GetKeyState(VK_SHIFT)

[Pascal]

During startup of my program i would like to check the state of the SHIFT key (left or right)
to bypass some parts of the programm.

I used GetKeyState(VK_SHIFT) <> 0 to determine if one of the keys is pressed. But this
does not seem to be the right way to do it as this does not work reliable.

Any suggestions?

[balazsszekely]

Try this:

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormCreate(Sender: TObject);
2. var
3.   ShiftState: TShiftState;
4. begin
5.   ShiftState := GetKeyShiftState;
6.   if ssShift in ShiftState then
7.     //...
8.   else
9.     //...
10. end;

[Fungus]

I'm pretty sure you need to check the high order bit, like: (GetKeyState(VK_SHIFT) And $80) <> 0 in order to figure out if the key is pressed or not. The low order bit will toggle on/off for each keypress, so checking for non-zero is not reliable

[Pascal]

I'm pretty sure you need to check the high order bit, like: (GetKeyState(VK_SHIFT) And $80) <> 0 in order to figure out if the key is pressed or not. The low order bit will toggle on/off for each keypress, so checking for non-zero is not reliable

I found both implementations: with mask $8000 and without mask. Both do not work. Without mask i've never seen a value other than 0 or 1.
Toggling of bit 0 corresponds to my values seen during runtime.

[Pascal]

Try this:

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormCreate(Sender: TObject);
2. var
3.   ShiftState: TShiftState;
4. begin
5.   ShiftState := GetKeyShiftState;
6.   if ssShift in ShiftState then
7.     //...
8.   else
9.     //...
10. end;

Does not work, as GetKeyShiftState looks like this:

Code: Pascal  [Select][+][-]

1. function GetKeyShiftState: TShiftState;
2. begin
3.   Result := [];
4.   if (GetKeyState(VK_CONTROL) and $8000) <> 0 then
5.     Include(Result, ssCtrl);
6.   if (GetKeyState(VK_SHIFT) and $8000) <> 0 then
7.     Include(Result, ssShift);
8.   if (GetKeyState(VK_MENU) and $8000) <> 0 then
9.     Include(Result, ssAlt);
10.   if ((GetKeyState(VK_LWIN) and $8000) <> 0) or ((GetKeyState(VK_RWIN) and $8000) <> 0) then
11.     Include(Result, ssMeta);
12.   if (GetKeyState(VK_LWIN) < 0) or (GetKeyState(VK_RWIN) < 0) then
13.     Include(Result, ssMeta);
14. end;

GetKeyState(VK_SHIFT) never delivered any values other than 0 or 1 to me.

[Fungus]

Since GetKeyState return a one byte value (shortint) the bitmap $8000 must be invalid, so this must be a bug or a mistake.

Code: Pascal  [Select][+][-]

1. Function IsKeyDown(Const VirtualKeyCode: Integer): Boolean; Inline;
2. Begin
3.   Result:= (GetKeyState(VirtualKeyCode) And $80) <> 0;
4. End;

https://msdn.microsoft.com/en-us/library/windows/desktop/ms646301(v=vs.85).aspx

EDIT: Short or Shortint may be 2-bytes on 64bit systems, though. But on Linux Mint 64bit the method above works.

[rvk]

GetKeyState is defined as returning a Smallint in FPC/Windows.

Code: Pascal  [Select][+][-]

1. function GetKeyState(nVirtKey: Integer): Smallint; {$IFDEF IF_BASE_MEMBER}virtual;{$ENDIF}

And a SmallInt is 2 bytes:
http://freepascal.org/docs-html/ref/refsu5.html

"SHORTs are 16-bit integers"
Look at the data-definitions of SHORT from Microsoft:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa383751(v=vs.85).aspx

On my Windows machine the GetKeyShiftState with ShiftState works.

[Pascal]

Since GetKeyState return a one byte value (shortint) the bitmap $8000 must be invalid, so this must be a bug or a mistake.

Code: Pascal  [Select][+][-]

1. Function IsKeyDown(Const VirtualKeyCode: Integer): Boolean; Inline;
2. Begin
3.   Result:= (GetKeyState(VirtualKeyCode) And $80) <> 0;
4. End;

https://msdn.microsoft.com/en-us/library/windows/desktop/ms646301(v=vs.85).aspx

EDIT: Short or Shortint may be 2-bytes on 64bit systems, though. But on Linux Mint 64bit the method above works.

Here on Windows x64 SHORT = smallint = 2 byte.
But anyway i just tested the output of GetKeyState(VK_SHIFT) without mask, but i do not get any other value than 0 and 1 without any correlation to the real state of the shift key.

[Handoko]

I tested both GetMem and Fungus suggestions on Linux 64-bit.

Here is the result:
- Both won't work on TForm.OnCreate
- Both work correctly on TForm.OnActivate

[Pascal]

I tested both GetMem and Fungus suggestions on Linux 64-bit.

Here is the result:
- Both won't work on TForm.OnCreate
- Both work correctly on TForm.OnActivate

I have to use it in OnCreate / OnShow.
Both places do not work here.

[rvk]

Weird... You are on Windows? What Lazarus version do you have?
(O, I already see, latest trunk)

What do you get with the following?
A TTimer and TMemo on your form and this as TimerEvent:

Code: Pascal  [Select][+][-]

1. procedure TForm1.Timer1Timer(Sender: TObject);
2. begin
3.   Memo1.Lines.Add(IntToStr(GetKeyState(VK_SHIFT) and $8000));
4. end;

When holding shift I get 32768 and releasing it I get 0 in the Memo1.

[Handoko]

@Pascal
Try to start a new project, drop a TLabel and put this code below to see if it work or not.

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, StdCtrls, LCLIntf, LCLType;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     Label1: TLabel;
16.     procedure FormActivate(Sender: TObject);
17.   private
18.     { private declarations }
19.   public
20.     { public declarations }
21.   end;
22.  
23. var
24.   Form1: TForm1;
25.  
26. implementation
27.  
28. {$R *.lfm}
29.  
30. { TForm1 }
31.  
32. procedure TForm1.FormActivate(Sender: TObject);
33. begin
34.   if (GetKeyState(VK_SHIFT) And $80) <> 0 then
35.     Label1.Caption := 'It works!';
36. end;
37.  
38. end.

[Fungus]

Sorry, shortint / short is of course a signed word of 2 bytes

On a form drop a TEdit and a TButton, create an OnClick handler for the button and try this code:

Code: Pascal  [Select][+][-]

1. uses ..., LCLType, LCLIntf;
2.  
3. Function GetKeyMask(Key: Integer): String;
4. Var K, I: Smallint; //Changed from Shortint to Smallint
5. Begin
6.   K:= LCLIntf.GetKeyState(Key);
7.   Result:= '';
8.   For I:= 15 DownTo 0 Do
9.     If (K And (1 Shl I)) <> 0 Then Result:= Result + '1'
10.     Else Result:= Result + '0';
11. End;
12.  
13. procedure Button1Click(Sender: TObject);
14. begin
15.   Edit1.Text:= GetKeyMask(VK_SHIFT);
16. end;

I'm not 100% sure, but GetKeyState may be declared both in Windows and LCLIntf and this may be what's causing variation. Stick with the one in LCLIntf

On Linux Mint 64bit the output is "1111111110000001" when shift is down, and "0000000000000001" when it is up. The low order bit toggles for each key press registred and this seems to be the case for all keys, not only the ones who actually can toggle (like CAPS, NUMLOCK etc.). If this is a bug or a workaround, I do not know.

[rvk]

Sorry, shortint / short is of course a signed word of 2 bytes

Well, yes and no, and that's where the confusion is.
A Shortint in FPC is actually a signed byte.
But @Microsoft they are talking about SHORT and THAT is a 2 byte signed word.
In FPC that translates to a Smallint. Neat, huh

In Windows the GetKeyState does need to be masked with $8000 because they are talking about the high-bit of a SHORT.
But I noticed in GTK2 sources of FPC it is somehow masked(?) with 127 (so leaving the 128 ($80) for held down).
I think that's an incompatibility (or bug) between GTK and Windows implementation.

[Fungus]

@rvk: You are right about the short small stuff. I've changed the shortint to smallint in my previous example, output remains the same though. Probably because memory aligment expands a single byte type to 4/8 bytes