Minimal Allegro5 C++

#include <cstdio>
#include <allegro5/allegro.h>
#include <allegro5/allegro_font.h>
#include <allegro5/allegro_primitives.h>

template <class M = const char*, class E = int>
E log(M msg, E error = 0)
{
    printf(msg);
    return error;
}

int screenW = 640;
int screenH = 360;
int scaleWin = 2;
bool quit = false;

int xMouse = 0;
int yMouse = 0;

ALLEGRO_KEYBOARD_STATE keyState;
ALLEGRO_MOUSE_STATE mouseState;

ALLEGRO_FONT *font = nullptr;
ALLEGRO_DISPLAY *display = nullptr;
ALLEGRO_BITMAP *buffer = nullptr;

void update()
{
    al_get_keyboard_state(&keyState);
    al_get_mouse_state(&mouseState);

    xMouse = mouseState.x / scaleWin;
    yMouse = mouseState.y / scaleWin;

    if (al_key_down(&keyState, ALLEGRO_KEY_ESCAPE))
        quit = true;
}
void render()
{
    al_set_target_bitmap(buffer);
    al_clear_to_color(al_map_rgb(0, 32, 64));
    al_draw_text(font, al_map_rgb(255, 255, 255), screenW/2, screenH-12, ALLEGRO_ALIGN_CENTER, "- PathFinding AStar -");

    al_draw_line(0, yMouse + .5,
                 screenW, yMouse + .5,
                 al_map_rgba(55, 125, 100, 25), 0);

    al_draw_line(xMouse + .5, 0,
                 xMouse + .5, screenH,
                 al_map_rgba(55, 125, 100, 25), 0);

    al_set_target_backbuffer(display);
    al_draw_scaled_bitmap(
        buffer,
        0,0,
        screenW,screenH,
        0,0,
        screenW*scaleWin, screenH*scaleWin,
        0);

    al_flip_display();
}

int init()
{
    al_init();
    al_init_font_addon();
    al_init_primitives_addon();

    al_install_keyboard();
    al_install_mouse();

    display = al_create_display(screenW*scaleWin, screenH*scaleWin);
    buffer = al_create_bitmap(screenW, screenH);
    font = al_create_builtin_font();

    return log("init OK !\n");
}
int done()
{
    al_destroy_bitmap(buffer);
    al_destroy_display(display);
    al_destroy_font(font);

    return log("done OK !\n");
}

int run()
{
    if (init())
        quit = true;
    while (!quit)
    {
        update();
        render();
    }
    if (done())
        return log("done ERROR !\n");
    return log("End of Run !\n");
}
int main()
{
    if (run())
        return log("run ERROR !\n");

    return log("END of MAIN !\n");
}