This patch implements the Qt5- and Qt6-based builds with CMake

--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,134 @@
+cmake_minimum_required(VERSION 3.18.4)
+
+SET(QCustomPlot_MAJOR_VERSION "2")
+SET(QCustomPlot_MINOR_VERSION "1")
+SET(QCustomPlot_PATCH_VERSION "0")
+
+set(QCustomPlot_VERSION "${QCustomPlot_MAJOR_VERSION}.${QCustomPlot_MINOR_VERSION}.${QCustomPlot_PATCH_VERSION}")
+set(QCustomPlot_SOVERSION "${QCustomPlot_MAJOR_VERSION}.${QCustomPlot_MINOR_VERSION}")
+
+PROJECT(QCustomPlot LANGUAGES CXX VERSION ${QCustomPlot_VERSION})
+
+set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${CMAKE_CURRENT_SOURCE_DIR}/cmake)
+
+include(GNUInstallDirs)
+include(FeatureSummary)
+
+#-----------------------------------------------------------#
+# Dependencies
+#-----------------------------------------------------------#
+
+set(REQUIRED_QT_COMPONENTS Core Widgets PrintSupport)
+
+set(MIN_REQUIRED_QT5_VERSION "5.12")
+set(MIN_REQUIRED_QT6_VERSION "6.2.0")
+
+if (NOT USE_QT_VERSION)
+  # FIXME: find_package(QT NAMES Qt6 Qt5 ...) seems to prefer Qt5 on my system
+  find_package(Qt6 ${MIN_REQUIRED_QT6_VERSION} COMPONENTS ${REQUIRED_QT_COMPONENTS} REQUIRED)
+  if (NOT Qt6_FOUND)
+    find_package(Qt5 ${MIN_REQUIRED_QT5_VERSION} COMPONENTS ${REQUIRED_QT_COMPONENTS} REQUIRED)
+    set(QT_VERSION_MAJOR 5)
+  else()
+    set(QT_VERSION_MAJOR 6)
+  endif()
+else()
+  find_package(Qt${USE_QT_VERSION} ${MIN_REQUIRED_QT${USE_QT_VERSION}_VERSION}
+    COMPONENTS ${REQUIRED_QT_COMPONENTS} REQUIRED)
+  set(QT_VERSION_MAJOR ${USE_QT_VERSION})
+endif()
+
+# Determine the names of the output library depending on the version of Qt:
+
+if(${QT_VERSION_MAJOR} EQUAL "5")
+
+  message("The Qt version to build against is 5")
+
+  set(LIB_NAME QCustomPlot)
+  set(CMAKE_CONFIG_FILE_NAME ${LIB_NAME}Config.cmake)
+  set(CMAKE_CONFIG_LIB_NAMES QCustomPlot libQCustomPlot)
+
+endif()
+
+if(${QT_VERSION_MAJOR} EQUAL "6")
+
+  message("The Qt version to build against is 6")
+
+  set(LIB_NAME QCustomPlotQt6)
+  set(CMAKE_CONFIG_FILE_NAME ${LIB_NAME}Config.cmake)
+  set(CMAKE_CONFIG_LIB_NAMES QCustomPlotQt6 libQCustomPlotQt6)
+
+endif()
+
+#-----------------------------------------------------------#
+# Definitions
+#-----------------------------------------------------------#
+
+set(QCUSTOMPLOT_TARGET_PREFIX "${LIB_NAME}")
+set(QCUSTOMPLOT_INSTALL_INCLUDEDIR "${CMAKE_INSTALL_INCLUDEDIR}/${LIB_NAME}")
+
+#-----------------------------------------------------------#
+# Compiler Settings
+#-----------------------------------------------------------#
+
+#set(CMAKE_CXX_STANDARD 17)
+
+set(CMAKE_AUTOMOC ON)
+set(CMAKE_AUTORCC ON)
+set(CMAKE_AUTOUIC ON)
+
+# Only enable strict warnings in debug mode
+set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -Wall -Wextra -Werror -pedantic")
+
+# As per the author of the library, we should export the symbols under
+# MS-Windows.
+add_definitions(-DQCUSTOMPLOT_COMPILE_LIBRARY)
+
+#-----------------------------------------------------------#
+# Sources
+#-----------------------------------------------------------#
+
+add_library(${LIB_NAME} SHARED qcustomplot.cpp)
+
+set_target_properties(${LIB_NAME} PROPERTIES
+  VERSION ${QCustomPlot_VERSION}
+  SOVERSION ${QCustomPlot_SOVERSION})
+
+target_link_libraries(${LIB_NAME}
+  Qt${QT_VERSION_MAJOR}::Widgets
+  Qt${QT_VERSION_MAJOR}::PrintSupport)
+
+#-----------------------------------------------------------#
+# Installation
+#-----------------------------------------------------------#
+
+install(TARGETS ${LIB_NAME}
+  EXPORT ${LIB_NAME}Targets
+  LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+  ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+  RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+  INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
+
+install(FILES qcustomplot.h DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}")
+
+install(EXPORT ${LIB_NAME}Targets
+  FILE ${LIB_NAME}Targets.cmake
+  NAMESPACE ${LIB_NAME}::
+  DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${LIB_NAME})
+
+include(CMakePackageConfigHelpers)
+
+configure_package_config_file(${CMAKE_CURRENT_SOURCE_DIR}/cmake/Config.cmake.in
+  "${CMAKE_CURRENT_BINARY_DIR}/${LIB_NAME}Config.cmake"
+  INSTALL_DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${LIB_NAME})
+
+install(FILES
+  "${CMAKE_CURRENT_BINARY_DIR}/${LIB_NAME}Config.cmake"
+  DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${LIB_NAME})
+
+#-----------------------------------------------------------#
+# Summary
+#-----------------------------------------------------------#
+
+feature_summary(FATAL_ON_MISSING_REQUIRED_PACKAGES WHAT ALL)
+
--- /dev/null
+++ b/cmake/Config.cmake.in
@@ -0,0 +1,5 @@
+@PACKAGE_INIT@
+
+include("${CMAKE_CURRENT_LIST_DIR}/@LIB_NAME@Targets.cmake")
+
+check_required_components(@LIB_NAME@)