Advanced MFC Programming

Chapter 4. Button
……
CRect rect;
Three DCs are declared here. To draw a bitmap, we must create a memory DC, select the bitmap into it
and copy the bitmap from the memory DC to the target DC. The target could be either a device or a
memory block (we could copy bitmap between two memory DCs). A DC can select only one bitmap at any
time.
When there is no mask bitmap, variable memDC is used to perform normal bitmap drawing: it is used to
select the normal bitmap, and copy it directly to the target DC. When there is a mask bitmap, memDC will be
used along with memDCMask to implement transparent background drawing.
Variable memDCImage is used to act as the target memory DC and implement transparent background
drawing. It will be used in conjunction with bmpImage, which will be selected into memDCImage. To draw the
bitmap, first we need to copy the image pattern from the target device to the memory bitmap, then copy the
source bitmap to the memory bitmap (perform AND and XOR drawings). Finally, we can output the result
from the memory bitmap to the target device.
Variable bmpImage is used to create bitmap in memory.
Variable memDCMask is used to select mask bitmap image.
Pointer pDC will be used to store the pointer of the target device context that is created from hDC
member of structure DRAWITEMSTRUCT.
Pointers pBitmap and pBitmapMask will be used to store the pointers to the normal bitmap (could be
one of the bitmaps indicating the four states of the button) and the mask bitmap respectively.
The other three CBitmap pointers pOld, pOldMask and pOldImage are used to select the bitmaps out of
the DCs (When the bitmaps are being selected into the DCs, these pointers are used to store the bitmaps
selected out of the DCs. After bitmap drawing is finished, we can select old bitmaps back into the DCs, this
will select our bitmaps out of the DCs automatically).
Variable state is used to store the current state of button.
The following portion of function MCBitmapButton::DrawItem(…) shows how to choose appropriate
bitmaps:
……
ASSERT(lpDIS != NULL);
ASSERT(m_bitmap.m_hObject != NULL);
pBitmap=&m_bitmap;
if(m_bitmapMask.m_hObject != NULL)
{
pBitmapMask=&m_bitmapMask;
}
else pBitmapMask=NULL;
state=lpDIS->itemState;
if
(
(state & ODS_SELECTED) &&
(m_bitmapSel.m_hObject != NULL)
)
{
pBitmap=&m_bitmapSel;
}
else if
(
(state & ODS_FOCUS) &&
(m_bitmapFocus.m_hObject != NULL)
)
{
pBitmap=&m_bitmapFocus;
}
else if
(
(state & ODS_DISABLED) &&
(m_bitmapDisabled.m_hObject != NULL)
)
{
pBitmap=&m_bitmapDisabled;
}
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