MiniLibX

Basic introduction, tutorials, tips & tricks.

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How to use the “param” for event handlers in MLX?

Only one pointer sure seems cheap. You can’t even use mlx_pixel_put with that!

Let’s modify a previous tutorial where we drew a pixel in the middle of the window, and combine it with the other tutorial about event handlers. This time we’ll draw the same pixel only after a mouse button is pressed.

int mouse_event(int button, int x, int y, void *param)
{
    // Soon...
}

int main()
{
    void *mlx = mlx_init();
    void *win = mlx_new_window(mlx, 640, 360, "Event Parameters");

    mlx_mouse_hook(win, &mouse_event, 0);

    mlx_loop(mlx);
}

It’s about time you learned the importance of structs. Let’s define a simple structure for our whole program. We can use this to hold both pointers grouped together and easily accessible.

typedef struct  s_program
{
    void *mlx;
    void *win;
}               t_program;

When we assign the value of void *mlx to tutorial.mlx, the value of the pointer is copied so that they both point to the same address in memory.

int main()
{
    void *mlx = mlx_init();
    void *win = mlx_new_window(mlx, 640, 360, "Event Parameters");

    t_program tutorial;
    tutorial.mlx = mlx;
    tutorial.win = win;

    mlx_mouse_hook(win, &mouse_event, &tutorial);

    mlx_loop(mlx);
}

Now, when mouse_event is called, you can typecast param to a type you know it will be. t_program in this case.

int mouse_event(int button, int x, int y, void *param)
{
    t_program *tutorial = param;
    
    mlx_pixel_put(tutorial->mlx, tutorial->win, 640/2, 360/2, 0xFFFFFF);
    
    return (1);
}