Advanced MFC Programming

Chapter 9. Font
Two local variables nSelIndexBgn and nSelIndexEnd are declared here, they are used to store the
values of CGDIDoc::m_nSelIndexBgn and CGDIDoc::m_nSelIndexEnd retrieved from the document. If the
value of CGDIDoc::m_nSelIndexEnd is less than the value of CGDIDoc::m_nSelIndexBgn (In this case, the
selection is made from right to left), we need to swap their values.
If there is no currently selected text, we simply call CDC::TextOut(…) as usual to output the plain text.
Otherwise we swap the two indices if m_nSelIndexEnd is less than m_nSelIndexBgn, and set the text
alignment by calling function CDC::SetTextAlign(…) using TA_UPDATECP flag. This will cause the output
origin to be updated to the end of the text after each CDC::TextOut(…) call. If we do not set this alignment,
the coordinates passed to function CDC::TextOut(…) indicate a position relative to the upper-left corner of
the window. With TA_UPDATECP alignment style, when we call function CDC::TextOut(…), the coordinates
passed to this function will be interpreted as a position relative to the new origin (which is the end of the
text that is output by function CDC::TextOut(…) last time). This is very useful if we want to output several
segments of strings. In the sample, the old alignment flag is stored in variable uTextAlign, and is restored
after the text is output.
We divide the text string into three segments: the first segment starts from the beginning of the text and
ends at the beginning of the selection. We output this sub-string using normal text and background colors.
The second segment is the selected portion, before drawing this sub-string we need to swap the text and
background colors so that the selected part will be drawn highlighted. The rest part is the third sub-string,
which is also drawn using the normal text and background colors. Each time function CDC::TextOut(…) is
called, the output coordinates are specified as (0, 0). If the alignment flag is not set to TA_UPDATECP, the
three segments will all be drawn starting from the same origin.
Setting Selection Indices
Now we can change the values of CGDIDoc::m_nSelIndexBgn and CGDIDoc::m_nSelIndexEnd to
highlight any portion of the text string. From user’s point of view, this should happen when the mouse is
clicked and dragged over the text. In order to implement this, we need to respond to WM_LBUTTONDWON,
WM_LBUTTONUP and WM_MOUSEMOVE messages.
When left button is pressed down, we need to first reset the values of CGDIDoc::m_nSelIndexBgn and
CGDIDoc::m_nSelIndexEnd to -1, because we need to unselect any currently highlighted text. Then we can
update the value of CGDIDoc::m_nSelIndexBgn to the current caret index. When mouse moves with the left
button held down, we need to set the value of CGDIDoc::m_nSelIndexEnd to the current caret index (the
caret will move with the mouse cursor). The same thing needs to be done when mouse’s left button is
released. For these purposes, a new function ResetSelection() is declared in class CGDIDoc, which will be
called to reset the selection indices. Also, function CGDIDoc::SetCaret(…) is modified. The following is a
portion of the updated class CGDIDoc:
……
……
class CGDIDoc : public CDocument
{
public:
}
void SetCaret(CPoint);
void ResetSelection()
{
m_nSelIndexBgn=m_nSelIndexEnd=-1;
UpdateAllViews(NULL);
}
Function CGDIDoc::ResetSelection() is implemented inline, it just resets the values of
m_nSelIndexBgn and m_nSelIndexEnd to -1, then updates the view window. The following shows the
modified portion of function CGDIDoc::SetCaret(…):
……
void CGDIDoc::SetCaret(CPoint point)
{
dc.SelectObject(ptrFtOld);
m_nCaretIndex=nIndex;
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