Qwt User's Guide 6.2.0

Public Types | Public Member Functions | List of all members
QwtRasterData Class Referenceabstract

QwtRasterData defines an interface to any type of raster data. More...

`#include <qwt_raster_data.h>`

Inheritance diagram for QwtRasterData:

## Public Types
enum | Attribute { WithoutGaps = 0x01 }
| Raster data attributes. More...
enum | ConrecFlag { IgnoreAllVerticesOnLevel = 0x01 , IgnoreOutOfRange = 0x02 }
| Flags to modify the contour algorithm. More...
typedef QMap< double, QPolygonF > | ContourLines
| Contour lines.
typedef QFlags< Attribute > | Attributes
typedef QFlags< ConrecFlag > | ConrecFlags

## Public Member Functions
| QwtRasterData ()
| Constructor.
virtual | ~QwtRasterData ()
| Destructor.
void | setAttribute (Attribute, bool on=true)
bool | testAttribute (Attribute) const
virtual QwtInterval | interval (Qt::Axis) const =0
virtual QRectF | pixelHint (const QRectF &) const
| Pixel hint. More...
virtual void | initRaster (const QRectF &, const QSize &raster)
| Initialize a raster. More...
virtual void | discardRaster ()
| Discard a raster. More...
virtual double | value (double x, double y) const =0
virtual ContourLines | contourLines (const QRectF &rect, const QSize &raster, const QList< double > &levels, ConrecFlags) const

## Detailed Description

QwtRasterData defines an interface to any type of raster data.

QwtRasterData is an abstract interface, that is used by QwtPlotRasterItem to find the values at the pixels of its raster.

Gaps inside the bounding rectangle of the data can be indicated by NaN values ( when WithoutGaps is disabled ).

Often a raster item is used to display values from a matrix. Then the derived raster data class needs to implement some sort of resampling, that maps the raster of the matrix into the requested raster of the raster item ( depending on resolution and scales of the canvas ).

QwtMatrixRasterData implements raster data, that returns values from a given 2D matrix.

See also
  QwtMatrixRasterData

Definition at line 42 of file qwt_raster_data.h.

## Member Typedef Documentation

## ◆ Attributes

typedef QFlags<Attribute > QwtRasterData::Attributes

An ORed combination of Attribute values.

Definition at line 74 of file qwt_raster_data.h.

## ◆ ConrecFlags

typedef QFlags<ConrecFlag > QwtRasterData::ConrecFlags

An ORed combination of ConrecFlag values.

Definition at line 86 of file qwt_raster_data.h.

## Member Enumeration Documentation

## ◆ Attribute

enum QwtRasterData::Attribute

Raster data attributes.

Additional information that is used to improve processing of the data.

Enumerator
WithoutGaps | The bounding rectangle of the data is spanned by the interval(Qt::XAxis) and interval(Qt::YAxis). WithoutGaps indicates, that the data has no gaps ( unknown values ) in this area and the result of value() does not need to be checked for NaN values. Enabling this flag will have an positive effect on the performance of rendering a QwtPlotSpectrogram. The default setting is false. Note NaN values indicate an undefined value

Definition at line 54 of file qwt_raster_data.h.

## ◆ ConrecFlag

enum QwtRasterData::ConrecFlag

Flags to modify the contour algorithm.

Enumerator
IgnoreAllVerticesOnLevel | Ignore all vertices on the same level.
IgnoreOutOfRange | Ignore all values, that are out of range.

Definition at line 77 of file qwt_raster_data.h.

## Member Function Documentation

## ◆ contourLines()

QwtRasterData::ContourLines QwtRasterData::contourLines | ( | const QRectF & | rect,
|  | const QSize & | raster,
|  | const QList< double > & | levels,
|  | ConrecFlags | flags
| ) |  | const
| virtual

Calculate contour lines

Parameters

  rect | Bounding rectangle for the contour lines
  raster | Number of data pixels of the raster data
  levels | List of limits, where to insert contour lines
  flags | Flags to customize the contouring algorithm

Returns
  Calculated contour lines

An adaption of CONREC, a simple contouring algorithm. http://local.wasp.uwa.edu.au/~pbourke/papers/conrec/

Definition at line 286 of file qwt_raster_data.cpp.

## ◆ discardRaster()

void QwtRasterData::discardRaster | ( |  | ) |
| virtual

Discard a raster.

After the composition of an image QwtPlotSpectrogram calls discardRaster().

The default implementation does nothing, but if data has been loaded in initRaster(), it could deleted now.

See also
  initRaster(), value()

Definition at line 237 of file qwt_raster_data.cpp.

## ◆ initRaster()

void QwtRasterData::initRaster | ( | const QRectF & | area,
|  | const QSize & | raster
| ) |  |
| virtual

Initialize a raster.

Before the composition of an image QwtPlotSpectrogram calls initRaster(), announcing the area and its resolution that will be requested.

The default implementation does nothing, but for data sets that are stored in files, it might be good idea to reimplement initRaster(), where the data is resampled and loaded into memory.

Parameters

  area | Area of the raster
  raster | Number of horizontal and vertical pixels

See also
  initRaster(), value()

Definition at line 221 of file qwt_raster_data.cpp.

## ◆ interval()

virtual QwtInterval QwtRasterData::interval | ( | Qt::Axis |  | ) | const
| pure virtual

Returns
  Bounding interval for an axis

See also
  setInterval

Implemented in QwtMatrixRasterData.

## ◆ pixelHint()

QRectF QwtRasterData::pixelHint | ( | const QRectF & | area | ) | const
| virtual

Pixel hint.

pixelHint() returns the geometry of a pixel, that can be used to calculate the resolution and alignment of the plot item, that is representing the data.

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 ).

An empty hint indicates, that there are values for any detail level.

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 recommending to render 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

Reimplemented in QwtMatrixRasterData.

Definition at line 267 of file qwt_raster_data.cpp.

## ◆ setAttribute()

void QwtRasterData::setAttribute | ( | Attribute | attribute,
|  | bool | on = `true`
| ) |  |

Specify an attribute of the data

Parameters

  attribute | Attribute
  on | On/Off /sa Attribute, testAttribute()

Definition at line 189 of file qwt_raster_data.cpp.

## ◆ testAttribute()

bool QwtRasterData::testAttribute | ( | Attribute | attribute | ) | const

Returns
  True, when attribute is enabled

See also
  Attribute, setAttribute()

Definition at line 201 of file qwt_raster_data.cpp.

## ◆ value()

virtual double QwtRasterData::value | ( | double | x,
|  | double | y
| ) |  | const
| pure virtual

Returns
  the value at a raster position

Parameters

  x | X value in plot coordinates
  y | Y value in plot coordinates

Implemented in QwtMatrixRasterData.