CMake child project can't call OpenGL functions, but parent project can - c++

Question

I have a Parent CMake project and a Child CMake project, inside the parent cmake project I can call any OpenGL function and it works perfectly fine, but inside the child project I can't call any OpenGL functions directly, only through the parent projects functions will it work.
Parent Project:
cmake_minimum_required (VERSION 3.8)
project(LumiumEngine)
set(CMAKE_DEBUG_POSTFIX "-d")
set(LUMI_DIR "LumiumEngine")
# SDL2
find_package(SDL2 CONFIG REQUIRED)
add_library(${PROJECT_NAME} SHARED "${LUMI_DIR}/System/Window.hpp" "${LUMI_DIR}/System/Window.cpp")
# glad
set(GLAD_DIR "${CMAKE_HOME_DIRECTORY}/external/glad")
add_library("glad" "${GLAD_DIR}/src/glad.c")
target_include_directories("glad" PUBLIC "${GLAD_DIR}/include")
target_include_directories(${PROJECT_NAME} PUBLIC "${SDL2_INCLUDE_DIRS}" "${GLAD_DIR}/include")
target_link_libraries(${PROJECT_NAME} PUBLIC SDL2::SDL2 SDL2::SDL2main "glad" "${CMAKE_DL_LIBS}")
set_target_properties(${PROJECT_NAME} PROPERTIES
ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_HOME_DIRECTORY}/${PROJECT_NAME}/lib"
RUNTIME_OUTPUT_DIRECTORY "${CMAKE_HOME_DIRECTORY}/${PROJECT_NAME}/bin"
)
install(DIRECTORY bin
DESTINATION "${CMAKE_HOME_DIRECTORY}/Lumin"
FILES_MATCHING
PATTERN "*.dll"
PATTERN "*.ilk" EXCLUDE
PATTERN "*.pdb" EXCLUDE
)
Child Project:
cmake_minimum_required (VERSION 3.8)
project(Lumin)
set(CMAKE_DEBUG_POSTFIX "-d")
# find OpenGL
find_package(OpenGL REQUIRED)
add_executable(${PROJECT_NAME} "main.cpp" "${CMAKE_HOME_DIRECTORY}/external/glad/src/glad.c")
target_link_libraries(${PROJECT_NAME} PUBLIC "${OPENGL_LIBRARIES}" LumiumEngine)
set_target_properties(${PROJECT_NAME} PROPERTIES
RUNTIME_OUTPUT_DIRECTORY "${CMAKE_HOME_DIRECTORY}/${PROJECT_NAME}/bin"
)
The child project is dependent on parent project, (in the parent-parent directory i just add both of these project as sub directories and add_dependency(Child Parent), the proper .dlls and .libs should be loaded in, from my understanding I load SDL2, SDL2main, glad in the parent project and then load in OpenGL + all the libraries from Parent since they were added with the PUBLIC tag
The code is not the issue, since I created a project with two sub projects in Visual Studio with the same code which worked. Is there a library that i'm missing? It also might be an issue with compiling the OpenGL Loader `glad'.
I think the main issue that is confusing me is why do OpenGL functions hidden by an abstraction layer in my Parent project work fine but when i call OpenGL functions in my Child project I get an "Exception Thrown at 0x00010..." at the OpenGL call. Thanks for any help or guidance.
Edit: Adding a code example:
This is my Window.cpp from the Parent project LumiumEngine
#include "Window.hpp"
#include <glad/glad.h>
lumi::Window::Window()
{
m_shouldClose = true;
}
lumi::Window::~Window()
{
SDL_Quit();
}
bool lumi::Window::createWindow(std::string title, int xPos, int yPos, int width, int height, unsigned int flags)
{
// Set SDL as ready and init SDL
SDL_SetMainReady();
if (SDL_Init(SDL_INIT_VIDEO) != 0)
{
SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "SDL Init Error", "Could not init SDL2", NULL);
SDL_Quit();
return false;
}
SDL_GL_LoadLibrary(NULL); // Default OpenGL is fine.
// Request an OpenGL 4.5 context (should be core)
SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 5);
// Also request a depth buffer
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
// create the window
m_pWindow = SDL_CreateWindow(title.c_str(), xPos, yPos, width, height, flags);
if (m_pWindow == nullptr)
{
SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "SDL Window Error", "Could not create a window", NULL);
SDL_Quit();
return false;
}
// create the openGL context
m_glContext = SDL_GL_CreateContext(m_pWindow);
if (m_glContext == nullptr)
{
SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "SDL Window Error", "Could not create an openGL context with version 4.5", NULL);
SDL_Quit();
return false;
}
printf("OpenGL loaded\n");
gladLoadGLLoader(SDL_GL_GetProcAddress);
printf("Vendor: %s\n", glGetString(GL_VENDOR));
printf("Renderer: %s\n", glGetString(GL_RENDERER));
printf("Version: %s\n", glGetString(GL_VERSION));
m_shouldClose = false;
glViewport(0, 0, width, height);
glClearColor(.2f, .4f, .6f, 1.0f);
return true;
}
bool lumi::Window::isOpen()
{
return !m_shouldClose;
}
Child Project main.cpp
#include <LumiumEngine/System/Window.hpp>
#include <glad/glad.h>
int main(int argc, char **argv)
{
lumi::Window window;
if (window.createWindow("Hello World", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 800, 600, SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL))
{
glClearColor(0.2f, 0.4f, 0.6f, 1.0f); // exception occurs here, as you can see it's after i create a valid OpenGL context
while (window.isOpen())
{
//window.display();
}
}
return 1;
}
Notice how i call the same exact OpenGL function glClearColor() inside my createWindow function and it runs perfectly fine. I can verify that it works by calling window.display which calls glClear(GL_COLOR_BUFFER_BIT); then SDL_GL_SwapBuffers()
Side note: I tried just getting rid of the child project and making the Parent project into a executable instead of a library and it works fine, but i really would like to be able to make LumiumEngine a library so i can call it from multiple projects in the future. I'm completely stumped at the moment.

Answer 1

Blahhh!
So for some reason you have to manually load OpenGL through glad again in the Child Project, even though it has already been called in the parent project and we have verified that we had a valid OpenGL Context. The simple fix for this was to add a:
gladLoadGLLoader(SDL_GL_GetProcAddress)
call after the SDL window was created:
#include <LumiumEngine/System/Window.hpp>
#include <glad/glad.h>
int main(int argc, char **argv)
{
lumi::Window window;
if (window.createWindow("Hello World", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 800, 600, SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL))
{
gladLoadGLLoader(SDL_GL_GetProcAddress);
glClearColor(0.2f, 0.4f, 0.6f, 1.0f); // THIS WORKS NOW!!
while (window.isOpen())
{
window.display();
}
}
return 1;
}
Such a simple fix for a simple problem that was giving me a major headache.