Drop support of QT4

[SunBlack]

Support of Qt4 ended end of 2015. Is it still required to support it? With current modernization of PCL code we could drop supportof it and clean CMake code and switch to new way to include Qt in CMake

[taketwo]

I'm in favor of dropping Qt4 support. Any other opinions @PointCloudLibrary/maintainers?

[SergioRAgostinho]

Agreed 👍

[UnaNancyOwen]

Me too 👍

[taketwo]

We should think what to do with the apps that are only enabled with Qt4. Try to upgrade? Remove? Removing doesn't sound right to me. @SunBlack are you willing to invest time into upgrade?

[SergioRAgostinho]

Try to upgrade, although I confess my Qt experience is non existent.

[SunBlack]

@SunBlack are you willing to invest time into upgrade?

I tried to take a short look on this. But I'm not able to compile current master of PCL with VTK 8.1 (I got always unresolved symbols). And I don't really have enough time to look why I have this trouble.

[taketwo]

I've just realized that we do not have apps that are only enabled with Qt4. The reason I thought so is because some apps are guarded in CMake scripts with:

pcl/apps/CMakeLists.txt

Line 75 in b35b8c7

if (QT4_FOUND AND VTK_USE_QVTK)

However, it does not mean that they are Qt4-only. In the end of the finder script for Qt5 we have the following block:

pcl/cmake/pcl_find_qt5.cmake

Lines 76 to 77 in b35b8c7

	# Trick the remainder of the build system.
	set(QT4_FOUND TRUE)

So I'd say it's safe to drop Qt4 support. @SunBlack you are welcome to work on this and we will try to help you.

[SunBlack]

@SunBlack you are welcome to work on this and we will try to help you.

How I already wrote: I'm not able to compile PCL with VTK (VS2017). Tried it with stable VTK 8.1 and current master of VTK (8.2). As far as I can see you are even not building PCL with VTK on your build jobs on Windows, so I don't know if it is a issue by me or a general issue.

[taketwo]

Yes, at the moment our Windows CI builds are without VTK. Pipelines took very long and even ran out of disk space when we tried to enable VTK. Nevertheless, to the best of my knowledge, VS2017 is able to compile PCL with VTK. @UnaNancyOwen successfully produced an All-in-one installer for the latest release a few hours ago.

What exactly is the problem you are experiencing?

[SunBlack]

What exactly is the problem you are experiencing?

1>   Creating library D:/pcl_build/lib/pcl_cc_tool_interface_release.lib and object D:/pcl_build/lib/pcl_cc_tool_interface_release.exp
1>abstract_tool.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: void __cdecl vtkProp3D::SetUserMatrix(class vtkMatrix4x4 *)" (__imp_?SetUserMatrix@vtkProp3D@@QEAAXPEAVvtkMatrix4x4@@@Z)
1>abstract_tool.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: class vtkSmartPointerBase & __cdecl vtkSmartPointerBase::operator=(class vtkObjectBase *)" (__imp_??4vtkSmartPointerBase@@QEAAAEAV0@PEAVvtkObjectBase@@@Z)

vtk libraries are missing in target pcl_cc_tool_interface, but are e.g. correctly passed to pcl_cc_statistical_outlier_removal.