When the WM_CREATE message is processed, the variables required for scrolling are initialized. Use the CreateCompatibleDC function to create a compatible device context (DC), the CreateBitmap function to create a bitmap, and the SelectObject function to select the bitmap for the DC. Note that a compatible DC is also known as a memory DC.
The device-specific information about the display device is retrieved. If a compatible DC is created for the screen, as in the example, use the GetDeviceCaps function to get this information. The information includes the number of adjacent color bits per pixel, the number of color planes, and the height and width of the DC.