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XGP WRITUP and WRITES are superceded by INFO; XGP >

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Lars Brinkhoff
2018-12-06 10:08:57 +01:00
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Character Mode for the XGP
The PDP-11 program for the XGP interprets character strings in files
in the following format:
Byte Usual meaning Escape significance
0 Null - byte is ignored Normal
1 Normal XGP ESCAPE 1
2 Normal XGP ESCAPE 2
3 Normal XGP ESCAPE 3
4 Normal XGP ESCAPE 4
5-7 Normal Reserved
10 Backspace Normal
11 TAB Normal
12 LF Normal
13 Normal Reserved
14 FF Normal
15 CR Normal
16-37 Normal Reserved
40-176 Normal Normal
177 ESCAPE Normal
Normal means the definition of this byte in the current font will be
printed. If this byte is undefined in the current font, it will be
ignored.
ESCAPE causes the next byte to have an alternate meaning selected
from the column "Escape significance".
Backspace spaces to the left the width of
one space in the current font, including inter-character
spacing.
TAB produces a column select to the column which is at least the
width of a blank to the right of the current column position, and
some multiple of 8 blank widths to the right of the left margin.
(this computation of the width includes the inter character spacing)
LF activates the current text line. The current text will be queued
to printed. This line will be printed at a vertical location such
that the distance between the baselines of of it and the preceeding line
is equal to the vertical spacing parameter, unless this would cause
the subscripts of the former line to overlap vertically with the superscripts
of this line. It will then be pushed down to make this not the case.
FF, like LF, activates the text. In addition, FF causes a page
eject after the current text line is printed. FF also sets the
defalut Y position to the first line below the top of page margin on
the new page.
The program will automatically form feed when the next text line would
place characters below the bottom margin. Sequential form feeds will
increment the page number but will otherwise be ignored.
CR causes a column select to the current left margin to be
generated. This can be used to produce overprinting.
XGP ESCAPE 1 ('177&'001) causes the next 7 bits to be read as a
special operation code. The following codes are implemented:
0-3 Font select.
The code, 0 to 3 is taken as the font identification
number of the font to use.
4-37 Reserved for future use.
40 XGP Column Selector
The next 14 bits are taken as the
x-position to print at next. (The intention is to
allow arbitrary width spaces for text justification.)
41 XGP Underscore
The next 7 bits are taken as the scan-line number on
which to underscore. It is taken as a 2's complement
increment to the base line. Zero is on the baseline,
positive bytes are down from it. Underscores outside
the range of the other characters on the line will be
ignored. The next 14 bits are taken as the length
of the underscore.
42 Line space.
This does a line feed and then takes the byte as the
number of lines between this line's baseline and the
baeline of the following line.
43 Base-line adjust.
The next 7 bits are taken in two's complement as the
base-line adjustment to the current font. The
adjustment sticks until reset by another adjust
command or a font select. The intention is to allow a
font to be used for subscripts and superscripts.
(Increment baseline for superscript, decrement for
subscript).
** 44 Print the paper page number.
The paper page number is set to 1 by a form feed. It
is incremented each time the paper is cut. The
decimal value of this count is printed.
** 45 Accept heading text.
The next byte is a count of bytes to follow. Those
bytes will be read into the heading line. When that
count is exhausted, the heading line will be printed.
If a line feed or line space command is given that
would cause text to be printed below the current text
area, a form feed is inserted by the XGP and if a
heading is defined, it will be printed.
46 Start Underline.
Set the left end of an underline. See Stop Underline.
47 Stop Underline.
The next byte is the scan line on which to write the
underline (same as XGP Underscore). The extent of
the underscore is defined by this command and Start
Underline. If this command is not preceded by a Start
Underline, it will underline from the left margin.
Beware of column selects. No underline will happen
until this command is given.
50 Takes the next byte as the intercharacter spacing
This is reset to zero at the end of each line.
XGP ESCAPE 2 ('177&'002) causes the next 7 bits to be taken as the
column increment. This quantity is signed: 0-77 are positive
increments 100 to 177 are negative increments (100  -100, 177  -1).
XGP ESCAPE 3 ('177&'003) causes the next 2 bytes to be taken as the
scan line number on which to start this text line. Scan line 0 is
the first scan line on the page (immediately following the cut).
The topmost scanline of the present text line will be placed on the
scan line indicated in this command.
** XGP ESCAPE 4 ('177&'004). This escape is used to specify a vector.
It is followed by 11 bytes describing the vector:
2 bytes Y0 Scan line number of first line of vector.
2 bytes X0 Column position of left edge of first line
of the vector.
3 bytes DX Delta X. 1 bit of sign; 11 bits of integer;
9 bits of fraction.
2 bytes N The number of scan lines on which this vector
is visible.
2 bytes W The column width of each scan-line.
The XGP service must be presented with vectors sorted by
ascendending values of Y0. If the vectors are not sorted, the
output will be wrong.
The escape significance of codes 5 through 10, 13, and 16 through
37 is not defined at the present time but reserved for future use.
$

This file has been superceded by INFO; XGP >