

void Q3Painter::drawArc ( const QRect & r, int a, int alen )

Draws an arc defined by the rectangle r, the start angle a and the arc length alen.

The angles a and alen are 1/16th of a degree, i.e. a full circle equals 5760 (16*360). Positive values of a and alen mean counter-clockwise while negative values mean the clockwise direction. Zero degrees is at the 3 o'clock position.

Example:

 QPainter p(myWidget);
 p.drawArc(QRect(10,10, 70,100), 100*16, 160*16); // draws a "(" arc