Chapter 8 GDI Orientation and Transformations Visual C++ and MFC Fundamentals
There are various types of bitmap, based on the number of colors that the bitmap can
display. First of all, a bitmap can be monochrome in which case each pixel corresponds
to 1 bit. A bitmap can also be colored. The number of colors that a bitmap can display is
equal to 2 raised to the number of pits/pixel. For example, a simple bitmap uses only 4
pits/pixel or 4 bpp can handle only 24 = 16 colors. A more enhanced bitmap that requires
8 bpp can handle 28 = 256 colors. Bitmaps are divided in two categories that control their
availability to display on a device.A device-independent bitmap (DIB) is a bitmap that is designed to be loaded on any
application or display on any device and produce the same visual effect. To make this
possible, such a bitmap contains a table of colors that describes how the colors of the
bitmap should be used on pixels when displaying it. The characteristics of a DIB are
defined by the BITMAPINFO structure.A device-dependent bitmap (DDB) is a bitmap created from the BITMAP structure the
dimensions of the bitmap.7.3.2 Bitmap Creation...................................................................................
Unlike the other GDI tools, creating a bitmap usually involves more steps. For example,
you may want to create a bitmap to display on a window. You may create another bitmap
to paint a geometric area, in which case the bitmap would be used as a brush.Before creating a bitmap as a GDI object, you should first have a bitmap. You can do this
by defining an array of unsigned hexadecimal numbers. Such a bitmap can be used for a
brush.To create and manipulate bitmaps, the MFC library provides the CBitmap class. The use
of this class depends on the type of bitmap you want to create and how you want to use
that bitmap. One way you can use a bitmap is to display a picture on a window. To do
this, you must first have a picture resource. Although the Image Editor built-in Microsoft
Visual C++ is meant to help with regular application resources, it has a problem handling
a bitmap that displays more than 16 colors. The remedy used is to import the bitmap you
want to use. Once your bitmap is ready, call the CBitmap::LoadBitmap() method. Its
syntaxes:BOOL LoadBitmap(UINT nIDResource);
BOOL LoadBitmap(LPCTSTR lpszResourceName);The first version takes, as argument, the identifier of the bitmap you want to use. If the
bitmap is recognized by its name, you can use the second version of this method and
provide the lpszResourceName argument.Before selecting the newly created bitmap object, allocate a block of computer memory
that would hold the bitmap and can then copy it to the actual device. This job can be
taken care of by the CDC::CreateCompatibleDC() method. Its syntax is:virtual BOOL CreateCompatibleDC(CDC* pDC);This method takes a pointer to a device context. If it is successful, it returns TRUE or a
non-zero value. If it is not, it returns FALSE or 0.