Project Overview

This project is a terminal-based animation of a steam locomotive. It displays a moving train on the terminal, with options to alter its appearance and behavior.

Tech Stack

• C: The primary programming language.
• ncurses: A library for creating text-based user interfaces in the terminal.

High-Level Architecture

The core logic resides in sl.c.

• main function (sl.c): Parses command-line arguments to set options, initializes the ncurses environment, and enters a loop to render the train.
• option function (sl.c): Parses command-line flags to enable different features like accidents, flying, or specific locomotive models.
• add_sl, add_D51, add_C51 functions (sl.c): These functions are responsible for drawing different representations of the locomotive and its associated elements (coal car, passenger car) at a given horizontal position (x). They use static arrays of strings defined in sl.h to represent the train's frames.
• add_smoke function (sl.c): Animates smoke particles emanating from the locomotive. It manages a static array of smoke structures to track their position, pattern, and type.
• add_man function (sl.c): Draws a small figure, presumably a person, in case of an "accident" option.
• my_mvaddstr function (sl.c): A helper function to print strings to the ncurses screen, handling potential out-of-bounds drawing.
• sl.h: Contains definitions for the various character arrays that form the train's sprites, as well as constants for dimensions and patterns.

Entry Points

1. main function in sl.c: This is the primary entry point.
2. Execution Flow:
   • The main function is called with command-line arguments.
   • It initializes the ncurses screen using initscr().
   • It enters a loop that iterates from COLS - 1 down to a point where the train is off-screen.
   • Inside the loop, based on the LOGO, C51, or default settings, one of add_sl, add_C51, or add_D51 is called to draw the train at the current horizontal position x.
   • getch() is called to wait for user input (though it's non-blocking due to nodelay(stdscr, TRUE)).
   • refresh() updates the terminal display.
   • usleep(40000) introduces a delay to control the animation speed.
   • Once the loop breaks (train is off-screen), endwin() is called to restore the terminal to its normal state.

Key Concepts

1. Ncurses Initialization and Control: The main function sets up the ncurses environment using initscr(), noecho(), curs_set(0), nodelay(stdscr, TRUE), leaveok(stdscr, TRUE), and scrollok(stdscr, FALSE). Understanding these functions is crucial for how the terminal display is managed.
2. Sprite-Based Animation: The train and its components are represented by static arrays of character strings (sl, d51, c51, coal, car in sl.c, and the D51STR*, LOGO*, etc. in sl.h). The animation is achieved by cycling through these arrays to display different frames.
3. Command-Line Options: The option function and the loop in main that calls it demonstrate how command-line arguments (like -a, -F, -l, -c) modify the program's behavior (accidents, flying, different locomotive models).
4. Coordinate System and Drawing: The my_mvaddstr function and its usage within the add_* functions show how characters are placed on the terminal screen using (y, x) coordinates. The animation loop manipulates the x coordinate to create the illusion of movement.
5. Smoke Animation: The add_smoke function implements a particle system for smoke. It uses a static array S to store the state of each smoke particle (position, pattern, kind) and updates their positions and appearance in each animation frame.