How to get the exact world coordinates of mouse click position

Question

I have a mesh loaded (assimp) in 3D environment in OpenGL. I want to move it along the mouse click (dragging) from one point to another. My present solution is behaving weirdly, the unprojected location is not correct and also I need to find a good way to move mesh along the mouse drag.

I am using unproject method as below:

glm::vec3 unProject(glm::vec3 win, glm::mat4 model, glm::mat4 proj, glm::vec4 viewport)
{
    glm::mat4 Inverse = glm::inverse(proj * model);
    glm::vec4 tmp = glm::vec4(win, 1);
    tmp.x = (tmp.x - (viewport[0])) / (viewport[2]);
    tmp.y = (tmp.y - (viewport[1])) / (viewport[3]);
    tmp.x = tmp.x * (2) - (1);
    tmp.y = tmp.y * (2) - (1);
    glm::vec4 obj = Inverse * tmp;
    obj /= obj.w;
    return glm::vec3(obj);
}

along with a mouse callback

void mouse_callback(GLFWwindow* window, int button, int action, int mods)
{
    if (button == GLFW_MOUSE_BUTTON_LEFT) {
        if(GLFW_PRESS == action){

            int screen_w, screen_h;
            int pixel_w, pixel_h;
            double xpos,ypos,zpos;

            glfwGetWindowSize(window, &screen_w, &screen_h);
            glfwGetFramebufferSize(window, &pixel_w, &pixel_h);
            glfwGetCursorPos(window, &xpos, &ypos);

            glm::vec2 screen_pos=glm::vec2(xpos, ypos);
            glm::vec2 pixel_pos=screen_pos * glm::vec2(pixel_w, pixel_h) / glm::vec2(screen_w, screen_h);
            
            glm::vec3 win=glm::vec3(pixel_pos.x, pixel_h-pixel_pos.y, 0.0f);

            glReadPixels((GLint)win.x, (GLint)win.y, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &win.z);
            
            //Fix
            pixel_pos = pixel_pos + glm::vec2(0.5f, 0.5f);  //Test
            win = glm::vec3(pixel_pos.x, pixel_h-pixel_pos.y, win.z);

            glm::vec4 viewport(0.0f,0.0f,(float)screen_w, (float)screen_h);
            glm::mat4 transformMatrix = glm::mat4(1.0);
            clickLocInWorld = unProject(win, camera.calculateViewMatrix() * transformMatrix, projection, viewport);

    //clamp z-axis
    if(clickLocInWorld.z > 10.0f)
        clickLocInWorld.z = 10.0f;
    if(clickLocInWorld.z < -10.0f)
        clickLocInWorld.z = -10.0f;


            std::cout << "screen " << xpos << " " << ypos << " " << zpos << std::endl;
            std::cout << "world " << clickLocInWorld.x << " " << clickLocInWorld.y << " " << clickLocInWorld.z << std::endl;
        }
    }
}

I am trying to clamp z-axis, but need a proper way.

Also, I am trying to translate the model in 3D using

        presentSpawnLoc = clickLocInWorld - presentSpawnLoc;
    model = glm::translate(model, presentSpawnLoc);
    model = glm::scale(model, glm::vec3(2.f, 2.f, 2.f));
    glUniformMatrix4fv(uniformModel, 1, GL_FALSE, glm::value_ptr(model));

        
        glBindVertexArray(VAO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO);
    glDrawElements(GL_TRIANGLES, indexCount, GL_UNSIGNED_INT, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    glBindVertexArray(0);