QPaintDevice Class Reference


The QPaintDevice is the base class of objects that can be painted. (details) (complete member list)

#include <qpaintd.h>

Inherited by QPicture, QPixmap, QPrinter and QWidget.

Public Members

Protected Members

Related Functions

(Note that these are not member functions.)

Detailed Description

The QPaintDevice is the base class of objects that can be painted.

A paint device is an abstraction of a two-dimensional space that can be drawn into using a painter (see QPainter). The drawing capabilities are implemented by the subclasses: QWidget, QPixmap, QPicture and QPrinter.

The default coordinate system of a paint device has its origin located at the top left position. X increases to the left and Y increases to the bottom. The unit is one pixel. A user-defined coordinate system can be specified to the painter (see Q2DMatrix).

Here is an example how to draw on a paint device:

void GiraffeWidget::paintEvent( QPaintEvent * e ) {
  QPainter p;                           // our painter
  p.begin( this );                      // start painting
  p.setPen( red );                      // blue outline
  p.setBrush( yellow );                 // yellow fill
  p.drawEllipse( 10,20, 100,100 );      // 100x100 ellipse at 10,20
  p.end();                              // painting done
}

The bit block transfer is an extremely useful operation for copying pixels from one paint device to another (or to itself). It is implemented as the global function bitBlt().

This code demonstrates how to scroll the contents of a widget 10 pixels to the right:

    QWidget  w;
    bitBlt( &w, 10, 0, &w, 0, 0, -1, -1 );

Warning: Qt requires that a QApplication object must exist before any paint devices can be created. Paint devices access window system resources, and these resources are not initialized before an application object is created.


Member Function Documentation

QPaintDevice::QPaintDevice (uint devflags)

Constructs a paint device with internal flags devflags. This constructor can only be invoked from subclasses of QPaintDevice.

QPaintDevice::~QPaintDevice ()

Destroys the paint device and frees window system resources.

bool QPaintDevice::cmd (int, QPDevCmdParam *)

Internal virtual function that interprets drawing commands from the painter.

Implemented by subclasses that have no direct support for drawing graphics (for instance QPicture). Reimplemented in QPicture.

int QPaintDevice::devType () const

Returns the device type identifier: PDT_WIDGET, PDT_PIXMAP, PDT_PRINTER or PDT_PICTURE.

Display * QPaintDevice::display () const

Returns a pointer to the X display (X-Windows only).

HDC QPaintDevice::handle () const

Returns the window system handle of the paint device (Windows only).

HPS QPaintDevice::handle () const

Returns the window system handle of the paint device (OS/2 PM only).

WId QPaintDevice::handle () const

Returns the window system handle of the paint device (X-Windows only).

bool QPaintDevice::isExtDev () const

Returns TRUE if the device is a so-called external paint device.

External paint devices cannot be bitBlt'ed from.

long QPaintDevice::metric (int) const

Internal virtual function that returns paint device metrics.

Implemented by all subclasses. Reimplemented in QPixmap and QWidget.

bool QPaintDevice::paintingActive () const

Returns TRUE if the device is currently active (someone has called QPainter::begin() and not yet QPainter::end() on this device).


Related Functions

void bitBlt (QPaintDevice *dst, int dx, int dy, const QPaintDevice *src, int sx, int sy, int sw, int sh, RasterOp rop)

This function copies a block of pixels from one paint device to another (bitBlt means bit block transfer).

Arguments:

If sw is 0 or sh is 0, then bitBlt will do nothing.

If sw is negative, then bitBlt calculates sw = src->width - sx.
If sh is negative, then bitBlt calculates sh = src->height - sy.

The rop parameter can be one of:

There are some restrictions:

  1. The src device must be QWidget or QPixmap. You cannot copy pixels from a picture or a printer (external device).
  2. The src device may not have pixel depth greater than dst. You cannot copy from an 8 bit pixmap to a 1 bit pixmap.

void bitBlt (QPaintDevice *dst, const QPoint &dp, const QPaintDevice *src, const QRect &sr, RasterOp rop=CopyROP)

Synonymous bitBlt with the destination point dp and source rectangle sr.


This file is part of the Qt toolkit, copyright 1995 Troll Tech, all rights reserved.

It was generated from the following files:


Generated at 16:17, 1995/06/30 by the webmaster at Troll Tech