Advanced MFC Programming

Chapter 9. Font
width of different characters may vary, we need to make careful calculation before moving the caret to the
next position.
Every class derived from the CWnd supports caret, the steps of implementing caret are as follows: 1)
Create a caret with specific style. 2) Show the caret. 3) Destroy the caret before the window is destroyed.
The following three member functions can be used to create a caret:
void CWnd::CreateSolidCaret(int nWidth, int nHeight);
void CWnd::CreateGrayCaret(int nWidth, int nHeight);
void CWnd::CreateCaret(CBitmap *pBitmap);
The first member function allows us to create a solid caret, here parameters nWidth and nHeight
specify the dimension of the caret. Similarly, the second function can be used to create a gray caret. The
last function can create a caret from a bitmap so that the caret can have a custom pattern.
After the caret is created, we can call function CWnd::ShowCaret() to display the caret or call function
CWnd::HideCaret() to hide the caret.
The difficult thing on managing caret is to set its position. Because every character may have a
different width, when the user presses arrow keys, we can not advance the caret with fixed distance each
time. We must move the caret forward or backward according to the width of the character located before
(or after) the caret. In order to do this, we can either calculate the new caret position each time, or we can
store the starting position of each character in a table and obtain the caret position from it whenever the
caret needs to be moved. In the sample, the latter solution is used.
Sample
Sample 9.5\GDI demonstrates how to implemnt caret. It is based on sample 9.4\GDI.
First, some new variables and functions are added to class CGDIDoc for caret implementation:
class CGDIDoc : public CDocument
{
protected:
CGDIDoc();
DECLARE_DYNCREATE(CGDIDoc)
CString m_szText;
CFont m_ftDraw;
CDWordArray m_arCaret;
int m_nCaretIndex;
int m_nCaretVerSize;
……
public:
CString GetText(){return m_szText;}
CFont *GetFont(){return &m_ftDraw;}
void ForwardCaret();
void BackwardCaret();
POINT GetCaretPosition();
int GetCaretVerSize(){return m_nCaretVerSize;}
CGDIView *CGDIDoc::GetCGDIView();
//{{AFX_VIRTUAL(CGDIDoc)
public:
};
Two variables m_nCaretIndex and m_nCaretVerSize are added. The first variable is the index
indicating the position of the caret. The second variable is the caret’s vertical size. This is necessary
because for fonts with different sizes, we need to create different carets, whose vertical size should be the
same with the current font’s height.
Five functions are added to the class, among them, function CGDIDoc::GetCaretVerSize() provides
us a way of obtaining the current caret’s vertical size in class CGDIView; and function CGDIDoc::
GetCaretPosition() converts the caret index to a position within the client window (The function returns
a POINT type value). It is implemented as follows:
POINT CGDIDoc::GetCaretPosition()
{
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