Using Mouse Input
This section covers tasks associated with mouse input.
- Tracking the Mouse Cursor
- Drawing Lines with the Mouse
- Processing a Double Click Message
- Selecting a Line of Text
- Using a Mouse Wheel in a Document with Embedded Objects
- Retrieving the Number of Mouse Wheel Scroll Lines
Tracking the Mouse Cursor
Applications often perform tasks that involve tracking the position of the mouse cursor. Most drawing applications, for example, track the position of the mouse cursor during drawing operations, allowing the user to draw in a window's client area by dragging the mouse. Word-processing applications also track the cursor, enabling the user to select a word or block of text by clicking and dragging the mouse.
Tracking the cursor typically involves processing the WM_LBUTTONDOWN, WM_MOUSEMOVE, and WM_LBUTTONUP messages. A window determines when to begin tracking the cursor by checking the cursor position provided in the lParam parameter of the WM_LBUTTONDOWN message. For example, a word-processing application would begin tracking the cursor only if the WM_LBUTTONDOWN message occurred while the cursor was on a line of text, but not if it was past the end of the document.
A window tracks the position of the cursor by processing the stream of WM_MOUSEMOVE messages posted to the window as the mouse moves. Processing the WM_MOUSEMOVE message typically involves a repetitive painting or drawing operation in the client area. For example, a drawing application might redraw a line repeatedly as the mouse moves. A window uses the WM_LBUTTONUP message as a signal to stop tracking the cursor.
In addition, an application can call the TrackMouseEvent function to have the system send other messages that are useful for tracking the cursor. The system posts the WM_MOUSEHOVER message when the cursor hovers over the client area for a certain time period. It posts the WM_MOUSELEAVE message when the cursor leaves the client area. The WM_NCMOUSEHOVER and WM_NCMOUSELEAVE messages are the corresponding messages for the nonclient areas.
Drawing Lines with the Mouse
The example in this section demonstrates how to track the mouse cursor. It contains portions of a window procedure that enables the user to draw lines in a window's client area by dragging the mouse.
When the window procedure receives a WM_LBUTTONDOWN message, it captures the mouse and saves the coordinates of the cursor, using the coordinates as the starting point of the line. It also uses the ClipCursor function to confine the cursor to the client area during the line drawing operation.
During the first WM_MOUSEMOVE message, the window procedure draws a line from the starting point to the current position of the cursor. During subsequent WM_MOUSEMOVE messages, the window procedure erases the previous line by drawing over it with an inverted pen color. Then it draws a new line from the starting point to the new position of the cursor.
The WM_LBUTTONUP message signals the end of the drawing operation. The window procedure releases the mouse capture and frees the mouse from the client area.
LRESULT APIENTRY MainWndProc(HWND hwndMain, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
HDC hdc; // handle to device context
RECT rcClient; // client area rectangle
POINT ptClientUL; // client upper left corner
POINT ptClientLR; // client lower right corner
static POINTS ptsBegin; // beginning point
static POINTS ptsEnd; // new endpoint
static POINTS ptsPrevEnd; // previous endpoint
static BOOL fPrevLine = FALSE; // previous line flag
switch (uMsg)
{
case WM_LBUTTONDOWN:
// Capture mouse input.
SetCapture(hwndMain);
// Retrieve the screen coordinates of the client area,
// and convert them into client coordinates.
GetClientRect(hwndMain, &rcClient);
ptClientUL.x = rcClient.left;
ptClientUL.y = rcClient.top;
// Add one to the right and bottom sides, because the
// coordinates retrieved by GetClientRect do not
// include the far left and lowermost pixels.
ptClientLR.x = rcClient.right + 1;
ptClientLR.y = rcClient.bottom + 1;
ClientToScreen(hwndMain, &ptClientUL);
ClientToScreen(hwndMain, &ptClientLR);
// Copy the client coordinates of the client area
// to the rcClient structure. Confine the mouse cursor
// to the client area by passing the rcClient structure
// to the ClipCursor function.
SetRect(&rcClient, ptClientUL.x, ptClientUL.y,
ptClientLR.x, ptClientLR.y);
ClipCursor(&rcClient);
// Convert the cursor coordinates into a POINTS
// structure, which defines the beginning point of the
// line drawn during a WM_MOUSEMOVE message.
ptsBegin = MAKEPOINTS(lParam);
return 0;
case WM_MOUSEMOVE:
// When moving the mouse, the user must hold down
// the left mouse button to draw lines.
if (wParam & MK_LBUTTON)
{
// Retrieve a device context (DC) for the client area.
hdc = GetDC(hwndMain);
// The following function ensures that pixels of
// the previously drawn line are set to white and
// those of the new line are set to black.
SetROP2(hdc, R2_NOTXORPEN);
// If a line was drawn during an earlier WM_MOUSEMOVE
// message, draw over it. This erases the line by
// setting the color of its pixels to white.
if (fPrevLine)
{
MoveToEx(hdc, ptsBegin.x, ptsBegin.y,
(LPPOINT) NULL);
LineTo(hdc, ptsPrevEnd.x, ptsPrevEnd.y);
}
// Convert the current cursor coordinates to a
// POINTS structure, and then draw a new line.
ptsEnd = MAKEPOINTS(lParam);
MoveToEx(hdc, ptsBegin.x, ptsBegin.y, (LPPOINT) NULL);
LineTo(hdc, ptsEnd.x, ptsEnd.y);
// Set the previous line flag, save the ending
// point of the new line, and then release the DC.
fPrevLine = TRUE;
ptsPrevEnd = ptsEnd;
ReleaseDC(hwndMain, hdc);
}
break;
case WM_LBUTTONUP:
// The user has finished drawing the line. Reset the
// previous line flag, release the mouse cursor, and
// release the mouse capture.
fPrevLine = FALSE;
ClipCursor(NULL);
ReleaseCapture();
return 0;
case WM_DESTROY:
PostQuitMessage(0);
break;
// Process other messages.
}
}
Processing a Double Click Message
To receive double-click messages, a window must belong to a window class that has the CS_DBLCLKS class style. You set this style when registering the window class, as shown in the following example.
BOOL InitApplication(HINSTANCE hInstance)
{
WNDCLASS wc;
wc.style = CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = (WNDPROC) MainWndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wc.hCursor = LoadCursor(NULL, IDC_IBEAM);
wc.hbrBackground = GetStockObject(WHITE_BRUSH);
wc.lpszMenuName = "MainMenu";
wc.lpszClassName = "MainWClass";
return RegisterClass(&wc);
}
A double-click message is always preceded by a button-down message. For this reason, applications typically use a double-click message to extend a task that it began during a button-down message.
Selecting a Line of Text
The example in this section is taken from a simple word-processing application. It includes code that enables the user to set the position of the caret by clicking anywhere on a line of text, and to select (highlight) a line of text by double-clicking anywhere on the line.
LRESULT APIENTRY MainWndProc(HWND hwndMain, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
HDC hdc; // handle to device context
TEXTMETRIC tm; // font size data
int i, j; // loop counters
int cCR = 0; // count of carriage returns
char ch; // character from input buffer
static int nBegLine; // beginning of selected line
static int nCurrentLine = 0; // currently selected line
static int nLastLine = 0; // last text line
static int nCaretPosX = 0; // x-coordinate of caret
static int cch = 0; // number of characters entered
static int nCharWidth = 0; // exact width of a character
static char szHilite[128]; // text string to highlight
static DWORD dwCharX; // average width of characters
static DWORD dwLineHeight; // line height
static POINTS ptsCursor; // coordinates of mouse cursor
static COLORREF crPrevText; // previous text color
static COLORREF crPrevBk; // previous background color
static PTCHAR pchInputBuf; // pointer to input buffer
static BOOL fTextSelected = FALSE; // text-selection flag
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;
dwLineHeight = tm.tmHeight;
// Allocate a buffer to store keyboard input.
pchInputBuf = (LPSTR) GlobalAlloc(GPTR,
BUFSIZE * sizeof(TCHAR));
return 0;
case WM_CHAR:
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;
nCurrentLine += 1;
break;
default: / displayable character
ch = (char) wParam;
HideCaret(hwndMain);
// Retrieve the character's width, and display the
// character.
hdc = GetDC(hwndMain);
GetCharWidth32(hdc, (UINT) wParam, (UINT) wParam,
&nCharWidth);
TextOut(hdc, nCaretPosX,
nCurrentLine * dwLineHeight, &ch, 1);
ReleaseDC(hwndMain, hdc);
// Store the character in the buffer.
pchInputBuf[cch++] = ch;
// Calculate the new horizontal position of the
// caret. If the new position exceeds the maximum,
// insert a carriage return and reposition the
// caret at the beginning of the next line.
nCaretPosX += nCharWidth;
if ((DWORD) nCaretPosX > dwMaxCharX)
{
nCaretPosX = 0;
pchInputBuf[cch++] = 0x0D;
++nCurrentLine;
}
ShowCaret(hwndMain);
break;
}
SetCaretPos(nCaretPosX, nCurrentLine * dwLineHeight);
nLastLine = max(nLastLine, nCurrentLine);
break;
// Process other messages.
case WM_LBUTTONDOWN:
// If a line of text is currently highlighted, redraw
// the text to remove the highlighting.
if (fTextSelected)
{
hdc = GetDC(hwndMain);
SetTextColor(hdc, crPrevText);
SetBkColor(hdc, crPrevBk);
hResult = StringCchLength(szHilite, 128/sizeof(TCHAR), pcch);
if (FAILED(hResult))
{
// TODO: write error handler
}
TextOut(hdc, 0, nCurrentLine * dwLineHeight,
szHilite, *pcch);
ReleaseDC(hwndMain, hdc);
ShowCaret(hwndMain);
fTextSelected = FALSE;
}
// Save the current mouse-cursor coordinates.
ptsCursor = MAKEPOINTS(lParam);
// Determine which line the cursor is on, and save
// the line number. Do not allow line numbers greater
// than the number of the last line of text. The
// line number is later multiplied by the average height
// of the current font. The result is used to set the
// y-coordinate of the caret.
nCurrentLine = min((int)(ptsCursor.y / dwLineHeight),
nLastLine);
// Parse the text input buffer to find the first
// character in the selected line of text. Each
// line ends with a carriage return, so it is possible
// to count the carriage returns to find the selected
// line.
cCR = 0;
nBegLine = 0;
if (nCurrentLine != 0)
{
for (i = 0; (i < cch) &&
(cCR < nCurrentLine); i++)
{
if (pchInputBuf[i] == 0x0D)
++cCR;
}
nBegLine = i;
}
// Starting at the beginning of the selected line,
// measure the width of each character, summing the
// width with each character measured. Stop when the
// sum is greater than the x-coordinate of the cursor.
// The sum is used to set the x-coordinate of the caret.
hdc = GetDC(hwndMain);
nCaretPosX = 0;
for (i = nBegLine;
(pchInputBuf[i] != 0x0D) && (i < cch); i++)
{
ch = pchInputBuf[i];
GetCharWidth32(hdc, (int) ch, (int) ch, &nCharWidth);
if ((nCaretPosX + nCharWidth) > ptsCursor.x) break;
else nCaretPosX += nCharWidth;
}
ReleaseDC(hwndMain, hdc);
// Set the caret to the user-selected position.
SetCaretPos(nCaretPosX, nCurrentLine * dwLineHeight);
break;
case WM_LBUTTONDBLCLK:
// Copy the selected line of text to a buffer.
for (i = nBegLine, j = 0; (pchInputBuf[i] != 0x0D) &&
(i < cch); i++)
{
szHilite[j++] = pchInputBuf[i];
}
szHilite[j] = '\0';
// Hide the caret, invert the background and foreground
// colors, and then redraw the selected line.
HideCaret(hwndMain);
hdc = GetDC(hwndMain);
crPrevText = SetTextColor(hdc, RGB(255, 255, 255));
crPrevBk = SetBkColor(hdc, RGB(0, 0, 0));
hResult = StringCchLength(szHilite, 128/sizeof(TCHAR), pcch);
if (FAILED(hResult))
{
// TODO: write error handler
}
TextOut(hdc, 0, nCurrentLine * dwLineHeight, szHilite, *pcch);
SetTextColor(hdc, crPrevText);
SetBkColor(hdc, crPrevBk);
ReleaseDC(hwndMain, hdc);
fTextSelected = TRUE;
break;
// Process other messages.
default:
return DefWindowProc(hwndMain, uMsg, wParam, lParam);
}
return NULL;
}
Using a Mouse Wheel in a Document with Embedded Objects
This example assumes a Microsoft Word document with various embedded objects:
- A Microsoft Excel spreadsheet
- An embedded list box control that scrolls in response to the wheel
- An embedded text box control that does not respond to the wheel
The MSH_MOUSEWHEEL message is always sent to the main window in Microsoft Word. This is true even if the embedded spreadsheet is active. The following table explains how the MSH_MOUSEWHEEL message is handled according to the focus.
| Focus is on | Handling is as follows |
|---|---|
| Word document | Word scrolls the document window. |
| Embedded Excel spreadsheet | Word posts the message to Excel. You must decide if the embedded application should respond to the message or not. |
| Embedded control | It is up to the application to send the message to an embedded control that has the focus and check the return code to see if the control handled it. If the control did not handle it, then the application should scroll the document window. For example, if the user clicked a list box and then rolled the wheel, that control would scroll in response to a wheel rotation. If the user clicked a text box and then rotated the wheel, the whole document would scroll. |
This following example shows how an application might handle the two wheel messages.
/************************************************
* this code deals with MSH_MOUSEWHEEL
*************************************************/
#include "zmouse.h"
//
// Mouse Wheel rotation stuff, only define if we are
// on a version of the OS that does not support
// WM_MOUSEWHEEL messages.
//
#ifndef WM_MOUSEWHEEL
#define WM_MOUSEWHEEL WM_MOUSELAST+1
// Message ID for IntelliMouse wheel
#endif
UINT uMSH_MOUSEWHEEL = 0; // Value returned from
// RegisterWindowMessage()
/**************************************************
INT WINAPI WinMain(
HINSTANCE hInst,
HINSTANCE hPrevInst,
LPSTR lpCmdLine,
INT nCmdShow)
{
MSG msg;
BOOL bRet;
if (!InitInstance(hInst, nCmdShow))
return FALSE;
//
// The new IntelliMouse uses a Registered message to transmit
// wheel rotation info. So register for it!
uMSH_MOUSEWHEEL =
RegisterWindowMessage(MSH_MOUSEWHEEL);
if ( !uMSH_MOUSEWHEEL )
{
MessageBox(NULL,"
RegisterWindowMessag Failed!",
"Error",MB_OK);
return msg.wParam;
}
while (( bRet = GetMessage(&msg, NULL, 0, 0)) != 0)
{
if (bRet == -1)
{
// handle the error and possibly exit
}
else
{
if (!TranslateAccelerator(ghwndApp,
ghaccelTable,
&msg))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
}
return msg.wParam;
}
/************************************************
* this code deals with WM_MOUSEWHEEL
*************************************************/
LONG APIENTRY MainWndProc(
HWND hwnd,
UINT msg,
WPARAM wParam,
LPARAM lParam)
{
static int nZoom = 0;
switch (msg)
{
//
// Handle Mouse Wheel messages generated
// by the operating systems that have built-in
// support for the WM_MOUSEWHEEL message.
//
case WM_MOUSEWHEEL:
((short) HIWORD(wParam)< 0) ? nZoom-- : nZoom++;
//
// Do other wheel stuff...
//
break;
default:
//
// uMSH_MOUSEWHEEL is a message registered by
// the mswheel dll on versions of Windows that
// do not support the new message in the OS.
if( msg == uMSH_MOUSEWHEEL )
{
((int)wParam < 0) ? nZoom-- : nZoom++;
//
// Do other wheel stuff...
//
break;
}
return DefWindowProc(hwnd,
msg,
wParam,
lParam);
}
return 0L;
}
Retrieving the Number of Mouse Wheel Scroll Lines
The following code allows an application to retrieve the number of scroll lines using the SystemParametersInfo function.
#ifndef SPI_GETWHEELSCROLLLINES
#define SPI_GETWHEELSCROLLLINES 104
#endif
#include "zmouse.h"
/*********************************************************
* FUNCTION: GetNumScrollLines
* Purpose : An OS independent method to retrieve the
* number of wheel scroll lines
* Params : none
* Returns : UINT: Number of scroll lines where WHEEL_PAGESCROLL
* indicates to scroll a page at a time.
*********************************************************/
UINT GetNumScrollLines(void)
{
HWND hdlMsWheel;
UINT ucNumLines=3; // 3 is the default
OSVERSIONINFO osversion;
UINT uiMsh_MsgScrollLines;
memset(&osversion, 0, sizeof(osversion));
osversion.dwOSVersionInfoSize =sizeof(osversion);
GetVersionEx(&osversion);
if ((osversion.dwPlatformId == VER_PLATFORM_WIN32_WINDOWS) ||
( (osversion.dwPlatformId == VER_PLATFORM_WIN32_NT) &&
(osversion.dwMajorVersion < 4) ) )
{
hdlMsWheel = FindWindow(MSH_WHEELMODULE_CLASS,
MSH_WHEELMODULE_TITLE);
if (hdlMsWheel)
{
uiMsh_MsgScrollLines = RegisterWindowMessage
(MSH_SCROLL_LINES);
if (uiMsh_MsgScrollLines)
ucNumLines = (int)SendMessage(hdlMsWheel,
uiMsh_MsgScrollLines,
0,
0);
}
}
else if ( (osversion.dwPlatformId ==
VER_PLATFORM_WIN32_NT) &&
(osversion.dwMajorVersion >= 4) )
{
SystemParametersInfo(SPI_GETWHEELSCROLLLINES,
0,
&ucNumLines, 0);
}
return(ucNumLines);
}