Advanced MFC Programming

Chapter 11. Sample: Simple Paint
case default function CBitmapButton::DrawItem(…) will be called). If we do not override this function, we
will not be notified when buttons need to be updated.
Since this sample is supposed to be used for palette device (Of course, it can be run on a non-palette
device), we will let each button display a color contained in a different entry of the logical palette. In order
to do this, we should let different button have a different index that represents a different entry of the
logical palette. For this purpose, a variable m_nPalIndex and two functions (GetPaletteIndex() and
SetPaletteIndex(…)) are added to class CColorButton. In function CColorButton::DrawItem(…), this
value is used as the index to the application’s logical palette for button drawing:
……
……
else
{
pDC=CDC::FromHandle(lpDrawItemStruct->hDC);
pPalOld=pDC->SelectPalette(pPal, FALSE);
pDC->RealizePalette();
pDC->FillSolidRect
(
&lpDrawItemStruct->rcItem,
PALETTEINDEX(m_nPalIndex)
);
pDC->SelectPalette(pPalOld, FALSE);
}
We use macro PALETTEINDEX to retrieve the actual color contained in the palette entry. As usual, before
doing any drawing, we have to select the logical palette into the DC and realize it.
Class CFBButton is similar. Two variables m_BgdIndex and m_FgdIndex are added to class CGDIDoc
representing the currently selected foreground and background colors. Their values can be retrieved and set
through calling functions CGDIDoc::GetBgdIndex(), CGDIDoc::GetFgdIndex(), CGDIDoc::
SetBgdIndex(…), CGDIDoc::SetFgdIndex(…). Two variables are declared in the document class instead of
color bar class because their values may need to be accessed from the view. Since the document is the
center of the application, we should put the variables in the document so that they can be easily accessed
from other classes.
Function CFBButton::Drawitem(…) implements drawing a rectangle filled with current background
color overlapped by another rectangle filled with current foreground color. Like class CColorButton, the
color is retrieved from the logical palette contained in the document. The following code fragment shows
how the background rectangle is drawn:
……
……
brush.CreateSolidBrush(PALETTEINDEX(nBgdIndex));
rect=lpDrawItemStruct->rcItem;
rect.InflateRect(-2, -2);
rect.left+=rect.Width()/4;
rect.top+=rect.Height()/4;
pBrOld=pDC->SelectObject(&brush);
pDC->Rectangle(rect);
pDC->DrawEdge(rect, EDGE_ETCHED, BF_RECT);
pDC->SelectObject(pBrOld);
Variable nBgdIndex is an index to the logical palette, the whole area that needs to be painted is
specified by lpDrawItemStruct->rcItem (lpDrawItemStruct is the pointer passed to function
DrawItem(…)). When drawing the rectangle, we see that a margin of 2 is left first (This is done through
calling function CRect:: InflateRect(…)), then the width and height of the rectangle are set to ¾ of their
original values. The foreground rectangle has the same dimension, but overlaps the background rectangle.
To add more fluff to the application, the border of both rectangles has a 3D effect, which is implemented by
calling function CDC::DrawEdge(…).
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