C / C++ / MFC

Because memory device contexts allow both color and monochrome bitmaps, the format of the bitmap returned by the CreateCompatibleBitmap function differs when the specified device context is a memory device context. However, a compatible bitmap that was created for a nonmemory device context always possesses the same color format and uses the same color palette as the specified device context.

Note: When a memory device context is created, it initially has a 1-by-1 monochrome bitmap selected into it. If this memory device context is used in CreateCompatibleBitmap, the bitmap that is created is a monochrome bitmap. To create a color bitmap, use the hDC that was used to create the memory device context, as shown in the following code...

CClientDC dc(this);<br />
CDC tempDC;<br />
tempDC.CreateCompatibleDC(NULL);<br />
CBitmap tempBMP;<br />
tempBMP.CreateCompatibleBitmap(&dc, w*zoom_const,h*zoom_const);<br />
tempDC.SelectObject(&tempBMP);	<br />
dib->Draw(&tempDC, 0,0,w*zoom_const,h*zoom_const,0,0,w,h);		<br />
dc.BitBlt( 0, 0, w*zoom_const,h*zoom_const, &tempDC, sp.x, sp.y, SRCCOPY);

CClientDC dc(this);<br />
if (zoom_const >1)<br />
{<br />
CDC tempDC;<br />
tempDC.CreateCompatibleDC(NULL);<br />
if (m_bZoomUpdate)//update bitmap for the first time when zoom_const changes<br />
{<br />
GetDocument()->m_zoomedBMP.CreateCompatibleBitmap(&dc, w*zoom_const,h*zoom_const);<br />
tempDC.SelectObject(&GetDocument()->m_zoomedBMP);<br />
dib->Draw(&tempDC, 0,0,w*GetDocument()->zoom_const,h*GetDocument()->zoom_const,0,0,w,h);		<br />
m_bZoomUpdate = false;<br />
}<br />
else<br />
tempDC.SelectObject(&GetDocument()->m_zoomedBMP);<br />
dc.BitBlt( 0, 0, w*zoom_const,h*zoom_const, &tempDC, sp.x, sp.y, SRCCOPY);<br />
}<br />
else //zoom_const =1<br />
dib->Draw(&dc, 0,0,w*zoom_const,h*zoom_const,sp.x,sp.y,w,h);

Kiran Satish wrote:

Is there any limit on the max size of a compatible bitmap that you can create??

if (GetDocument()->zoom_const >100)// if magnification is more than 100%
{
  CDC tempDC;
  tempDC.CreateCompatibleDC(NULL);			
  if (GetDocument()->m_bZoomUpdate)//magnify the image
  {	
    GetDocument()->m_zoomedBMP.DeleteObject(); //m_zoomedBMP is an object of CBitmap
    GetDocument()->m_zoomedBMP.CreateCompatibleBitmap(&dc, w*GetDocument()->zoom_const/100,h*GetDocument()->zoom_const/100);
    tempDC.SelectObject(&GetDocument()->m_zoomedBMP);
    dib->Draw(&tempDC, 0,0,w*GetDocument()->zoom_const/100,h*GetDocument()->zoom_const/100,0,0,w,h);
    GetDocument()->m_bZoomUpdate = false; //reset the magnification flag
  }
  else //otherwise just redraw the already magnified image
    tempDC.SelectObject(&GetDocument()->m_zoomedBMP);
  dc.BitBlt( 0, 0, w*GetDocument()->zoom_const/100,h*GetDocument()->zoom_const/100, &tempDC, sp.x, sp.y, SRCCOPY);
}
else // draw the image at 100%
  dib->Draw(&dc, 0,0,w*GetDocument()->zoom_const/100,h*GetDocument()->zoom_const/100,sp.x,sp.y,w,h);

led mike wrote:

it's just a bad idea

Mark Salsbery wrote:

A combination of these APIs should do everything you need:

led mike wrote:

well exclusive of providing the user with a decent experience

Mark Salsbery
Microsoft MVP - Visual C++