---
name: "QwtNullPaintDevice"
section: "3"
platform: "linux"
package: "libqwt-doc"
version: "6.1.4-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/QwtNullPaintDevice"
---

# QwtNullPaintDevice(3)

A null paint device doing nothing.

## NAME

QwtNullPaintDevice - A null paint device doing nothing.

## SYNOPSIS

`#include <qwt_null_paintdevice.h>`

Inherits QPaintDevice.

Inherited by **QwtGraphic**, and QwtStyleSheetRecorder.

### Public Types

enum **Mode** { **NormalMode**, **PolygonPathMode**, **PathMode** }\
 Render mode.

### Public Member Functions

**QwtNullPaintDevice** ()\
 Constructor.  virtual **~QwtNullPaintDevice** ()\
 Destructor.  void **setMode** (**Mode**)\
 **Mode** **mode** () const\
 virtual QPaintEngine \* **paintEngine** () const\
 See QPaintDevice::paintEngine()  virtual int **metric** (PaintDeviceMetric) const\
 virtual void **drawRects** (const QRect \*, int)\
 See QPaintEngine::drawRects()  virtual void **drawRects** (const QRectF \*, int)\
 See QPaintEngine::drawRects()  virtual void **drawLines** (const QLine \*, int)\
 See QPaintEngine::drawLines()  virtual void **drawLines** (const QLineF \*, int)\
 See QPaintEngine::drawLines()  virtual void **drawEllipse** (const QRectF &)\
 See QPaintEngine::drawEllipse()  virtual void **drawEllipse** (const QRect &)\
 See QPaintEngine::drawEllipse()  virtual void **drawPath** (const QPainterPath &)\
 See QPaintEngine::drawPath()  virtual void **drawPoints** (const QPointF \*, int)\
 See QPaintEngine::drawPoints()  virtual void **drawPoints** (const QPoint \*, int)\
 See QPaintEngine::drawPoints()  virtual void **drawPolygon** (const QPointF \*, int, QPaintEngine::PolygonDrawMode)\
 See QPaintEngine::drawPolygon()  virtual void **drawPolygon** (const QPoint \*, int, QPaintEngine::PolygonDrawMode)\
 See QPaintEngine::drawPolygon()  virtual void **drawPixmap** (const QRectF &, const QPixmap &, const QRectF &)\
 See QPaintEngine::drawPixmap()  virtual void **drawTextItem** (const QPointF &, const QTextItem &)\
 See QPaintEngine::drawTextItem()  virtual void **drawTiledPixmap** (const QRectF &, const QPixmap &, const QPointF &)\
 See QPaintEngine::drawTiledPixmap()  virtual void **drawImage** (const QRectF &, const QImage &, const QRectF &, Qt::ImageConversionFlags)\
 See QPaintEngine::drawImage()  virtual void **updateState** (const QPaintEngineState &)\
 See QPaintEngine::updateState()

### Protected Member Functions

virtual QSize **sizeMetrics** () const =0\

## Detailed Description

A null paint device doing nothing.

Sometimes important layout/rendering geometries are not available or changeable from the public Qt class interface. ( f.e hidden in the style implementation ).

**QwtNullPaintDevice** can be used to manipulate or filter out this information by analyzing the stream of paint primitives.

F.e. **QwtNullPaintDevice** is used by **QwtPlotCanvas** to identify styled backgrounds with rounded corners.

## Member Enumeration Documentation

### enum QwtNullPaintDevice::Mode

Render mode.

**See also:**

**setMode()**, **mode()**

**Enumerator**

- *NormalMode*

  *All vector graphic primitives are painted by the corresponding draw methods*

- *PolygonPathMode*

  *Vector graphic primitives ( beside polygons ) are mapped to a QPainterPath and are painted by drawPath. In PathMode mode only a few draw methods are called:*

- •

  **drawPath()**

- •

  **drawPixmap()**

- •

  **drawImage()**

- •

  **drawPolygon()**

- *PathMode*

  *Vector graphic primitives are mapped to a QPainterPath and are painted by drawPath. In PathMode mode only a few draw methods are called:*

- •

  **drawPath()**

- •

  **drawPixmap()**

- •

  **drawImage()**

## Member Function Documentation

### int QwtNullPaintDevice::metric (PaintDeviceMetric deviceMetric) const` [virtual]`

*See QPaintDevice::metric()*

**Parameters:**

*deviceMetric Type of metric*

**Returns:**

*Metric information for the given paint device metric.*

**See also:**

**sizeMetrics()**

### QwtNullPaintDevice::Mode QwtNullPaintDevice::mode () const

**Returns:**

*Render mode*

**See also:**

**setMode()**

### void QwtNullPaintDevice::setMode (Mode mode)

*Set the render mode*

**Parameters:**

*mode New mode*

**See also:**

**mode()**

### virtual QSize QwtNullPaintDevice::sizeMetrics () const` [protected]`, ` [pure virtual]`

**Returns:**

*Size needed to implement* **metric()**

*Implemented in* **QwtGraphic***.*

## Author

*Generated automatically by Doxygen for Qwt User's Guide from the source code.*