=====================================================================
GRAPHICS ON CP/M KAYPROS
by Peter Donnelly
964 Heywood Ave., Apt. 220
Victoria, B.C.
Canada V8V 2Y5
January 1986
=====================================================================
The graphics capabilities of the Kaypro are generally not well
documented; indeed, buyers of the new Kaypro 1 might read the user's
guide from cover to cover without obtaining the slightest hint that
their machine has graphics at all.
The purpose of this article is to assemble some facts so that
the reader can use the Kaypro graphics fully - at least, as fully as
can be done without resorting to machine language. As far as I know,
what is said here applies to all CP/M Kaypros manufactured since
1984, and to earlier model 10s.
1. ESCAPE SEQUENCES
Some screen functions are handled through escape sequences: that
is, a string consisting of the ^[ character plus one or more other
characters is sent to the screen. In MBASIC the sequence "ESCape, B,
0" (as it appears in the Kaypro manual) would take the form:
PRINT CHR$(27) + "B0";
or PRINT CHR$(27); "B0";
When variable integers form part of an escape sequence they are
sent in the form of the character having that ASCII decimal number.
For example, to position the cursor at row R, column C, where the
general form of the sequence is "ESC, =, row + 32, col + 32", you
would use this command:
PRINT CHR$(27) + "=" + CHR$(R + 32) + CHR$(C + 32);
Escape sequences can also be sent from the system prompt by pressing
the ESC key followed by the appropriate letter keys, then RETURN. The
system will echo the command to the screen, followed by a question
mark, and as a result the escape sequence will take effect. This is
handy when you break out of a program unexpectedly and find that your
cursor has disappeared or that everything is still in inverse video,
and you want to restore things to normal without a cold boot. (It's
also handy - though this has nothing to do with graphics - for
sending escape sequences to set up a printer. Just add ^P to the
sequence.)
2. CONTROL CHARACTERS
Certain control characters, when ordered to be printed to the
CRT, will manipulate screen output; these are summarized in the
appendix. They can be sent by a program, or like escape sequences
they can be entered at the system prompt. For example, to clear the
screen at the prompt just type CTRL-Z RETURN.
Cursor movement through control characters is limited. You
cannot backspace, for example, over an empty part of the screen;
something has to have been printed there, if only spaces.
3. CURSOR ADDRESSING
The cursor can be sent to any point on the screen through the
escape sequence mentioned in paragraph 1 above.
MBASIC has a peculiarity worth mentioning. Because there is a
limit on how much it will handle as a string without a carriage
return, you cannot just keep sending the cursor from one point to
another with an input loop; if you do, MBASIC will respond by
spitting out odd characters and line feeds. The solution is to insert
into the loop another command like PRINT CHR$(30) (with no
semicolon).
Remember, every time the cursor prints a character it will
advance. Thus the last column of row 24 is effectively off-limits if
you want to preserve a whole screenful of graphics; when you print
something there the cursor will try to drop down and thus force
everything to scroll up a line.
4. STATUS LINE
The so-called status line is the 25th line of the screen, and it
is only accessible through direct cursor addressing. If you turn on
"status line preservation," anything printed on the line will remain
there despite whatever happens on the screen above, whether scrolling
or clearing.
5. SPECIAL EFFECTS
The four special video effects - inverse video, reduced
intensity, blinking, and underlining - can be toggled on and off with
escape sequences and can be used in any combination. They affect only
what is printed while they are toggled on, and they apply to all
characters, whether keyboard characters or graphics.
The Kaypro has no true highlighting; the only way the effect can
be emulated is to print most things at half-intensity and the
"highlighted" strings at normal intensity. But of course this makes
it necessary for the user to adjust his screen brightness control.
My own view is that half-intensity should never be used for text
except in combination with inverse video. A number of programs,
including a few commercial ones, use a combination of normal and
half-intensity text to highlight key letters in menus and so on, and
the result is less than satisfactory. Most people, I'm sure, have
their screens adjusted so that normal text is comfortably readable,
and at this setting half-intensity uninverted text almost disappears.
(Particularly puzzling is TURBO PASCAL's installation for "Kaypro
with highlight," where what ought to be highlighted is in fact
printed at half-intensity; and if you turn your screen up to make
these parts reasonably visible, everything else including the text on
the editing screen becomes uncomfortably bright. While it's possible
to modify this feature, the installation program doesn't allow a long
enough escape sequence to set highlighting to half-intensity AND
inverse.)
6. THE ASCII GRAPHICS
(A.) In addition to the ordinary keyboard characters, the Kaypro
terminal is capable of displaying a number of graphics characters
each occupying one "cell," the screen being made up of 25 by 80 such
cells. All post-1984 machines have what might be called "block
graphics" associated with the upper part of the ASCII set. Any of
these graphics can be displayed by a simple command to send the
character of the appropriate number to the screen, e.g. PRINT
CHR$(255).
The characters are made up of eight pixels or tiny squares, each
either green ("on") or black ("off"). These graphics can be seen as
eight-bit binaries where the upper right corner is the least
significant bit, the upper left the next most significant, and so on
to the lower left corner, which represents the most significant bit,
or 2 to the 7th power. A cell may be mapped as follows, with the
numbers representing the amount added to the bit value of the
character if that pixel is "on":
-----------
| 2 | 1 |
-----------
| 8 | 4 |
-----------
| 32 | 16 |
-----------
|128 | 64 |
-----------
The first of the graphics characters is #128, a blank space,
with a bit value of 0; the last is #255, which is lacking only the
lower left corner and so has a value of the sum of the first 7 powers
of 2, or 127. It is thus possible to derive the form of any of these
graphics characters from its ASCII number, the bit value being the
ASCII number minus 128.
Having reached the upper limit of the ASCII set without finding
any characters which have the lower left corner filled in, we now
have to go into inverse video, where we encounter another 128
symbols, each the negative image of its counterpart and thus having
the inverse (or ones complement) bit image; #128, for example, binary
0000 0000, now becomes a full block whose on-bits, 1111 1111, total
255. The bit value of each inverse character is 383 minus its ASCII
number.
The state of any pixel in a given graphics character can be
determined by an arithmetic "and" test. Let "y" be the bit value of
the character as determined from its ASCII number and the state of
inverse video, let "x" be the power of 2 corresponding to the
position of the pixel in question, and let "pixelon" be a Boolean
returning "true" if the pixel is illuminated. The statement in Pascal
would then take the form:
if (x and y) > 0 then pixelon else not pixelon;
This determination is the key to writing a routine to translate the
screen graphics into terms your printer can understand. (See section
11 below.)
(B.) The Kaypro video controller is capable of displaying a number
of other graphics including thin horizontal, vertical, and diagonal
lines, triangular blocks, and mathematical symbols. Each of these
graphics is, again, associated with an ASCII number, this time in the
range 0-31. (One of the triangles also shows up mysteriously as #127,
the DEL character.)
Unfortunately, these graphics won't always appear on demand. To
begin with, your programming language may interpret a character in
this range as a control code. MBASIC, for example, always treats
CHR$(9) as a horizontal tab. (Ever notice that you can't use it as
part of an escape sequence in an MBASIC printer set-up?) Second, the
operating system itself may also insist on treating certain
characters as control codes (e.g. #7 as a bell, #13 as a carriage
return).
In the Kaypros running CP/M 2.2u it appears that ALL characters
in the lower range are scooped up before reaching the screen, even
those that have no active control function. A command like PRINT
CHR$(1) produces nothing at all.
On "older newer" models like my '84 2X it's possible to print 20
or so of these low-range characters with simple "write" commands in
Pascal, and most of these are also accessible through MBASIC. I can
also conjure them up by typing the matching control code at the
system prompt and pressing RETURN. But there's no way to coax out the
graphics that lie behind active control codes like ^G, ^J, ^M, and
^Z.
It is a frustrating situation for the programmer. One could have
hoped for a simple escape sequence that would somehow disable the
control codes and allow the full potential of the video chip to be
exploited. However, if such a sequence exists it is a well-kept
secret. Consequently if you want to see the full menu of Kaypro
graphics, or use them, you'll have to turn to the KBOARD segment of
the commercial program REMBRANDT (by DG Systems), which accesses them
by doing an end-run around the BIOS and taking direct control of the
video chip. Where the capable author of that program has gone I dare
say not many will follow.
7. PIXEL GRAPHICS
Since each block graphics character is made up of 4 rows and 2
columns of pixels, the screen may be seen as an array of 100 by 160
pixels, and with the appropriate escape sequence we can fill in any
individual pixel on the screen.
The terminal is not actually printing every pixel location
independently; it's really just assigning an ASCII block graphic to
each cell of eight pixel locations and changing it whenever a pixel
is added or taken away. For the programmer this doesn't make a great
deal of difference, but you will notice that a pixel is printed in
half-intensity when it is plunked down among half-intensity
neighbors. You will also find that pixels can't be printed in a cell
where there is already a keyboard character, even if there wouldn't
be any actual overlap.
8. VIDEO MODE
So far all I've been able to discover about video mode is that
when it's turned on you must print a graphics character twice, or two
graphics characters in succession, before anything appears on the
screen. Then what you see is the first character printed normally,
and the second character superimposed with the bits "swapped"; i.e.
the value of the least significant bit is traded for the most
significant, and so on. Thus #129 (upper right bit "on") and #255
(lower left bit "off") can be printed together to make a solid block,
and indeed all the block graphics with the high bit (lower left
corner) "on" can be generated by superimposing a "swapped" #129 on
the ASCII characters from #128 to #255. This is another way of doing
what one can do with inverse video; whether it has any advantages I
cannot say.
9. THE TYPE COMMAND
The TYPE command will read any text file, and text files can
include graphics and escape sequences.
Most word-processing programs won't normally allow the insertion
of non-keyboard characters into text. You can sneak them in with
Xpert Software's XTRAKEY, which allows you to turn any keyboard
character into a block graphic by setting the high bit "on," i.e.
adding 128 to the ASCII number. The graphics won't show up within the
word-processing program, but they will be TYPEable. (WordStar users
must go into non-document mode to prepare TYPEable files, since
document mode uses the high bit for its own purposes.)
For portability, TYPEable files and indeed any graphics routines
shouldn't include characters that might not show up on another
machine such as the Kaypro 1 - namely the phantom graphics from the
lower part of the ASCII set. On such machines these characters will
not even show up as spaces; rather nothing at all will be printed,
and so the alignment of columns will be thrown out of whack.
10. GRAPHICS UNDER ZCPR
The alternative operating system ZCPR disables the Kaypro
graphics, and while there is a command to re-enable them, helpful
programmers can save the user the trouble by poking the byte FF into
location 004F at the beginning of any graphics routine, and restoring
the value 00 at the end. There appears to be no conflict with CP/M.
11. PRINTING GRAPHICS
It would be nice if you could print any graphics character just
by sending the appropriate ASCII number to the printer, but
unfortunately this is not the case. Most dot-matrix printers have
italics and international characters associated with the upper half
of the ASCII set; if there is an alternative graphics set, it will be
for the IBM system.
Consequently, to print the Kaypro block graphics you must put
the printer in "graphics mode" and define which pins are to be fired
at each impact. This means breaking the graphic character into its
two component columns and examining each of these for "on" pixels,
then converting the bit-sum of the column into the byte required by
your printer so that it knows which pins to fire as it prints that
column. How many pins you will use for each pixel, and how many times
they will be fired, will depend on the size and proportions of the
desired result. For example, using standard density graphics on the
Epson - 480 dots per line - to reproduce the full width of the screen
(160 pixel columns) as the full width of the paper, the pins would be
fired 3 times for every column, and 2 of the 8 pins would be used for
each "on" pixel.
As for the graphics in the lower part of the ASCII set, they
would presumably have to be individually designed as "downloadable
characters" - a large task - and then downloaded to the printer to be
printed in text mode.
12. AVAILABLE SOFTWARE
At least three commercial and two non-commercial drawing
programs are now available for the Kaypro. I will describe briefly
those I've had experience with.
SCS-DRAW (Second City Software, Box 267960, Chicago IL 60626)
A very likeable program for designing images to be printed to
paper. Drawing is done in black on a large green canvas of 336 x 362
pixels, a portion of which is displayed in a window that occupies
about two-thirds of the screen, the rest being taken up by a menu and
window-position indicator. While inversion is used to good effect
(you can draw a line that shows black against green and green against
black), every pixel is simply either on or off, and hence there are
no real video effects like half-intensity or blinking. A nice touch
is that you can draw or erase a single pixel without leaving "move"
status, saving much confusion. Text can be added in a choice of
rudimentary fonts and enlarged to as much as banner size. There are
many other features including cut-and-paste, merging of images in
various ways, automatic drawing of lines, circles, and rectangles,
easy block erase, rapid cursor moves, pattern-fill, and on-screen
enlargement in two separate dimensions. Options at the printing stage
enable further enlargement, flipping, rotating, and repeating of
images. The program is helpful, quick, and easy to use throughout.
REMBRANDT (DG Systems, 22458 Ventura Bvd., Ste. E, Woodland Hills, CA
91364)
REMBRANDT is both screen- and printer-oriented, a good all-round
program that is the only one to exploit all the graphics capabilities
of the Kaypro. Drawing is done with the entire ASCII set - all 256
characters - on a full-screen canvas. You have 10 graphics characters
on your "palette" at one time, choosing one by striking a number key
- painting by numbers, as it were. Ordinary keyboard characters can
be typed in anytime. Access to the fine-line graphics makes possible
much more varied effects than the block graphics allow, such as
graphs that look like they're drawn on graph paper. Screens can be
chained together for presentation in a "slide-show" format with
various effects such as fade-in. Auxiliary programs will prepare
various types of graphs automatically from entered data. REMBRANDT
puts out good printed images, and reproduces half-intensity on paper
as well as on the screen, but as a printing program it is less
flexible than SCS-DRAW; nor is the overall presentation as attractive
and fast-moving.
DDRAW (non-commercial; available from many sources)
This pioneer program uses pixel drawing and keyboard characters
on a full-screen canvas. Features include automatic drawing of
circles, lines, and rectangles and filling of enclosed areas. All the
video effects are available; they are added to blocks after they have
been drawn. The cut-and-paste routine is limited to smallish areas
with no text, but you can store up to four details (called
subpictures) in memory to be shuffled about at will. An optional
status line keeps track of the cursor position and the drawing/
erasing/moving status, and there is a separate screen giving a menu
of commands. Files can be saved in TYPEable format, something that is
not true of either of the commercial programs reviewed. DDRAW fully
supports the Gemini printer; my Panasonic (a machine similar to the
Epson) will print the graphics small but not text and graphics
combined.
ARTIE (non-commercial; if all else fails, send me a postal money
order for $5 at the above address)
My own entry into the field. ARTIE uses the ASCII graphics,
including (on machines where they are TYPEable) some from the lower
range. Graphics can be chosen from a palette above the canvas or from
a separate menu. You can cover the canvas more quickly than with
DDRAW, but that program is better for detailed sketching. (DDRAW
files can be read into ARTIE screens, so it's possible to have the
best of both programs.) The canvas is only 20 lines but an auxiliary
program links two files to make a 24-line display. Details can be cut
and moved or written to file, then read back into the screen with
various video effects added. Rapid fill and empty functions; disk
logging and directory of relevant files; five help screens as well as
status-line reminders; a toggle for the keyboard clicker - ARTIE is
definitely built for comfort, which is why it weighs in at 50k or so
on disk. So far the Panasonic and Diablo/Juki printers are supported,
but the emphasis is on preparing screen displays.
By the way, the Juki printer that has been distributed with
many Kaypros is supported by SCS-DRAW and REMBRANDT as well as ARTIE.
The process may be painfully slow, noisy, and ribbon-consuming, but
your daisy-wheel printer CAN produce some very good graphics.
=====================================================================
APPENDIX
ESCAPE SEQUENCES, CONTROL CODES, AND PORT COMMANDS
Cursor left ^H ASCII 7 decimal
Cursor right ^L 12
Cursor down ^J 10
Cursor up ^K 11
Erase from cursor to end of screen ^W 23
Erase from cursor to end of line ^X 24
Clear screen ^Z 26
(also cancels special effects)
Home cursor ^^ 30
The following are all preceded by ESC, character #27:
Insert line E | contrary to
Delete line R | manuals
Inverse video on/off B0/C0
Reduced intensity on/off B1/C1
Blinking on/off B2/C2
Underlining on/off B3/C3
Cursor visible/invisible B4/C4
Video mode on/off B5/C5
Remember/recover cursor position B6/C6
Status line preservation on/off B7/C7
Cursor address =, row + 32, col + 32
Where row and col refer to the matrix of 100 by 160:
Print pixel *, row + 31, col + 31
Erase pixel #32 (space), row + 31, col + 31
Print line L, row1 + 31, col1 + 31, row2 + 31, col2 + 31
Erase line D, row1 + 31, col1 + 31, row2 + 31, col2 + 31
The following two commands are shown in their MBASIC format:
Stop cursor blinking OUT 28, 10: OUT 29, 0
Turn cursor to underline OUT 28, 10: OUT 29, 15*
(* or 79 or 111 for blink rate)
In Pascal these commands would take the form port[28]:= 10; etc.
=====================================================================
POSTSCRIPT
I would like to offer my thanks to those who have shared their
knowledge of this somewhat obscure subject; I will not name them,
because the mistakes here are all my own. Corrections and additions
will be most welcome at the above address.
=====================================================================