input_keydown

#Input.KeyDown

##Syntax Input.KeyDown (var chars : array char of boolean)

##Description The Input.Keydown procedure allows a program to read which keys are currently being pressed. This procedure is different from getch in that it allows a program to detect when a user presses and releases a button. As such, it is not to be used in conjunction with getch.

The procedure can be used in games where an action takes place while a key is depressed.

##Example Determine if the T key is pressed. Note that we check for the lower case letter.

    var chars : array char of boolean
    Input.KeyDown (chars)
    if chars ('t') then
        put "The T key is pressed"
    end if

##Details The array returned is a list of all the characters. A key is currently pressed if the array element with the corresponding character is true. For example, the a key is pressed is chars ('a') is true. Note that each key is individually represented, so if the user has pressed Shift+a to get a 'A', then Input.KeyDown would register Shift and 'a' as pressed, but not 'A'.

A full list of all the possible characters that can be set with Input.KeyDown can be found in the Key Codes appendix.

##Details The array returned is a list of all the characters. A key is currently pressed if the array element with the corresponding character is true. For example, the a key is pressed is chars ('a') is true. Note that each key is individually represented, so if the user has pressed Shift+a to get a 'A', then Input.KeyDown would register Shift and 'a' as pressed, but not 'A'.

##Details The number of keys that can be pressed simultaneously is hardware dependent. Most keyboards can detect a minimum of two keys + Shift + Control + Alt. This means that if you are designing a two player game to be played at a single keyboard and you wish to make certain that players cannot �hog the keyboard� by holding down keys, you should not use more than 6 different keys and three of them should be the Shift, Control and Alt keys.

##Example The program reads the keyboard and displays a message while the arrow keys are pressed. It can detect up to all four arrow keys pressed at once.

    var chars : array char of boolean
    loop
        Input.KeyDown (chars)
        locate (1, 1)
        if chars (KEY_UP_ARROW) then
            put "Up Arrow Pressed  " ..
        else
            put "                  " ..
        end if
        if chars (KEY_RIGHT_ARROW) then
            put "Right Arrow Pressed  " ..
        else
            put "                     " ..
        end if
        if chars (KEY_LEFT_ARROW) then
            put "Left Arrow Pressed  " ..
        else
            put "                    " ..
        end if
        if chars (KEY_DOWN_ARROW) then
            put "Down Arrow Pressed  " ..
        else
            put "                  " ..
        end if
    end loop

##Example Another example is available that checks for all possible keys.

##Status Exported qualified.

This means that you can only call the function by calling Input.KeyDown, not by calling KeyDown.