Selecting a Line of Text - Win32 Programmer's Reference

Custom Search

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(hwndMain, uMsg, wParam, lParam)

HWND hwndMain;

UINT uMsg;

WPARAM wParam;

LPARAM lParam;

{

HDC hdc; /* handle of 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; /* address of input buffer */

static BOOL fTextSelected = FALSE; /* text-selection flag */

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(0xFFFFFFFF);

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);

TextOut(hdc, 0, nCurrentLine * dwLineHeight,

szHilite, lstrlen(szHilite));

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));

TextOut(hdc, 0, nCurrentLine * dwLineHeight, szHilite,

lstrlen(szHilite));

SetTextColor(hdc, crPrevText);

SetBkColor(hdc, crPrevBk);

ReleaseDC(hwndMain, hdc);

fTextSelected = TRUE;

break;

. /* Process other messages. */

default:

return DefWindowProc(hwndMain, uMsg, wParam, lParam);

}

return NULL;

}

Last news from Greatis Software

    Nostalgia .Net     .Net is powerful, but not all-powerful, so sometimes we need to use Win32 API for our .Net applications. It's simple enough with Platform Invoke if you have Win32 skill, but we do not always have time to dig the ancient documentation, declare the special types that are compatible with Win32, find the values of the Win32's constants and so on. Nostalgia .Net offers several simple-to-use classes, and components that will allow you to forget about the headache of Win32 and just use the power of Win32 in your application the same way as you use the native. Net classes. More »

Recommended software for developers

    Ultimate Pack     Component pack for Delphi and C++ Builder that contains runtime form designer, runtime object inspector, print suite and much more for the very special price. More »

    Form Designer .Net     Unique runtime form design solution that allows to edit any form in .Net WinForms application at runtime with full source codes for only 300 euro! More »

    Print Suite .Net     Print Suite .Net is a set of components for easy printing texts, images and grids from your WinForms applications. Full C# source codes are available More »

    Gradient Controls .Net     Gradient Controls .Net offers controls with gradient background feature. Labels, panels and so on... Full C# source codes are available More »

    Greatis iGrid     iGrid plots drawing grid right over your desktop, so you can use it everywhere, with any drawing application without any special plugins for different graphic editors. More »

All the contacts and projects

Dmitry Vasiliev (just.dmitry)

More Online Helps

Win32 Programmer's Reference
Win32 Multimedia Programmer's Reference
OLE Programmer's Reference
Microsoft Windows Pen API Programmer's Reference
Microsoft Windows Sockets 2 Reference
Microsoft Windows Telephony API (TAPI) Programmer's Reference
Unix Manual Pages

greatis just4fun network