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 }
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.

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

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:

setPaintAttribute(), testPaintAttribute()

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.

Member Function Documentation

int QwtPlotRasterItem::alpha () const

Returns:

Alpha value of the raster item

See also:

setAlpha()

QRectF QwtPlotRasterItem::boundingRect () const [virtual]

Returns:

Bounding rectangle of the data

See also:

QwtPlotRasterItem::interval()

Reimplemented from QwtPlotItem.

QwtPlotRasterItem::CachePolicy QwtPlotRasterItem::cachePolicy () const

Returns:

Cache policy

See also:

CachePolicy, setCachePolicy()

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

Draw the raster data.

Parameters:

painter Painter
xMap X-Scale Map
yMap Y-Scale Map
canvasRect Contents rectangle of the plot canvas

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:

orientation Orientation, Qt::Horizontal means a X axis
map Scale map for rendering the plot item
area Area to be painted on the image
imageSize Image size
pixelSize Width/Height of a data pixel

Returns:

Calculated scale map

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

Returns:

Bounding interval for an axis

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

Parameters:

axis X, Y, or Z axis

Reimplemented in QwtPlotSpectrogram.

void QwtPlotRasterItem::invalidateCache ()

Invalidate the paint cache

See also:

setCachePolicy()

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:

area In most implementations the resolution of the data doesn't depend on the requested area.

Returns:

Bounding rectangle of a pixel

See also:

render(), renderImage()

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:

xMap X-Scale Map
yMap Y-Scale Map
area Requested area for the image in scale coordinates
imageSize Requested size of the image

Returns:

Rendered image

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()