How to extract correctly cased CharCode from WM_KeyUp or whereever

Question

I'm trying to process WM_KeyUp messages to identify which alphanumeric key (if any) was pressed, in a case-sensitive manner. In TApplicationEvents we have the OnMessage handler which in my project is assigned to

procedure TForm1.DoOnAppMessage(var Msg: tagMSG; var Handled: Boolean);
var
  CH : Char;
  [...]
begin
  Inc(MsgCount);

  case Msg.Message of
    WM_KeyUp : begin
      CH := Chr(Msg.WParam);
      // do something with CH
    end;

  end; { case ]

That's fine, so far as it goes, except of course that I always get the upper case version of the letter.

So I evidently need to decode the Msg's LParam instead. Googling around, I've come across numerous examples of decoding the LParam, but none I can find deals with what I would have thought would be the "simple" task of getting alphanumeric keys rendered in the correct case. My q is, please could someone show me how to do that.

Please note: I know I could get the correctly capitalised letters by handling the WM_Char message but I can't use that in the real-life situation I'm trying to deal with (which is actually inside a keyboard hook).

Answer 1

I found a solution to this based on an earlier SO q&a, which involves setting up a low-level keyboard hook. Initially when I tried this I got the same results as with the code posted in my q, namely that all the returned characters were lower-cased.

Interestingly, the thing which made the difference between no capitalisation and correct capitalisation - which the code below does - was one of the 4 lines containing calls to GetKeyState, namely KeyState[VK_SHIFT] := GetKeyState(VK_SHIFT). Without that, the characters returned were all lower-case (unlike the ones from the code in my q, which were all upper case);

type
  TOutProc = procedure(AString : String) of object;
var
  OutProc : TOutProc; // requires assignment to a suitable proc in the host application

type
  PKbdLlHookStruct = ^TKbdLlHookStruct;

  TKbdLlHookStruct = packed record
    vkCode: DWORD;
    scanCode: DWORD;
    flags: DWORD;
    time: DWORD;
    dwExtraInfo: DWORD;
  end;

const
  WH_KEYBOARD_LL   =   13;

var
  FKeyboardLayoutHandle: HKL;
  hhkLowLevelKybd:   HHOOK;

function LowLevelKeyBoardProc(nCode:   Integer;   awParam:   WPARAM;
  alParam:   LPARAM):   LRESULT;   stdcall;
const
  LLKHF_UP             =  $0080;
var
  act:   PKbdllHookStruct;
  CH : Char;
  S : String;
  KeyState : TKeyboardState;
  NewChar: array[0..1] of Char;
begin

  //  adapted from https://stackoverflow.com/q/1590983
  if (nCode = HC_ACTION) then begin
    case awParam  of
      WM_SYSKEYDOWN,
      WM_KEYUP,
      WM_SYSKEYUP: begin
        act := PKbdLlHookStruct(alParam);
        if awParam=WM_KEYUP then begin
          FillChar(NewChar,2,#0);
          GetKeyboardState(KeyState);
          //  Next four lines from https://stackoverflow.com/a/10480563
          KeyState[VK_CAPITAL] := GetKeyState(VK_CAPITAL);
          KeyState[VK_SHIFT] := GetKeyState(VK_SHIFT);
          KeyState[VK_CONTROL] := GetKeyState(VK_CONTROL);
          KeyState[VK_MENU] := GetKeyState(VK_MENU);

          if ToAsciiEx(act^.vkCode, act^.scanCode, KeyState, NewChar, 0, FKeyboardLayoutHandle) = 1 then
          CH := NewChar[0];
          if (CH in [#8, #10, #13]) Or (CH >= ' ') then begin
            S := CH;
            OutProc(S);
            GetClassName(GetForegroundWindow, @ClassBuffer, 100);
          end;
        end;
      end; { case }
    end;  { case }
  end;

  Result := CallNextHookEx(hhkLowLevelKybd, nCode, awParam, alParam);
end;