Video graphics system equipped with a graphics cursor

Video graphics system which, by means of a graphics cursor, permits the identification of encoded surfaces of images represented on a screen. In order to do this, there are added to the parameters of the encoded surface, for each surface, an identifier which can be read by slices in the course of readings effected on a plurality of successive frames. An identification memory permits the accumulation of all the slices until the complete acquisition of the identifier. This situation is brought to the attention of the user.

BACKGROUND OF THE INVENTION 
The invention relates to a video graphics system equipped with a graphics 
cursor and with a comparator which compares the positional co-ordinates 
X.sub.C, Y.sub.C of the graphics cursor with the co-ordinates X.sub.D, 
Y.sub.D of each element of each line, the elements being explored in 
accordance with a scanning by frames, the graphics cursor interacting with 
the image delivered by the video graphics system. 
A video graphics system of this type is known from the document EP 0 229 
986 (US 4 706 074). It describes a graphics system which stores image data 
and which is equipped with a cursor, by means of which it is possible to 
insert data into the image. In order to do this, the cursor selects a zone 
of the image in which this transformation is to be effected and the system 
determines this zone on the basis of the coordinates supplied by the 
cursor. 
The object of this document is therefore to combine the information 
emanating from the cursor route and from the image data route. 
Thus, this device does not permit the referencing within an image, of 
characteristic features which are specific to it, each image zone moreover 
having no identification code. 
SUMMARY OF THE INVENTION 
The technical problem posed is that of being able to identify image 
portions by means of a graphics cursor, the reference of which is 
positioned on a desired zone. 
The solution to this problem is that the video graphics system comprises : 
an image memory which, in the course of successive loadings, temporarily 
stores : 
(a) numerical parameters regularly explored describing encoded surfaces 
relating to two-dimensional images, 
(b) and an N bit identifier, specific to each encoded surface in such a 
manner that the N bits are successively loaded into image memory, by 
slices of N/P bits in the course of P successive loadings where P is 
greater than 1, each loading being followed by a reading of the image 
memory in order to display the image visually in accordance with the 
successive frames of the scanning by frames, 
and a graphics controller with receives the slices of N/P bits at each read 
frame and reconstructs the N bit identifier of an encoded surface after P 
successive frames, the controller comprising an identification circuit 
equipped with a comparator and with an identification memory which stores 
the identifier while accumulating the slices of N/P bits in the cyclic 
sequence of the reading when the comparator has detected the identity of 
the coordinates (X.sub.C, Y.sub.C) and of the co-ordinates (X.sub.D, 
Y.sub.D), the complete identifier stored being used by the video graphics 
controller to identify the encoded surface to which this identifier 
relates. 
The graphics system according to the invention uses a buffer image memory 
which is alternatively loaded in a given cyclic sequence and then read in 
a different cyclic sequence. It operates on images formed of encoded 
surfaces which may remain identical among themselves in the course of a 
plurality of successive operations of loading and then of reading into 
memory before being renewed in their turn. 
Preferably, the images constituted from encoded surfaces are synthesizing 
images. Such images are, for example, those described in the document EP 0 
215 510 (U.S. Pat. No. 4,812,988), the contents of which is incorporated 
in the present disclosure as a reference and in which the encoded surfaces 
are formed from polygons. The latter are processed by the algorithm of the 
depth memory (Z-buffer) in order to display visually in two dimensions 
encoded images in which only the portions of polygons which are closest to 
an observation point appear. 
On such a two-dimensional image it is desirable to be able to reference the 
portions of the encoded surfaces visually displayed and to locate them in 
the image memory which stores all the data specific to the encoded 
surfaces. 
In order to do this, according to the invention, there is added to the 
coding describing the topology of each polygon an identifier which is 
likewise stored in image memory. This identifier is an N bit code which is 
delivered by slices with the parameters describing the encoded surface on 
each loading into image memory : 
1 identifier bit during P=N frames; 
or alternatively N/P identifier bits during P frames. 
The controller may thus receive the entire identifier at the conclusion of 
P read frames. This limits the size of the image memory part which stores 
the identifier part. The polygon may thus be identified and utilized 
either for the visual display thereof or for any other processing, for 
example the display of an index. 
The localization of the encoded surface is effected by displacing a 
graphics reference on the surface of the screen of a visual display device 
with the aid of a box provided with a lever activated by the user in 
accordance with the customary techniques known to a person skilled in the 
art. 
Thus the graphics controller has available the co-ordinates X.sub.C, 
Y.sub.C of the position of the graphics reference. It also has available, 
by means of a counter/incrementor, the position X.sub.D, Y.sub.D of a 
current point moving on each image element of each scanning line, for 
which the corresponding data to be displayed are in the image memory. When 
these co-ordinates are identical, the position of the reference is 
determined and the identifier can then be stored in the identification 
memory after the prescribed number of frames, and then processed by the 
controller as described previously. The reference must remain within the 
same encoded surface in the course of the prescribed number of frames, in 
order effect the identification. 
The graphic cursor will permit : 
to identification of the positions of the reference on the screen and 
determine the coded area in which it is positioned, 
generation of the reference by itself, 
movement of the reference on the screen by the user.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1A represents a video graphics system 10 which comprises a graphics 
controller 11 equipped with an identification circuit 12. The latter 
receives the co-ordinates (X.sub.C, Y.sub.C) specific to the reference of 
the graphics cursor by means of a box 13 activated by the user. These 
co-ordinates (X.sub.C, Y.sub.C) are employed to display a reference 14 on 
the screen 19 of a visual display device 16. The graphics controller 11 
determines the co-ordinates (X.sub.D, Y.sub.D) of a current point of the 
screen 19, to which data in the image memory 15 correspond. The visual 
display device 16 operates in the video mode, in accordance with scanning 
lines and frames. The computer 18 transmits to the image memory 15 both 
the data to be displayed on the screen (field 15.sub.1 of the memory) and 
the N/P bit identifier slice (field 15.sub.2 of the memory). At each 
frames, the identifier part is replaced by a following slice. The data to 
be displayed of the screen are determined in accordance with the algorithm 
executed for the determination of the image either by the computer 18 
itself or by a specialized circuit 18.sub.1 which is itself controlled by 
the computer 18. This circuits is for example, that described in the 
document EP 0 215 510 (U.S. Pat. No. 4,812,988). 
When the identification circuit 12 has detected the identity of the 
co-ordinates (X.sub.C, Y.sub.C) and of the co-ordinates (X.sub.D, 
Y.sub.D), the successive slices of the N/P identifier are stored 
(connection 9) in an identification memory 17 in the course of the 
predetermined number of frames. When the entirety of the N bits of the 
identifier is received, the latter is then transmitted to the computer 18, 
which identifies the encoded surface which relates thereto. The computer 
18 transmits to the image memory 15 information permitting the 
representation on the screen of the visual display device 16, of the 
images formed from encoded surfaces. The display of an index on the screen 
or any other means permits the attention of the user to be drawn to the 
identification obtained. 
FIG. 1B represents the screen 19 of the visual display device 16, on which 
an encoded surface 20 and a graphics reference 14 associated with the box 
13 are represented. 
FIG. 2A and 2B represent the mechanism for encoding the identifier. An 
encoded surface will be characterized by the data field F2 in the form, 
for example, of vertices or of edges of polygons, for example as described 
in the document EP 0 215 510(U.S. Pat. No. 4,812,988). According to the 
invention, there is associated with this field F2 a second field F1 which 
constitutes an identifier of this encoded surface. Such a field F1 may be 
constituted from 1 or more bits, for example 8 bits, in accordance with 
FIG. 2B. This field F1 of N bits will be capable of being detected over a 
number P of frames. Thus, taking the example with N=8 bits, it is possible 
to effect 4 loadings into image memory and then to detect over four frames 
(P=4) four times 2 identifier bits. Depending upon the desired speed for 
effecting this exchange, it is possible to load/detect the 8 bits, bit 
after bit, over 8 successive loadings/frames or any other combination. 
FIG. 3 represents the identification circuit 12 which permits the 
processing of the identifier. The graphics controller 11 comprises the 
identification circuit 12 and a counter/incrementor 31. The latter 
supplies the co-ordinates X.sub.D, Y.sub.D of a current point of the 
screen to which data in the image memory correspond. The circuit 12 also 
receives the coordinates X.sub.C, Y.sub.C input by the box manipulated by 
the user. These co-ordinates are stored in registers 32.sub.1, 32.sub.2, 
33.sub.1, 33.sub.2. The data X.sub.C and X.sub.D on the one hand and 
Y.sub.C and Y.sub.D on the other hand are compared respectively in the 
comparators 34.sub.1 and 34.sub.2. When there is identity in twos, the 
gate 35 delivers a signal which enables the input of the N/P bit slice 
(connection 9) of the identifier I.sub.D into the identification memory 
17. The mechanism is maintained during the desired number P of frames by a 
control signal C emanating from the computer 18. When the identifier has 
been received in its entirety, it is transmitted by the connection 36 to 
the computer 18 (FIG. 1A), which displays a specified index on the screen 
of the visual display device 16 or warns the user that the encoded surface 
has been identified. 
FIG. 4, 5, 6 and 7 represent the acquisition of an identifier over four 
successive frames. Let it be assumed that an encoded surface 41 is to be 
identified and that an encoded surface 42 does not form the subject of an 
identification. The graphics cursor is, for example, positioned at X.sub.C 
=2 and Y.sub.C =3. When the counter/incrementor delivers the co-ordinates 
X.sub.D =2 and Y.sub.D =3, there is then identity. Let an identifier 
encoded over 8 bits be represented in the figures in decimal notation, in 
order to facilitate the representation. At the first frame (FIG. 4), the 
identifier memory acquires the term "1" of the identifier. Then, in the 
course of the 2nd, 3rd, 4th frame (FIGS. 6 and 7), it acquires 
respectively the terms "3" and then "0" and then "2", in order to have 
available, at the end of the 4 frame, the complete identifier "2031". The 
identifier of the other encoded surface 42 has itself also proceeded, but 
has not given rise to identification. 
The identifier "2031" is then transmitted to the computer 18, for example, 
in order to permit a search, within the image memory 18, for all the data 
relating to this encoded surface 41, in order to effect the intervention 
desired by the user.