void ImGui::ErrorCheckNewFrameSanityChecks(): Assertion `g.IO.DisplaySize.x >= 0.0f && g.IO.DisplaySize.y >= 0.0f && "Invalid DisplaySize value!"' failed.

[JulioJPinto]

Im currently trying to implement ImGUI in an Engine im developing. Unfortunately everytime i try to run it its not working and I cant figure out why.

Im using OpenGL and Freeglut. Im following the example for opengl_2 and glut but it simply isnt working when i run it with my engine.

here are my code functions for setup, render and shutdown

void setupMenu()
{
    // Setup Dear ImGui context
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();

    // Setup Dear ImGui style
    ImGui::StyleColorsDark();

    // Setup Platform/Renderer backends
    ImGui_ImplGLUT_Init();
    ImGui_ImplOpenGL3_Init();
}

void shutDownMenu()
{
    
    ImGui_ImplOpenGL3_Shutdown();
    ImGui_ImplGLUT_Shutdown();
    ImGui::DestroyContext();
}


void renderMenu() {
    ImGui_ImplOpenGL3_NewFrame();
    ImGui_ImplGLUT_NewFrame();
    ImGui::NewFrame();

    ImGuiIO& io = ImGui::GetIO();

    ImGui::Begin("General Controls");

    ImGui::Text("FPS: %f", io.Framerate);

    ImGui::End();

    ImGui::Render();
    io = ImGui::GetIO();
    glViewport(0, 0, (GLsizei) io.DisplaySize.x, (GLsizei) io.DisplaySize.y);
    ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
}

Im rendering the menu after my models and i want it to be reshapable like the one in the example

[PathogenDavid]

It doesn't look like you're installing the GLUT callbacks, see the comments here:

imgui/backends/imgui_impl_glut.h

Lines 34 to 44 in b908494

	// You can call ImGui_ImplGLUT_InstallFuncs() to get all those functions installed automatically,
	// or call them yourself from your own GLUT handlers. We are using the same weird names as GLUT for consistency..
	//------------------------------------ GLUT name ---------------------------------------------- Decent Name ---------
	IMGUI_IMPL_API void ImGui_ImplGLUT_ReshapeFunc(int w, int h); // ~ ResizeFunc
	IMGUI_IMPL_API void ImGui_ImplGLUT_MotionFunc(int x, int y); // ~ MouseMoveFunc
	IMGUI_IMPL_API void ImGui_ImplGLUT_MouseFunc(int button, int state, int x, int y); // ~ MouseButtonFunc
	IMGUI_IMPL_API void ImGui_ImplGLUT_MouseWheelFunc(int button, int dir, int x, int y); // ~ MouseWheelFunc
	IMGUI_IMPL_API void ImGui_ImplGLUT_KeyboardFunc(unsigned char c, int x, int y); // ~ CharPressedFunc
	IMGUI_IMPL_API void ImGui_ImplGLUT_KeyboardUpFunc(unsigned char c, int x, int y); // ~ CharReleasedFunc
	IMGUI_IMPL_API void ImGui_ImplGLUT_SpecialFunc(int key, int x, int y); // ~ KeyPressedFunc
	IMGUI_IMPL_API void ImGui_ImplGLUT_SpecialUpFunc(int key, int x, int y); // ~ KeyReleasedFunc

But more importantly:

imgui/backends/imgui_impl_glut.h

Lines 4 to 6 in b908494

	// !!! GLUT/FreeGLUT IS OBSOLETE PREHISTORIC SOFTWARE. Using GLUT is not recommended unless you really miss the 90's. !!!
	// !!! If someone or something is teaching you GLUT today, you are being abused. Please show some resistance. !!!
	// !!! Nowadays, prefer using GLFW or SDL instead!

Please use literally anything other than GLUT.

(To FreeGLUT's credit, it did get revived after it got lumped into that statement. However it's still the least featured Dear ImGui backend and very few people use it.)

[JulioJPinto]

Thanks for the help! I will look into it. Unfortunately this is for a College project where we were taught to use GLUT and it's due rather soon, so changing for something like GLFW isn't an option at this point. If i manage to fix it i will let it know here 👍

[JulioJPinto]

Thank you so much for the help. We ended up managing to do some simple menus to give information about our scenes and to do some toggles.

[PathogenDavid]

Glad I could help! Looks like a cool project, best of luck with your degree!