Display control system

• US 4,369,441 A
• Filed: 09/18/1980
• Issued: 01/18/1983
• Est. Priority Date: 09/18/1980
• Status: Expired due to Term

• Current Assignee: Vector Automation, Inc.
• Original Assignee: Louis Wohlmuth
• Inventors: Wohlmuth, Louis
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US06/188,288
• Time in Patent Office: 852 Days
• Field of Search: 340/736, 340/738, 340/739, 340/742, 340/733
• US Class Current: 345/16
• CPC Class Codes: G09G 1/08 the beam directly tracing characters, the information to be displayed controlling the deflection and the intensity as a function of time in two spatial co-ordinates, e.g. according to a cartesian co-ordinate system

Abstract

A random refresh vector-generator type display system using a hybrid digital/analog vector generating technique. A digital vector generator decomposes medium length vectors into sub-vectors which are then drawn by an analog vector generator including a delay line. The system utilizes a long vector drawing technique wherein the first portion of a long vector is drawn at a first speed, the middle portion is drawn at a greater speed, and the final portion is drawn at the first speed. A feed forward circuit compensates for the sluggish response of deflection amplifiers of a display monitor so as to more precisely define beginning and end points of vectors. These amplifiers are further compensated by a delta theta circuit which temporarily freezes the system clock to allow the amplifier time to settle so that successive vectors will form sharp corners.

Claims

1. In a display system synthesizing an image from a source of digital vector commands, a vector generating system providing in response to a digital vector command, analog deflection signals for an electronically driven display comprising:

a digital vector generator for generating, in response to a vector defined by said digital vector command, one or more digital subvector commands of substantially constant length; and

an analog vector generator for generating, in response to each subvector command, a deflection signal for coupling to said display for drawing the sub-vector defined by the sub-vector command.

2. A system according to claim 1 wherein said analog vector generator comprises:

a delay line having intermediate output taps; and

means for summing the signals from said intermediate taps.

3. A system according to claim 2 wherein said means for summing comprises a resistor network.

4. A system according to claim 1 wherein said digital vector generator comprises:

means for identifying the length of a vector defined by a vector command coupled thereto; and

a look-up table for selecting the number of sub-vectors into which said vector is to be divided.

5. A method for generating, in response to a digital vector command, an analog deflection signal for an electronic display, comprising the steps of:

generating, in response to said digital vector command, one or more digital sub-vector commands;

generating, for each digital sub-vector command, an analog deflection signal for driving said electronic display.

6. A method according to claim 5 wherein said step of generating an analog deflection signal comprises the steps of:

generating a plurality of delayed signals, each such delayed signal having a different amount of delay from the other delayed signals; and

summing said delayed signals to produce said deflection signal.

7. In a graphics display control system which receives a digital display command and provides in response thereto a deflection signal suitable for driving a display monitor to display an image representative of said digital display command, the improvement comprising:

means for generating, in response to said digital display command, one or more digital sub-vector commands; and

means for generating, for each digital sub-vector command, an analog deflection signal for driving a display, the analog generating means comprising;

a delay line having a plurality of intermediate output taps, said delay line receiving at its input voltage steps corresponding to a vector defined by a vector command; and

a summing resistor network for summing signals derived at each of said intermediate outputs of said delay line, to provide a smooth deflection signal for coupling to said display monitor.

8. In a display system synthesizing an image from a source of digital vector commands, a method for drawing vectors comprising the steps of:

decomposing a vector defined by a vector command into sub-vectors having fractional coordinates of said vector by dividing the coordinates of said vector by 2^M where M is the smallest number that yields sub-vectors equal to or less than a predetermined maximum sub-vector length; and

generating 2^M sub-vector commands, each such command defining a sub-vector, by successive addition of fractional coordinate values derived by said step of decomposing;

drawing each sub-vector in the same predetermined period of time so that each sub-vector is drawn with a constant velocity.

9. In a display system synthesizing an image from a source of digital vector commands, a vector generating system comprising:

means for decomposing a vector defined by a vector command into sub-vectors having fractional coordinates of said vector by dividing the coordinates of said vector by 2^M where M is the smallest number that yields vectors equal to less than a predetermined maximum sub-vector length; and

means for generating 2^M sub-vector commands, each such command defining a sub-vector, by successive addition of fractional coordinate values derived by said step of decomposing;

means for drawing each sub-vector in the same predetermined period of time so that each sub-vector is drawn with a constant velocity.

10. A system according to claim 9 wherein said means for decomposing comprises:

means for identifying the length of a vector defined by a vector command coupled thereto; and

a look-up table for selecting the number of sub-vectors into which said vector is to be divided.

11. In a display system synthesizing an image from a source of digital vector commands, a method for drawing vectors having greater than a first predetermined length comprising the steps of:

first decomposing a long vector of greater than a first predetermined length into at least two medium vectors of not greater than a second predetermined length less than said first predetermined length by dividing the coordinates of said long vector by 2^N where N is the smallest number that yields vectors equal to or less than said second predetermined length;

second decomposing each of said medium vectors into one or more sub-vectors having fractional coordinates of said medium vector by dividing the coordinates of said medium vector by 2^M where M is the smallest number that yields vectors equal to or less than a maximum sub-vector length;

generating 2^M sub-vector commands, each such command defining a sub-vector, by successive addition of fractional coordinate values derived by said second decomposing step; and

drawing each sub-vector.

12. In a display system synthesizing an image from a source of digital vector commands, a vector generating system for drawing vectors having greater than a first predetermined length comprising:

first means for decomposing a long vector of greater than a first predetermined length into at least two medium vectors of not greater than a second predetermined length less than said first predetermined length by dividing the coordinates of said long vector by 2^N where N is the smallest number that yields vectors equal to or less than said second predetermined length;

second means for decomposing each of said medium vectors into one or more sub-vectors having fractional coordinates of said medium vector by dividing the coordinates of said medium vector by 2 where M is the smallest number that yields vectors equal to or less than a maximum sub-vector length;

means for generating 2^M sub-vector commands, each such command defining a sub-vector, by successive addition of fractional coordinate value derived by said second decomposing step; and

means for drawing each sub-vector.

13. A method for writing a vector on an electronic display comprising the steps of:

writing a first portion of said vector at a first constant speed;

writing a second portion of said vector at a second constant speed greater than said first speed; and

writing a third portion of said vector at a third constant speed less than said second constant speed.

14. A method according to claim 13 wherein said third speed is equal to said first speed.

15. In a graphics display control system for receiving display commands and providing in response thereto signals suitable for driving a monitor to display a pattern representative of said display command, the improvement comprising the use of a delta theta circuit comprising:

means for comparing the angle between first and second successive vectors;

means for determining a delay based upon the comparison in said means for comparing;

means for delaying said second vector by said delay in order to allow time for an amplifier of said monitor to settle, thereby improving the appearance of the display of successive parallel or near parallel vectors and sharp corners between two successive vectors.

16. An improvement according to claim 15 wherein said means for delaying comprises means for temporarily freezing a system clock associated with said graphics display control system.

17. In a graphics display control system for receiving vector commands and providing in response thereto signals suitable for driving a monitor to display a pattern representative of said display commands, the improvement comprising the use of a feed forward circuit comprising:

means for generating, in response to the change in direction of the current vector from its predecessor vector, a step signal representative of said difference;

means for adding said step signal to an analog vector signal related to said current vector to pre-distort the analog vector signal to compensate for the sluggishness of an amplifier associated with said monitor, thereby providing a sharp corner between said current vector and said predecessor vector.

18. An improvement according to claim 17 wherein said step signal is related to the first derivative of the current vector.

19. An improvement according to claim 17 wherein said step signal is related to the second derivative of the current vector.

20. A graphics display control system for generating signals suitable for driving an electronic display to produce a picture in accordance with digital display commands comprising:

a digital vector generator for receiving said display commands and generating sub-vectors in response thereto;

an arithmetic logic unit circuit coupled to the output of said digital vector generator for computing successive beam positions during vector generation and for storing the digital representation of a current beam position;

a digital to analog converter, coupled to the output of said arithmetic logic unit circuit, for generating an analog signal related to the successive beam positions computed by said arithmetic logic unit circuit;

an analog vector generator coupled to the output of digital to analog converters for generating analog sub-vectors responsive to the analog signal provided by said digital to analog converter and related to the sub-vectors generated by said digital vector generator.

21. A graphic display control system according to claim 20 further including a feed forward circuit for providing a step signal related to the slope of a sub-vector generated by said digital vector generator, said step signal for being combined with the output signal of said analog vector generator for improving the response of an output amplifier associated with said electronic display.

22. A graphics display control system according to claim 20 further including a grey level circuit for providing a brightness value signal related to the length of a sub-vector generated by said digital vector generator, said grey level circuit providing a signal for controlling the brightness of a line drawn on said electronic display by said graphic display control system.

23. A graphics display control system according to claim 20 further including a delta theta circuit for comparing first and second adjacent sub-vectors generated by said digital vector generator and providing in response thereto a delay of said second sub-vector allowing an amplifier associated with said electronic display to settle so as to display a sharp corner between said first and second sub-vectors.

24. A graphic display control system according to claim 23 wherein said delta theta circuit comprises means for computing a direction code for each of said two sub-vectors;

means for comparing the direction code of each sub-vector with the direction code of the other; and

means for determining a delay appropriate for the sub-vector generation process.

25. A graphics display control system according to claim 20 further including a texture generator coupled to the output of said digital vector generator for controlling the on and off periods of a writing beam of said electronic display.