RL LoS

//calc()
//sx,sy is the top corner of the screen, dw,dh are the width&height of the screen
//visi=0 represents invisible, visi=1 represents visible, tile=0 represents empty, tile=1 represents wall
{
    for(i=sx;i<sx+dw;i=i+1)
    for(j=sy;j<sy+dh;j=j+1)
    {
        visi[ i , j ] = 0;
    }
    j = sy;
    for(i=sx;i<sx+dw;i=i+1)
    {
        check();
    }
    j = sy + dh;
    for(i=sx;i<sx+dw;i=i+1)
    {
        check();
    }
    i = sx;
    for(j=sy;j<sy+dh;j=j+1)
    {
        check();
    }
    i = sx + dw;
    for(j=sy;j<sy+dh;j=j+1)
    {
        check();
    }
}
//check()
{
    cx = px;
    cy = py;
    d = point_direction( cx , cy , i , j );
    for(k=0;k<point_distance( cx , cy , i , j );k=k+1)
    {
        fx = round( cx + lengthdir_x( k , d ) );
        fy = round( cy + lengthdir_y( k , d ) );
        visi[ fx , fy ] = 1;
        if tile[ fx , fy ] == 1
        {
            exit;
        }
    }
}