The sample in Tutorial 2 (DDEX2) takes a bitmap and puts it in the back buffer, and then it flips between the back buffer and the primary buffer. This is not a very realistic approach to displaying bitmaps. The sample in this tutorial (DDEX3) expands on the capabilities of DDEX2 by including two off-screen buffers in which the two bitmaps—one for the even screen and one for the odd screen—are stored. It uses the IDirectDrawSurface3::BltFast method to copy the contents of an off-screen surface to the back buffer, and then it flips the buffers and copies the next off-screen surface to the back buffer.
The new functionality demonstrated in DDEX3 is shown in the following steps: