Vplot
(or, why I took 7 ½ years to graduate...)
Reproducible research workshop
UBC, Vancouver, 2006
Joseph A. Dellinger
geojoe@freeusp.org
Where did Vplot come from?
• SEP was one of the first users of Unix
• Jon just loved to buy fancy new graphics devices
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Gould (200 dpi printer)
Varian (300 dpi printer)
Several flavors of Tektronix
Gigi (oooh, 8 colors!)
Envision (even better, 8 _settable_ colors!)
RasterTek (the “Movie” machine: 256 settable colors! WOW!)
• Each of these devices had its own proprietary protocol
• People wanted to plot on all those different devices
without having to rewrite their program for each one!
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Where did Vplot come from?
• Rob Clayton, circa 1979, came up with the idea
of a “virtual device”
• The “V” originally stood for vector because
originally the language only supported lines,
polygons, and text
• Dave Hale (?) invented a vector font for it
(Later we also added Hershey fonts, which look nicer...)
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Where did Vplot come from?
• The virtual device had its own proprietary binary
encoding, just like all the other devices of the time did.
• Commands were an ascii single character possibly
followed by one or more short ints (not too dissimilar to
“tektronix vector language”) or a null-terminated text string
• “e” – “erase”
• “m short short” – move to x, y
• “d short short” – draw from current position to x, y
• “c short” - change to new pen color (0-7)
• “T short short text \0” – print vector text of given height and orientation
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Where did Vplot come from?
• The virtual device had a plottable area and
resolution designed to be compatible with the
various devices of the time
• 600dpi (multiple of 200dpi and 300dpi)
• 8 colors
• 4 by 3 aspect-ratio screen
• screen 10.24 inches tall
• a “pen” filter was written for each device to
translate vplot language into that device’s
language
• very quickly the different pen programs started diverging
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... and Joe arrived
• I was given the job of writing a new “pen” program for the
envision (a fancy color text / graphics terminal)
• ... and maintaining the existing diverging pen programs
• ... and fixing all the bugs in them
(YIKES!)
• I ended up writing a whole new routine for reading vplot.
That was the “device-independent” part.
• It called a structure of function pointers.
• That “dev” structure contained the only device-dependent
code.
• I ripped out the device-dependent subroutines and grafted
them onto my new structure, unifying all the diverse codes.
• New vplot commands such as “raster” could be supported
and immediately work consistently on ALL devices (!!!)
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The device structure
struct device{
/* control routines */
int (*open)();
int (*reset)();
int (*message)();
int (*erase)();
int (*close)();
The even better trick: generic high-level routines.
These digested complex commands into simpler ones.
For example: a polygon could be filled by drawing
vectors back and forth inside it, like mowing the lawn.
/* low level output * called by the generic high level output routines
*/
int (*plot)();
int (*startpoly)();
int (*midpoly)();
int (*endpoly)();
/* high level output */
int (*vector)();
int (*marker)();
int (*text)();
int (*area)();
If you didn’t care about supporting the device efficiently,
int (*raster)();
all you really needed to support were these low-level
int (*point)();
routines plus the control ones, and the device could then
int (*attributes)();
do “everything”. Slowly, perhaps, but it worked.
/* input */
int (*getpoint)();
int (*interact)();
};
That’s how we could add “raster” capabilities to vplot and
immediately have EVERY device suddenly able to do
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raster.
Supporting a new device
• First, support the commands for “move”, “draw”, “erase”,
“change drawing color”
• Add in other routines as needed to improve plotting
efficiency
• One person could be writing and debugging one devicedependent routine while another person worked on
another. The device-independent and device-dependent
parts could be worked on simultaneously as well.
• Vplot had an extensive test suite that deviously
exercised every part of the language, so you could test
whether new code was really working or not, and check
that no unanticipated bugs had been introduced.
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For example, this one tests whether polygon fill is working properly.
Drawing a polygon that intersects a clipping window can be a little
tricky. A majority of the intrinsic native “polygon” commands on
devices we bought failed this test, so we ended up using the generic
vplot routine much of the time. It often even turned out that filling a
polygon by drawing a bunch of vectors was faster than using the
device’s built-in polygon fill command, too.
This one tests whether the width of fat lines, height of characters, positions
of characters, and dashed-line intervals are all true to scale.
Oh, but we’re so much more advanced today!
• Really? I’m not so sure.
Today our incompatible plotting devices
are called:
– X [8-bit, 16-bit, 24-bit, different screen resolutions
and shapes...]
– gif, tiff, jpeg, png, etc...
– postscript, encapsulated postscript,
postscript level 3, etc
– fig, etc...
• Maybe vplot still has a place...
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Challenges
• Even the concept of a “virtual device” is
surprisingly slippery:
– Fit to screen, or true scale?
– Aspect ratio of screen?
– Color, black and white, grey scale, or grey simulated by
dithering?
– Black background or white? If black is white, what happens to the
other colors, then? Does raster invert too?
– Should text scale anisotropically or not?
– How to handle multi-frame plots?
– How to shield the user from device inadequacies?
(e.g., generic routines for missing capabilities, pixc + greyc,
dithering in software, limited number of colors...)
• We did the best we could...
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Oops, hit a bug in the ppt postscript converter!
This should be a uniform grey scale. It does a
really sucky job on fattening vectors, too.
Letting vplot rasterize the plot
produced a more pleasing result.
“Lost” Lore
• Test suite
(I still have a copy...)
• Documentation
(of that, too)
• Forgotten commands
• Plotting tricks
• Tricks with text
• Tricks with vppen
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Vplot documentation and tests
Tests:
TEST_align
TEST_alignh
TEST_aspect_ratio
TEST_clipping
TEST_colormask
TEST_colors
TEST_coltab
TEST_Cyrillic
TEST_erase
TEST_greycol
Documentation man pages:
libvplot.mn
pspen.1
pen.mn
pstexpen.1
TEST_hatch
TEST_limit
TEST_orient
TEST_pattern
TEST_rascolor
raspen.1
vplot.mn
TEST_raster
TEST_size
TEST_text
TEST_white
vplotraster.mn
vplottext.mn
vppen.1
xtpen.1
Description of how to support a new device:
vplothacker.txt
Folks don’t expect codes to have test suites or documentation....
and so even if you do have it originally, it tends to first get forgotten,
then lost. Madagascar/RSF is built around the premise that tests
should exist.
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Forgotten commands
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Some plotting tricks
Note, I plotted the dashed line twice!
First thick and black, then thinner and red.
The dashed line is from “Contour”, using
the same plot position as the raster plot.
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pldb < fig.v | sed –e ‘s/Cusp/Asparagus/’ | plas > fig2.v
vplot2gif fig2.v fig2.gif yscale=.5 txscale=1.5 dashscale=3
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Spike k1=5 n1=10 | Graph title=‘\s200 \F11 CHebyshchev\^\s100 2’ out=plot.v
vplot2gif plot.v plot.gif fat=3 scale=1.5 yscale=.7
Vplot fonts support ligatures. Here note “CH” and “shch” are single characters. 19
pstexpen align.v align.eps fat=4 color=y
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pstexpen align.v align.eps fat=4 color=y yscale=.6 txscale=1.2
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pstexpen align.v align.eps fat=4 color=y yscale=.6 txscale=1.2 \
txsquare=no
Programs that include text in their graphics should justify their
output text properly, so that labels grow and shrink the right way.
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vppen: the pen filter for the virtual vplot device
• There are quite a lot of parameters that can
be used to transform a plot while plotting it
• Once you like the result, plot it with “vppen”
• It then writes back out a vplot file that will
produce what you see without needing any
transformation parameters
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vppen align.v fat=4 yscale=.6 txscale=1.2 txsquare=no > alignv.v
pstexpen alignv.v alignv.eps color=y
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Other things vppen can do
•
Instead of plotting, it can tell you the size
and position of a plot (this is how
vplot2gif and pstexpen can work)
vppen stat=y *.v
demo_bering.v:
demo_impulse.v:
demo_jon.v:
demo_reciprocity.v:
h=
h=
h=
h=
7.81
5.85
6.39
6.61
w= 12.07; x=(
w= 7.95; x=(
w= 13.45; x=(
w= 6.20; x=(
0.42, 12.49) y=(
0.62, 8.56) y=(
0.14, 13.60) y=(
0.70, 6.90) y=(
1.07,
0.77,
0.74,
0.40,
8.88)
6.62)
7.12)
7.01)
All 4: h= 8.48 w= 13.46; x=(
Total 4 plot frames.
0.14, 13.60) y=(
0.40,
8.88)
It can also combine plots in various ways...
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vppen demo*.v gridnum=2,2 grid=2 > junk
pstexpen junk junk.eps color=y fat=2
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vppen demo*.v gridnum=2,2 grid=2 rotate=-20 > junk
pstexpen junk junk.eps color=y fat=2
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If you really go crazy
then you can put some
quite complicated stuff
together with vplot.
This figure predates
the existence of
matlab, mathematica,
and postscript...
Where to from here?
• Enhance programs like “Wiggle”, “Graph”,
“Grey” to better use vplot?
• Use some of the system’s features that
were never really used, such as:
– named groups
– the “interact” option
– user-defined fonts
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Where to from here?
• Keep the rendering software but switch to
a more modern plot language?
• Take the chance to abandon backwards
compatibility and fix a few things?
• Take the chance to make some
improvements such as anti-aliasing raster,
more colors at a time, etc?
• How can “lore” be preserved?
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Care to hear more about any of
these technical points?
• The concept of a “virtual device” is slippery:
– Should text scale anisotropically or not?
– Black background or white? If black is white, what happens to the
other colors, then? Does raster invert too? What happens if you
redefine color 0 (= the background color) halfway through?!
– Color, black and white, grey scale, or grey simulated by
dithering?
– Fit to screen (size=r), or true scale (size=a)?
– Aspect ratio of screen (stretchy or rigid)?
– How to handle multi-frame plots?
– How to shield the user from device inadequacies?
(e.g., generic routines for missing capabilities, pixc + greyc,
dithering issues, limited number of colors: vp_rascoltab...)
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Thanks!
• to Sergey for inviting me
• to BP for letting me come
• to all the people who helped create and
support vplot, especially:
Jon Claerbout,
Glenn Kroger,
Dave Nichols, and
Steve Cole
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