Aucbvax.2060
fa.works
utzoo!duke!decvax!ucbvax!cfh@CCA-UNIX
Fri Jul 3 10:13:23 1981
Re: Question to field: Bit Mapped displays
In response to your message of Thu Jul 2 20:26:38 1981:
Bit Map refers to the way a picture is stored, i.e. one
bit (or aggregate of bits for color) of memory for each
addressable point on the screen. As opposed to the older
"display list" technique where the picture is stored as a
list of line segments, etc.
Raster-scan refers to the method by which the picture is
refreshed on the screen, in this case, as a series of
horizontal lines, starting at the top of the screen and
moving down. As opposed to "stroke writers" which move
the beam in arbitrary directions to draw individual
graphic primitives.
The earliest displays were stroke writers. The TX-0 at MIT
moved a beam on a CRT under the direct control of the CPU.
In some sense, this was the first personal computer, as
refreshing the display didn't leave too many cycles for
anything else. Later, the direct view storage tube (DVST)
allowed the picture to be written just once instead of
being refreshed 30 or more times per second. Only problem
was that the only way to change anything on the screen was
to erase the entire screen in a blinding flash which took
5 seconds. By the way, contrary to current publicity about
the STAR, the Advanced Remote Display Station (ARDS) storage
tube terminal was the first to offer the "mouse" as an input
device.
Stroke writers are still in common use in the CAD/CAM area.
They typically employ high-performance (expensive) analogue
circuitry to draw vectors of much higher resolution than are
currently feasible with raster displays. Resolutions of
4096x4096 are not uncommon.
The raster scanned bit map display is rapidly taking over
the display scene. It is cheaper to build circuits which
move the beam in nice sraight lines across the screen than
to build in the ability to turn corners.
To answer your question, for all intents and purposes,
raster-bitmap and bitmap mean the same thing.
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