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Bit blit
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.
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.
The name derives from the BitBLT routine for the Xerox Alto computer, standing for bit-boundary block transfer. Dan Ingalls, Larry Tesler, Bob Sproull, and Diana Merry programmed this operation at Xerox PARC in November 1975 for the Smalltalk-72 system. Dan Ingalls later implemented a redesigned version in microcode.
The development of fast methods for various bit blit operations gave impetus to the evolution of computer displays from using character graphics (text mode) to using raster graphics (bitmap) for everything. Machines that rely heavily on the performance of 2D graphics (such as video game consoles) often have special-purpose circuitry called a blitter.
A classic use for blitting is to render transparent sprites onto a background. In this example a background image, a sprite, and a 1-bit mask are used. As the mask is 1-bit, there is no possibility for partial transparency via alpha blending.
A loop that examines each bit in the mask and copies the pixel from the sprite only if the mask is set will be much slower than hardware that can apply exactly the same operation to every pixel. Instead a masked blit can be implemented with two regular BitBlit operations using the AND and OR raster operations.
The sprite is drawn in various positions over the image to produce this:
Hub AI
Bit blit AI simulator
(@Bit blit_simulator)
Bit blit
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.
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.
The name derives from the BitBLT routine for the Xerox Alto computer, standing for bit-boundary block transfer. Dan Ingalls, Larry Tesler, Bob Sproull, and Diana Merry programmed this operation at Xerox PARC in November 1975 for the Smalltalk-72 system. Dan Ingalls later implemented a redesigned version in microcode.
The development of fast methods for various bit blit operations gave impetus to the evolution of computer displays from using character graphics (text mode) to using raster graphics (bitmap) for everything. Machines that rely heavily on the performance of 2D graphics (such as video game consoles) often have special-purpose circuitry called a blitter.
A classic use for blitting is to render transparent sprites onto a background. In this example a background image, a sprite, and a 1-bit mask are used. As the mask is 1-bit, there is no possibility for partial transparency via alpha blending.
A loop that examines each bit in the mask and copies the pixel from the sprite only if the mask is set will be much slower than hardware that can apply exactly the same operation to every pixel. Instead a masked blit can be implemented with two regular BitBlit operations using the AND and OR raster operations.
The sprite is drawn in various positions over the image to produce this: