"Invalid DisplaySize value!" failed | ImGui Docking + SDL2 + OpenGL

[TarekDafay]

Hello folks,
I'm on my second project using dearImGui. This time in combination with sdl2 and glad instead of glfw and wiith the docking branch.
I first started my project on Windows with VS2022, where the code ran well, but now on Linux with CMAKE I'm encountering a lot of issues with the same code. I managed to fix them except for this Assertion:

REF_ANALYTICS: /home/tarek/personalFiles/Coding/RefAnalytics/libraries/ImGui/imgui.cpp:9681: void ImGui::ErrorCheckNewFrameSanityChecks(): Assertion `g.IO.DisplaySize.x >= 0.0f && g.IO.DisplaySize.y >= 0.0f && "Invalid DisplaySize value!"' failed.

The last 2 days I tried to fix it, by Googling, reading docs and experimenting, but couldn't fix my issue. Does anyone know what I'm doing wrong here?

Code:
main.cpp

#include <stdio.h>

#include <SDL_Window.h>
#include <Gui.h>

#include <iostream>

// Main code
int main(int argc, char** argv)
{

    int test;


    SDL_Window window = SDL_Window("Ref Analytics", 1280, 720);

    Gui gui;


    gui.Init(window.getWindow(), window.glsl_version(), window.glContext());
    //glClearColor(0.0f,0.0f,.0f,1.0f);
    while (!window.isClosed())
    {
        window.pollEvents();
        gui.NewFrame(window.getWindow());
        gui.Render();
        SDL_GL_SwapWindow(window.getWindow());
    }

    gui.Shutdown();

    return 0;
}

Gui.cpp

#include <Gui.h>
#include <thread>
//#include <VideoPlayer.h>

#include <iostream>

void Gui::Init(SDL_Window* window, const char* glsl_version, SDL_GLContext gl_context)
{
    auto version = ImGui::GetVersion();
    std::cout << version << "\n";
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO();
    io.DisplaySize = ImVec2(1280,720);
    io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;       // Enable Keyboard Controls
    io.ConfigFlags |= ImGuiConfigFlags_DockingEnable;           // Enable Docking


    
    ImGui::StyleColorsDark();

    ImGuiStyle& style = ImGui::GetStyle();

    ImGui_ImplSDL2_InitForOpenGL(window, gl_context);
    ImGui_ImplOpenGL3_Init(glsl_version);



    ImGui::StyleColorsDark();
}

void Gui::NewFrame(SDL_Window* window)
{
    // feed inputs to dear imgui, start new frame
    ImGui_ImplOpenGL3_NewFrame();
    ImGui_ImplSDL2_NewFrame(window);
    ImGui::NewFrame();


}

void Gui::Render()
{
    ImGui::Render();
    ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());

}

void Gui::Shutdown()
{
    ImGui_ImplOpenGL3_Shutdown();
    ImGui_ImplSDL2_Shutdown();
    ImGui::DestroyContext();

    

}

bool Gui::Player()
{
    

    int frame_width;
    int frame_height;
    unsigned char* data = nullptr;
    ImGui::Begin("Player", NULL);


    
    if (!initialized )
    {
        vplayer = VideoPlayer("H:\\programming\\RefAnalytics\\RefAnalytics\\videos\\Video2.mp4");
        vplayer.open_file(&initialized);
        initialized = true;


    }

    double test = 1;
    if (!vplayer.read_frame())
    {
        printf("Couldn't read frame\n");
        return false;
    }

    ImGui::Image((void*)(intptr_t)vplayer.glTexture(), ImVec2(vplayer.frame_width, vplayer.frame_height));

    ImGui::End();


    static bool show = false;
    return true;
} 

void Gui::Timeline()
{
    ImGui::Begin("Timeline", NULL);

    ImGui::End();
}

void Gui::Dockspace()
{
    static bool DockspaceOpen = true;
    static bool opt_fullscreen = true;
    static bool opt_padding = false;

    static ImGuiDockNodeFlags dockspace_flags = ImGuiDockNodeFlags_None;
    ImGuiWindowFlags window_flags;// = ImGuiWindowFlags_MenuBar;
    if (opt_fullscreen)
    {
        const ImGuiViewport* viewport = ImGui::GetMainViewport();
        ImGui::SetNextWindowPos(ImVec2(0.0f, 0.0f));
        ImGui::SetNextWindowSize(ImGui::GetIO().DisplaySize);
        ImGui::SetNextWindowViewport(viewport->ID);
        ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
        ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
        window_flags |= ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoMove;
        window_flags |= ImGuiWindowFlags_NoBringToFrontOnFocus | ImGuiWindowFlags_NoNavFocus;
    }
    else
    {
        dockspace_flags &= ~ImGuiDockNodeFlags_PassthruCentralNode;

    }

    if (!opt_padding)
        ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0.0f, 0.0f));
    if (!opt_padding)
        ImGui::PopStyleVar();

    if (opt_fullscreen)
        ImGui::PopStyleVar(2);

    if (ImGuiConfigFlags_DockingEnable)
    {
        ImGuiID dockspace_id = ImGui::GetID("MyDockSpace");
        //ImGui::DockSpace(dockspace_id, ImVec2(0.0f, 0.0f), dockspace_flags);
        ImGui::DockSpaceOverViewport();
    }


}

SDL_Window.cpp:

#include "SDL_Window.h"
#include <iostream> 

SDL_Window::SDL_Window(const std::string& title, int width, int height) : _title(title), _width(width), _height(height)
{
    if (!InitWindow())
    {
        _closed == true;
    }
}


bool SDL_Window::InitWindow()
{
    if (SDL_Init(SDL_INIT_VIDEO) != 0)
    {
        std::cerr << "Failed to initialize SDL.\n";
        return 0;
    }

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS,SDL_GL_CONTEXT_FORWARD_COMPATIBLE_FLAG);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION,3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION,0);


    SDL_WindowFlags window_flags = (SDL_WindowFlags) (SDL_WINDOW_RESIZABLE | SDL_WINDOW_OPENGL);
    SDL_Window* window = SDL_CreateWindow(_title.c_str(), SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, _width, _height,  SDL_WINDOW_RESIZABLE | SDL_WINDOW_OPENGL);

    if (window == nullptr)
    {
        std::cerr << "Failed to create Window.\n";
        return 0;
    }

    _glContext = SDL_GL_CreateContext(window);



    return true;
}



void SDL_Window::pollEvents()
{
    SDL_Event event;

    bool LCTRL = false;
    bool Q = false;

    if (SDL_PollEvent(&event))
    {
        
        switch (event.type) {
        case SDL_QUIT:
            _closed = true;
            break;

        case SDL_TEXTINPUT:
            for (int i = 0; event.text.text && event.text.text[i]; ++i) {
                if (event.text.text[i] == 'Q') {
                    _closed = true;
                }
            }
            break;
        
        case SDL_WINDOWEVENT:
        if(event.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
            
        }

        break;
        default: 
            break;
        }
    }


}

[ocornut]

The last 2 days I tried to fix it, by Googling, reading docs and experimenting, but couldn't fix my issue. Does anyone know what I'm doing wrong here?

Compare your code to what examples/example_sdl2_opengl3/main.cpp is doing.

I'm not sure that's the reason for this specific problem, but for example: you are not calling ImGui_ImplSDL2_ProcessEvent() anywhere.

PS: Most of the code in your gui::Dockspace() function is unused, since you only need to call DockspaceOverViewport() there.

[TarekDafay]

Thanks for your answer. I implemented your suggestion and took another look at the file and saw that I forgot to call SDL_GL_MakeCurrent(). Now it runs and I hope that solved it :)

Im gonna take another look at my gui::Dockspace() function to optimize it. Thank you very much for your help.