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_KEYDOWN

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Samuel Gomes edited this page Nov 8, 2022 · 1 revision

The _KEYDOWN function returns whether modifying keys like CTRL, ALT, SHIFT, and any other keys are pressed.

Syntax

return% = _KEYDOWN(code&)

  • The return value is -1 if a specified key is pressed or 0 if it was not pressed. It can be used to monitor key combinations.
  • The POSITIVE LONG code value can be from any function key that needs to be monitored in a key press combination.
  • Unicode references:
      1. What is the glyph represented by that UNICODE value: Unicode Format Info
      1. Which fonts support the characters I want to use: Unicode Fonts
      1. What was the format again?: Unicode Formats
    • A UTF32 value is usually(but by no means always!) the same as a UTF16 value just with the top 2 bytes set to 0.
  • An important difference between INKEY$ and _KEYHIT is how they work when CTRL, ALT or SHIFT are used. INKEY$ returns a different code if you hold down CTRL, ALT or SHIFT before pressing F1 (for example). _KEYHIT will return the same code regardless of which modifiers were used but you can check _KEYDOWN to see which modifying keys are being used.
  • Keyboards with Alt Gr key: _KEYHIT may return both Alt(100307) and Ctrl(100306) codes when key is pressed or released.
  • Linux with foreign keyboards: SHELL _HIDE "setxkbmap us" will setup a keyboard to read US Scancodes.

                       **The QB64 Virtual Key constant values used: **

         **0-255**: [ASCII](ASCII) values (Refer to [http://en.wikipedia.org/wiki/Code_page_437 CP437])

         **256-65535**: [ASCII](ASCII) character codes (unaffected by SHIFT/ALT/CTRL modifiers)
                  Use [CVI](CVI) to convert ASCII 2-byte codes to _KEYDOWN values.

'                                **_KEYDOWN Keyboard Values**
'
**'Esc  F1    F2    F3    F4    F5    F6    F7    F8    F9    F10   F11   F12   Sys  ScL Pause**                  
' 27 15104 15360 15616 15872 16128 16384 16640 16896 17152 17408 34048 34304 +316 +302 +019
**'`~  1!  2@  3#  4$  5%  6^  7&  8*  9(  0) -_ =+ BkSp   Ins   Hme   PUp   NumL   /     *    -** 
'126 33  64  35  36  37  94  38  42  40  41 95 43   8   20992 18176 18688 +300   47    42   45
** 96 49  50  51  52  53  54  55  56  57  48 45 61*
**'Tab Q   W   E   R   T   Y   U   I   O   P  [{  ]}  \|   Del   End   PDn   7Hme  8/▲   9PU   + **
' 9  81  87  69  82  84  89  85  73  79  80 123 125 124 21248 20224 20736 18176 18432 18688 43
**   113 119 101 114 116 121 117 105 111 112  91  93  92                    55    56    57 *
**'CapL   A   S   D   F   G   H   J   K   L   ;:  '" Enter                   4/◄-   5    6/-►  
'+301  65  83  68  70  71  72  74  75  76  58  34  13                     19200 19456 19712  **E**
**      97 115 100 102 103 104 106 107 108  59  39                          52    53    54 *   **n**                                    
**'Shift   Z   X   C   V   B   N   M   ,<  .>  /?    Shift       ▲           1End  2/▼   3PD   t**
'+304   90  88  67  86  66  78  77  60  62  63    +303       18432        20224 20480 20736  **e**
**      122 120  99 118  98 110 109  44  46  47                             49    50    51 *   **r**
**'Ctrl   Win  Alt     Spacebar      Alt  Win  Menu  Ctrl   ◄-   ▼   -►      0Ins        .Del **
'+306  +311 +308       32         +307 +312 +319  +305 19200 20480 19712  20992       21248 13 
'                                                                     *     48          46*
'
'     **    Lower value = LCase/NumLock On __________________ + = add 100000 **



         **65536-&H40000000: QB64-specific Virtual Key codes:**

                        CONST KEY_PAUSE& = 100019
                        CONST KEY_NUMLOCK& = 100300
                        CONST KEY_CAPSLOCK& = 100301
                        CONST KEY_SCROLLOCK& = 100302
                        CONST KEY_RSHIFT& = 100303
                        CONST KEY_LSHIFT& = 100304
                        CONST KEY_RCTRL& = 100305
                        CONST KEY_LCTRL& = 100306
                        CONST KEY_RALT& = 100307
                        CONST KEY_LALT& = 100308
                        CONST KEY_RMETA& = 100309 'Left 'Apple' key (MacOSX)
                        CONST KEY_LMETA& = 100310 'Right 'Apple' key (MacOSX)
                        CONST KEY_LSUPER& = 100311 'Left "Windows" key
                        CONST KEY_RSUPER& = 100312 'Right "Windows"key
                        CONST KEY_MODE& = 100313 '"AltGr" key
                        CONST KEY_COMPOSE& = 100314
                        CONST KEY_HELP& = 100315
                        CONST KEY_PRINT& = 100316
                        CONST KEY_SYSREQ& = 100317
                        CONST KEY_BREAK& = 100318
                        CONST KEY_MENU& = 100319
                        CONST KEY_POWER& = 100320
                        CONST KEY_EURO& = 100321
                        CONST KEY_UNDO& = 100322 
                        CONST KEY_KP0& = 100256
                        CONST KEY_KP1& = 100257
                        CONST KEY_KP2& = 100258
                        CONST KEY_KP3& = 100259
                        CONST KEY_KP4& = 100260
                        CONST KEY_KP5& = 100261
                        CONST KEY_KP6& = 100262
                        CONST KEY_KP7& = 100263
                        CONST KEY_KP8& = 100264
                        CONST KEY_KP9& = 100265
                        CONST KEY_KP_PERIOD& = 100266
                        CONST KEY_KP_DIVIDE& = 100267
                        CONST KEY_KP_MULTIPLY& = 100268
                        CONST KEY_KP_MINUS& = 100269
                        CONST KEY_KP_PLUS& = 100270
                        CONST KEY_KP_ENTER& = 100271
                        CONST KEY_KP_INSERT& = 200000
                        CONST KEY_KP_END& = 200001
                        CONST KEY_KP_DOWN& = 200002
                        CONST KEY_KP_PAGE_DOWN& = 200003
                        CONST KEY_KP_LEFT& = 200004
                        CONST KEY_KP_MIDDLE& = 200005
                        CONST KEY_KP_RIGHT& = 200006
                        CONST KEY_KP_HOME& = 200007
                        CONST KEY_KP_UP& = 200008
                        CONST KEY_KP_PAGE_UP& = 200009
                        CONST KEY_KP_DELETE& = 200010
                        CONST KEY_SCROLL_LOCK_MODE& = 200011
                        CONST KEY_INSERT_MODE& = 200012

         **&H40000000 up**: [Unicode](Unicode) using the **cyberbit.ttf** font when available.

              **Use [_KEYHIT](_KEYHIT) to find the key codes to be monitored by _KEYDOWN! **

Comparing the _KEYDOWN returns using CONST values with 2 byte INKEY$ returns.

CONST RSHIFT& = 100303
CONST LSHIFT& = 100304
DO
    x = _KEYHIT
    IF x = CVI(CHR$(0) + CHR$(59)) THEN
        IF _KEYDOWN(LSHIFT&) OR _KEYDOWN(RSHIFT&) THEN
            PRINT "KEYHIT: SHIFT + F1"
        ELSE
            PRINT "KEYHIT: F1"
        END IF
    END IF
    k$ = INKEY$         'compare key press return values
    IF k$ = CHR$(0) + CHR$(59) THEN PRINT "INKEY$: F1"
    IF k$ = CHR$(0) + CHR$(84) THEN PRINT "INKEY$: SHIFT+F1"
LOOP UNTIL k$ = CHR$(27)     'escape key exit

How to calculate the _KEYDOWN codes of the 2 byte INKEY$ arrow key codes using CVI.

SCREEN 12 

x = 320: y = 240
col = _RGB(255, 0, 0)
radius = 20

DO
    CLS
    LOCATE 1, 1: PRINT "Use the arrow keys to move the circle."
    CIRCLE (x, y), radius, col
    PAINT (x, y), col    

    IF _KEYDOWN(CVI(CHR$(0) + "P")) THEN y = y + 1   '_KEYDOWN(20480)
    IF _KEYDOWN(CVI(CHR$(0) + "H")) THEN y = y - 1   '_KEYDOWN(18432)
    IF _KEYDOWN(CVI(CHR$(0) + "K")) THEN x = x - 1   '_KEYDOWN(19200)
    IF _KEYDOWN(CVI(CHR$(0) + "M")) THEN x = x + 1   '_KEYDOWN(19712)

    _DISPLAY
    _LIMIT 100 'limit to 100 frames per second
LOOP

Explanation: When CVI is used with a 2 byte code, the code of the first character(0) is added to the second character code which is multiplied by 256. In the example, code zero is added to the ASCII code of "P" which is 80. CVI multiplies 80 * 256 = 20480.

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