SDL_PollEvent not responding to events

Question

I'm creating a game in OpenGL and having issues with SDL_PollEvent not picking up all events, for instance, if I press and hold a key, I have to wait ~1-3 seconds before the program realises what I have just done. This is my main.cpp:

#include <GL/glew.h>
#include <GL/GL.h>
#include <SDL\SDL.h>
#include "Display.h"
#include "Mesh.h"
#include "Shader.h"
#include "Texture.h"
#include "Transform.h"
#include "Camera.h"
#include <iostream>

#define WIDTH 800
#define HEIGHT 600

int main(int argc, char *argv[])
{
    Display Display(800, 600, "OpenGL");

    Vertex vertices[] = { Vertex(glm::vec3(-0.5, -0.5, 0), glm::vec2(0.0, 0.0)),
                          Vertex(glm::vec3(0, 0.5, 0), glm::vec2(0.5, 1.0)),
                          Vertex(glm::vec3(0.5, -0.5, 0), glm::vec2(1.0, 0.0)), };

    unsigned int indices[] = { 0,1,2 };

    SDL_Init(SDL_INIT_EVERYTHING);

//  Mesh Car("./res/Test2.obj");
//  Mesh Test(vertices, sizeof(vertices) / sizeof(vertices[0]), indices, sizeof(indices)/sizeof(indices[0]));
    Mesh Ground("./res/Ground2.obj");
    Shader shader("./res/basicShader");
//  Texture texture("./res/CarUV.png");
    Texture test("./res/ground.jpg");
    Camera camera(glm::vec3(0, 0, -14), 70.f, (float)WIDTH / (float)HEIGHT, 0.01f, 1000.0f);
    Transform transform;
    const Uint8 *keyState;

    transform.GetPos().x = 0;
    transform.GetPos().y = 0;
    transform.GetPos().z = 0;
    transform.GetRot().x = 80;
    transform.GetRot().y = 0;
    transform.GetRot().z = 0;

    float counter = 0.0f;

    while (!Display.IsClosed())
    {

            Display.Clear(0.0f, 0.15f, 0.3f, 1.0f);

            float sinCounter = sinf(counter);
            float cosCounter = cosf(counter);

            SDL_Event ev;

            while (SDL_PollEvent(&ev) != 0)
            {
                keyState = SDL_GetKeyboardState(NULL);

                if (keyState[SDL_SCANCODE_W])
                {
                    camera.MoveForward(1);
                    std::cout << "keypress" << std::endl;
                }
                else if (keyState[SDL_SCANCODE_S])
                {
                    camera.MoveBackward(1);
                }
                if (keyState[SDL_SCANCODE_A])
                {
                    camera.MoveRight(1);
                }
                else if (keyState[SDL_SCANCODE_D])
                {
                    camera.MoveLeft(1);
                }
                if (keyState[SDL_SCANCODE_Y])
                {
                    camera.RotateY(0.1);
                }
                if (keyState[SDL_SCANCODE_X])
                {
                    camera.RotateX(0.1);
                }
            }

            //transform.SetScale(glm::vec3(cosCounter, cosCounter, cosCounter));
            shader.Bind();
            test.Bind(0);
            shader.Update(transform, camera);
            //Car.draw();
            Ground.draw();

            Display.Update();
            counter += 1.0f;
    }
    return 0;
}

All the functions do what they're named after and work properly.

EDIT:

I've done some testing and removing Display.clear(); and Display.update(); fixes the problem however this is not a viable solution.

EDIT 2:

Just as extra information the program originally worked, then I started fiddling around with it and the event handler screwed up.

Answer 1

As @HolyBlackCat has said in the comments, in this part of the code:

while (SDL_PollEvent(&ev) != 0)
{
    //if statements here 
}

The while loop is unnecessary, as you already have one in the form of:

while (!Display.IsClosed())
{
    //main game loop
}

And having another while loop inside will just cause issues.

Anyway hope this helps and please don't mark as the answer if @HolyBlackCat creates one or this doesn't work for you. Cheers.