SKETCHPAD
`A MAN-MACHINE GRAPHICAL COMMUNICATION SYSTEM*
`
`Ivan E. Sutherland
`Consultant, Lincoln Laboratory**
`Massachusetts Institute of Technology
`
`I.
`INTRODUCTION
`The Sketchpad system makes it possible for
`a man and a computer
`to converse rapidly
`through
`the medium of line drawings. Here(cid:173)
`tofore, most interaction between man and com(cid:173)
`puters has been slowed down Ly the need to
`reduce all communication to writ ten statements
`that can be typed;
`in the past, we have been
`writing
`letters
`to rather
`than conferring with
`our computers. For many types of communica(cid:173)
`tion, such as describing
`the shape of a me(cid:173)
`chanical part or the connections of an electrical
`circuit,
`typed statements
`can prove cumber(cid:173)
`some. The Sketehpad system, by eliminating
`typed statements
`(except for legends) in favor
`of line drawings, opens up a new area of man(cid:173)
`machine communication.
`
`AN INTRODUCTORY EXAMPLE
`To understand what is possible with the sys(cid:173)
`tem at present let us consider using it to draw
`the hexagonal pattern
`in Figure 4. We wi11
`issue specific commands with a sd of push but(cid:173)
`tons, turn functions on and off with switches,
`indicate position information and point to exist(cid:173)
`ing drawing parts with the light pen, rotate
`and magnify picture parts by turning knobs,
`and observe the drawing on the display system.
`This equipment as provided at Lincoln Labora-
`
`tory;s TX-2 computer 1 is shown in Figure 1.
`When our drawing is complete it may be inked
`on paper, as were all the drawings in this paper,
`by a PACE plotter. 15
`If we point the light pen at the display sys(cid:173)
`tem and press a button called "draw," the com(cid:173)
`puter will construct a straight
`line segment
`which stretches
`like a rubber band from the
`
`~'Sil·'
`Iii!!!'
`l!u:I
`
`-•·r __ ..._,
`
`Figure 1. TX-2 operating area-Sketchpad
`in use. On
`the display can be seen part of a bridge similar
`to those
`of Figure 15. The Author
`is holding the light pen. The
`push buttons "draw,"
`"move," etc., are on the box in
`front of the Author. Part of the bank of toggle switches
`can be seen behind the Author. The size and position of
`the part of tne total picture
`seen on the display are
`controlled by the four black knobs just above the tables.
`
`of Electrical Engineering, M.I.T.,
`tothe Department
`• This paper is based in part on a thesis submitted
`partial
`fulfillment of the requirements
`for the Degree of Doctor of Philosophy.
`u Operated with the support of the U.S. Army, Navy,and Air Force ..
`
`in
`
`507
`
`Falkbuilt Ex. 1019, Page 001
`
`

`

`PROCEEDINGS-SPRING
`
`JOINT COMPUTER CONFERENCE, 1963
`
`A. SIX SIDED FIGURE
`
`B. TO BE INSCRIBED IN CIRCLE
`
`location of the pen as
`to the present
`initial
`shown in Figure 2. Additional presses of the
`lines, leaving the
`button will produce additional
`closed irregular hexagon shown in Figure 3A.
`To make the hexagon regular, we can inscribe
`it in a circle. To draw the circle we place the
`light pen where the center is to be and press the
`leaving behind a center
`button "circle center,"
`point. Now, choosing a point on the circle
`(which fixes the radius) we press the button
`time getting a circle arc
`this
`again,
`"draw''
`length only is controlled by light
`whose angular
`pen position as shown in Figure 2.
`
`/
`.,,,.,,,
`
`I
`
`I
`
`/
`
`.,,... -,
`\
`-.=-..sTART DRAW l
`' ,---------...... ,
`---
`PATH OF LIGHT PEN
`" (
`\ '
`' ' J
`
`LINE SEGMENT
`
`D DO
`0
`0
`E{}J
`
`C. BY MOVING EACH CORNER
`
`D. ON TO CIRCLE
`
`E. MAKE SIDES EQUAL
`
`0
`~80
`000
`
`F. ERASE CIRCLE
`
`PATH OF LIGHT PEN
`I.,-------,
`____ .,,,
`
`\
`
`/
`(
`/
`I
`I
`l
`START DRAW__..;
`CIRCLE CENTER/
`
`\
`\
`I
`
`I
`I
`I
`I
`\
`
`TERMINATE-,
`
`ARC OBTAINED-
`,
`
`\
`
`.... ,
`
`'
`
`,_.,. .... _ ..... ----c
`
`\
`1
`I
`
`Figure 2. Steps for drawing straight
`arcs.
`
`lmei and circle
`
`Next we move the hexagon into the circle by
`to a corner of the hexagon and press(cid:173)
`pointing
`the corner fol(cid:173)
`ing the bu.tton "move" so that
`two rubber band
`lows the light pen, stretching
`to the
`it. By pointing
`line segments behind
`
`G. CALL 7 HEXAGONS
`
`H. JOIN CORNERS
`
`Figure
`
`3.
`
`Illustrative
`
`example,
`
`see text.
`
`the
`that
`terminating, we indicate
`circle and
`corner is to lie on the circle. Each corner is in
`this way moved onto the circle at roughly equal
`spacing as shown in Figure 3D.
`the vertices of the
`that
`We have indicated
`hexagon are to lie on the circle, and they will
`our further
`throughout
`remain on the circle
`If we also insist that the sides
`manipulations.
`of the hexagon be of equal length, a regular
`hexagon will be constructed.
`With Sketchpad we can say, in effect, make
`to that line, pointing
`this line equal in length
`to the lines with the light pen. The computer
`(if it is possi(cid:173)
`satisfies all existing conditions
`ble) whenever we turn on a toggle switch. This
`in(cid:173)
`done, we have a complete regular hexagon
`the entire
`in a circle. We can erase
`scribed
`circle by pointing to any part of it and pressing
`is
`the "delete" button. The completed hexagon
`shown in Figure 3F.
`
`508
`
`Falkbuilt Ex. 1019, Page 002
`
`

`

`SKETCHPAD: A MAN-MACHINE GRAPHICAL COMMUNICATION SYSTEM
`
`in Figure 4
`To make the hexagonal pattern
`we wish to attach a large number of hexagons
`together by their corners, and so we designate
`the six corners of our hexagon as attachment
`points by pointing
`to each and p~essing a but(cid:173)
`ton. We now file away the basic hexagon and
`begin work on a fresh "sheet of paper" by
`changing a switch setting. On the new sheet
`we assemble, by pressing a buttqn
`to create
`each hexagon as an "instance" or subpicture,
`six hexagons around a central seventh
`in ap(cid:173)
`proximate position as shown in Figure 3G. A
`subpicture may be positioned with the light pen,
`rotated or scaled by turning
`the knobs, or fixed
`in position by a termination
`signal, but its in(cid:173)
`ternal shape is fixed.
`By pointing
`to the corner of one hexagon,
`pressing a button, and then pointing
`to the
`corner of another hexagon, we can fasten those
`corners
`together, because
`these corners have
`been designated as attachment
`points.
`If we
`attach two corners of each outer hexagon to the
`appropriate
`corners of the inner hexagon,
`the
`seven are uniquely related, and the computer
`will reposition
`them as shown
`in Figure 3H.
`An entire group of hexagons, once assembled,
`can be treated as a symbol. An "instance" of
`the entire group can be called up on another
`"sheet of paper" as a subpicture and assembled
`with other groups or with single hexagons
`to
`make a very large pattern.
`
`INTERPRETATION
`EXAMPLE
`
`OF INTRODUCTORY
`
`example above we used
`In the introductory
`the light pen both to position parts of the draw(cid:173)
`ing and to point to existing parts. We also saw
`in action
`the very general
`subpicture,
`con(cid:173)
`and definition copying capabilities of
`straint,
`the system.
`Subpicture:
`The original hexagon might just as well have
`been anything else: a picture of a transistor,
`a roller bearing, or an airplane wing. Any
`~umber of different symbols may be drawn,
`m terms of other simpler symbols if desired,
`and any symbol may be used as often as
`desired.
`Constraint:
`When we asked that the vertices of the hexa(cid:173)
`gon lie on the circle we were making use of
`
`between picture parts
`a basic relationship
`that is built into the system. Basic relation(cid:173)
`ships
`(atomic constraints)
`to make
`lines
`vertical, horizontal, parallel, or perpendicu(cid:173)
`lar;
`to make points
`lie on lines or circles;
`to make symbols appear upright, vertically
`above one another or be of equal size; and
`to relate symbols
`to other drawing parts
`such as points and lines -have been included
`in the system. Specialized constraint
`types
`may be added as needed.
`
`Definition Copying:
`We made the sides of the hexagon be equal
`in length by pressing a button while pointing
`to the side in question. Had we defined a
`composite operation
`such as
`to make
`two
`lines both parallel and equal in length, we
`could have &PPlied it just as easily.
`
`IMPLICATIONS OF INTRODUCTORY
`EXAMPLE
`
`is en(cid:173)
`As we have seen, a Sketchpad drawing
`tirely different from the trail of carbon left on
`a piece of paper.
`Information
`about how the
`drawing
`is tied together
`is stored
`in the com(cid:173)
`puter as well as the information which gives
`the drawfog
`its particular
`appearance.
`Since
`the drawing
`is tied together,
`it will keep a use(cid:173)
`ful appearance even when parts of it are- moved.
`For example, when we moved the corners of the
`hexagon onto the circle, the lines next to each
`corner were automatically moved so that
`the
`closed topology of the hexagon was preserved.
`Again, since we indicated
`that
`the corners of
`the hexagon were to lie on the circle, they re(cid:173)
`mained on the circle
`throughout
`our further
`manipulations.
`As well as storing how the various parts of
`the drawing are related, Sketchpad stores
`the
`structure of .the subpictures used. For example,
`the storage for the hexagonal pattern of Figure
`4 indicates that this pattern
`is made of smaller
`patterns which are
`in turn made of smaller
`patterns which are composed of single hexa(cid:173)
`gons.
`If the master hexagon
`is changed,
`the
`entire appearance but not the structure of the
`hexagonal pattern will be changed. For ex(cid:173)
`ample, if we change the basic hexagon
`into a
`semicircle, the fish scale pattern shown in Fig(cid:173)
`ure 4 instantly
`results.
`
`509
`
`Falkbuilt Ex. 1019, Page 003
`
`

`

`PROCEEDINGS-SPRING
`
`JOINT COMPUTER CONFERENCE, 1963
`
`lattice with half hexagon
`Figure 4. Hexagonal
`semicircle as basic elements.
`
`and
`
`SKETCHPAD AND THE DESIGN
`PROCESS
`Construction of a drawing with Sketchpad
`is itself a model of the design process. The
`locations of the points and lines of the drawing
`model the variables of a design, and the geo(cid:173)
`metric constraints
`applied
`to the points and
`lines of the· drawing model the design con(cid:173)
`straints which limit the values of. design varia(cid:173)
`bles. The ability of Sketchpad
`to satisfy
`the
`geometric constraints applied to the parts of a
`drawing models the ability of a good designer
`to satisfy all the design conditions imposed by
`the limitations of his materials, cost, etc.
`In
`fact, since designers
`in many fields produce
`nothing
`themselves but a drawing of a part,
`design conditions may well be thought of as
`applying to the drawing of a part rather
`than
`to the part itself. When such design conditions
`are added to Sketchpad's vocabulary of con(cid:173)
`straints,
`the computer will be able to assist a
`user not only in arriving at a nice looking
`drawing, but also in arriving at a sound design.
`
`PRESENT USEFULNESS
`As more and more applications have been
`made, it has become clear that the properties
`of Sketchpad drawings make them most useful
`in four broad areas:
`For Storing and Updating Drawings:
`Each time a drawing
`is made, a description
`of that drawing
`is stored
`in the computer
`in a form that is readily transferred
`to mag(cid:173)
`netic tape. A library of drawings will thus
`develop, parts of which may be used in other
`drawings at only a fraction of the invest(cid:173)
`ment of time that was put into the original
`drawing.
`For Gaining Scientific or Engineering Under(cid:173)
`Standing of Operations That Can Be Described
`Graphically:
`
`A drawing in the Sketchpad system may con(cid:173)
`tain explicit statements about the relations
`between
`its parts so that as one part
`is
`changed the implications of this change be(cid:173)
`come evident throughout
`the drawing. For
`instance, Sketchpad makes it easy to study
`mechanical
`linkagE~s, observing
`the path of
`some parts when others are moved.
`As a Topological
`Input Device for Circuit
`Simulators, etc.:
`Since the storage structure of Sketchpad re(cid:173)
`flects the topology of any circuit or diagram,
`it can serve as an input for many network
`or circuit simulating programs. The addi(cid:173)
`tional effort
`required
`to draw a circuit
`completely from scratch with the Sketchpad
`system may well be recompensed
`if
`the
`properties
`of
`the circuit
`are obtainable
`through simulation of the circuit drawn.
`For Highly Repetitive Drawings:
`The ability of the computer to reproduce any
`drawn symbol anywhere at the press of a
`button, and to recursively include subpictures
`within subpictures makes it easy to produce
`drawings which are composed of huge num(cid:173)
`bers of parts all similar in shape.
`
`II. RING STRUCTURE
`The basic n-component element structure de(cid:173)
`scribed by Ross 10 has been somewhat expanded
`in the implementation of Sketchpad so that all
`references made to a particular n-component
`element or block are collected together by a
`string of pointers which originates within that
`block. For example, not only may
`the end
`points of a line segment be found by following
`pointers
`in the line block ( n-component ele(cid:173)
`ment), but also all the line segments which
`terminate on a particular point may be found by
`following a string of pointers which starts
`within the point block. This string of pointers
`closes on itself; the last pointer points back to
`the first, hence the name "ring." The ring
`points both ways to make it easy to find both the
`next and the previous member of the ring in
`case, as when deleting, some change must be
`made to them.
`
`BASIC OPERATIONS
`The basic ring structure operations are:
`1. Inserting a new member
`into a ring at
`
`510
`
`Falkbuilt Ex. 1019, Page 004
`
`

`

`SKETCHPAD: A MAN-MACHINE GRAPHICAL COMMUNICATION
`
`SYSTEM
`
`some specified location on it, usually first
`or last.
`from a ring.
`2. Removing a member
`in
`3. Putting all the members of one ring,
`order, into another at some specified loca(cid:173)
`tion in it, usually first or last.
`some auxiliary operation on
`4. Performing
`each member of a ring in either forward
`or reverse order.
`These basic ring structure operations are im(cid:173)
`plemented by short sections of program defined
`lan(cid:173)
`in the compiler
`instructions
`as MACRO
`treatment of zero and one
`guage. By suitable
`member rings, the basic programs operate with(cid:173)
`out making special cases.
`are used for setting up new n(cid:173)
`Subroutines
`in free spaces in the stor(cid:173)
`component elements
`are
`age structure. As parts of the drawing
`deleted, the registers which were used to rep(cid:173)
`resent them become free. New components are
`set up at the end of the storage area, lengthen(cid:173)
`ing it, while free blocks are allowed to accumu(cid:173)
`late. Garbage collection periodically compacts
`the storage structure by removal of the free
`blocks.
`
`GENERIC STRUCTURE, HIERARCHIES
`
`can perform
`The main part of Sketchpad
`basic operations on any drawing part, calling
`to particular
`specific
`routines
`for help from
`types of parts when that is necessary. For ex(cid:173)
`ample, the main program can show any part
`on the display system by calling the appropriate
`display subroutine. The big power of the clear(cid:173)
`cut separation of the general and the specific
`is that it is easy to change the details of specific
`re(cid:173)
`to get quite different
`parts of the program
`the general
`sults without any need to change
`parts.
`the separation
`In the data storage structure
`of general and specific is accomplished by col(cid:173)
`in a ring
`lecting all things of one type together
`under a generic heading. The generic heading
`contains all the information which makes this
`type of thing different from all other types of
`itself
`things. Thus the data storage structure
`contains all the specific information. The gen(cid:173)
`together under
`eric blocl<s are further gathered
`as
`blocks,
`or generic-generic
`super-generic
`shown in Figure 5.
`
`UNIVERSE
`
`VARIABLES
`
`HOLOERS
`
`CONSTRAINTS
`
`TOPO$
`
`The 11-component ele(cid:173)
`structure.
`Figure 5. Generic
`ments for each point or line, etc., are collected under the
`generic blocks "lines," "points," etc., shown.
`
`SKETCHPAD
`EXPANDING
`Addition of new types of things to the Sketch(cid:173)
`re-·
`pad system's vocabulary of picture parts
`quires only the construction of a new generic
`and the writing of
`block (about 20 registers)
`for the new type. The
`subroutines
`appropriate
`to write, as they
`subroutines might be easy
`usually are for new constraints, or difficult to
`write, as for adding ellipse capability, but at
`faces one
`task
`finite, well-defined
`least a
`to add a new ability to the system. Without a
`it would be almost impossible
`generic structure
`to handle a
`required
`instructions
`to add the
`new type of element.
`
`III. LIGHT PEN
`the light pen* is time shared
`In Sketchpad
`input for
`the functions of coordinate
`between
`positioning picture parts on the drawing and
`to existing
`for pointing
`input
`demonstrative
`picture parts to make changes. Although almost
`input device could be
`any kind of coordinate
`used instead of the light pen for positioning,
`light pen
`the
`input uses
`the demonstrative
`to remove
`optics as a sort of analog computer
`all but a very few picture
`from consideration
`its field of
`to fall within
`parts which happen
`time. Draw(cid:173)
`view, saving considerable program
`ing systems using storage display gevices of
`type may not be practical be(cid:173)
`the Memotron
`loss of this analog computation
`cause of the
`feature.
`
`light pens should
`• The reader unacquainted with
`to the paper on Man-Machine Console Facilities
`refer
`in this issue.
`by Stotz"
`
`511
`
`Falkbuilt Ex. 1019, Page 005
`
`

`

`PROCEEDINGS-SPRING
`
`JOINT COMPUTER CONFERENCE, 1963
`
`PEN TRACKING
`
`the
`tracking,*
`pen
`establish
`initially
`To
`Sketchpad user must inform the computer of an
`initial pen location. This has come to be known
`as "inking-up" and is done by "touching" any
`existing line or spot on the display, whereupon
`the tracking cross appears.
`If no picture has
`INK are always
`yet been drawn,
`the letters
`displayed for this purpose. Sketchpad uses loss
`of tracking as a "termination
`signal"
`to stop
`drawing. The user signals
`that he is finished
`drawing by flicking the pen too fast for the
`tracking program
`to follow.
`
`DEMON~TRA TIVE USE OF PEN
`the 90 7< of the time that
`the light
`During
`pen and display system are free from the track(cid:173)
`ing chore, spots are very rapidly displayed
`to
`exhibit
`the drawing being built, and thus the
`lines and circles of the drawing appear. The
`light pen is sensitive to these spots and reports
`any which fall within its field of view. Thus, a
`table of the picture parts seen by the light pen
`is assembled during
`each complete display
`cycle. At the end of a display cycle this table
`contains all the picture parts
`that could even
`remotely be considered as being "aimed at."
`The one-half
`inch diameter
`field of view of
`the light pen, although well suited to tracking
`is relatively
`large for pointing. Therefore,
`th~
`Sketchpad
`system will reject any seen part
`which is further
`from the center of the light
`pen than some small minimum distance· about
`1/a inch was found to be suitable. Fo; every
`kind of picture part some method must be pro(cid:173)
`vided for computing
`its distance from the light
`pen center or indicating
`that this computation
`cannot be made.
`After eliminating all parts seen by the pen
`which lie outside the smaller effective field of
`view, the Sketchpad
`system considers objects
`topologically related
`to the ones actually seen.
`~nd points of lines and attachment points of
`instances
`(subpictures)
`are especially
`impor(cid:173)
`tant. One can thus aim at the end point of a
`li~e even though only the
`line
`is displayed.
`Figure 6 outlines
`the various
`regions within
`which the pen must lie to be considered aimed
`at a line. segment, a circle arc, their end points
`or their intersection.
`
`'
`
`PSEUDO PEN LOCATION
`When the light pen is aimed at a picture part,
`the exact location of the light pen is ignored in
`favor of a "pseudo pe,n location" exactly on the
`If no object
`is aimed at, the
`part aimed at.
`pseudo pen location
`is taken
`to be the actual
`pen location. The pseudo pen location
`is dis(cid:173)
`played as a bright dot which
`is used as the
`"point of the pencil" in all drawing operations.
`As the light pen is moved into the areas out(cid:173)
`lined in Figure 6 the dot will lock onto the
`existing parts of the drawing, and any moving
`picture parts will jump to their new locations
`as the pseudo pen location moves to lie on the
`appropriate picture part.
`-....
`,,A
`\
`.... ,,
`I
`)
`
`/
`
`/
`
`AT LINE
`/
`,/'
`-"'------<
`'
`,
`.... ,,. 7-·
`,,
`..L~ ~------(cid:173)
`I
`1
`--1---...,-;;------t--
`~-------'-✓
`\-~-----,,'/'
`:
`I
`AT INTERSECTION
`
`+-AT
`\
`I ✓ '\
`4+--AT
`\j
`,_.,
`\
`I
`
`CIRCLE
`
`POINT
`
`lie to "aim at"
`in which pen must
`Figure 6. Areas
`existing drawing parts
`(solid Jines).
`
`the basic drawing creation and
`just
`With
`functions of "draw," "move," and
`manipulation
`"delete," and the power of the pseudo pen loca(cid:173)
`tion and demonstrative
`language programs,
`it
`is possible to make fairly extensive drawings.
`Most of the constructi.ons no.r;mally provided by
`straight
`edge and compass are available
`in
`highly accurate
`form. Most important,
`how(cid:173)
`ever, the pseudo pen location and demonstra(cid:173)
`tive language give the means for entering
`the
`topological properties of a drawing
`into
`the
`machine.
`
`IV. DISPLAY GENERATION
`The display system, or "scope," on the TX-2
`is a ten bit per axis electrostatic
`deflection
`system able to display spots at a maximum rate
`of about 100,000 per second. The coordinates
`of the spots which are to be seen on the display
`are stored in a large table so that computation
`and display may proceed
`independently.
`If,
`instead of displaying each spot successively, the
`
`512
`
`Falkbuilt Ex. 1019, Page 006
`
`

`

`SKETCHPAD: A MAN-MACHINE GRAPHICAL COMMUNICATION SYSTEM
`
`in a random
`them
`display program displays
`order or with interlace,
`the flicker of the dis(cid:173)
`play is reduced greatly.
`
`the scope corners. Now which of
`be identical,
`these intersections
`are actually
`to be used as
`starts of circle arcs?
`
`MARKING OF DISPLAY FILE
`Of the 36 bits available to store each display
`spot in the display file, 20 give the coordinates
`of that spot for the display system, and the
`remaining 16 give the address of the n-compo(cid:173)
`nent element which is responsible
`for adding
`that spot to the display. Thus, all the spots in
`a line are tagged with the ring structure
`ad(cid:173)
`dress of that
`line, and all the spots in an in(cid:173)
`stance (subpicture)
`are tagged as belonging to
`that
`instance. The tags are used to identify
`the particular part of the drawing being aimed
`at by the light pen.
`is being moved by
`If a part of the drawing
`the light pen, its display spots will be recom(cid:173)
`puted as quickly as possible to show it in suc(cid:173)
`cessive positions. The display spots for such
`moving parts are stored at the end of the dis(cid:173)
`play file so that the display of the many non(cid:173)
`moving parts need not be disturbed. Moving
`parts are made invisible to the light pen.
`
`MAGNIFICATION OF PICTURES
`The shaft position encoder knobs below the
`scope (see Figure 1) are used to tell the pro(cid:173)
`gram to change the display scale factor or the
`portion of the page displayed. The range of
`magnification of 2000 available makes it pos(cid:173)
`sible to work, in effect, on a 7-inch square por(cid:173)
`tion of a drawing about ¼ mile on a side.
`For a magnified picture, Sketchpad computes
`which portion (s) of a curve will appear on the
`display and generates display spots for those
`portions only. The "edge detection" problem
`is the problem of finding suitable end points for
`the portion of a curve which appears on the
`display.
`is
`the edge detection problem
`In concept
`trivial.
`In terms of program
`time for lines and
`circles the problem
`is a small fraction of the
`total computational
`load of the system, but in
`terms of program
`logical complexity
`the edge
`detection problem
`is a difficult one. For ex(cid:173)
`ample, the computation of the intersection of
`a circle with any of the edges of the scope is
`easy, but computation of the intersection of a
`circle with all four edges may result in as many
`as eight intersections, some pairs of which may
`
`LINE AND CIRCLE GENERATION
`All of Sketchpad's
`displays are generated
`from straight
`line segments, circle arcs, and
`single points. The generation of 'the lines and
`circles is accomplished by means of the differ(cid:173)
`ence equations:
`Xi-1 + AX
`Xi=
`for lines, and
`
`(1)
`
`(2)
`
`i indicate succes(cid:173)
`for circles, where subscripts
`c indicates
`the
`sive display spots, subscript
`circle center, and R is the radius of the circle
`in Scope Units.
`In implementing
`these differ(cid:173)
`ence equations
`in the program,
`the fullest pos(cid:173)
`sible use is made of the coordinate arithmetic
`capability of the TX-2 so that both the x and y
`equation computations
`are performed
`in par(cid:173)
`allel on 18 bit subwords. Even so, about o/.i. of
`the total Sketchpad computation
`time is spent
`in line and circle generation. A vector and
`circle generating display would materially
`re(cid:173)
`duce the computational
`load of Sketchpad.
`For computers which do only one addition
`at a time, the difference equations:
`
`I
`X; = Xi-1 + R (Yi-1 -
`
`y.)
`
`(3)
`
`should be used to generate circles. Equations
`(3) approximate a circle well enough and are
`known to close exactly both in theory and when
`implemented, because the x and y equations are
`dissimilar.
`
`DIGITS AND TEXT
`is dis(cid:173)
`Text, to put legends on a drawing,
`played by means of special tables which indi(cid:173)
`cate the locations of line and circle segments
`to make up the letters and numbers. Each piece
`of text appears as a single line of not more
`
`513
`
`Falkbuilt Ex. 1019, Page 007
`
`

`

`PROCEEDINGS-SPRING
`
`JOINT COMPUTER CONFERENCE, 1963
`
`than 36 equally spaced characters which can
`be changed by typing. Digits
`to display
`the
`value of an indicated scalar at any position and
`in any size and rotation are formed from the
`same type face as text. It is possible to display
`up to five decimal digits with sign; binary
`to
`decimal conversion
`is provided, and
`leading
`zeros are suppressed.
`Subpictures, whose use was seen in the in(cid:173)
`troductory example above, are each represented
`in storage as a single n-component element.
`A subpicture
`is said to be an "instance" of its
`"master picture." To display an instance, all
`of the lines, text, etc. of its master picture must
`be shown in miniature on the display. The in(cid:173)
`stance display program makes use of the line,
`circle, number, and text display programs and
`itself
`to expand
`the internal
`structure of the
`instance.
`
`DISPLAY OF ABSTRACTIONS
`The usual picture
`for human consumption
`displays only lines, circles,
`text, digits, and
`instances. However, certain very useful ab(cid:173)
`stractions which give the drawing
`the proper(cid:173)
`ties desired by the user are represented
`in the
`ring structure
`storage. For example, the fact
`that
`the start and end points of a circle arc
`should be equidistant
`from the circle's center
`point is represented
`in storage by a ''constraint"
`block. To make it possible for a user to manip(cid:173)
`ulate these abstractions, each abstraction must
`if desired.
`be able to be seen on the display
`Not only does displaying abstractions make it
`possible for the human user to know that they
`exist, but also makes it possible for him to aim at
`them with the light pen and, for example, erase
`them. To avoid confusion, the display for par(cid:173)
`ticular
`types of objects may be turned on or
`off selectively by toggle switches. Thus,
`for
`example, one can turn on display of constraints
`as well as or instead of the lines and circles
`which are normally seen.
`is on, con(cid:173)
`If their selection
`toggle switch
`straints
`are displayed as shown
`in Figure 7.
`The central circle and code letter are located
`at the average
`location of the variables con(cid:173)
`strained. The four arms of a constraint extend
`from the top, right side, bottom, and left side
`of the circle
`to the first, second,
`third, and
`fourth variables constrained,
`respectively.
`If
`fewer than four variables are constrained, ex-
`
`®
`
`Figure 7. Display of constraints.
`
`In Figure 7 the con(cid:173)
`cess arms are omitted.
`straints
`are shown applied
`to "dummy varia(cid:173)
`bles," each of which shows as an X.
`Another abstraction
`that can be displayed
`if desired
`is the value of a set of digits. For
`example,
`in Figure 8 are shown three sets of
`digits all displaying
`the same scalar value,
`-5978. The digits
`themselves may be moved,
`rotated, or changed
`in size, without changing
`the value displayed.
`If we wish to change the
`value, we point at its abstract display,
`the #
`seen in Figure 8. The three sets · of digits
`in
`Figure 8 all° display
`the same value, as indi(cid:173)
`cated by the lines connecting
`them
`to the #;
`changing
`this value would make all three sets
`of digits change. Constraints may be applied
`independently
`to either the position of the digits
`or their value as indicated by the
`two con(cid:173)
`straints
`in the figure.
`
`V. RECURSIVE FUNCTIONS
`In the process of making the Sketchpad sys(cid:173)
`tem operate, a few very general functions were
`developed which make no reference at all to
`the specific types of entities on which they oper-
`
`-5
`
`-
`
`CONSTRAINT MAKES
`DIGETS UPRIGHT
`
`-
`
`CONSTRAINT ON
`SCALAR VALUE
`
`Figu1·e 8. Three
`
`sets of digits displaying
`scalar value.
`
`the same
`
`514
`
`Falkbuilt Ex. 1019, Page 008
`
`

`

`SKETCHPAD: A MAN-MACHINE GRAPHICAL COMMUNICATION SYSTEM
`
`ate. These general functions g-ive the Sketch(cid:173)
`pad system
`the ability
`to operate on a wide
`range of problems. The motivation for making
`the functions as general as possible came from
`the desire
`to get as much r<!sult as possible
`from
`the programming
`effort
`involved. For
`example,
`the general
`function
`for expanding
`instances makes
`it possible for Sketchpad
`to
`handle any
`fixed geometry
`subpicture.
`The
`power obtained
`from the small set of gener(cid:173)
`alized functions in Sketchpad
`is one of the most
`important
`results of the resea1·ch.
`In order of historical development, the recur(cid:173)
`sive functions
`in use in the Sketchpad system
`are:
`it pos(cid:173)
`1. Expansion of instances, making
`sible to have subpictures within subpic(cid:173)
`tures
`to as many levels as desired.
`2. Recursive deletion, whereby
`removal of
`certain picture parts will remove other
`picture parts
`in order
`to maintain con(cid:173)
`sistency
`in the ring structure.
`3. Recursive merging, whereby combination
`of two similar picture parts forces com(cid:173)
`bination of similarly rel al eel other picture
`parts, making possible application of com(cid:173)
`plex definitions to an object picture.
`
`RECURSIVE DELETING
`If a thing upon which other things depend is
`deleted,
`the de1,endent
`thin{Js must be deleted
`also. For example, if a point is to be deleted,
`all lines which terminate on the point must also
`be deleted. Otherwise, since
`the n-component
`elements for lines contain no positional
`infor(cid:173)
`mation, where would these lines end? Similarly,
`deletion of a variable
`requires deletion of all
`constraints on that variable; a constraint must
`have variables
`to act on.
`
`RECURSIVE MERGING
`If two things of the same ty11<' which are in(cid:173)
`dependent are merged, a si11r,!1· thing of that
`type results, and all things which devended on
`things depend on the re(cid:173)
`either of the merged
`sult* of the me,·_qer. For example, if two points
`are merged, all lines which previously
`termi.:
`nated on either point now terminate on the
`single resulting point. In Sketchpad,
`if a thing
`is being moved with the light pen and the ter(cid:173)
`mination flick of the pen is given while aiming
`at another
`thing of the same
`type,
`the
`two
`
`things will merge. Thus, if one moves a point
`to another point and terminates,
`the points will
`merge, connecting all lines which formerly
`ter(cid:173)
`minated on either. This makes
`it possible
`to
`draw closed polygons.
`type which do
`If
`two
`things of
`the same
`depend on other things are merged,
`the things
`de7Jended on by one will be forced
`to merge,
`respectively, with
`the
`things depended on by
`the other. The