My Image is replaced by Font Image

[home3d2001]

Hi there,

I am using GLFW3 +imgui ( off of master branch ) + imgui_impl_glfw_gl3.h to create GUI in my app.

I load my image in the GPU and pass the textureID to ImGui::Image. After this, I was hoping to see my image but instead I see the font image.

Here is the my code:

#include <WindowApp.h>
#include <imgui.h>
#include <imgui_impl_glfw_gl3.h>

void 
WindowApp::initialize()
{
    // initialize GLFW
    if (glfwInit())
        std::cout << "GLFW initialized successfully!" << '\n';

    // Set all the required options for GLFW
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_SAMPLES, m_multiSample);
    glfwWindowHint(GLFW_DEPTH_BITS, 24);
    glfwWindowHint(GLFW_RED_BITS, 8);
    glfwWindowHint(GLFW_GREEN_BITS, 8);
    glfwWindowHint(GLFW_BLUE_BITS, 8);
    glfwWindowHint(GLFW_ALPHA_BITS, 8);

    // create glfw window and its openGL context
    m_window = glfwCreateWindow(m_width, m_height, m_windowTitle.c_str(), nullptr, nullptr);
    if (m_window)
    {
        std::cout << "Window created successfully!" << '\n';
        glfwMakeContextCurrent(m_window);
    }

    // glad
    gladLoadGL();

    glfwSwapInterval(1);

    ImGui::CreateContext();
    ImGui_ImplGlfwGL3_Init(m_window, false);

    // load my load image
    glGenTextures(1, &m_id);
    glBindTexture(GL_TEXTURE_2D, m_id);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    m_image = std::make_shared<Image>("someImage.png");
    assert( m_image );
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, m_image ->width(), m_image ->height(), 0, GL_BGR, GL_UNSIGNED_BYTE, m_image ->data());
}

void 
WindowApp::drawLoop()
{
    while (!glfwWindowShouldClose(m_window))
    {
        glfwPollEvents();
 
        ImGui_ImplGlfwGL3_NewFrame();

        ImGui::Begin("Debug Window", NULL, ImGuiWindowFlags_AlwaysAutoResize);

        float w = static_cast<float>(m_image ->width());
        float h = static_cast<float>(m_image ->height());
        ImGui::Image(reinterpret_cast<ImTextureID*>(&m_id), ImVec2(w, h));

        ImGui::End();

        ImGui::Render();
        ImGui_ImplGlfwGL3_RenderDrawData(ImGui::GetDrawData());
        
        glfwSwapBuffers(m_window);
    }

    ImGui_ImplGlfwGL3_Shutdown();
    ImGui::DestroyContext();
    glfwTerminate();
}

And here is what I get:

Could you tell me if this is this a bug in "imgui_impl_glfw_gl3.h"? or am I doing something wrong?

Best Regards,

H

[JSandusky]

ImGui::Image(reinterpret_cast<ImTextureID*>(&m_id), ImVec2(w, h));

Wrong.

ImGui::Image((ImTextureID)m_id, ImVec2(w, h));

[home3d2001]

I tried this before but strangely visual studio 2015 compiler didn't like it.

        ImGui::Image((ImTextureID)m_id, ImVec2(w, h));  // error C2220: warning treated as error - no 'object' file generated
                                                        // warning C4312: 'type cast': conversion from 'GLuint' to 'ImTextureID' of greater size

I tried following which compiles fine but still doesn't fix my issue:

 ImTextureID vPtr = &m_id;
 ImGui::Image(vPtr, ImVec2(w, h));

[home3d2001]

Oh!! This is a x64 bit app!!!

std::cout << sizeof(GLuint)  <<  '\n';  // 4 bytes
std::cout << sizeof(ImTextureID) << '\n'; //8 bytes

I did the following which fixed my issue:

ImGui::Image((ImTextureID)static_cast<uintptr_t>(m_id), ImVec2(w, h));

I still don't see why the earlier code didn't work:

ImGui::Image(reinterpret_cast<ImTextureID*>(&m_id), ImVec2(w, h));

[ocornut]

Your earlier code didn’t work because are passing an address to the GLuint instead of passing the value.

Using:

(ImTextureID)(intptr_t)m_id

Should work without warnings.

[ocornut]

Closing this now, also tried to clarify the FAQ about this.

[ocornut]

I have now written a tutorial to cover image file loading for common graphics API:
https://github.com/ocornut/imgui/wiki/Image-Loading-and-Displaying-Examples