cmake: included option for qt 6 compilation

Also fixed minor Qt 6 issue

CMakeLists.txt

@@ -18,6 +18,7 @@ cmake_minimum_required(VERSION 3.13 FATAL_ERROR)
 
 project(olive-editor VERSION 0.2.0 LANGUAGES CXX)
 
+option(BUILD_QT6 "Build with Qt 6 over 5 (experimental)" OFF)
 option(BUILD_DOXYGEN "Build Doxygen documentation" OFF)
 option(BUILD_TESTS "Build unit tests" OFF)
 option(USE_WERROR "Error on compile warning" OFF)
@@ -110,10 +111,14 @@ set(QT_LIBRARIES
 if (UNIX AND NOT APPLE)
   list(APPEND QT_LIBRARIES DBus)
 endif()
+if (BUILD_QT6)
+  set(QT_NAME Qt6)
+else()
+  set(QT_NAME Qt5)
+endif()
 find_package(QT
   NAMES
-    Qt6
-    Qt5
+    ${QT_NAME}
   REQUIRED
   COMPONENTS
     ${QT_LIBRARIES}
@@ -251,6 +256,6 @@ add_subdirectory(ext)
 add_subdirectory(app)
 
 if (BUILD_TESTS)
-enable_testing()
-add_subdirectory(tests)
+  enable_testing()
+  add_subdirectory(tests)
 endif()

app/dialog/export/codec/av1section.cpp

@@ -39,7 +39,7 @@ AV1Section::AV1Section(int default_crf, QWidget *parent) :
   CodecSection(parent)
 {
   QGridLayout* layout = new QGridLayout(this);
-  layout->setMargin(0);
+  layout->setContentsMargins(0, 0, 0, 0);
 
   int row = 0;
   layout->addWidget(new QLabel(tr("Preset:")), row, 0);
@@ -104,7 +104,7 @@ AV1CRFSection::AV1CRFSection(int default_crf, QWidget *parent) :
   QWidget(parent)
 {
   QHBoxLayout* layout = new QHBoxLayout(this);
-  layout->setMargin(0);
+  layout->setContentsMargins(0, 0, 0, 0);
 
   crf_slider_ = new QSlider(Qt::Horizontal);
   crf_slider_->setMinimum(kMinimumCRF);

ext/CMakeLists.txt

@@ -17,4 +17,5 @@
 add_subdirectory(core)
 
 set(KDDockWidgets_STATIC ON CACHE INTERNAL "Force KDDockWidgets to build statically")
+set(KDDockWidgets_QT6 ${BUILD_QT6} CACHE INTERNAL "Conform KDDockWidgets' Qt 6 setting to ours")
 add_subdirectory(KDDockWidgets)