There are only a handful of plotting libraries in the Qt ecosystem, the mainstream ones being QCustomPlot, Qwt, Qt Charts, and KDChart.
After Qt 6.8 the former Qt Charts (2-D) and Qt DataVisualization (3-D) were merged into a unified Qt Graphs module (note: not Qt Graphics). The new back-end is built entirely on Qt Quick Scene Graph (QSG) + Qt Quick 3D, completely abandoning the aging Graphics-View / QPainter pipeline.
However, Qt Graphs must be embedded through QQuickWidget or QQuickWindow, which means the QML runtime is mandatory and C++ support is poor—complaints on the forum are numerous.
Although Qt Graphs is Qt’s official “unified” future, that future probably will not arrive within the next three years, and it drops support for older systems such as Windows 7 and is unfriendly to embedded devices.
Therefore, QCustomPlot, Qwt, Qt Charts, and KDChart will remain the practical choices for the next few years.

• QCustomPlot is the simplest and most attractive, and enjoys the widest adoption.
  Just include qcustomplot.h and qcustomplot.cpp and you are ready to go (official docs).
  It also supports Qt 6.
  Its biggest drawback, however, is the GPL license, which is highly “viral”: any program that uses QCustomPlot must itself be GPL—a deal-breaker for commercial use.

• Qwt is a veteran plotting library (official docs) with solid performance, yet its deployment difficulty deters many users.
  It is licensed under LGPL, which is relatively commercial-friendly.

• Qt Charts is Qt’s own plotting package (official docs) but its performance is poor—arguably very low—and unsuitable for scientific computing.
  Worse, Qt Charts has no LGPL option; the open-source version is GPL v3, so using it in a project forces the entire project to be open-sourced under GPL v3.

• KDChart is KDAB’s plotting library (official docs).
  Starting with KDChart 3.0 it is MIT-licensed, making it extremely commercial-friendly.
  Its rendering style, however, is mediocre—reminiscent of Excel 2003.
  A unique feature is Gantt charts, unavailable in the other three.

Hence, for commercial projects you are effectively limited to Qwt and KDChart 3.0.
Because the Qwt author has ceased maintenance, I personally prefer Qwt: its architecture conforms better to software-engineering principles and its large-scale rendering performance is superior.
QCustomPlot delivers out-of-the-box interactive features such as mouse zooming and axis scaling, whereas Qwt requires more code to achieve the same, yet it offers finer-grained control.
When my own projects need plotting I therefore choose Qwt, enhancing and optimizing it with the features I need—hence this project.

I have taken over maintenance of the final official Qwt release, adding the features I need while gradually refining existing ones, e.g., its outdated default styling.

Project repositories:

• GitHub: https://github.com/czyt1988/QWT
• Gitee: https://gitee.com/czyt1988/QWT

Goals and current progress:

• CMake support
• Qt 6 support
• C++11 modernization
• Merged into single header/source for easier inclusion
• Optimize rendering for ultra-large data sets
• Provide integrated interaction helpers for simpler usage
• Modernized visual style
• Figure class for layout management
• Add parasite-axis support for unlimited axes

In short, I will keep maintaining Qwt so it becomes a license-friendly, high-performance, and easy-to-use Qt plotting library.

Qwt7.0 now supports CMake; qmake may be dropped in the future.
After installing Qwt you can simply link it in your project:

target_link_libraries(${YOUR_APP_TARGET} PUBLIC qwt::qwt)

Following the example of QCustomPlot, I have merged the entire Qwt library into QwtPlot.h and QwtPlot.cpp.
Drop these two files into your project and you are ready to go.

Example CMakeLists.txt:

# QwtPlot requires Core Gui Widgets Svg Concurrent OpenGL PrintSupport
find_package(QT NAMES Qt6 Qt5 COMPONENTS Core REQUIRED)
find_package(Qt${QT_VERSION_MAJOR} 5.8 COMPONENTS Core Gui Widgets Svg Concurrent OpenGL PrintSupport REQUIRED)

add_executable(YOUR_APP_TARGET
    main.cpp
    QwtPlot.h
    QwtPlot.cpp
)

target_link_libraries(YOUR_APP_TARGET
    PUBLIC
    Qt${QT_VERSION_MAJOR}::Core
    Qt${QT_VERSION_MAJOR}::Gui
    Qt${QT_VERSION_MAJOR}::Widgets
    Qt${QT_VERSION_MAJOR}::Svg
    Qt${QT_VERSION_MAJOR}::Concurrent
    Qt${QT_VERSION_MAJOR}::OpenGL
    Qt${QT_VERSION_MAJOR}::PrintSupport
)

The original Qwt style used an outdated beveled look inconsistent with modern aesthetics.
I therefore redesigned it.
Qwt 6.3:

Qwt 7.0:

Key changes: removed the default sunken style, placed axes flush against the plot area, overall appearance now aligns with contemporary design.

Inspired by Python’s matplotlib, Qwt now provides a Figure container for effortless multi-plot layouts:

The new QwtFigure class supports grid layouts (similar to matplotlib’s subplot).

Scientific plotting often requires multiple axes, e.g., multiple Y axes sharing one X axis, or vice versa.
Currently even QCustomPlot only supports two axes in the same direction; we will implement parasite axes to allow an arbitrary number, following matplotlib’s approach.

Qwt performs acceptably up to a few million points, but begins to stutter beyond 3 million.
We will introduce a decimation algorithm to handle tens or even hundreds of millions of points efficiently.

Provide out-of-the-box helpers such as data picking and rulers, and incorporate effects inspired by ECharts.

See CHANGES.MD for detailed logs.

examples/simpleplot

examples/barchart

examples/barchart

examples/scatterplot

examples/curvedemo

examples/cpuplot

examples/realtime

examples/oscilloscope

examples/polardemo

examples/spectrogram

examples/spectrogram

playground/vectorfield

examples/stockchart

examples/bode

examples/friedberg

playground/plotmatrix

playground/scaleengine

playground/rescaler

playground/graphicscale

examples/splineeditor

examples/sysinfo

examples/distrowatch

examples/rasterview

examples/rasterview

playground/svgmap

examples/animated

playground/curvetracker

examples/refreshtest

examples/legends

playground/symbols

playground/shapes

examples/controls

examples/controls

examples/controls

examples/controls

examples/radio

playground/timescale

examples/dials

examples/dials