In this challenging homework, we will learn how to use arrays and for loops by implementing a text input field.

A text input field allows a user to type a message inside of a computer program. You've used these things your whole life, but probably haven't given them much thought.

Let's change that. 🙂👍

• Try playing around with one of the search bars on this web page.
  • What happens when you...
    • press the B key on your keyboard?
    • press SHIFT + B?
    • press the LEFT_ARROW_KEY?
    • press the RIGHT_ARROW_KEY?
    • press BACKSPACE?
    • press COMMAND + A (or CONTROL + A on Windows)?
    • press the left mouse button?
    • hold the mouse and drag?
    • press B while some text is highlighted?
    • press BACKSPACE while some text is highlighted?
    • double-click?

We need to store a sequence of characters that we'll be changing a lot.

We will use an array, specifically an array of characters (char[]).

• We can cast variables from one type to another
  • The syntax (Bar)(foo) "cast foo to type Bar"
  • NOTE: Casting is a "special tactic" in modern Java; we will only ever use it on this lab (and even then, probably only once)

• char's are integers (but they are NOT int's)
• We can use a cast to find a char's "integer equivalent"
  • (int)('A') is 65
  • (int)('0') is 48
• NOTE: The char's are "in order"
  • (int)('A') is 65
  • (int)('B') is 66
  • (int)('C') is 67
  • ...
  • (int)('a') is 97
  • (int)('b') is 98
  • (int)('c') is 99
  • ...
• We can add char's and subtract char's

  int i = ('B' - 'A'); // 1
  
  // NOTE: We needed to "cast to a char" because, in Java, a char plus an int is an int
  char c = (char) ('c' + i); // 'd'
  
  ++c; // 'e'

• char[] buffer; stores the user's message as an array of characters
  • buffer can store a message of length at most buffer.length
• int length; is the length of the current message stored in buffer
  • if (length == 0) then message is empty
  • if (length == buffer.length) then the message completely fills the buffer
• int cursor; is the current cursor position
  • 0 means all the way to the left
  • 1 means in between buffer[0] and buffer[1]

• the left side of the canvas is $x = 0.0$
• the right side of the canvas is $x = \texttt{buffer.length}$
• we are using a monospaced font; this means each character is the same width;
  • for simplicity, we have each character be $1.0$ unit wide
  • buffer[0] is drawn from $x = 0.0$ to $x = 1.0$
  • cursor should be drawn at $x = \texttt{cursor}$
• example
  • here is the message COW written in a monospaced font
    • cursor is 3
    • buffer.length is 4

    #####   #####   #   # |
    #       #   #   #   # |
    #       #   #   # # # |
    #####   #####    # #  |
  0       1       2       3       4   -> x
  

• the bottom of the canvas is $y = -1.0$ and the top is $y = 2.0$

• All features must match the behavior of a typical text input field
  • For example, pressing BACKSPACE should turn CO|W (length 3) into C|W (length 2); NOTE: the | is the cursor
  • You are responsible for discovering what the correct behavior of all commands is by experimenting with a real-world text input field

• A-

  • User can press A-Z (any of the keys A, B, ...)
  • User can press 0-9
  • User can press SHIFT + A, SHIFT + B ...
  • Draw the cursor bar (location of cursor as a vertical line)
  • User can press the space bar
    • HINT: this is the character ' '
  • User can press LEFT_ARROW
  • User can press RIGHT_ARROW
  • User can press BACKSPACE

• A

  • Make the cursor bar blink
    • NOTE: you will want to introduce a frame or time variable to keep track of the current frame / time
  • Click the mouse to move cursor to the closest int
  • If the user presses ENTER while the buffer contains Passw0rd, replace the contents of the buffer with accepted
    • HINT: some repetition here is OK

• A+

  • Click and drag the mouse to select/highlight a sequence of characters
    • HINT: int select = 0;
    • NOTE: pressing BACKSPACE while characters are selected must do the right thing
    • NOTE: pressing A, B, ... should also do the right thing
  • Double-click the mouse to select all characters
  • Press COMMAND + A or CONTROL + A to select all characters
    • NOTE: we want our app to be "cross platform" (work on both Mac and Windows)

• A++

  • Build a full raw text editor like TextEdit/Notepad

• You may NOT use any fancy Java standard library functions; stick to basic for loops, if statements, and the functions inside Cow.java
• You may NOT use the Java String class anywhere.
• You may NOT create any new arrays (just modify the contents of buffer)
• You may NOT use excessive repetition (for example, don't use separate if statements for c == 'A', c == 'B', c == 'C', ...)
• You may NOT have any out of bounds errors

class HW02 extends Cow {
    public static void main(String[] arguments) {

        char[] buffer = new char[8];
        int length = 0;
        int cursor = 0;

        canvasConfig(0.0, -1.0, buffer.length, 2.0, WHITE, 512);
        while (beginFrame()) {

            // TODO

            HW02_drawText(buffer, length, BLACK);
        }
    }
}

for (char c = 'A'; c <= 'Z'; ++c) { ... }

(char)('a' + (c - 'A'))