Advanced MFC Programming

Chapter 9. Font
}
dc.SelectObject(ptrFtOld);
m_nCaretIndex=nIndex;
GetCGDIView()->RedrawCaret();
In order to find out all the possible caret positions, we need to obtain the dimension of different substrings.
For example, the caret positions of text “abcde” can be calculated from the dimensions of following
sub-strings: “a”, “ab”, “abc”, “abcd”, “abcde”. In the above function, first a DC that does not belong to any
window is created, then the current font is selected into this DC, and function CDC::GetTextExtent(…) is
called to obtain the dimension of each sub-string. Because we have only one line text, only the horizontal
size is meaningful to us.
A loop is implemented to do the comparison. For the nth loop, we create a sub-string that contains
text’s first character to nth character, obtain its dimension, and calculate the distance from the position of
the last character of the sub-string to the current position of mouse cursor. After the loop finishes, we
choose the smallest distance and set m_nCaretIndex to the corresponding caret index.
Cursor Shape
For a text editor, when the mouse is over its editable area, usually the mouse cursor should be changed
to an insertion cursor. This indicates that the user can input text at this time. This feature can also be
implemented in our sample application.
To set mouse cursor’s shape, we need to call API function ::SetCursor(…). The input parameter to
this function is an HCURSOR type handle.
A cursor can be prepared as a resource and then be loaded before being used. After the cursor is
loaded, we can pass its handle to function ::SetCursor(…) to change the current cursor shape. Besides the
cursor prepared by the user, there also exist some standard cursors that can be loaded directly.
We can call function CWinApp::LoadCursor(…) to load a user-defined cursor, and call function
CWinApp::LoadStandardCursor(…) to load a standard cursor. The following table lists some of the
standard cursors:
Cursor ID
IDC_ARROW
IDC_IBEAM
IDC_WAIT
IDC_CROSS
Meaning
Arrow cursor
Text-insertion cursor
Hourglass cursor
Cross-hair cursor
In the sample, an HCURSOR type variable is declared in class CGDIView, and the insertion cursor is
loaded in function CGDIView::OnInitialUpdate():
……
……
class CGDIView : public CScrollView
{
protected:
HCURSOR m_hCur;
}
void CGDIView::OnInitialUpdate()
{
}
m_hCur=AfxGetApp()->LoadStandardCursor(IDC_IBEAM);
We need to respond to WM_SETCURSOR message in order to change the cursor shape. By handling this
message, we have a chance to customize the default cursor when it is within the client window of the
application. Upon receiving this message, we can check if the mouse position is over the editable text. If so,
we need to change the cursor by calling API function ::SetCursor(…). In this case, we need to return a
TRUE value and should not call the default message handler. If the cursor should not be changed, we need
to call the default message handler to let the cursor be set as usual.
262