QwtPlotRasterItem Class Reference
A class, which displays raster data. More...
#include <qwt_plot_rasteritem.h>
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
- 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()
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