CGAL users discussion list

[Aleksey Yakovlev <>]

Theodore, the doc page below is probably closest to what you want:

https://doc.cgal.org/latest/Manual/devman_create_and_use_a_cmakelist.html#secexample

I have a directory with a bunch of small tests and one CMake config file - this file is below. I don't use the CGAL-provided "create_single_source_cgal_program" helper script (sorry, CGAL developers).

cmake_minimum_required(VERSION 3.12)

set(CMAKE_BUILD_TYPE Debug)
set(CGAL_DO_NOT_WARN_ABOUT_CMAKE_BUILD_TYPE TRUE)
set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_FLAGS "-no-pie -ggdb -O0")

project(CGAL)

set(CMAKE_PREFIX_PATH $ENV{HOME}/apps/CGAL/current)
find_package(${PROJECT_NAME} REQUIRED COMPONENTS Qt6)

if(${PROJECT_NAME}_FOUND)
  message("-- Found ${PROJECT_NAME} ${CGAL_VERSION}")
else()
  message(FATAL_ERROR "${PROJECT_NAME} is not found")
endif()

if(${PROJECT_NAME}_Qt6_FOUND)
  message("-- Found ${PROJECT_NAME}_Qt6")
else()
  message(FATAL_ERROR "${PROJECT_NAME}_Qt6 is not found")
endif()

file(GLOB MY_SOURCES ${CMAKE_SOURCE_DIR}/tc????.cpp)

foreach(src ${MY_SOURCES})
  get_filename_component(MY_PROJECT ${src} NAME_WLE)
  project(${MY_PROJECT})
  add_executable(${PROJECT_NAME} ${PROJECT_NAME}.cpp)
  target_link_libraries(${PROJECT_NAME} CGAL::CGAL CGAL::CGAL_Basic_viewer)
endforeach(src)

My tests are similar to your one - some geom object plus drawing it using "CGAL::draw". The building log for one test is below - however I build from the Linux command line. You build on Windows using VC - may be to try the Windows command line as well?

aleksey@cheetah:~/EX/lg-cpp-library-cgal-basic-viewer$ make tc0100
[  7%] Automatic MOC for target CGAL_Qt6_moc_and_resources
[  7%] Built target CGAL_Qt6_moc_and_resources_autogen
[ 14%] Generating ui_ImageInterface.h
[ 21%] Generating qrc_CGAL.cpp
[ 28%] Generating qrc_File.cpp
[ 35%] Generating qrc_Input.cpp
[ 42%] Generating qrc_Triangulation_2.cpp
[ 50%] Building CXX object CMakeFiles/CGAL_Qt6_moc_and_resources.dir/CGAL_Qt6_moc_and_resources_autogen/mocs_compilation.cpp.o
[ 57%] Building CXX object CMakeFiles/CGAL_Qt6_moc_and_resources.dir/qrc_CGAL.cpp.o
[ 64%] Building CXX object CMakeFiles/CGAL_Qt6_moc_and_resources.dir/qrc_Input.cpp.o
[ 71%] Building CXX object CMakeFiles/CGAL_Qt6_moc_and_resources.dir/qrc_File.cpp.o
[ 78%] Building CXX object CMakeFiles/CGAL_Qt6_moc_and_resources.dir/qrc_Triangulation_2.cpp.o
[ 85%] Linking CXX static library libCGAL_Qt6_moc_and_resources.a
[ 85%] Built target CGAL_Qt6_moc_and_resources
[ 92%] Building CXX object CMakeFiles/tc0100.dir/tc0100.cpp.o
[100%] Linking CXX executable tc0100
[100%] Built target tc0100

All the best,

Aleksey

On Sun, Mar 16, 2025 at 2:36 PM Theodore Omtzigt <> wrote:

Aleksey: thanks for that pointer. I made the changes, but it still fails with the same error:

Here is the compilation log. Maybe that contains a hint:

```

Rebuild started at 1:26 PM...
1>------ Rebuild All started: Project: ZERO_CHECK, Configuration: Debug x64 ------
1>1>Checking Build System
2>------ Rebuild All started: Project: CGAL_Qt6_moc_and_resources, Configuration: Debug x64 ------
2>Automatic MOC for target CGAL_Qt6_moc_and_resources
2>Generating ui_ImageInterface.h
2>Generating qrc_CGAL.cpp
2>Generating qrc_Input.cpp
2>Generating qrc_File.cpp
2>Generating qrc_Triangulation_2.cpp
2>Building Custom Rule F:/Users/tomtz/dev/branes/clones/dfa-dynamics/viz/CMakeLists.txt
2>mocs_compilation_Debug.cpp
2>qrc_CGAL.cpp
2>qrc_Input.cpp
2>qrc_File.cpp
2>qrc_Triangulation_2.cpp
2>Generating Code...
2>CGAL_Qt6_moc_and_resources.vcxproj -> F:\Users\tomtz\dev\branes\clones\dfa-dynamics\build_msvc\VS17-Debug\viz\Debug\CGAL_Qt6_moc_and_resources.lib
3>------ Rebuild All started: Project: simple, Configuration: Debug x64 ------
3>Building Custom Rule F:/Users/tomtz/dev/branes/clones/dfa-dynamics/viz/CMakeLists.txt
3>simple.cpp
3>simple.vcxproj -> F:\Users\tomtz\dev\branes\clones\dfa-dynamics\build_msvc\VS17-Debug\viz\Debug\simple.exe
========== Rebuild All: 3 succeeded, 0 failed, 0 skipped ==========
========== Rebuild completed at 1:26 PM and took 32.315 seconds ==========

```

The guidance came from the chat bots (Claude.ai to be exact). Typically, the chatbots are able to bring together the missing documentation, but in CGAL/Qts case all the chatbots (Gemini, Claude, ChatGPT, Grok) are silent, from which I deduce that there is no documentation generated to explain how to enable the Qt basic viewer with CGAL. Reading the CGAL manual, I have not seen a single reference to how to set up a demo program that pulls in the required dependencies.

Please educate me if I have missed specific guidance or documentation on how to set up this CGAL Qt integration.

 

On Sun, Mar 16, 2025 at 11:42 AM Aleksey Yakovlev <> wrote:

What I can see right away is the absence of the "CGAL::CGAL" target in the link command. It should be like below:

target_link_libraries(${DFA_SIMPLE_OBJECT} PRIVATE CGAL::CGAL CGAL::CGAL_Basic_viewer)

Also it makes sense to check the Qt6 status after the "find_package":

if(CGAL_Qt6_FOUND)

....

On Fri, Mar 14, 2025 at 4:50 PM Theodore Omtzigt <> wrote:

Here is the CMakeLists.txt for that application:

find_package(CGAL COMPONENTS Qt6)
if(CGAL_FOUND)
    set(DFA_SIMPLE_OBJECT simple)
    include_directories(${CGAL_INCLUDE_DIRS})
    add_definitions(-DCGAL_USE_BASIC_VIEWER)
    add_executable(${DFA_SIMPLE_OBJECT} simple.cpp)
    target_include_directories(${DFA_SIMPLE_OBJECT} PUBLIC
        ${DFATOOLS_ROOT}/include
    )
    target_link_libraries(${DFA_SIMPLE_OBJECT} PRIVATE CGAL::CGAL_Basic_viewer)
    set_target_properties(${DFA_SIMPLE_OBJECT} PROPERTIES FOLDER "viz")

else()
    message(FATAL_ERROR "CGAL not found")
endif()

and the CMake build pulls  in the vcpkg toolchain file via a CMakePresets.json.

and cgal is installed via:

> vcpkg install cgal[qt]

 

On Fri, Mar 14, 2025 at 3:40 PM Aleksey Yakovlev <> wrote:

Hi, you need to provide more information about how you build your test - including all config files.

On Fri, Mar 14, 2025, 10:39 AM Theodore Omtzigt <> wrote:

we are trying the CGAL Qt integration but when running the example from the CGAL documentation site:

#include <CGAL/Linear_cell_complex_for_combinatorial_map.h>
#include <CGAL/draw_linear_cell_complex.h>
 
using LCC=CGAL::Linear_cell_complex_for_combinatorial_map<3>;
using Point=LCC::Point;
 
int main()
{
  LCC lcc;
  lcc.make_hexahedron(Point(0,0,0), Point(5,0,0),
                      Point(5,5,0), Point(0,5,0),
                      Point(0,5,4), Point(0,0,4),
                      Point(5,0,4), Point(5,5,4));
  CGAL::draw(lcc);
 
  return EXIT_SUCCESS;
}

We get this error message:

qt.qpa.plugin: Could not find the Qt platform plugin "windows" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

What is the magic decoder ring that isn't mentioned in the CGAL documentation site to visualize CGAL data structures with Qt?

 

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