Bit blit

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Bit blit (also written BITBLT, BIT BLT, BitBLT, Bit BLT, Bit Blt etc., which stands for bit block transfer) is a data operation commonly used in computer graphics in which several bitmaps are combined into one using a boolean function. A two-bitmap form is called block transfer (BLT) in UEFI Graphics Output Protocol. The operation involves at least two bitmaps: a "source" (or "foreground") and a "destination" (or "background"), and possibly a third that is often called the "mask". The result may be written to a fourth bitmap, though often it replaces the destination. The pixels of each are combined using a program-selectable raster operation, a bit-wise boolean formula. The most obvious raster operation overwrites the destination with the source. Others may involve AND, OR, XOR, and NOT operations. The Commodore Amiga's graphics chipset (and others) could combine three source bitmaps using any of the 256 possible 3-input boolean functions. Modern graphics software has almost completely replaced bitwise operations with more general mathematical operations used for effects such as alpha compositing. This is because bitwise operations on color displays do not usually produce results that resemble the physical combination of lights or inks. Some software still uses XOR to draw interactive highlight rectangles or region borders; when this is done to color images, the unusual resulting colors are easily seen.