Public Types¶

enum CachePolicy { NoCache, PaintCache, ScreenCache }

Public Member Functions¶

QwtPlotRasterItem (const QString &title=QString::null)
QwtPlotRasterItem (const QwtText &title)
virtual ~QwtPlotRasterItem ()
int alpha () const
CachePolicy cachePolicy () const
virtual void draw (QPainter *p, const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QRect &rect) const
void invalidateCache ()
virtual QSize rasterHint (const QwtDoubleRect &) const
void setAlpha (int alpha)
void setCachePolicy (CachePolicy)

Protected Member Functions¶

virtual QImage renderImage (const QwtScaleMap &xMap, const QwtScaleMap &yMap, const QwtDoubleRect &area) const =0

enum QwtPlotRasterItem::CachePolicy¶

• NoCache
  renderImage() is called, whenever 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 only useful for improving the performance of hide/show operations. All other situations are already handled by the plot canvas cache.
• ScreenCache
  The screen cache is an image in size of the screen. As long as the scales don't change the target image is scaled from the cache. This might improve the performance when resizing the plot widget, but suffers from scaling effects.

The default policy is NoCache

int QwtPlotRasterItem::alpha () const¶

Returns:

See also:

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

Returns:

See also:

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

Draw the raster data. Parameters:

Implements QwtPlotItem.

Reimplemented in QwtPlotSpectrogram.

void QwtPlotRasterItem::invalidateCache ()¶

Invalidate the paint cache

See also:

QSize QwtPlotRasterItem::rasterHint (const QwtDoubleRect &) const [virtual]¶

Returns the recommended raster for a given rect. F.e the raster hint can be used to limit the resolution of the image that is rendered.

The default implementation returns an invalid size (QSize()), what means: no hint.

Reimplemented in QwtPlotSpectrogram.

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

Renders an image for an area

The format of the image must be QImage::Format_Indexed8, QImage::Format_RGB32 or QImage::Format_ARGB32

Parameters:

Implemented in QwtPlotSpectrogram.

void QwtPlotRasterItem::setAlpha (intalpha)¶

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::CachePolicypolicy)¶

Change the cache policy

The default policy is NoCache

Parameters:

See also: