The Bit-Block Transfer

As I mentioned earlier, you can think of the entire video display as one big bitmap. The pixels you see on the screen are represented by bits stored in memory on the video display adapter board. Any rectangular area of the video display is also a bitmap, the size of which is the number of rows and columns it contains.

Let’s begin our journey into the world of bitmaps by copying an image from one area of the video display to another. This is a job for the powerful BitBlt function.

Bitblt (pronounced “bit blit”) stands for “bit-block transfer.” The BLT originated as an assembly language instruction that did memory block transfers on the DEC PDP-10. The term “bitblt” was first used in graphics in connection with the SmallTalk ...

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