Geometrical Display Generator

This application describes a geometrical figure generator that is used to define an alarm window in the invention described in application Ser. No. 06/531,774 entitled "Display System for Monitoring and Alarm System" filed concurrently herewith by Lawrence Keith Stephens now U.S. Pat. No. 4,588,987. The invention described in this application may also be used to advantage in the schematic display generator that is the subject of application Ser. No. 06/499,458 filed by Lawrence Keith Stephens on May 31, 1983, entitled "Schematic Building Cursor Charactor". All of these applications are assigned to a common assignee.

The subject invention is generally directed to the generation and display of geometric figures on a graphics screen, and more particularly, the invention is a user-friendly procedure that uses a cursor placement device such as a joy stick to both define the initial position and size of the geometrical figure. By geometrical figure, I mean a predefined figure of generally symmetrical shape such as a circle, square, rectangle or other rhombic figure, triangle, trapezoid, or other polygon.

There are many situations in the operation of computer generated graphics displays where the user desires to generate, for example, a circle. Typically, this is done by invoking a circle generating program which requires the user to input first the center of the circle on the graphics display and then to input the radius of the circle. The program then generates a circle with that center and radius on the graphics display. This procedure works well for many applications but presumes prior knowledge of the user as to where and what size the circle should be. In the case of free hand drawings and schematics, the user may not in fact have such prior knowledge and therefore must resort to a tedious trial and error process of graphics generation. Moreover, since the program is specifically written to generate circles, the user has no choice in the generation and display of other geometric figures unless programs are written that are specifically tailored for the desired figures. These problems can be overcome by the use of a digitizer pad as an input to the computer. A digitizer pad would permit the user to generate any size or shape of geometrical figure at any location on the graphics screen, but commercially available digitizer pads are very expensive and are therefore generally used in correspondingly expensive computer aided design (CAD) systems.

It is therefore an object of the present invention to provide a user-friendly method of drawing geometric figures on a graphics screen.

It is a further object of the invention to provide a procedure for drawing geometric figures on a graphics screen which is both easy to use and is practiced with relatively inexpensive hardware.

The foregoing and other objects of the invention are accomplished by using an inexpensive cursor positioning device such as a joy stick, track ball or "mouse". The preferred embodiment of the invention is described in terms of a joy stick being the cursor positioning element, but it will be understood by those skilled in the art that other well known devices such as track balls and "mice" which are used as cursor positioning elements can be used just as effectively as the joy stick. In addition to the joy stick, an ENTER key is required for the practice of the invention, but many cursor positioning devices are equipped with one or more buttons, one of which can be used to provide the function of the ENTER key. In the practice of the invention, the type of geometric figure is chosen, typically from a menu displayed for that purpose, and then the user is prompted to point to the desired location of the figure. The user accomplishes this by moving the cursor to the desired location and pressing the ENTER key. At this point, the cursor is XORed to remove it from the screen, and an initial small sized geometrical figure of the type chosen is drawn on the screen. The user then uses the joy stick to cause the figure to increase in size. When the desired size has been attained, the user indicates this by pressing the ENTER key. At this point, size and position of the geometrical figure is stored and the cursor is redisplayed.

The location of the cursor for the original pointing of location may conveniently be the center of the geometric figure. In the preferred embodiment of the invention, the center is in fact chosen for the generation of circles, but the center is not the only location that may be used for the pointing of location of the geometric figure. In my copending application Ser. No. 06/531,774 entitled "Display for Monitoring and Alarm System" now U.S. Pat. No. 4,588,987, I generate boxes which are used as alarm windows on schematic displays. The convention I have chosen in that application is to require the user to point to the upper left corner of the box. The box increases in size to the right horizontally and vertically downwardly from this point as the user moves the joy stick down and to the right. Obviously other conventions will suggest themselves to those of ordinary skill in the art based on the following detailed description of the invention.

The foregoing and other objects, aspects and advantages of the invention will be better understood from the following detailed description of the invention taken with reference to the accompanying drawings in which

FIG. 1 is a flow chart illustrating in simplified form one specific example of drawing a circle according to the techniques of the invention; and

FIG. 2 is a flow chart illustrating in simplified form another specific example of drawing a box or rectangle according to the techniques of the invention.

The invention will be described by way of specific examples adapted for use on the IBM Personal Computer. Obviously, the invention is not limited to this specific microcomputer system or even to microcomputer systems and may have useful application to minicomputer systems or even main frame computer systems. However, the invention is particularly useful in microcomputer systems because of the relative economies of such systems and the fact that the invention is itself correspondingly inexpensive.

The first example is the drawing of a circle. The program, which is set forth in more detail hereinafter, presumes that the circle drawing process is used in conjunction with the schematic generator described in my earlier copending application Ser. No. 06/499,458 entitled "Schematic Building Cursor Character". In that application, the cursor symbol is chosen from among a plurality of symbols in a symbol table. These symbols are used in the actual construction of the schematic display by placing the symbols at desired locations on the graphics screen and then reading them into memory in response to an interrupt signal produced by the operator pressing a button on the joy stick control. Thus, the first steps in the specific example given of generating a circle involve the exclusive ORing of the old cursor symbol to remove it from the graphics screen and saving the old symbol height and width for later recall. Then, the new cursor symbol's height and width is initialized and the new cursor symbol is exclusive ORed onto the graphics screen. Typically, the new cursor symbol is a conventional small square or rectangle and may blink on and off. Clearly, if the circle generation technique according to the invention were to be used in an environment where the cursor symbol was not initially a schematic character symbol, then the process of exclusive ORing the old cursor symbol and saving its dimensions would not be required.

The user enters the circle generation mode by making the appropriate selection from a menu. Once in the circle mode, the user is prompted to point to the location on the graphics screen where s/he would like the center of the circle. This is done by moving the joy stick, but as previously mentioned, other cursor positioning devices could be used. When the cursor is positioned to the desired location of the center of the circle, the user presses the button on the joy stick or the ENTER key to signify selection. The button pressing generates an interrupt which is trapped by the program and control is passed to a subroutine which sets a flag signifying the occurance. Control returns to the program's main loop which checks the flag at a designated point and gives control to the circle routine. The circle routine first exclusive ORs the cursor off the screen and then prompts the user with various circle options. These include change of color (by pressing function key F9), terminate circle expansion (by pressing function key F10 ), and expand the circle one pixel in radius (by pressing the joy stick button). The circle routine begins by drawing an initial three pixel circle at the initial pointing and starts looping until the function key F10 is pressed. Inside the loop, if function key F9 is pressed, the color variable is changed. Also, the old circle is continuously removed from the screen by exclusive ORing and the position and size data of the old circle are saved. If during this operation and joy stick button or the "+" key is pressed, the radius variable is increased by one pixel and compared to a maximum value of 30 . If it is greater than 30 , then it is set equal to 30 . The new circle is then drawn on the screen. After the function key F10 has been pressed signifying that the user wants the circle expansion to terminate, the circle position and size are saved and the user is prompted to select a fill color for the circle. The user makes a selection from a menu provided for that purpose, and the circle is then filed with the selected color. At this point in the routine, the routine returns to the point in the program at which the circle generation routine was entered. The FIG. 1 is a flow chart which illustrates the circle drawing process just described.

Those skilled in the art will recognize that various modifications can be made from the basic procedure just described for circle generation. First, while the specific example is described in terms of a color graphics embodiment where both the circumference of the circle and the interior of the circle may be selected to have different colors, the procedure is equally well suited for monochrome graphics without these choices of color. The basic technique is the ability to point to the desired center of the circle with the cursor and then to expand the circle until the desired size has been reached. Second, while the specific example requires the user to press either the button on the joy stick or the "+" key to expand the circle by one pixel increments, some other key or control can be used to accomplish the same result. For example, the joy stick which was originally used to move the cursor to point to the center of the circle could, after the joy stick button or the ENTER key was pressed, then be used to expand the circle by pushing the joy stick in one direction until the desired size was reached. The use of the joy stick for this function would make possible user control in how fast the circle expanded in size, i.e. a slight deflection of the joy stick would produce a slow expansion and a greater deflection of the joy stick would produce a correspondingly greater expansion rate of the circle. Also, it would be possible to decrease the size of the circle by moving the joy stick in the opposite direction. A similar result could be achieved by pressing the "-" key.

The next specific example is the drawing of a square or a rectangle. This example is used in my copending application Ser. No. 06/531,774 entitled "Display for Monitoring and Alarm System", now U.S. Pat. No. 4,588,987, and is used to define an alarm window. The chief differences between this example and the specific example of drawing a circle are that (1) the pointing with the cursor is not made to the center of the geometric figure and (2) expansion of the figure is accomplished by manipulating the joy stick. More specifically, the pointing is made to the upper left corner of the square or rectangle. Expansion of the square or rectangle is then accomplished by deflecting the joy stick down and to the right. FIG. 2 is a flow chart which illustrates the box or rectangle drawing process just described.

From these specific examples, those skilled in the art will understand that the basic principles of the invention can be expanded to include many other geometric figures of generally symmetrical shape that are susceptible of being stored in a graphics character memory. These figures require some predefined symmetry upon which expansion in one pixel increments is based. For example, in the circle case, expansion is based on increasing the radius by one pixel increments. In the square or rectangle case, expansion is based on increasing the horizontal x and vertical y dimensions in one pixel increments or some ratio of x to y dimensions.

The following is a listing of the applicant's schematic generator program which includes the complete programs for the two specific examples described hereinabove, which program was written using the IBM Personal Computer BASIC Compiler, version 1.00: ##SPC1##