Advanced MFC Programming

Chapter 8. DC, Pen, Brush and Palette
}
lpLogPal->palPalEntry[i].peBlue=i;
lpLogPal->palPalEntry[i].peFlags=NULL;
}
VERIFY(m_palDraw.CreatePalette(lpLogPal));
delete [](BYTE *)lpLogPal;
In the function a LOGPALETTE type pointer is declared, we need to use it to store the buffers allocated
for creating the logical palette. The buffers are allocated through using “new” method. The following is the
formulae that is used to calculate the size of the total bytes needed for creating logical palette:
size of structure LOGPALETTE + (number of entries-1)×(size of structure PALETTEENTRY)
Next the palette entries are filled with 256 colors ranging from dark blue to bright blue. After the
logical palette is created, these buffers can be released.
The following is the updated function CGDIView::OnDraw(…) in sample 8.8-1\GDI:
void CGDIView::OnDraw(CDC *pDC)
{
CBrush brush;
CRect rect;
CPalette *ptrPalOld;
int i;
CGDIDoc *pDoc=GetDocument();
ASSERT_VALID(pDoc);
ptrPalOld=pDC->SelectPalette(&m_palDraw, FALSE);
pDC->RealizePalette();
}
GetClientRect(rect);
rect.bottom+=255;
rect.bottom/=256;
for(i=0; iFillRect(rect, &brush);
brush.DeleteObject();
rect.OffsetRect(0, rect.Height());
}
pDC->SelectPalette(ptrPalOld, FALSE);
Each time the client window needs to be painted, we first call function CDC::SelectPalette(…) to
select the logical palette into the device context and call function CDC::RealizePalette() to let the colors
in the logical palette be mapped to the system palette. When creating the brushes, instead of using RGB
macro to specify an R, G, B combination, we need to use PALETTEINDEX macro to indicate a color contained
in the logical palette.
Sample 8.8-2\GDI is implemented almost in the same way: first a CPalette type variable m_palDraw is
declared in class CGDIView, and the palette is created in its constructor. In function CGDIView::OnDraw(…),
before the client window is painted, the logical palette is selected into the device context. The following is
the modified function CGDIView::OnDraw(…):
void CGDIView::OnDraw(CDC *pDC)
{
CPen pen;
CPen *ptrPenOld;
CRect rect;
int i;
CPalette *ptrPalOld;
CGDIDoc *pDoc=GetDocument();
ASSERT_VALID(pDoc);
ptrPalOld=pDC->SelectPalette(&m_palDraw, FALSE);
226