---
name: "qwtchangelog"
section: "3"
platform: "linux"
package: "libqwt-doc"
version: "6.1.4-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/qwtchangelog"
---

# qwtchangelog(3)

What's new in Qwt 6.1

## NAME

qwtchangelog - What's new in Qwt 6.1

## New plot items

- •

  **QwtPlotBarChart**\
  \
    Bar chart, see 'examples/distrowatch'

- •

  **QwtPlotMultiBarChart**\
  \
    Chart of grouped bars - stacked or aligned side by side. See 'examples/barchart'

- •

  **QwtPlotTradingCurve**\
  \
    Candlestick or OHLC charts typically used to describe price movements over time. See 'examples/stockchart'

- •

  **QwtPlotShapeItem**\
  \
    A plot item to display rectangles, circles, polygons and all other type of shapes ( built from intersections or unifications ), that can be expressed by a QPainterPath. See 'examples/itemeditor'

- •

  **QwtPlotLegendItem**\
  \
    A legend on the plot canvas. See 'examples/legends'

- •

  **QwtPlotZoneItem**\
  \
    A horizontal or vertical section

- •

  **QwtPlotTextLabel**\
  \
    In opposite to a **QwtPlotMarker** the text is not aligned to a plot coordinate but according to the geometry of the canvas ( f.e top/centered for a title ). See 'playground/curvetracker'.

## Scales beyond linear and logarithmic transformations

QwtScaleTransformation has been replaced by **QwtTransform** and its derived classes:

- •

  **QwtTransform**

- •

  **QwtNullTransform**

- •

  **QwtLogTransform**

- •

  **QwtPowerTransform**

Individual transformations ( f.e. different scaling for special sections ) can be implemented by overloading **QwtTransform** ( see playground/scaleengine ).

**QwtLinearScaleEngine** and **QwtLogScaleEngine** are not limited to base 10 anymore.

### Datetime scales

A set of a new classes for displaying datetime values:

- •

  **QwtDate**\
  \
    A collection of methods to convert between QDateTime and doubles

- •

  **QwtDateScaleEngine**\
  \
    A scale engine that aligns and finds ticks in terms of datetime units.

- •

  **QwtDateScaleDraw**\
  \
    A scale draw mapping values to datetime strings.

Scales for Qt::UTC and Qt::LocalTime are supported.

## Redesign of the dial and meter widgets

Many parts of the class design of the dial and meter widgets were left over from the 90s ( Qwt 0.2, Qt 1.1 ).

The derivation tree is simpler and more logical:

- •

  **QwtAbstractScale** is a QWidget

- •

  **QwtAbstractSlider** is a **QwtAbstractScale**. ( for sliders without scales QAbstractSlider should be the base class )

- •

  **QwtThermo** is also a **QwtAbstractScale**

- •

  **QwtDial**, **QwtKnob**, **QwtSlider** are derived from **QwtAbstractSlider**

- •

  **QwtCounter** is derived from QWidget

QwtDoubleRange has been removed.

All classes use the terminology known from QAbstractSlider - as far as possible. The extended **system for scales** is completely supported.

## Basic support for an OpenGL plot canvas

**QwtPlotGLCanvas** offers the option to draw plot items using an OpenGL paint engine ( QPaintEngine::OpenGL/OpenGL2 ), This is not what could be implemented with native OpenGL, but it offers hardware acceleration in environments, where the raster paint engine is the only option. ( f.e Qt4/Windows, or Qt5 on all platforms ).

**QwtPlotGLCanvas** is in an experimental state and is not recommended for average use cases.

## A new system for plot legends

**QwtLegend** has been decoupled from **QwtPlot** and can be replaced by application specific implementations. Plot items and the legend exchange the information using **QwtLegendData**.

**QwtPlotLegendItem** is a new plot item that displays a legend on the plot canvas.

The following examples demonstrate how to use the new system:

- •

  examples/legends\
  \
    shows how to use the new legend system

- •

  examples/stockchart\
  \
    implementats a QTreeView with checkable items as legend

## Off-screen paint device for vector graphics

**QwtGraphic** can be copied like QImage or QPixmap but is scalable like QSvgGenerator. It is implemented as a record/replay paint device like QPicture.

## QwtWidgetOverlay

**QwtWidgetOverlay** is a base class for implementing widget overlays - primarily used for use cases like graphical editors or running cursors for the plot canvas.

The following examples show how to use overlays:

- •

  examples/itemeditor

- •

  examples/curvetracker

**QwtPicker** ( -\> **QwtPlotPicker**, **QwtPlotZoomer** ) internally uses **QwtWidgetOverlay** now, making it easier to implement individual rubber bands.

## QwtSymbol

New symbol types have been introduced:

- •

  **QwtSymbol::Path**

- •

  **QwtSymbol::Pixmap**

- •

  **QwtSymbol::Graphic**

- •

  **QwtSymbol::SvgDocument**

**QwtSymbol** autodetect the most performant paint strategy for a paint device what is in most situations using a QPixmap cache.

**QwtSymbol::setPinPoint()** allows one to align the symbol individually, f.e to the position of the peak of an arrow.

## QwtPlotCurve

Some optimizations that got lost with introducing the floating point based render code with Qwt 6.0 have been reenabled. Other specific optimizations have been added.

New paint attributes:

- •

  **QwtPlotCurve::FilterPoints**

- •

  **QwtPlotCurve::MinimizeMemory**

- •

  **QwtPlotCurve::ImageBuffer**

QwtPlotCurve::CacheSymbols has been removed, as caching is implemented in **QwtSymbol** now. \
\
  **QwtPlotCurve::drawLines()**, **QwtPlotCurve::drawDots()**, **QwtPlotCurve::drawSteps()** and **QwtPlotCurve::drawSticks()** are virtual now.

## QwtPlot

A footer similar to a title has been added.

QwtPlot::ExternalLegend is obsolete with the new **system for legends**. The signals QwtPlot::legendClicked(), QwtPlot::legendChecked() have been removed. Applications need to connect to **QwtLegend::clicked()** and **QwtLegend::checked()**.

To support using an OpenGL canvas **QwtPlot::setCanvas** has been added. This has 2 important implications for the application code:

- •

  **QwtPlot::canvas()** returns QWidget and needs to be casted, when using methods of **QwtPlotCanvas**.

- •

  **QwtPlotCanvas** can be created and assigned in application code, what makes it possible to derive and overload methods.

The initialization of a plot canvas with Qwt 6.1 will probably look like this:

```
QwtPlotCanvas* canvas = new QwtPlotCanvas();
canvas->setXY( ... );
...
plot->setCanvas( canvas );
```

To have a consistent API **QwtPlot::setPlotLayout()** has been added,

## Other

### QwtScaleDiv

The following methods have been added:

- •

  **QwtScaleDiv::inverted()**

- •

  **QwtScaleDiv::bounded()**

- •

  **QwtScaleDiv::isEmpty()**

- •

  **QwtScaleDiv::isIncreasing()**

- •

  QDebug operator

The following methods have been removed:

- •

  QwtScaleDiv::isValid(), QwtScaleDiv::invalidate()\
  \
    The valid state was left over from early Qwt versions indicating a state of the autoscaler.

### QwtScaleEngine

The following methods have been added:

- •

  **QwtScaleEngine::setBase()**

- •

  **QwtScaleEngine::setTransformation()**

### QwtPlotLayout

The following flags have been added:

- •

  **QwtPlotLayout::IgnoreTitle**

- •

  **QwtPlotLayout::IgnoreFooter**

- •

  **QwtPlotLayout::setAlignCanvasToScale()**

### QwtPlotCanvas

Rounded borders ( like with style sheets ) can configured using **QwtPlotCanvas::setBorderRadius()**;

### Other changes

- •

  **QwtWeedingCurveFitter**\
  \
    **QwtWeedingCurveFitter::setChunkSize()** has been added, with drastic performance improvements for huge sets of points.

- •

  **QwtPlotRenderer** The frame of the plot canvas can be rendered, what makes the result even closer to WYSWYG. **QwtPlotRenderer::exportTo()** has been added.

- •

  **QwtSystemClock** For Qt \>= 4.9 **QwtSystemClock** uses QElapsedTimer internally. As it doesn't support a similar feature, QwtSystemClock::precision() has been removed.

- •

  QwtPlotAbstractSeriesItem\
  \
    QwtPlotAbstractSeriesItem has been split into **QwtPlotSeriesItem** and QwtPlotAbstractSeriesStore.

- •

  **QwtText**\
  \
    A metatype declaration has been added, so that **QwtText** can be used with QVariant.

- •

  **QwtEventPattern**, **QwtPanner**, **QwtMagnifier**\
  \
    Forgotten Qt3 leftovers have been fixed: int -\> Qt::KeyboardModifiers

- •

  QPen Qt5/Qt4 incompatibility The default pen width for Qt5 is 1, what makes it a non cosmetic. To hide this nasty incompatibility several setPen() methods have been added the build pens with a width 0. See QPen::isCosmetic(),

- •

  qwtUpperSampleIndex()\
  \
    A binary search algorithm for sorted samples

- •

  **QwtMatrixRasterData** **QwtMatrixRasterData::setValue()** has been added

- •

  **QwtPicker** QwtPicker::rubberBandWidget(), QwtPicker::trackerWidget() have been replaced by **QwtPicker::rubberBandOverlay()**, **QwtPicker::trackerOverlay()**. **QwtPicker::rubberBandMask()** has been added. QwtPicker::pickRect() has been replaced by **QwtPicker::pickArea()**

- •

  **QwtPlotItem** **QwtPlotItem::ItemInterest** has been added. **QwtPlotItem::setRenderThreadCount()** was shifted from **QwtPlotRasterItem**.

- •

  ...

## Summary of the new classes

- •

  **QwtAbstractLegend**

- •

  **QwtDate**

- •

  **QwtDateScaleDraw**

- •

  **QwtDateScaleEngine**

- •

  **QwtGraphic**

- •

  **QwtLegendData**

- •

  **QwtLegendLabel**

- •

  **QwtPainterCommand**

- •

  **QwtPixelMatrix**

- •

  **QwtPlotAbstractBarChart**

- •

  **QwtPlotBarChart**

- •

  **QwtPlotMultiBarChart**

- •

  **QwtPlotGLCanvas**

- •

  **QwtPlotLegendItem**

- •

  **QwtPlotShapeItem**

- •

  **QwtPlotTextLabel**

- •

  **QwtPlotTradingCurve**

- •

  **QwtPlotZoneItem**

- •

  QwtPointData

- •

  **QwtPointMapper**

- •

  **QwtTransform**, **QwtNullTransform**, **QwtLogTransform**, **QwtPowerTransform**

- •

  **QwtWidgetOverlay**