breham algorith why ther are two difernct case for difernt slopes code example

Example: Bresenham's line algorithm

static void bresenham(int x1, int y1, int x2, int y2) 
    { 
        int m_new = 2 * (y2 - y1); 
        int slope_error_new = m_new - (x2 - x1); 
      
        for (int x = x1, y = y1; x <= x2; x++) 
        { 
            System.out.print("(" +x + "," + y + ")\n"); 
  
            // Add slope to increment angle formed 
            slope_error_new += m_new; 
  
            // Slope error reached limit, time to 
            // increment y and update slope error. 
            if (slope_error_new >= 0) 
            { 
                y++; 
                slope_error_new -= 2 * (x2 - x1); 
            } 
        } 
    }