Test for keypress

[Neil]

Is there a way of testing if a key has been pressed without having to wait for it.

[Tedd]

GetKeyState -- http://msdn.microsoft.com/en-us/library/ms646301.aspx

[Neil]

Thanks for the link Tedd.
I've had a look at it & from what I understand is that all I've got to do is call that API & test the Hi bit of eax. If it's set then get that key from the buffer & act on it, correct me if I'm wrong.

[jj2007]

GetKeystate is typically used in combination with a WM_KEYDOWN message to check whether Shift or Control are pressed.

>test the Hi bit of eax

Watch your step. It's actually the high bit of ax...

[Neil]

Thanks for the info jj2007

[hutch--]

Neil,

I use this type of code for processing hotkeys in the message loop with a WM_KEYUP message.

Code Select Expand


            invoke GetAsyncKeyState,VK_CONTROL
            rol eax, 16
            cmp ax, 1111111111111111b
            jne hkout


Tell us this much, are you talking about a console app or a GUI app ?

[Tedd]

I've had a look at it & from what I understand is that all I've got to do is call that API & test the Hi bit of eax. If it's set then get that key from the buffer & act on it, correct me if I'm wrong.

Call the function when you want to check whether the key has been pressed, then test the high bit of eax.
You don't really need to 'get' the key, since you already know it was pressed (since you're the one checking it); any extra keypress messages will be eaten by DefaultWindowProc.

There's a compatibility issue - as jj says, test the high bit of ax. It's a rewritten 16-bit function, so the return value used to be a short, meaning it 'was' the high bit of ax, but now the correct one is the high bit of eax. But, all high bits get set for this reason - so either will work.

GetAsyncKeyState is for checking whether the key is down 'right now.'

[jj2007]

I use this type of code for processing hotkeys in the message loop with a WM_KEYUP message.

Code Select Expand


            invoke GetAsyncKeyState,VK_CONTROL
            rol eax, 16
            cmp ax, 1111111111111111b
            jne hkout


Win32hlp: If the most significant bit is set, the key is down, and if the least significant bit is set, the key was pressed after the previous call to GetAsyncKeyState. The return value is zero if a window in another thread or process currently has the keyboard focus.

"return value is zero" is imho a bit misleading, because the classic use of GetAsyncKeyState is to check whether in the active thread, not your own thread, somebody has pressed a key.

There's a compatibility issue - as jj says, test the high bit of ax. It's a rewritten 16-bit function, so the return value used to be a short, meaning it 'was' the high bit of ax, but now the correct one is the high bit of eax. But, all high bits get set for this reason - so either will work.

MSDN: SHORT GetAsyncKeyState...  :wink

[Tedd]

SHORT GetAsyncKeyState...  :wink

The documentation wasn't updated so attentively, luckily the code was - if in doubt, test it :P

[PBrennick]

Hutch and I have been working on our editors for a long time so we can assure you that his method is sound. The only difference I would suggest is that the test should be only done when the transitional state is 'UP'. For example:

Code Select Expand


    .if msg.message == WM_KEYDOWN   ; Was a key pressed?
      .if msg.wParam == VK_ESCAPE   ; Escape key?
      .endif
    .endif
    .if msg.message == WM_KEYUP
    ; Function keys should be processed here
      .if msg.wParam == VK_F3

      .elseif msg.wParam == VK_F4

      .elseif msg.wParam == VK_F5

      .endif
      invoke  GetAsyncKeyState, VK_CONTROL
      rol     eax, 16
      cmp     ax, 1111111111111111b
      jne     ProcessMessage ; Enter the message loop

      .if msg.wParam == 46h             ; Ctrl + F
        ; Take action on this hotkey
      .endif
      ; ...more of the same

    .endif


Works like a charm. Take close note on the difference between a function key and a control key sequence.

hth,
-- Pal

[Neil]

hutch, I'm using it in a console app.

I've read the other replies & I still haven't got my head around it yet, but I'm working on it.

Basically what I'm trying to do is run a loop & each pass through I want to know if one of either 2 keys has been pressed, one to break out of the loop i.e, cancel it & the other to run some more code which either breaks out of the loop if some condition is met or if not loop again. I achieved this in my DOS days by checking if a key was in the keyboard buffer at bottom of memory, but obviously I need another method now.

[hutch--]

Neil,

The stuff above is for a normal GUI app, console is another planet. If you are just after the functionality, have a look at the two macros "inkey" and "getkey" which both use the MSVCRT library to provide the functionality. Greg Lyon wrote both of these are they have been very reliable.

[Tedd]

Code Select Expand


invoke GetKeyState, VK_CONTROL    ;or whichever key you want to check
test eax,80000000h
jz @F

;key was pressed - do whatever

@@:


It doesn't need to be done in response to WM_KEYDOWN/UP - so it should work for a console window too (not that I can test this right now :bdg)

[Neil]

Thanks hutch,

I'm familiar with the macros & both wait for a keypress which is not what I want.

Tedd that looks promising

[Neil]

Tedd,

Tested that piece of code & it appears to work O.K.  Got to do some more testing before I'm completely sure.