Drawing pixels which connect 2 points - c

Question

I'm trying to draw the direction of my player on a minimap. I have the ending point of where to draw and the starting point. I'd like to connect the two to actually draw the direction the player is facing.
I have found the ending point using the player direction X and Y.
I'm working with pixels.
I'm only allowed to use my school's library for drawing into a window.
Here's how I get the endpoint and starting point (x and y being the player's coordinate (int), dir_x and dir_y are doubles for the direction (double), start.x and y are (ints)).
start.x = x * MAP_ELEM_PX_SIZE + MAP_PLAYER_PX_SIZE / 2 + (MAP_PLAYER_PX_SIZE + 5) * pos.dir_x;
start.y = y * MAP_ELEM_PX_SIZE + MAP_PLAYER_PX_SIZE / 2 + (MAP_PLAYER_PX_SIZE + 5) * pos.dir_y;
end.x = x * MAP_ELEM_PX_SIZE + MAP_PLAYER_PX_SIZE / 2;
end.y = y * MAP_ELEM_PX_SIZE + MAP_PLAYER_PX_SIZE / 2;
I first tried by just iterating over the x and y at the same time like in this method
int draw_dir_ray(t_coord start, t_coord end, t_win *win)
{
int i;
int j;
i = 0;
j = 0;
if (start.x < end.x)
i = 1;
else if (start.x > end.x)
i = -1;
if (start.y < end.y)
j = 1;
else if (start.y > end.y)
j = -1;
while (start.x != end.x || start.y != end.y)
{
set_pixel(win, start.x, start.y, 0x009E00);
if (start.x != end.x)
start.x += i;
if (start.y != end.y)
start.y += j;
}
return (1);
}
Here are a few screenshots of what it's rendering. As you can see it's not really the expected result...
(Though I tried to give the most informations I can provide some more if needed)

Answer 1

Thanks to you guys I searched at the Bresenham's line algorithm and implemented it this way !
int draw_dir_ray(t_coord start, t_coord end, t_win *win)
{
int dx;
int dy;
int sx;
int sy;
int err;
int e2;
dx = abs(end.x - start.x);
dy = -abs(end.y - start.y);
sx = start.x < end.x ? 1 : -1;
sy = start.y < end.y ? 1 : -1;
err = dx + dy;
while (1)
{
set_pixel(win, start.x, start.y, 0xFF0000);
set_pixel(win, start.x - 1, start.y, 0xFF0000);
set_pixel(win, start.x, start.y - 1, 0xFF0000);
set_pixel(win, start.x - 1, start.y - 1, 0xFF0000);
if (start.y == end.y && start.x == end.x)
break ;
e2 = 2 * err;
if (e2 >= dy)
{
err += dy;
start.x += sx;
}
if (e2 <= dx)
{
err += dx;
start.y += sy;
}
}
return (1);