参考：https://learn.microsoft.com/en-us/windows/win32/inputdev/about-keyboard-input
Character Messages
键盘敲击消息(keystroke message)并不提供字符按键的字符码。为了获取字符码，应用需要在其消息循环中调用函数TranlateMessage。此函数会发送WM_KEYDOWN或者WM_SYSKEYDOWN消息到键盘布局(keyboard layout). 键盘布局会检测消息中的虚拟键码，如果虚拟键码对应字符键，键盘布局会发送字符消息(character message)到消息队列的队头，此字符消息中会包含字符码。在消息循环的下一个循环中，会对此消息进行处理。
Nonsystem Character Messages
窗口过程函数(window procedure)可收到如下消息：WM_CHAR、WM_DEADCHAR、WM_SYSCHAR、WM_SYSDEADCHAR、WM_UNICHAR。TranslateMessage函数在处理WM_KEYDOWN消息时会生成WM_CHAR或者WM_DEADCHAR消息。同样在处理里WM_SYSKEYDOWN时会生成WM_SYSCHAR或者WM_SYSDEADCHAR消息。
应用程序在处理键盘输入时，通常只是会处理WM_CHAR或者WM_UNICHAR消息，而将其它所有消息交给DefWindowProc函数进行处理。WM_CHAR使用的是UTF-16或者ANSI字符集，而WM_UNICHAR则总是使用UTF-32。系统使用WM_SYSCHAR或者WM_SYSDEADCHAR来实现菜单助记符的功能。
字符消息的wParam成员中包含被按下字符键的字符码。字符码的值是什么取决于收到消息的窗口所属的窗口类。如果窗口类是使用 Unicode版本的RegisterClass函数进行注册的，那么系统为所有使用此类的窗口提供Unicode字符集，否则提供ANSI字符集。lParam成员的数据与生成字符消息之前一样。
Using Keyboard Input
窗口收到键盘的输入是以键盘敲击消息(keystroke message)或者字符消息(character message)的形式。与窗口相关的消息循环必须将键盘敲击消息转换为相应的字符消息。
Processing KeyStroke Messages
当用户敲击键盘时，拥有keyboard focus属性的窗口的window procedure会获取到键盘敲击消息。这些键盘敲击消息有：WM_KEYDOWN、WM_KEYUP、WM_SYSKEYDOWN、WM_SYSKEYUP。通常window procedure只会处理WM_KEYDOWN而忽略掉其它的键盘敲击消息。WM_KEYDOWN消息是当用户敲击按键时，由系统对其进行post操作。
当window procedure获取到WM_KEYDOWN消息时，它需要查看消息中的virtual-key code ,并依此code来确定如何处理此消息。virtual-key code 是存放在消息的wPrarm成员中的。通常，应用只处理由非字符按键产生的WM_KEYDOWN消息。这些消息包括功能键、光标移动按键、和特殊用途的按键，如 INS、DEL、HOME 和END。
Translating Character Messages
任何需要从用户获取字符输入的线程必须在消息循环中使用TranslateMessage函数。此函数检测keystroke message 中的virtual-key code,如果此code对应字符，则此函数会将一个字符消息放入消息队列。
Processing Character Messages
字符消息包括WM_CHAR、WM_DEADCHAR、WMSYSCHAR、WM_SYSDEADCHAR。通常，window procedure只会处理WM_CHAR而忽略其它字符消息。当用户按下任何下列按键时， TranslateMessage函数都会生成WM_CHAR消息。
- Any character key
- BACKSPACE
- ENTER(carriage return)
- ESC
- SHIFT+ENTER(linefeed)
- TAB
character code包含在消息的wParam中。
#define BUFSIZE 65535
#define SHIFTED 0x8000
LONG APIENTRY MainWndProc(HWND hwndMain, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
HDC hdc; // handle to device context
TEXTMETRIC tm; // structure for text metrics
static DWORD dwCharX; // average width of characters
static DWORD dwCharY; // height of characters
static DWORD dwClientX; // width of client area
static DWORD dwClientY; // height of client area
static DWORD dwLineLen; // line length
static DWORD dwLines; // text lines in client area
static int nCaretPosX = 0; // horizontal position of caret
static int nCaretPosY = 0; // vertical position of caret
static int nCharWidth = 0; // width of a character
static int cch = 0; // characters in buffer
static int nCurChar = 0; // index of current character
static PTCHAR pchInputBuf; // input buffer
int i, j; // loop counters
int cCR = 0; // count of carriage returns
int nCRIndex = 0; // index of last carriage return
int nVirtKey; // virtual-key code
TCHAR szBuf[128]; // temporary buffer
TCHAR ch; // current character
PAINTSTRUCT ps; // required by BeginPaint
RECT rc; // output rectangle for DrawText
SIZE sz; // string dimensions
COLORREF crPrevText; // previous text color
COLORREF crPrevBk; // previous background color
size_t * pcch;
HRESULT hResult;
switch (uMsg)
{
case WM_CREATE:
// Get the metrics of the current font.
hdc = GetDC(hwndMain);
GetTextMetrics(hdc, &tm);
ReleaseDC(hwndMain, hdc);
// Save the average character width and height.
dwCharX = tm.tmAveCharWidth;
dwCharY = tm.tmHeight;
// Allocate a buffer to store keyboard input.
pchInputBuf = (LPTSTR) GlobalAlloc(GPTR,
BUFSIZE * sizeof(TCHAR));
return 0;
case WM_SIZE:
// Save the new width and height of the client area.
dwClientX = LOWORD(lParam);
dwClientY = HIWORD(lParam);
// Calculate the maximum width of a line and the
// maximum number of lines in the client area.
dwLineLen = dwClientX - dwCharX;
dwLines = dwClientY / dwCharY;
break;
case WM_SETFOCUS:
// Create, position, and display the caret when the
// window receives the keyboard focus.
CreateCaret(hwndMain, (HBITMAP) 1, 0, dwCharY);
SetCaretPos(nCaretPosX, nCaretPosY * dwCharY);
ShowCaret(hwndMain);
break;
case WM_KILLFOCUS:
// Hide and destroy the caret when the window loses the
// keyboard focus.
HideCaret(hwndMain);
DestroyCaret();
break;
case WM_CHAR:
// check if current location is close enough to the
// end of the buffer that a buffer overflow may
// occur. If so, add null and display contents.
if (cch > BUFSIZE-5)
{
pchInputBuf[cch] = 0x00;
SendMessage(hwndMain, WM_PAINT, 0, 0);
}
switch (wParam)
{
case 0x08: // backspace
case 0x0A: // linefeed
case 0x1B: // escape
MessageBeep((UINT) -1);
return 0;
case 0x09: // tab
// Convert tabs to four consecutive spaces.
for (i = 0; i < 4; i++)
SendMessage(hwndMain, WM_CHAR, 0x20, 0);
return 0;
case 0x0D: // carriage return
// Record the carriage return and position the
// caret at the beginning of the new line.
pchInputBuf[cch++] = 0x0D;
nCaretPosX = 0;
nCaretPosY += 1;
break;
default: // displayable character
ch = (TCHAR) wParam;
HideCaret(hwndMain);
// Retrieve the character's width and output
// the character.
hdc = GetDC(hwndMain);
GetCharWidth32(hdc, (UINT) wParam, (UINT) wParam,
&nCharWidth);
TextOut(hdc, nCaretPosX, nCaretPosY * dwCharY,
&ch, 1);
ReleaseDC(hwndMain, hdc);
// Store the character in the buffer.
pchInputBuf[cch++] = ch;
// Calculate the new horizontal position of the
// caret. If the position exceeds the maximum,
// insert a carriage return and move the caret
// to the beginning of the next line.
nCaretPosX += nCharWidth;
if ((DWORD) nCaretPosX > dwLineLen)
{
nCaretPosX = 0;
pchInputBuf[cch++] = 0x0D;
++nCaretPosY;
}
nCurChar = cch;
ShowCaret(hwndMain);
break;
}
SetCaretPos(nCaretPosX, nCaretPosY * dwCharY);
break;
case WM_KEYDOWN:
switch (wParam)
{
case VK_LEFT: // LEFT ARROW
// The caret can move only to the beginning of
// the current line.
if (nCaretPosX > 0)
{
HideCaret(hwndMain);
// Retrieve the character to the left of
// the caret, calculate the character's
// width, then subtract the width from the
// current horizontal position of the caret
// to obtain the new position.
ch = pchInputBuf[--nCurChar];
hdc = GetDC(hwndMain);
GetCharWidth32(hdc, ch, ch, &nCharWidth);
ReleaseDC(hwndMain, hdc);
nCaretPosX = max(nCaretPosX - nCharWidth,
0);
ShowCaret(hwndMain);
}
break;
case VK_RIGHT: // RIGHT ARROW
// Caret moves to the right or, when a carriage
// return is encountered, to the beginning of
// the next line.
if (nCurChar < cch)
{
HideCaret(hwndMain);
// Retrieve the character to the right of
// the caret. If it's a carriage return,
// position the caret at the beginning of
// the next line.
ch = pchInputBuf[nCurChar];
if (ch == 0x0D)
{
nCaretPosX = 0;
nCaretPosY++;
}
// If the character isn't a carriage
// return, check to see whether the SHIFT
// key is down. If it is, invert the text
// colors and output the character.
else
{
hdc = GetDC(hwndMain);
nVirtKey = GetKeyState(VK_SHIFT);
if (nVirtKey & SHIFTED)
{
crPrevText = SetTextColor(hdc,
RGB(255, 255, 255));
crPrevBk = SetBkColor(hdc,
RGB(0,0,0));
TextOut(hdc, nCaretPosX,
nCaretPosY * dwCharY,
&ch, 1);
SetTextColor(hdc, crPrevText);
SetBkColor(hdc, crPrevBk);
}
// Get the width of the character and
// calculate the new horizontal
// position of the caret.
GetCharWidth32(hdc, ch, ch, &nCharWidth);
ReleaseDC(hwndMain, hdc);
nCaretPosX = nCaretPosX + nCharWidth;
}
nCurChar++;
ShowCaret(hwndMain);
break;
}
break;
case VK_UP: // UP ARROW
case VK_DOWN: // DOWN ARROW
MessageBeep((UINT) -1);
return 0;
case VK_HOME: // HOME
// Set the caret's position to the upper left
// corner of the client area.
nCaretPosX = nCaretPosY = 0;
nCurChar = 0;
break;
case VK_END: // END
// Move the caret to the end of the text.
for (i=0; i < cch; i++)
{
// Count the carriage returns and save the
// index of the last one.
if (pchInputBuf[i] == 0x0D)
{
cCR++;
nCRIndex = i + 1;
}
}
nCaretPosY = cCR;
// Copy all text between the last carriage
// return and the end of the keyboard input
// buffer to a temporary buffer.
for (i = nCRIndex, j = 0; i < cch; i++, j++)
szBuf[j] = pchInputBuf[i];
szBuf[j] = TEXT('\0');
// Retrieve the text extent and use it
// to set the horizontal position of the
// caret.
hdc = GetDC(hwndMain);
hResult = StringCchLength(szBuf, 128, pcch);
if (FAILED(hResult))
{
// TODO: write error handler
}
GetTextExtentPoint32(hdc, szBuf, *pcch,
&sz);
nCaretPosX = sz.cx;
ReleaseDC(hwndMain, hdc);
nCurChar = cch;
break;
default:
break;
}
SetCaretPos(nCaretPosX, nCaretPosY * dwCharY);
break;
case WM_PAINT:
if (cch == 0) // nothing in input buffer
break;
hdc = BeginPaint(hwndMain, &ps);
HideCaret(hwndMain);
// Set the clipping rectangle, and then draw the text
// into it.
SetRect(&rc, 0, 0, dwLineLen, dwClientY);
DrawText(hdc, pchInputBuf, -1, &rc, DT_LEFT);
ShowCaret(hwndMain);
EndPaint(hwndMain, &ps);
break;
// Process other messages.
case WM_DESTROY:
PostQuitMessage(0);
// Free the input buffer.
GlobalFree((HGLOBAL) pchInputBuf);
UnregisterHotKey(hwndMain, 0xAAAA);
break;
default:
return DefWindowProc(hwndMain, uMsg, wParam, lParam);
}
return NULL;
}
