ImGui with the glad openGL loader throws segmentation fault (core dumped)

Question

I am new to the ImGui library and recently i've been trying out the examples included. Everything worked like a charm until I changed the include (and functions) of gl3w to glad (the loader i would like to use). The moment I swapped between the two loaders I got a segmentation fault exception inside the imgui_impl_glfw_gl3.cpp file. I found a post which suggested that this may happen because of some functions failing to "bind" and producing nullpointers.

I have located the error in line 216 of imgui_impl_glfw_gl3.cpp this is the code in line 216:

glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);

I have also changed the include file in imgui_impl_glfw_gl3.cpp from gl3w to glad with no results.

This is the main function i am executing (it's the basic opengl3 example of imgui using glad):

#include "gui/imgui.h"
#include "gui/imgui_impl_glfw_gl3.h"
#include <stdio.h>
#include <glad/glad.h>    // This example is using gl3w to access OpenGL functions (because it is small). You may use glew/glad/glLoadGen/etc. whatever already works for you.
#include <GLFW/glfw3.h>

static void error_callback(int error, const char* description)
{
    fprintf(stderr, "Error %d: %s\n", error, description);
}

int main(int, char**)
{
    // Setup window
    glfwSetErrorCallback(error_callback);
    if (!glfwInit())
        return 1;
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow* window = glfwCreateWindow(1280, 720, "ImGui OpenGL3 example", NULL, NULL);
    glfwMakeContextCurrent(window);
    glfwSwapInterval(1); // Enable vsync
    glfwInit();

    // Setup ImGui binding
    ImGui_ImplGlfwGL3_Init(window, true);

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

    bool show_demo_window = true;
    bool show_another_window = false;
    bool algo = true;
    ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);

    // Main loop
    while (!glfwWindowShouldClose(window))
    {

        glfwPollEvents();
        ImGui_ImplGlfwGL3_NewFrame();

        // 1. Show a simple window.
        // Tip: if we don't call ImGui::Begin()/ImGui::End() the widgets automatically appears in a window called "Debug".
        {
            static float f = 0.0f;
            static int counter = 0;
            ImGui::Text("Hello, world!");                           // Display some text (you can use a format string too)
            ImGui::SliderFloat("float", &f, 0.0f, 1.0f);            // Edit 1 float using a slider from 0.0f to 1.0f    
            ImGui::ColorEdit3("COLORINES", (float*)&clear_color); // Edit 3 floats representing a color

            ImGui::Checkbox("Demo Window", &show_demo_window);      // Edit bools storing our windows open/close state
            ImGui::Checkbox("Booleanooooo", &algo);
            ImGui::Checkbox("Another Window", &show_another_window);

            if (ImGui::Button("Button"))                            // Buttons return true when clicked (NB: most widgets return true when edited/activated)
                counter++;
            ImGui::SameLine();
            ImGui::Text("counter = %d", counter);
            ImGui::Text("pues se ve que hay texto: %d", algo);
            ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);
        }

        {
            ImGui::Begin("VENTANA WAPA");
            ImGui::Text("POS SA QUEDAO BUENA VENTANA");

            static float yee = 0.0f;
            ImGui::SliderFloat("lel", &yee,1.0f,0.5f);

            ImGui::End();
        }

        // 2. Show another simple window. In most cases you will use an explicit Begin/End pair to name your windows.
        if (show_another_window)
        {
            ImGui::Begin("Another Window", &show_another_window);
            ImGui::Text("Hello from another window!");
            if (ImGui::Button("Close Me"))
                show_another_window = false;
            ImGui::End();
        }

        // 3. Show the ImGui demo window. Most of the sample code is in ImGui::ShowDemoWindow(). Read its code to learn more about Dear ImGui!
        if (show_demo_window)
        {
            ImGui::SetNextWindowPos(ImVec2(650, 20), ImGuiCond_FirstUseEver); // Normally user code doesn't need/want to call this because positions are saved in .ini file anyway. Here we just want to make the demo initial state a bit more friendly!
            ImGui::ShowDemoWindow(&show_demo_window);
        }

        // Rendering
        int display_w, display_h;
        glfwGetFramebufferSize(window, &display_w, &display_h);
        glViewport(0, 0, display_w, display_h);
        glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui::Render();
        glfwSwapBuffers(window);
    }

    // Cleanup
    //ImGui_ImplGlfwGL3_Shutdown();
    glfwTerminate();

    return 0;
}

I have no clue why this is happenning and I'm pretty new to openGL an ImGui so, any ideas? :(

Answer 1

Glad & gl3w are both extension loader libraries. They generally need to be initialized on a current GL context before use.

The original code called gl3wInit(). Yours is missing any sort of glad init.

Make sure you initialize glad (gladLoadGLLoader((GLADloadproc) glfwGetProcAddress)) after glfwMakeContextCurrent() and before you call any OpenGL functions.

Otherwise all the OpenGL function pointers glad declares will remain NULL. Trying to call NULL function pointers generally doesn't go well for a process.