A plethora of ways to ruin your gaming experience...
Let's start off by adding this mod as a dependency in your mod.json!
Optionally, you can shorten include paths in your code by adding the the full path as a private include directory through your CMakeLists.txt file. The rest of the documentation will use this practice in its code samples.
target_include_directories(${PROJECT_NAME} PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/geode-deps/cubicstudios.horriblemenu/include)You can directly access the Horrible Menu mod menu API by including the API.h file in your code. Make sure to include the horrible namespace to directly access all needed classes and methods.
#include <horrible/API.h>
using namespace horrible;