Note: Descriptions are shown in the official language in which they were submitted.
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VECTOR SCAN SYSTE~I FOR VIDEO GAME DISPLAY
TECIINICAL FIELD
Tllis invention relates to cathode ray tube (CRT) display systems and,
more particularly, to CRT displays employed in video games.
BRIEF DESCRIPTION OF DRAWINGS
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The invention and prior art are described with respect to the drawings
which comprise:
Figure 1 is a front elevation of a CRT as employed in a display
system.
Figure 2 is a partially cutaway side elevation through the CRl' of
Figure 2.
Figure 3 is a front elevation of a CRl' indicating the development of
a raster display.
Figure 4 is a simplified view of a raster display displaying an "A".
Figure 5 is a simplified drawing of a display painting an "A" with an
X-Y scan system.
Figure 6 is a graph showing the decay of the phosphors employed in a
CRT display with respect to the refresh rate necessary to prevent flicker.
Figure 7 is a block diagram showing one method of prior art genera-
tion of displays with an X-Y scan system.
Figure 8 shows an alternate prior art method of X-Y display genera-
tion.
Figure 9 is a simplified block diagram showing a video game environ-
ment as wherein the present invention is employed.
Figure 10 is a drawing showing a typical symbol as employed with the
present invention~
Figure 11 shows the construction of entries on the symbol definition
list as employed in the present invention.
U.S.S.N. 314,69~
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Figure 12 shows the construction of an entry on the display status
list as employed in the present invention.
Figure 13 is a block diagram showing a video game system as con-
structed according to the present invention.
Figure 14 is a block diagram of X-Y scan monitor system logic accord-
ing to the present invention.
BAC~GROUND ART
A typical CRT as employed in a display system is shown in front and
c-ltaway side views respectively in Figures 1 and 2. The CRT 10 comprises an
evacuated glass envelope 12 having a phosphor surface 14 on the inside of the
viewing area. Vertical and horizontal deflectors, 16 and 18, respectively, are
affixed about the neck 20 of the envelope 12. A cathode 22 emits electrons 24
which are drawn towards the phosphor surface 14. Electrons 24 striking the
phosphor surface 14 cause illumination thereof. By selectively energi7ing the
deflectors 16, 18, the path 26 followed by the electrons 24 can be moved hori-
~ontally and vertically.
Referring to Figure 3, the most common video display is shown. Such
a display has a "raster scan". The beam of electrons 24 is made to move hori-
zontally in electron-width strips from one side of the phosphor surface 14 to
the other and from the top to the bottom, as indicated by the solid and dashed
arrows in Figure 3. A first hori~ontal raster line is scanned from left to
right along the top as indicated by the solid arrow 28. With the electron beam
intensity turned off, -the non-illuminating beam is then moved down one raster
line and back to the left side of the screen as viewed in Figure 3 and as repre-
sented by the dashed arrow 30. The next raster line, as represented by the
solid arrow 32, is then displayed across the screen. This process repeats from
top to bottom until the last raster line, as represented by the solid arrow 34,
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is displayed. The display then begins at the top left by moving the non-
illuminated beam, as represented by the dashed arrow 36, from the ending point
to the begi~ming point.
~ uring the traversing of the raster lines by the electron beam,
images are created by varying the intensity of the beam. The type of image
created is shown in Figure 4 in simplified form. The number of actual raster
lines in a typical display is greater than that shown in Figure 4, but the over-
all effect is the same. That is, as represented by the figure "A" shown, accu-
rate horizontal lines can be created because the raster lines are horizontal.
By contrast, diagonal lines such as the legs of the "A" are created by a
sequence of staggered points as a best possible representation of a true diago-
nal line under the circumstances.
Video games which are emplGyed in the home market for use with the
CRT of a television set must use the raster drive of the television set. ~y
contrast, video games created for the stand-alone game market are not so re-
stricted. They can employ what is referred to as an "X-Y" scan system. Such a
system is shown in Figure 5. If one were -to create the same "A" display as
shown in Figure 4 using an X-Y scan system, it would be created as shown by the
arrows of Figure 5. The "X" and "Y" refer to moving positions of the electron
beam with reference to the typical X,Y coordinates of a two dimensional graph
system. Assuming the undeflected position of the beam is at the center of the
screen as viewed in Figure 5, the beam would first be moved (i.e., its X,Y posi-
tion established) to the bottom of the lef-t leg of the "A" in an un-illuminated
mode as :indicated by the dashed arrow 38. The beam would then be illuminated
and its X,Y position moved by use of the deflectors 16, 18 to the apex of *he
"A" as indicated by the solid arrow 40. It would then be moved from the apex
to the bottom of the right leg as indicated by the solid arrow 42. It would
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then be moved in its un-illuminated mode as indicated by the dashed arrow 44 in
preparation for drawing or "painting" the horizontal bar of the "A" as indi-
cated by the solid arrow 46. As can be seen, the "A" as painted by the X-Y dis-
play system is comprised of pure straight lines.
In a raster scan system, the raster scans rapidly across the screen
from top to bottom and then repeats. The screen, therefore, is in a constant
state o:E illumination as determined by the intensity modulation of the electron
beam. The phosphors of the phosphor surface 14, however, do not remain illumin-
ated. Once energized by being struck by an electron, they glow and then begin
to rapidly decay. This is illustrated in Figure 6 by line 48. If the phosphor
surface 14 is struck by an electron, it will glow and eventually the intensity
will diminish to zero. If the intensity is allowed to diminish below the level
indicated by dashed line 50 before being re-illuminated, the viewer will per-
ceive a flicker in the display. If the display is re-energized before that
level is reached, no flicker will be seen.
Such re-energizing or repain-ting is referred to as "refreshing" the
display. In typical prior art systems employing X-Y scan systems, this has
been done in several ways. Referring first to Figure 7, a system where the
operating programs dynamically creating the vectors of the display and the re-
fresh program are all contained within a main computer is shown. The main com-
puter is symbolized by the dashed box 52. On a time-sharing basis, the operat-
ing programs 5~ place vector descriptions in memory area 56. The refresh pro-
gram 58 accesses the memory area 56 and uses the descriptions therein to create
and refresh the display on the CRT of display 60.
Figure 8 shows an alternate approach where the display contains its
own logic portions fcr refreshing the display. The operating programs 5~ are
once again within the main computer indicated by the dashed box 52. In this
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case, however, the vector descriptions are contained in a commonly accessible
memory area 62. The display computer represeilted by the dashed box 64 contains
the refresh program 58 and can also access the common memory 62.
Turning now to Figure 9, the environment of the present invention is
shown. The computer 66 contains a game program 68 and a display creation and
re:Eresh program 70. The display refresh progranl 70 is connected to the CRT dis-
play 72 while the game program is connected to player consoles 7~ (usually one
or -two) containing such input devices as balltabs 76 and buttons 78. The fore-
going elements are all placed in a convenient housing having appropriate mecha-
nisms for coin operation thereof. The game consists of, for example, a"player 1" fighter symbol 80 and a "player 2" fighter symbol 82 controlled by
the two control panels 74, respectively. As the game program 68 senses the
changes in the balltabs 76 and buttons 78 of panels 74, the position of the
symbols 80, 82 are moved about display 72 in a manner to simulate controlled
flighi thereof. Each symbol 80, 82 is capable of firing a simulated "missile"
84 which, if placed into coincidence with the position of the opponents symbol
80, 82, will cause that symbol 80, 82 to be "destroyed" with an attendant award-
ing of points.
In such video games to date, the operation has been primarily as
shown in Figure 7. That is, the game program 68 continuously calculates and
places in memory the individual refresh vector descriptions of the game in pro-
gress for the refresh program 70. A typical video game in an arcade has a
limited life expectancy. As a game loses appeal, the amount of play quickly
drops below a point of financial viability. Thus, it is desirable to provide
a video gaming system which is easily converted to a new game.
Because of the components required to be employed, the amount of
memory available is fixed. Obviously, therefore, the more memory dedicated to
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the continued recalculation of vectors in order to produce the display symbols
of the dynamic game, the less memory is available for the logic of the game it-
self a.nd, therefore, the game cannot be as complex and graphic as desired to
impart a high interest level to the players. Wherefore, it is also desirable
to provide a video display scan system which employs a minimum amount of avail-
able memory.while preserving a maximum amount of available memory for use in
thc game logic of the program itself.
The time and cost of programming new games is also directly related
to the complexity of the task. Spatial orientation of displayed symbols can
occupy a significant amount of time with associated expenditure of funds with
respect to the development of a new game which could otherwise be better
employed in the development and coding of the game proper. Wherefore, it is
also desirable to provide a programming environment for video games wherein the
considerations necessary for the production of displayed symbols in the develop-
ment of new games is minimized.
DISCLOSU~E OF INVENTION
The present invention provides a video display system for a video ga.m-
ing system which is easily converted to a new game, which uses a minimum amount
of the available memory, and which minimizes the considerations for production
of new symbols in a new or revised game wherein a pre-established series of
individual symbols are selectively displayed in multiple combination as a re-
sult of programmed logic to convey movement of associated object within a de-
fined area by the improvement characterized by means for defining the respective
individual possible symbols as a plurality of interconnecting display lines of
given angle and length with respect to a common coordinate system; means for
maintaining the current status of the symbols to be actually displayed, said
means including indication of the individual possible symbol in said defining
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means associated with each display symbol and -the angle and positional ofset
thereof in the common coordinate system; wherein the programmed logic updates
only the status maintaining means; and, additionally, logic means for accessing
the status maintaining means and the symbol defining means and for producing
the display as a function thereof.
BEST MODE FOR CARRYING OUT TIIE INVENTION
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In a display system such as the stand-alone video game previously des-
cribed, a number of pre-defined symbols are employed. These symbols are
employed in combinations to create the dynamic display of moving symbols which
represents the display of the game. One such symbol which could be employed in
a game according to the present invention is shown in Figure 10. Such a symbol
86 can represent, for example, a space ship to be controlled either by a game
player or the computer. The ship symbol 86 can be represented as shown in
Figure 10 as a series of five interconnected vector lines begiTming with point
1'A" at the origin of a polar coordinate system. By beginning at a known origin,
the five line vectors which comprise the ship symbol 86 can be described by
employing only lengths and angles. The first line A,B is of a given length and
at a given angle from the origin. If one begins the electron beam at the
origin and paints a straight line for the given length A-B at the given angle
thereof, the elec-tron beam will terminate at a position corresponding to point
"B". If the beam is then moved along the length of line B-C at the angle tilere-
ofl it will terminate at the position of point "C". The same is true for the
line segments C-D, D-E, and E-A. If the length and angles of the five lines
are properly described, the lines will close upon themselves at point "A" com-
pleting the ship symbol 86. The present invention works on this basic premise.
Referring now to Figure 11, the individual symbols are described in a
symbol definition list having tabular entries of computer words for each indivi-
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dual line vector. In a tested embodiment employing eigh-t bit words, the first
word employs the most significant bit as a "last entry" flag; that is, if bit
eight o:E the first word of a four word entry is "1", t]lis is the last four word
entry of the list describing the particular symbol. If "0", it is not the last
entry of -the list. Similarly, bit one is a "display" or "non-display" flag.
If the bit is set to "1", the particular vector is to be displayed. That is,
thc intensity of the beam is to be "on". If the display bit is a "0", the
vector is only for moving the position of the beam and the beam is not to be
displayed, i.e. the beam intensity is turned off. Such a beam would correspond
to the dotted arrows 3S and 44 in Figure 5 needed to generate the "A". Bits
two through seven contain indicators concerning the color of the vector if it
is a color system as was the case with the tested embodiment being described.
The color designation methodology employed as part of the present
invention is of particular novelty and importance. Where a color display is
being employed, it is particularly useful to designate each player's controlled
symbol (such as the spaceship 86 of Figure 10) by a different color. This per-
mits rapid identification by a player of his symbol. Of course, color can be
employed to convey other information such as a change in point value or playing
characteristics of a particular symbol. The color benefi~s of the present
invention will be addressed further shortly.
Word two designates the length of the line vector and words three and
four designate the angle of the line. In the tested embodiment, a polar coordi-
nate system is used such that word three designate, the angle in degrees and
word -Eour designate the quadrant in which the line is to appear. Those skilled
ill the art will recognize that other word and bit assignments could be employed
with equal success.
Thus, according to the above description, the ship symbol 86 oE
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Figure 10 would occupy twenty words in the symbol definition list corresponding
to Figure 11. There would be one four word entry for each of the five lines
comprising the symbol for a total of twenty. Bit eight of the first word of
the first four entries would be a "0" and bit eight of the last four word entry
(i.e. bit eight of word 17) would be a "l" to indicate that as being the last
line vector description entry for that symbol.
In practicing the present inven-tion, each individual symbol to be
employed in the display is assigned an entry ~i.e. a sequence of ~word line
defining entries) on the symbol definition list as defined in ~igure 11.
Regardless of how many times the symbol may appear dynamically on the display
at any one time during the game, only one entry on the symbol definition list
is required.
Turning now to Figure 12, a single entry from the display status list
is shown. Each symbol presently active in the game (whether presently being
displayed or not) has an entry of ten words on the display sta-tus list. Again,
the entry of Figure 12 is shown with reference to a tested embodiment employing
an eight bit computer word utilized in a particular manner. Those skilled in
the art will recognize that the specifics of the number or words employed and
the bit assignments can be modified without the requirement of invention or
experimentation.
As with the entries of the symbol definition list of Figure 11, word
one of the display status list entry contains a "last entry" flag in bit eight,
a "display" or "non-display" flag in bit one, and color designation indication
in bits two through seven. Words two and three designate the offset in the X
coorclinate from the 0,0 origin. Words four and five designate the Y offset
from the origin. Note that the display screen layout and, therefore, the game
logic operates in cartesian coordinates while the symbol display logic operates
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in polar coordinates. The unique arrangement of tile present invention makes
this beneficial combination possible. Words eight and nine designate an angle
offset for the symbol and word ten is a size designation for the symbol when
displayed. As will be seen in a more detailed description hereinafter, these
offset capabilities provide ease of manipulation and action generation when the
present invention is employed in a video game environment.
Each entry of the display status list of Figure 12 in words six and
seven contains a pointer or address vector to the associated symbol on the
symbol definition list of Figure 11. For example, assuming that the five entry
(one for each line) symbol definition for the ship symbol 86 of Figure 10 be-
gins at memory location 3456, each entry on the display status list employing
the ship symbol 86 would have in words six and seven thereof the vector address
3456.
As should now be apparent, using the present inventiun, the game pro-
gram logic can create detailed symbol movement on the display by manipulating
the entries of Figu~e 12 on the display status list. For example, to rotate
the ship symbol 86 at any location in which it is an entry on the display
status list, that entry need only have the angle designator of words eight and
nine progressively increased. In similar manner, the ship can be moved in the
X clirection by increasing the X offset in words two and three or be moved in
the Y direction by increasing the offset in words four and five. Combined move-
ment is obtained by simultaneous changes to these values. Thus, the amount of
memory available for the logic of the game itself is greatly increased inasmuch
as very little is required for even complex manipulation of the display.
The size designator of word ten is of particular importance in that
complicated effects can be created by progressively increasing or decreasing
the size of a given symbol alone or in combination with other movements. For
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example, moving the ship symbol 86 from the bottom of the display to the top
and simultar,eously increasing its size from a small size -to a larger size
creates the illusion of motion towards the viewer. The amount of movement and
the amount of size increase govern the exact illusion created. The smaller the
amount of vertical movement coupled with each size increase, the more the ob-
ject looks like it is coming at the viewer horizontally.
The ease of color association and modification achievable with the
present invention should now be appreciated. For example, the basic definition
oE a player symbol (e.g., spaceship 86) employed by all players appears only
once on the symbol definition list of Figure 11. It can be assigned a basic or
universal color in that entry. By contrast, each individwal acti-ve spaceship
86 of each player will have a separate entry on the display status list of
Figure 12. Thus, all the ships of a particular player can be assigned an
associated color to override the basic color designation. An individual ship
symbol can have its own color designation changed to create special effec-ts
such as explosions. In a prior art game, the game logic would have had to
accomplish that at the display output format level for each symbol. With the
system of the present invention~ such color manipulation becomes a simple task
requiring a minimum of memory in the game logic. Since the designators occupy
the same location in a contiguous list of entries, the actual manipulation can
be accomplished by an index guided subrou-tine to effect even further savings.
Th:is, of course, would not be possible with otiler more complex prior art
approaches.
A game system employing the present invention is shown in Figure 13.
Tile game program 88 communicates with the player controls 90 and the display
status list 92 which has the active symbol entries as described in Figure 12.
The symbol definition list 9~ is pre-established in the manner of Figure 11.
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In actual practice, the game program 8~ and the symbol definition list 94 are
contained in programmable read only memory (PROM) while the display status list
92 is created at playtime in dynamic memory. Also contained in PROM is the dis-
play composition logic 96. The display composition logic 96 accesses the dis-
play status list 92 and the symbol definition list 94 and creates therefrom the
dynamic visual display on the CRT 98.
Turning now to Figure 14 the specific logic employed in display com-
position logic 96 is shown in block diagram form. As will be well understood
by -those skilled in the art, the logic of Figure 14 accomplishing the purposes
of the present invention can be implemented in many forms to achieve the same
functional results. For example, it could be done with software, firmware, or
hardwired logic. Any such implementation is easily accomplished by those skil-
led in the art from the flowchart of Figure 14 without experimentation and,
therefore, no further detail is included herein.
Upon initial entry and subsequent re-entry a-t block 14.01, the logic
first starts at the top of the display status list 92, i.e., the first entry
according to Figure 12. At block 14.02, it accesses the ten words comprising
the next entry, which, in the first instance, is the first entry. At decision
block 14.03, the logic makes a decision as to whether this entry is to be dis-
played or not. This is accomplished by testing bi-t one of word one. If the
entry is not to be displayed (i.e., bit one of word one is "0"), the logic con-
tinues to decision block 14.04 which then tests bit eight of word one to deter-
mine if this is the last entry on the display status list. If not, the logic
bumps to the next entry. In the illustrated embodiment9 this would, of course,
mean increasing the address of the first word of the entry by ten. The logic
then returns to block 14.02 to repeat the process with the next entry on dis-
play status list 92. If at decision block 14.04 the logic finds tha-t this was
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the las-t entry, i.e., bit eight of word one is a "l", the logic returns to
block 14.01 to scan, once again, the display status list 9Z. If des:ired, this
latter path could include a time delay assuring that the refresh cycle is re-
peated no faster than a given frequency.
Returning to decision block 14. 033 if the logic finds that this entry
on the display status list 92 is to be displayed, it proceeds to the logic
sequence beginning with block 14.06. At block 14.06, the logic initializes the
X,Y position at which the electron beam is to begin painting the particular
symbol associated with this entry. It will be remembered that the symbol as de-
fined in tlle symbol definition list 94 is with reference to an origin positionof 0,0. Thus, from words two, three, four and five of the entry on the display
status list 92, the logic must pick up the X and Y offsets and initialize the
position at which it is to begin painting the associated symbol.
The logic then moves to block 14.07 where it picks up the vector list
address from words 6 and 7. It should be remembered that this is the address
of the first word in the sequence of entries (described in detail in Figure 11)
on the symbol definition list which define the particular symbol to be associ-
ated with this entry on the display status list 92 at this particular time. It
should also be appreciated that to create particular effects, the game program
88 can easily change the vector address to that of one or more new "symbols".
Ilaving picked up the vector list address, the logic then moves to
block 14.08 where it accesses the next entry on the symbol definition list 94.
The first time through, of course, it is accessing the first entry. At block
14.09, the logic calculates the angle of the first vector. This angle is a com-
bination of the original angle contained in words three and four of the vector
definition and the angle offset contained in words eight and nine of the entry
on the display status list 92. Having determined the angle of the vector to be
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painted, the logic then moves to block 14.10 wherein the length of the vector
is calculated. Again, this is a combination of entries from both lists. The
basic length as originally defined is contained in word two of the entry on the
symbol definition list. This length is adjusted as a function of the size
indicator contained in word l0 of the entry on the display status list 92.
Ilaving now calculated the angle and length of the vector, the logic
moves to block 14.11 wherein the X,Y coordinates of the beam following the paint-
ing of the vector is calculated and stored. It will be noted that this calcula-
tiOII and updating of data is accomplished at this point because the beam may be
actively painted or, in the alternative, may be only a case of moving the elec-
tron beam between positions without actually illuminating the screen.
The logic then moves to decision block 14.12 wherein that latter ques-
tion is, in fact, asked. By testing bit one of word one of the entry, the
logic can determine whether the particular vector is to be displayed or not.
If it is, the logic moves to block 14.13 wherein associated color settings are
made according to the data contained in bits two through seven of word one of
both entries. The exact nature of the actual color adjustment is dependent
upon the system and, per se, forms no inventive portion of the present inven-
tion. Therefore, no greater detail is given. ~laving set the appropriate color
designations, the logic next paints the vector across the display screen at the
angle and for the length calculated. This is accomplished by the digital logic
outputting a sequence of commands which causes the actual display driver *o
have its deflection voltage changed in discrete and equal steps. This approach
is well known in the art and results in symbols of uniform intensity being gene-
rated regardless of variations in the lengths of the various line segments.
The logic in either case then moves to decision block 14.15 wherein bit eight
of wo:rd one is tested to see if this is the last vector of the symbol. If it
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is not, the logic moves to block 14.16 wherein the address is bumped by four to
the next entry and then returns to block l4.0~ to access the next entry and re-
peat the process. If it is the last vector, the logic moves to decision block
14.04 to continue as previously described.
Wherefore, it should be apparent from the foregoing description that
the present invention truly provides an environment for dynamic display systems
achieving the stated object.
