Plan C - Animate the Image Across the Screen

/* drawing.rs */
...
pub fn draw_d51image(delay: u64, fly: bool, oops: bool) {
    // Start ncurses, initializing "stdscr()".
    initscr();
...
    endwin();
} // end of draw_d51image()

...
pub fn draw_image(delay: u64, fly: bool, oops: bool) {
    // Start ncurses, initializing "stdscr()".
    initscr();

    // Don't echo keypresses to screen.
    noecho();

    // Turn off the display of the cursor.
    curs_set(CURSOR_VISIBILITY::CURSOR_INVISIBLE);

    // Get the screen dimensions.
    let mut screen_height = 0;
    let mut screen_width = 0;
    getmaxyx(stdscr(), &mut screen_height, &mut screen_width);
...

/* main.rs */

mod drawing;
mod get_options;
mod images;

use drawing::*;
use get_options::*;

fn main() {
    let (speed, fly, kind, oops, image_string) = parse_opts(); // Get the program options from the command-line, if any.
    // draw_d51(speed, fly, oops);
    let image_vecvec = string_to_stringvec(&image_string);
    // temporary code to test-print the vector
    for each_vec in image_vecvec {
        println!("{}", each_vec);
    }
    draw_image(speed, fly, kind, oops, image_vecvec);
} // end of main()

...
pub fn draw_image(delay: u64, fly: bool, kind: String, oops: bool, image_vecvec: Vec<Vec<String>>) {
    // Start ncurses, initializing "stdscr()".
    initscr();

    // Don't echo keypresses to screen.
    noecho();

    // Turn off the display of the cursor.
    curs_set(CURSOR_VISIBILITY::CURSOR_INVISIBLE);

    // Get the screen dimensions.
    let mut screen_height = 0;
    let mut screen_width = 0;
    getmaxyx(stdscr(), &mut screen_height, &mut screen_width);

    let d51: Vec<Vec<String>> = get_d51();
    let height = d51[0].len() as i32; // How tall is the D51?
    let mut row = screen_height - height; // Put the wheels at the bottom of the screen.
    let count_of_inner_vecs: usize = d51.len(); // How many animation cel frames in this image?
    let length: i32 = d51[0][0].len() as i32; // How long (width in screen columns/chars) is the train?
    let ms = Duration::from_millis(delay); // This is the "delay" converted to a format for the "sleep()" function below.
...

...
    let height = d51image_vecvec[0].len() as i32; // How tall is the D51image?
    let mut row = screen_height - height; // Put the wheels at the bottom of the screen.
    let count_of_inner_vecs: usize = d51image_vecvec.len(); // How many animation cel frames in this image?
    let length: i32 = d51image_vecvec[0][0].len() as i32; // How long (width in screen columns/chars) is the train?
    let ms = Duration::from_millis(delay); // This is the "delay" converted to a format for the "sleep()" function below.

    let mut current_inner_vec: usize = count_of_inner_vecs - 1; // Count down from highest-numbered frame; then repeat cycle.

    for col in ((-length)..screen_width).rev() {
        // Count down from right-edge until nose of train drags all of train off left-edge.
        let current_frame = &d51image_vecvec[current_inner_vec]; // Of the various inner_vecs, get the one we're drawing into its own variable.
        let mut line = row; // Keep "row" unaltered unless we're flying; use "line" within loop.
        for each_line in current_frame {
            my_mvaddstr(line, col, &each_line, screen_width, screen_height);
            line = line + 1;
        }
        refresh(); // Necessary to "bring to the forefront" the drawing we just did "in the back staging area".

        /* Pause so our eyes can see the frame. */
        thread::sleep(ms);

        if current_inner_vec > 0 {
            current_inner_vec = current_inner_vec - 1; // Prepare to display next frame.
        } else {
            // we've gotten down to last frame, so ...
            current_inner_vec = count_of_inner_vecs - 1; // ... start over.
            if fly {
                // And check to see if we're flying. If so...
                row -= 1; //... raise the next drawing one row up, and ...
                          // ... erase last (bottom) line drawn, using enough repeated spaces for train's length.
                line = row + height;
                my_mvaddstr(
                    line,
                    col,
                    &" ".repeat(length as usize),
                    screen_width,
                    screen_height,
                );
                // No need to refresh(); next frame will do it for us.
            }
        }
    }