[cups.general] Old HP-GL filetype identification -- further info

[John Meshkoff]

I've investigated further the HP-GL generated from the older autocad; it
was generated by the HP autocad driver, plhp.drv, chosing the venerable
HP-7580 pen plotter. This driver would have been in use in autocad
before the release of HP-GL/2 under PCL5 in 1990.

An xxd grep of plhp.drv for the hex beginning with 1b2e, as compared
with an hp-gl plot is revealing:

linus:/mnt/acad_10$ xxd plhp.drv | grep 1b2e
00016a0: 0000 0000 0000 0000 1b2e 283b 1b2e 4938  ..........(;..I8
00016b0: 313b 3b31 373a 0000 1b2e 4e3b 3139 3a00  1;;17:....N;19:.
00016d0: 643b 0000 1b2e 4938 313b 3b31 373a 1b2e  d;....I81;;17:..
linus:/mnt/acad_10$ xxd testplt.plt 
0000000: 1b2e 283b 1b2e 4938 313b 3b31 373a 1b2e  ..(;..I81;;17:..
0000010: 4e3b 3139 3a49 4e3b 5343 3b50 553b 5055  N;19:IN;SC;PU;PU
0000020: 3b53 5031 3b4c 543b 5653 3336 3b50 412d  ;SP1;LT;VS36;PA-
0000030: 3136 3736 342c 2d31 3036 3638 3b50 443b  16764,-10668;PD;
0000040: 5041 2d32 3534 302c 2d31 3036 3638 3b50  PA-2540,-10668;P
0000050: 412d 3235 3430 2c33 3535 363b 5041 2d31  A-2540,3556;PA-1
0000060: 3637 3634 2c33 3535 363b 5041 2d31 3637  6764,3556;PA-167
0000070: 3634 2c2d 3130 3636 383b 5055 3b50 4130  64,-10668;PU;PA0
0000080: 2c30 3b53 503b                           ,0;SP;
linus:/mnt/acad_10$ 

The first 14 bytes in all the plots match the bytes separated by 0000 in
the section of plhp.drv shown, so these will definitely identify early
autocad pre-HP-GL/2 HP-7580 plot files; I have not yet investigated
other HP plotter choices for plotfiles, but am tempted to do so, as the
initial hex strings shown could be either HP plotter-model generic or
plotter-model specific.

Hope this may be useful,

John

-- 
John Meshkoff                           johnpipe  at sonic dot net
"Who sees all beings in the Self, and the Self in all beings, hates 
none -- Isha Upanishad

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