NAME
QwtPlotRasterItem - A class, which displays raster data.
SYNOPSIS
#include <qwt_plot_rasteritem.h>
Inherits QwtPlotItem.
Inherited by QwtPlotSpectrogram.
Public Types
enum CachePolicy { NoCache, PaintCache, ScreenCache }
Public Member Functions
QwtPlotRasterItem (const QString &title=QString::null)
QwtPlotRasterItem (const QwtText &title)
virtual ~QwtPlotRasterItem ()
void setAlpha (int alpha)
int alpha () const
void setCachePolicy (CachePolicy)
CachePolicy cachePolicy () const
void invalidateCache ()
virtual void draw (QPainter *p, const QwtScaleMap &xMap, const
QwtScaleMap &yMap, const QRect &rect) const
virtual QSize rasterHint (const QwtDoubleRect &) const
Protected Member Functions
virtual QImage renderImage (const QwtScaleMap &xMap, const QwtScaleMap
&yMap, const QwtDoubleRect &area) const =0
Detailed Description
A class, which displays raster data.
Raster data is a grid of pixel values, that can be represented as a
QImage. It is used for many types of information like spectrograms,
cartograms, geographical maps ...
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.
QwtPlotRasterItem is only implemented for images of the following
formats: QImage::Format_Indexed8, QImage::Format_ARGB32.
See also:
QwtPlotSpectrogram
Member Enumeration Documentation
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
Constructor & Destructor Documentation
QwtPlotRasterItem::QwtPlotRasterItem (const QString & title =
QString::null) [explicit]
Constructor.
QwtPlotRasterItem::QwtPlotRasterItem (const QwtText & title) [explicit]
Constructor.
QwtPlotRasterItem::~QwtPlotRasterItem () [virtual]
Destructor.
Member Function Documentation
int QwtPlotRasterItem::alpha () const
Returns:
Alpha value of the raster item
See also:
setAlpha()
QwtPlotRasterItem::CachePolicy QwtPlotRasterItem::cachePolicy () const
Returns:
Cache policy
See also:
CachePolicy, setCachePolicy()
void QwtPlotRasterItem::draw (QPainter * painter, const QwtScaleMap & xMap,
const QwtScaleMap & yMap, const QRect & canvasRect) const [virtual]
Draw the raster data.
Parameters:
painter Painter
xMap X-Scale Map
yMap Y-Scale Map
canvasRect Contents rect of the plot canvas
Implements QwtPlotItem.
Reimplemented in QwtPlotSpectrogram.
void QwtPlotRasterItem::invalidateCache ()
Invalidate the paint cache
See also:
setCachePolicy()
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:
xMap Maps x-values into pixel coordinates.
yMap Maps y-values into pixel coordinates.
area Requested area for the image in scale coordinates
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 Alpha value
· 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:
alpha()
void QwtPlotRasterItem::setCachePolicy (QwtPlotRasterItem::CachePolicy
policy)
Change the cache policy
The default policy is NoCache
Parameters:
policy Cache policy
See also:
CachePolicy, cachePolicy()
Author
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