This chapter provides you with almost anything you'll need for successful
hp2xx applications. You'll probably soon operate hp2xx
by solely consulting the option summary (see section Option summary) or just
by calling hp2xx without any parameters to obtain its built-in
option summary.
hp2xx
The mode switch `-m string' tells hp2xx about the mode it
should use to generate output, i.e., the desired output format. hp2xx
can run in three different groups of modes: Generating vector graphics,
raster graphics, or "preview mode", i.e., displaying the graphics.
Preview is the default; see section Option summary for a list of all modes.
NOTE: The basic unit length within hp2xx is mm (millimeter).
This unit is always assumed except where noted otherwise.
In contrast to a real HP-GL plotter, hp2xx lets you decide freely
about the size of the picture. While preserving the picture's aspect ratio,
hp2xx will fit the picture into a window of width w and
height h. By default, w = h = 200 (mm). Set these basic
sizes using options `-w w' and `-h h'.
Sometimes you'll want to change the aspect factor of a picture, e.g., to spread out a square picture into landscape. Option `-a af' is used for this. af > 1 increases x/y ratio, 0 < af < 1 decreases x/y.
Example: Let's assume your picture covers a native coordinate range of
100...900 plotter units in x direction and 200...600 in y direction.
Thus, its width is double its height.
Using defaults, hp2xx will create a picture of size 200 x 100 mm,
while options `-w 100 -h 40' will lead to a picture of
size 80 x 40 mm, and `-w 100 -h 40 -a 0.5' results
in a 40 x 40 mm picture.
Alternatively, ignore explicit size control and rely on the true
HP-GL coordinates (and therefore: sizes) of the given input file(s).
Flag `-t' inhibits `-a -h -w' and lets hp2xx use true
HP-GL sizes, based on the assumption that 1 HP unit = 1/40 mm.
Some modes of hp2xx support page offsets, i.e., left
and upper margins added to the picture, probably in addition to some
hard margins which cannot be avoided. Currently, these modes are
eps, pcl, and pre. The left margin (offset) is modified
with option `-o off_left', while the upper margin can be
controlled via `-O off_upper'. off_left and off_upper
are specified in mm.
Option `-C' (center the picture) works in combination with options `-o -O' by modifying the offsets in such a way that the resulting picture is centered within the frame defined by options `-w -h'. Example: Assume that the picture is a square, and `-w 100 -h 40' are specified. A 40 mm square with an additional left margin of (100-40)/2 = 30 mm will be produced if option `-C' is given. If the actual width/height ration of the picture exactly matches the ratio defined by `-w -h', option `-C' has no effect.
Imagine a plotter with a pen carousel, e.g., like the model HP7550A. The carousel carries a (small) number of pens. Their colors and tip thicknesses (sizes) are selected by a human operator, while the plotter only receives commands like "Now use pen number 5". If you don't provide a pen, the plotter will move and "draw" without this pen if its number is selected.
hp2xx emulates a carousel of up to 8 pens of various colors and sizes.
By default, all pens are present, have foreground color
(typically black), and their tip thicknesses are one unit (1/10 mm).
(NOTE: in versions before 3.4.2, pen widths in raster modes were counted in
pixels, so the default in those versions was 1/10 mm for vector modes,
1 pixel for raster modes).
HPGL/2 commands NP,PC,PW may override this for up to 255 freely configurable pens.
Pen colors and sizes are represented by digits to allow for a compact
option list. There are 8 colors including background (usually white).
See section Option summary, the Option Summary, for a list of all colors. E.g., color 3 is green,
and color 7 means yellow. Permitted pen sizes are 0 ... 9 units in versions
before 3.4.3, or up to 3.5mm (using characters A to Z to denote the range from
1.0 to 3.5) in later versions.
NOTE: In versions of hp2xx before 3.4.3, all raster mode pen sizes
were approximated by double, triple, etc. width, and lines wider than 4 would
normally not give useful results. In 3.4.3, the line drawing algorithm has
been substantially improved and should render accurately scaled pen widths.
Options `-c c-string' and `-s s-string' tell
hp2xx about the pens to be placed in the carousel.
c-string and s-string are strings of 1 to 8 digits,
corresponding to special choices of pen 1 to 8.
Defaults are c-string = s-string = `11111111' unless the
hpgl file contains corresponding PC and/or PW commands. Specifying `-c'
or `-s' overrides the equivalent HPGL/2 command.
If you specify less than 8 pens, the remaining pens keep their defaults.
Examples:
hp2xx -p13 foo.hp
Show a preview of `foo.hp', drawing all lines with pen #2 three pixels wide instead of default 1 pixel, which applies to all other pens.
hp2xx -c12740 -p12230412 foo.hp
Here, pen #5 is "removed". Pens #1 and #7 keep their default sizes, all others are set to various sizes. Pen #2 is red, #3 is yellow, and #4 is blue, while all other pens keep `foreground' color, e.g., black.
If your HP-GL file contains the PC and/or PW commands introduced with HP-GL/2, these are interpreted to allow up to 255 pens. The special case where a pen is redefined to take on different colors is currently only supported in PostScript or PDF output mode. In all other modes, the last PC command encountered determines that pens' color for the entire plot.
There is a HP-GL command named `PG;' which amounts to a FormFeed.
Thus, there are multi-page HP-GL sources. While hp2xx was
designed for just one output picture per input file, there is a
simple way to cope also with multi-page sources:
hp2xx keeps track of the number of encountered `PG;' commands.
All code up to the next (if any) `PG;' command is considered a
single page. Pages are counted, starting at 1. You can ask hp2xx
to ignore all HP-GL commands other than on page n with option
`-P n', effectively filtering out any one-page graphics.
Sometimes, converting a whole page range makes sense, too. Therefore,
hp2xx also accepts page ranges via `-P n1:n2'.
The default is `-P 0' which selects all pages. The output will
be split into appropriate files whose name is derived from the base name
of the input file by appending the frame number before the filetype
extension. In preview mode, each page will display as a separate image -
in contrast to versions earlier than 3.4.3, which would render everything
in one image.
WARNING: Some HP-GL sources may start with a `PG;' so the first page of your graphics may be 2 instead of 1. Look for the number of encountered pages in the diagnostic output if you miss the expected page! If the detected coordinate range shows unreasonable numbers like 1e10, you'll be probably looking at an empty page.
All HP-GL graphics are decomposed by hp2xx into elementary
move and draw commands. Selecting a vector mode essentially defines the
conversion rules of such commands into specific formats.
The most popular and versatile vector format currently is
Encapsulated PostScript (EPS). (In fact, it is much more than just a
vector graphics format, but hp2xx uses only EPS's line drawing
features.) Many programs allow importation of EPS files, and PostScript
gives excellent printing results, so `-m eps' is highly
recommended. Recently, Adobe's Portable Document Format (PDF) has mostly taken
its place for formatted online documentation. For Web-based applications,
the Scalable Vector Graphics (SVG) format, a W3C standard, holds some promise
as a non-proprietary, XML-based format for vector images, not only on web pages.
In the engineering community, the 2D DXF format originally used by AutoCAD has
become a common denominator for the exchange of vector data. In the
machine-tooling community, a standardized vector format knows as G code
is widely used (though machine-specific limitations and extensions make it
not truely universal). Its implementation in hp2xx, selectable via
the `-m nc' option, should be suitable for hobbyists wishing to
do engraving, but it would not be wise to use it in professional
machine tooling.
Unix users may also want to use either Gnuplot or especially XFig
to annotate their plots. The native formats of these programs are directly
supported via the `-m gpt' and `-m fig' options.
The Enhanced Metafile Format was originally tied to the Microsoft Windows environment, but it has recently found more wide-spread use as one of the few vector formats supported by StarOffice and OpenOffice.
Currently, all other supported vector formats represent various compromises to persuade TeX or LaTeX into the generation of graphics. See section TeX formats, if you are specially interested in TeX.
Raster graphics are probably the most widely used graphics by now.
Many publishing programs accept rasterized graphics. It's likely you'll
use hp2xx primarily in some raster mode.
In addition to vector modes, all raster modes need the desired resolution
of an assumed underlying pixel grid to plot on, i. e., the number of
pixels per unit length within that grid.
A traditional measure is the number of "dots per inch" (DPI).
hp2xx makes an exception from its usual unit length mm and
lets you specify the traditional DPI values.
Option `-d num' affects both x and y direction, num being
the DPI value (an integer). if `-D num_y' is also specified,
num_y will override the num DPI value, but only for the y
direction.
Some programs were found, which generate HPGL output with too tight clipping
bounds, which lead, for example, to some parts of text characters clipped off.
Use option `-e num' to add some extra amount of space to clip areas
to work around such problems. For example, `-e 40' will add 40 extra
plotter units to every side of the clipping box, which corresponds to 1 mm
in true size.
There are plenty of raster formats on various platforms, much more
than hp2xx will ever handle. The supported raster formats
IMG, JPG, PBM/PPM, PCL, PCX, PNG and TIFF were chosen for their widespread use, their simplicity,
for actual demand, and for accessibility of specifications.
If your desired format is not supported, look for a converter. E.g., the
Portable Bitmap (PBM) project and more recently, the ImageMagick package
offer quite a variety of such converters.
Please note that the preview mode (which does not create any output file) is a special raster mode. Instead of going into some output file, the internal bitmap is transferred into display memory. Therefore, the above considerations apply also to preview mode.
Currently, there is only one well-tested printer format (not counting `eps', which is printable on PostScript printers): `pcl', which stands for HP PCL Level 3. Essentially it is a raster format, but it comes with a few restrictions and additional options which correspond to printer properties. It prints on HP Laserjet and HP Deskjet series printers and compatibles.
The restriction concerns the resolution (DPI) during rasterization. Due to
printer hardware limitations, only `-d 75', `-d 100', `-d 150',
and `-d 300' are recommended (hp2xx will emit a warning for other
values, but will try to create the desired output); option `-D' must not
be used. Some recent printer models do support 600, 720 or even higher
resolutions, but even for those the requirements both in terms of cpu load
and file size may be prohibitive at least on older systems.
There are two flags which may be useful if the output goes directly to a printer: Option `-i' initializes the printer and tries to select the required paper format before the output starts, and `-F' sends a FormFeed (ASCII 12) after the output.
For the HP Deskjet printer series, there is support of some "special"
commands; `-S 1' activates these. There is a limited support of color
modes available, too: For the DJ500C and newer models, hp2xx can
generate both CMY-based and CMYK-based color output (if colors are used:
see option `-c'). Supply option `-S 3' for CMY color mode, and
option `-S 4' for CMYK color mode (for the DJ550C). The Deskjet modes
automatically invoke TIFF compression (mode 2), while pure PCL Level 3
does not know about compression. NOTE: Some recent low-end Designjet
plotters (if ordered without the HPGL processor board) and probably also
some models of Deskjet use a sparsely documented variant called PCL3GUI
which appears to differ at least in the initialization sequence used.
Currently hp2xx will not work well -- maybe even not at all -- with
such printers.
A driver for the Esc/P2 raster language used by the Epson Stylus series
of inkjet printers has been added in hp2xx-3.4.0. This should work
at least for the small-format printers at 720 dpi.
Preview mode is hp2xx's default. Its use prior to all other
conversions is recommended since it offers a good impression of your
final results. Functionally it is also a raster mode.
Depending on your hardware and operating system platform,
hp2xx uses one of a variety of preview modules.
On GUIs, a window containing the graphics will pop up, while on other
systems the whole screen may be used for preview. You can control the
position of a preview window via options `-o' and `-O' in
a natural way. In full-screen previews, unused spaces are padded to the
right and bottom with background color.
Since there is no way for hp2xx to predict the actual size and
resolution of your preview device, e.g., screen, you may have to
gauge hp2xx's preview mode (using options `-whdD'). For example,
if your device effectively works at 86 DPI and offers an active area of
24 by 18 cm,
hp2xx -d86 -w240 -h180 foo.hp
will make maximum use of your screen area and give you correct sizes.
Since a single gauge will do for all future calls, you'll probably want
to create some one-line batch file for invoking hp2xx in preview
mode, correctly gauged for your screen.
Depending on page offsets and the selected sizes and resolutions, a preview may not fit on your screen. In that case, some preview modules simply clip the picture; others give a warning but let you continue (DOS), and others simply terminate.
The X11 viewer allows to pan the visible area using mouse button one (which usually corresponds to the left button), and supports one level of zoom around the current cursor position, selectable with button two (middle button, or right button on two-button mice).
DOS users: Most VGA cards offer high-resolution modes (SVGAs). Unfortunately,
there is no software standard for these modes. hp2xx lets you
utilize these modes anyway with just a little help from you.
Tell hp2xx the so-called mode byte of your favorite hi-res mode
via option `-V num'. Since hp2xx issues only standard
BIOS calls for mode switching, setting of color look-up table entries,
and pixel drawing, chances are good that your VGA card's hi-res modes
will work!
WARNING: You can damage your hardware by specifying inappropriate VGA modes! Generally you'll need a monitor which can sync on the horizontal frequency of the selected VGA hi-res mode, e.g., a multi-scan monitor. In case of doubt, switch off your monitor immediately!!
hp2xx features an on-line options summary. Invoking hp2xx
with option `-H', or with any illegal option or without any
parameter, will display about 2 pages of text. (Note: I'd have preferred
option `-h' for on-line help, but this option is needed by the
indispensable height parameter.)
The list of supported output files (displayed for the `-m' parameter)
shown in the help text always corresponds to the selection actually
compiled into that particular executable copy of hp2xx (which may
vary according to licensing considerations, local availability of third-party
libraries, or preferences of whoever built it).
During operation, hp2xx outputs various information about the current
HP-GL file and about hp2xx's actions. As usual, all this goes to
stderr. You can re-direct these diagnostics into a file even without
any help from a UNIX shell by specifying a log file using option
`-l logfile', or you may switch off diagnostics completely
with option `-q' (`quiet' mode). NOTE: Using both options
as in `-q -l logfile' is of no use as it will result in an
empty logfile.
Finally, there is a simple way to rotate whole pictures: Option `-r angle' rotates the picture counter-clockwise by the supplied angle (given in degrees). E.g.,
hp2xx -r90 foo.hp
will show the picture rotated by 90 degrees, letting vectors originally pointing left-to-right now point botttom-to-top. This may be handy e.g. for printing in landscape format. NOTE: The limiting rectangle supplied by `-hw' is not affected by `-r', so in order to obtain e.g. a full-page landscape picture on an A4 page, issue a command similar to:
hp2xx -m pcl -d 150 -r90 -h270 -w160 landscape.hp
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