CMake with include and source paths – basic setup

You need a CMakeLists.txt for each source subdirectory. Your structure should look something like this:

root
|-MainProject
| |-inc
| | '-main.h
| |-src
| | |-main.cpp
| | '-CMakeLists.txt
| '-CMakeLists.txt 
|-LibProject
| |-inc
| | '-test.h
| |-src
| | |-test.cpp
| | '-CMakeLists.txt
| '-CMakeLists.txt
'-CMakeLists.txt

Content of root/CMakeLists.txt:

project(MyProject)
add_subdirectory(MainProject)
add_subdirectory(LibProject)

Content of LibProject/CMakeLists.txt and MainProject/CMakeLists.txt:

add_subdirectory(src)

Content of LibProject/src/CMakeLists.txt:

# Notice name prefix of this variable, set by CMake according
# to value given with "project()" in the root CMakeLists.txt.
include_directories(${MyProject_SOURCE_DIR}/LibProject/inc)
add_library(LibProject test.cpp)

Content of MainProject/src/CMakeLists.txt:

include_directories(${MyProject_SOURCE_DIR}/MainProject/inc)
# I assume you want to use LibProject as a library in MainProject.
include_directories(${MyProject_SOURCE_DIR}/LibProject/inc)
link_directories(${MyProject_SOURCE_DIR}/LibProject/src)
add_executable(MainProject main.cpp)
target_link_libraries(MainProject LibProject)

Then configure and build with:

$ cd root
$ mkdir build
$ cd build
$ cmake ..
$ make