Public Types¶

enum CachePolicy { NoCache, PaintCache }
Cache policy The default policy is NoCache. enum PaintAttribute { PaintInDeviceResolution = 1 }
typedef QFlags< PaintAttribute > PaintAttributes
Paint attributes.

Public Member Functions¶

QwtPlotRasterItem (const QString &title=QString())
Constructor. QwtPlotRasterItem (const QwtText &title)
Constructor. virtual ~QwtPlotRasterItem ()
Destructor. void setPaintAttribute (PaintAttribute, bool on=true)
bool testPaintAttribute (PaintAttribute) const
void setAlpha (int alpha)
Set an alpha value for the raster data. int alpha () const
void setCachePolicy (CachePolicy)
CachePolicy cachePolicy () const
void invalidateCache ()
virtual void draw (QPainter *, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &canvasRect) const
Draw the raster data. virtual QRectF pixelHint (const QRectF &) const
Pixel hint. virtual QwtInterval interval (Qt::Axis) const
virtual QRectF boundingRect () const

Protected Member Functions¶

virtual QImage renderImage (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRectF &area, const QSize &imageSize) const =0
Render an image. virtual QwtScaleMap imageMap (Qt::Orientation, const QwtScaleMap &map, const QRectF &area, const QSize &imageSize, double pixelSize) const
Calculate a scale map for painting to an image.

enum QwtPlotRasterItem::CachePolicy¶

Cache policy The default policy is NoCache.

Enumerator

NoCache

renderImage() is called each time the item has to be repainted

PaintCache

renderImage() is called, whenever the image cache is not valid, or the scales, or the size of the canvas has changed.

This type of cache is useful for improving the performance of hide/show operations or manipulations of the alpha value. All other situations are handled by the canvas backing store.

enum QwtPlotRasterItem::PaintAttribute¶

Attributes to modify the drawing algorithm.

See also:

Enumerator

PaintInDeviceResolution

When the image is rendered according to the data pixels ( QwtRasterData::pixelHint() ) it can be expanded to paint device resolution before it is passed to QPainter. The expansion algorithm rounds the pixel borders in the same way as the axis ticks, what is usually better than the scaling algorithm implemented in Qt. Disabling this flag might make sense, to reduce the size of a document/file. If this is possible for a document format depends on the implementation of the specific QPaintEngine.

int QwtPlotRasterItem::alpha () const¶

Returns:

See also:

QRectF QwtPlotRasterItem::boundingRect () const [virtual]¶

Returns:

See also:

Reimplemented from QwtPlotItem.

QwtPlotRasterItem::CachePolicy QwtPlotRasterItem::cachePolicy () const¶

Returns:

See also:

void QwtPlotRasterItem::draw (QPainter * painter, const QwtScaleMap & xMap, const QwtScaleMap & yMap, const QRectF & canvasRect) const [virtual]¶

Draw the raster data.

Parameters:

Implements QwtPlotItem.

Reimplemented in QwtPlotSpectrogram.

QwtScaleMap QwtPlotRasterItem::imageMap (Qt::Orientation orientation, const QwtScaleMap & map, const QRectF & area, const QSize & imageSize, double pixelSize) const [protected], [virtual]¶

Calculate a scale map for painting to an image.

Parameters:

Returns:

QwtInterval QwtPlotRasterItem::interval (Qt::Axis axis) const [virtual]¶

Returns:

This method is intended to be reimplemented by derived classes. The default implementation returns an invalid interval.

Parameters:

Reimplemented in QwtPlotSpectrogram.

void QwtPlotRasterItem::invalidateCache ()¶

Invalidate the paint cache

See also:

QRectF QwtPlotRasterItem::pixelHint (const QRectF & area) const [virtual]¶

Pixel hint. The geometry of a pixel is used to calculated the resolution and alignment of the rendered image.

Width and height of the hint need to be the horizontal and vertical distances between 2 neighbored points. The center of the hint has to be the position of any point ( it doesn't matter which one ).

Limiting the resolution of the image might significantly improve the performance and heavily reduce the amount of memory when rendering a QImage from the raster data.

The default implementation returns an empty rectangle (QRectF()), meaning, that the image will be rendered in target device ( f.e screen ) resolution.

Parameters:

Returns:

See also:

Reimplemented in QwtPlotSpectrogram.

virtual QImage QwtPlotRasterItem::renderImage (const QwtScaleMap & xMap, const QwtScaleMap & yMap, const QRectF & area, const QSize & imageSize) const [protected], [pure virtual]¶

Render an image. An implementation of render() might iterate over all pixels of imageRect. Each pixel has to be translated into the corresponding position in scale coordinates using the maps. This position can be used to look up a value in a implementation specific way and to map it into a color.

Parameters:

Returns:

Implemented in QwtPlotSpectrogram.

void QwtPlotRasterItem::setAlpha (int alpha)¶

Set an alpha value for the raster data. Often a plot has several types of raster data organized in layers. ( f.e a geographical map, with weather statistics ). Using setAlpha() raster items can be stacked easily.

The alpha value is a value [0, 255] to control the transparency of the image. 0 represents a fully transparent color, while 255 represents a fully opaque color.

Parameters:

• alpha >= 0
  All alpha values of the pixels returned by renderImage() will be set to alpha, beside those with an alpha value of 0 (invalid pixels).
• alpha < 0 The alpha values returned by renderImage() are not changed.

The default alpha value is -1.

See also:

void QwtPlotRasterItem::setCachePolicy (QwtPlotRasterItem::CachePolicy policy)¶

Change the cache policy

The default policy is NoCache

Parameters:

See also:

void QwtPlotRasterItem::setPaintAttribute (PaintAttribute attribute, bool on = true)¶

Specify an attribute how to draw the raster item

Parameters:

bool QwtPlotRasterItem::testPaintAttribute (PaintAttribute attribute) const¶

Returns:

See also: