Adding Qt6 detection and compatibility, without breaking Qt5. -DUSE_QT6=AUTO|ON|OFF (default: AUTO; prefers Qt6 when available and CMake ≥3.16, ON forces Qt6, OFF forces Qt5). Also, a few version specific changes for API changes on Qt6, but it appears to work well.

Author: jonoomph

INSTALL.md

@@ -50,7 +50,7 @@ Libraries and executables have been labeled in the list below to help distinguis
 #### Qt 5 (libqt5)
 *   <http://www.qt.io/qt5/> **(Library)**
 
-*   Qt5 is used to display video, store image data, composite images,
+*   Qt5/Qt6 is used to display video, store image data, composite images,
     apply image effects, and many other utility functions,
     such as file system manipulation, high resolution timers, etc.
 
@@ -201,6 +201,7 @@ Following are some of the flags you might need to set when generating your build
 *   `-DCMAKE_PREFIX_PATH=/extra/path/to/search/for/libraries/`
 *   `-DUSE_SYSTEM_JSONCPP=0` (default: auto if discovered)
 *   `-DENABLE_MAGICK=0` (default: auto if discovered)
+*   `-DUSE_QT6=AUTO|ON|OFF` (default: `AUTO`; prefers Qt6 when available and CMake ≥3.16, `ON` forces Qt6, `OFF` forces Qt5)
 
 #### Options to compile bindings for a specific Python installation
 *   `-DPYTHON_INCLUDE_DIR=/location/of/python/includes/`

doc/INSTALL-LINUX.md

@@ -44,7 +44,8 @@ list below to help distinguish between them.
 
 ### Qt 5 (libqt5)
   * http://www.qt.io/qt5/ `(Library)`
-  * Qt5 is used to display video, store image data, composite images, apply image effects, and many other utility functions, such as file system manipulation, high resolution timers, etc...
+  * Qt5/Qt6 is used to display video, store image data, composite images, apply image effects, and many other utility functions, such as file system manipulation, high resolution timers, etc...
+  * Use the CMake option `-DUSE_QT6=ON|OFF|AUTO` (default AUTO) to pick a Qt major version; Qt6 builds require CMake 3.16+.
 
 ### CMake (cmake)
   * http://www.cmake.org/ `(Executable)`
@@ -166,6 +167,13 @@ software packages available to download and install.
                         swig
 ```
 
+If you want to build against Qt6 on Ubuntu 24.04 or newer, install the Qt6 dev stack instead and configure with the default `USE_QT6=AUTO` (prefers Qt6 when available) or `-DUSE_QT6=ON` to force it:
+
+```
+sudo apt install qt6-base-dev qt6-base-dev-tools qt6-tools-dev qt6-svg-dev
+```
+
+
 ## Linux Build Instructions (libopenshot-audio)
 To compile libopenshot-audio, we need to go through a few additional steps to manually build and 
 install it. Launch a terminal and enter:

doc/INSTALL-MAC.md

@@ -44,7 +44,8 @@ list below to help distinguish between them.
 
 ### Qt 5 (libqt5)
   * http://www.qt.io/qt5/ `(Library)`
-  * Qt5 is used to display video, store image data, composite images, apply image effects, and many other utility functions, such as file system manipulation, high resolution timers, etc...
+  * Qt5/Qt6 is used to display video, store image data, composite images, apply image effects, and many other utility functions, such as file system manipulation, high resolution timers, etc...
+  * Use the CMake option `-DUSE_QT6=ON|OFF|AUTO` (default AUTO) to pick a Qt major version; Qt6 builds require CMake 3.16+.
 
 ### CMake (cmake)
   * http://www.cmake.org/ `(Executable)`

doc/INSTALL-WINDOWS.md

@@ -46,7 +46,8 @@ have been labeled in the list below to help distinguish between them.
 
 ### Qt 5 (libqt5)
   * http://www.qt.io/qt5/ `(Library)`
-  * Qt5 is used to display video, store image data, composite images, apply image effects, and many other utility functions, such as file system manipulation, high resolution timers, etc...
+  * Qt5/Qt6 is used to display video, store image data, composite images, apply image effects, and many other utility functions, such as file system manipulation, high resolution timers, etc...
+  * Use the CMake option `-DUSE_QT6=ON|OFF|AUTO` (default AUTO) to pick a Qt major version; Qt6 builds require CMake 3.16+.
 
 ### CMake (cmake)
   * http://www.cmake.org/ `(Executable)`

examples/CMakeLists.txt

@@ -11,8 +11,45 @@
 
 include(GNUInstallDirs)
 
-# Dependencies
-find_package(Qt5 COMPONENTS Gui REQUIRED)
+# Qt selection matches the main library (USE_QT6 option, CMake 3.16+ needed for Qt6)
+set(_qt6_allowed TRUE)
+if(CMAKE_VERSION VERSION_LESS "3.16")
+  set(_qt6_allowed FALSE)
+  if(USE_QT6 STREQUAL "ON")
+    message(FATAL_ERROR "USE_QT6=ON requires CMake 3.16 or newer")
+  endif()
+endif()
+if(USE_QT6 STREQUAL "OFF")
+  set(_qt6_allowed FALSE)
+endif()
+
+set(_qt_selection "")
+if(USE_QT6 STREQUAL "ON")
+  if(NOT _qt6_allowed)
+    message(FATAL_ERROR "Qt6 support disabled by CMake version; set USE_QT6=OFF or upgrade CMake")
+  endif()
+  set(_qt_selection "Qt6")
+elseif(USE_QT6 STREQUAL "OFF")
+  set(_qt_selection "Qt5")
+else()
+  if(_qt6_allowed)
+    find_package(Qt6 COMPONENTS Core QUIET)
+    if(Qt6_FOUND)
+      set(_qt_selection "Qt6")
+    endif()
+  endif()
+  if(NOT _qt_selection)
+    set(_qt_selection "Qt5")
+  endif()
+endif()
+
+if(_qt_selection STREQUAL "Qt6")
+  set(QT_VERSION_MAJOR 6)
+else()
+  set(QT_VERSION_MAJOR 5)
+endif()
+
+find_package(Qt${QT_VERSION_MAJOR} COMPONENTS Gui REQUIRED)
 
 ############### CLI EXECUTABLES ################
 # Create test executable
@@ -27,7 +64,7 @@ target_compile_definitions(openshot-example PRIVATE
 target_link_libraries(openshot-example openshot)
 
 add_executable(openshot-html-example ExampleHtml.cpp)
-target_link_libraries(openshot-html-example openshot Qt5::Gui)
+target_link_libraries(openshot-html-example openshot Qt${QT_VERSION_MAJOR}::Gui)
 
 ############### PLAYER EXECUTABLE ################
 # Create test executable

src/CMakeLists.txt

@@ -314,23 +314,67 @@ endif()
 ### Qt Toolkit
 ###
 
+set(USE_QT6 "AUTO" CACHE STRING "Select Qt major version (AUTO, ON=Qt6, OFF=Qt5)")
+set_property(CACHE USE_QT6 PROPERTY STRINGS AUTO ON OFF)
+
 set(_qt_components Core Gui Widgets)
 
 # We also need QtSvg unless we have Resvg insetead.
 if(NOT HAVE_RESVG)
   list(APPEND _qt_components Svg)
 endif()
 
-find_package(Qt5 COMPONENTS ${_qt_components} REQUIRED)
+# Qt6 packages require newer CMake; gate support so older systems still build Qt5.
+set(_qt6_allowed TRUE)
+if(CMAKE_VERSION VERSION_LESS "3.16")
+  set(_qt6_allowed FALSE)
+  if(USE_QT6 STREQUAL "ON")
+    message(FATAL_ERROR "USE_QT6=ON requires CMake 3.16 or newer")
+  endif()
+endif()
+if(USE_QT6 STREQUAL "OFF")
+  set(_qt6_allowed FALSE)
+endif()
+
+set(_qt_selection "")
+if(USE_QT6 STREQUAL "ON")
+  if(NOT _qt6_allowed)
+    message(FATAL_ERROR "Qt6 support disabled by CMake version; set USE_QT6=OFF or upgrade CMake")
+  endif()
+  set(_qt_selection "Qt6")
+elseif(USE_QT6 STREQUAL "OFF")
+  set(_qt_selection "Qt5")
+else()
+  if(_qt6_allowed)
+    find_package(Qt6 COMPONENTS Core QUIET)
+    if(Qt6_FOUND)
+      set(_qt_selection "Qt6")
+    endif()
+  endif()
+  if(NOT _qt_selection)
+    set(_qt_selection "Qt5")
+  endif()
+endif()
+
+if(_qt_selection STREQUAL "Qt6")
+  set(QT_VERSION_MAJOR 6)
+else()
+  set(QT_VERSION_MAJOR 5)
+endif()
+
+find_package(Qt${QT_VERSION_MAJOR} COMPONENTS ${_qt_components} REQUIRED)
 
 foreach(_qt_comp IN LISTS _qt_components)
-  if(TARGET Qt5::${_qt_comp})
-    target_link_libraries(openshot PUBLIC Qt5::${_qt_comp})
+  if(TARGET Qt${QT_VERSION_MAJOR}::${_qt_comp})
+    target_link_libraries(openshot PUBLIC Qt${QT_VERSION_MAJOR}::${_qt_comp})
   endif()
 endforeach()
 
+string(REPLACE ";" ", " _qt_comp_list "${_qt_components}")
+message(STATUS "Found Qt${QT_VERSION_MAJOR} ${Qt${QT_VERSION_MAJOR}Core_VERSION_STRING} (components: ${_qt_comp_list})")
+
 # Keep track of Qt version, to embed in our version header
-set(QT_VERSION_STR ${Qt5Core_VERSION_STRING} CACHE STRING "Qt version linked with" FORCE)
+set(QT_VERSION_STR ${Qt${QT_VERSION_MAJOR}Core_VERSION_STRING} CACHE STRING "Qt version linked with" FORCE)
 mark_as_advanced(QT_VERSION_STR)
 
 ################### FFMPEG #####################

src/Qt/PlayerDemo.cpp

@@ -43,7 +43,7 @@ PlayerDemo::PlayerDemo(QWidget *parent)
     vbox->addWidget(menu, 0);
     vbox->addWidget(video, 1);
 
-    vbox->setMargin(0);
+    vbox->setContentsMargins(0, 0, 0, 0);
     vbox->setSpacing(0);
     resize(600, 480);
 

src/effects/LensFlare.cpp

@@ -107,14 +107,19 @@ static QColor shifted_hsv(const QColor &base, float h_shift,
                           float s_scale, float v_scale,
                           float a_scale = 1.0f)
 {
+    // Qt6 switched getHsvF/setHsvF to float; keep compatibility with Qt5 (qreal)
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+    float h, s, v, a;
+#else
     qreal h, s, v, a;
+#endif
     base.getHsvF(&h, &s, &v, &a);
     if (s == 0.0)
         h = 0.0;
-    h = std::fmod(h + h_shift + 1.0, 1.0);
-    s = std::clamp(s * s_scale, 0.0, 1.0);
-    v = std::clamp(v * v_scale, 0.0, 1.0);
-    a = std::clamp(a * a_scale, 0.0, 1.0);
+    h = static_cast<decltype(h)>(std::fmod(static_cast<double>(h + h_shift + 1.0), 1.0));
+    s = std::clamp(s * s_scale, static_cast<decltype(s)>(0.0), static_cast<decltype(s)>(1.0));
+    v = std::clamp(v * v_scale, static_cast<decltype(v)>(0.0), static_cast<decltype(v)>(1.0));
+    a = std::clamp(a * a_scale, static_cast<decltype(a)>(0.0), static_cast<decltype(a)>(1.0));
 
     QColor out;
     out.setHsvF(h, s, v, a);

tests/Caption.cpp

@@ -63,7 +63,9 @@ TEST_CASE("caption effect", "[libopenshot][caption]") {
 
     int argc = 1;
     char* argv[1] = {(char*)""};
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+#endif
     QApplication app(argc, argv);
 
     QApplication::processEvents();
@@ -202,4 +204,4 @@ TEST_CASE("caption effect", "[libopenshot][caption]") {
 
     // Close QApplication
     app.quit();
-}
+}