Distinguishing between impulses and continuous drag operations on a touch-sensitive surface

1. A drawing table for a computer animator to create or to modify a computer-generated image, comprising:

a touch-sensitive surface adapted to receive touch input from a touch object, wherein the computer-generated image is visible to the computer animator when the computer animator views the touch-sensitive surface; and

a processor connected to the touch-sensitive surface, wherein the processor is adapted to:

detect a touch between the touch object and the touch-sensitive surface at an initial location on the touch-sensitive surface;

create a human-unperceivable circle in response to the touch between the touch object and the touch-sensitive surface,

wherein the human-unperceivable circle is centered at the initial location of the touch,

wherein the human-unperceivable circle has a radius of an initial value at the time that the human-unperceivable circle is created, and

wherein, while the touch continues to be detected, the radius decreases from the initial value over time to a value less than the initial value;

determine whether any portion of a movement of the touch object on the touch-sensitive surface is outside the perimeter of the human-unperceivable circle at the time of the movement;

if any portion of the movement is outside the perimeter, then output a signal representing a graphical user interface operation; and

if no portion of the movement is outside the perimeter, then forgoing output of the signal representing the graphical user interface operation.

2. The drawing table of claim 1 , wherein the processor is further adapted to:

before outputting the signal representing the graphical user interface operation, determine whether the touch object is removed from the touch-sensitive surface;

if the touch object is removed, then output a mouse click operation as the signal representing the graphical user interface operation; and

if the touch object is not removed, then output a drag operation as the signal representing the graphical user interface operation.

3. The drawing table of claim 1 , wherein:

the radius of the human-unperceivable circle decreases at an exponential rate.

4. The drawing table of claim 3 , wherein:

the radius of the human-unperceivable circle decreases by an exponential factor of five over a half second.

5. The drawing table of claim 1 , further comprising:

a display coupled with the touch-sensitive surface and connected to the processor, wherein the display is adapted to display the computer-generated image through the touch-sensitive surface.

6. The drawing table of claim 1 , further comprising:

a projector connected to the processor, wherein the projector is adapted to project the computer-generated image onto the touch-sensitive surface.

7. The drawing table of claim 1 , wherein the touch object is a stylus.

8. A touchscreen device for displaying a computer-generated image and receiving input from a touch object, comprising:

(a) a touch-sensitive surface adapted to detect contact with the touch object;

(b) a display screen adapted to display the computer-generated image, wherein:

the display screen is visually aligned with the touch-sensitive surface such that the computer-generated image displayed on the display screen is visible to a user when the user views the touch-sensitive surface; and

(c) a processor connected to the touch-sensitive surface and the display screen, wherein the processor is adapted to:

detect a touch between the touch object and the touch-sensitive surface at an initial location on the touch-sensitive surface;

create a human-unperceivable circle in response to the touch between the touch object and the touch-sensitive surface,

wherein the human-unperceivable circle is centered at the initial location of the touch,

wherein the human-unperceivable circle has a radius of an initial value at the time that the human-unperceivable circle is created, and

wherein, while the touch continues to be detected, the radius decreases from the initial value over time to a value less than the initial value;

produce an output signal representing a graphical user interface drag operation, if the touch object is touching the touch-sensitive surface, and if any portion of a touch object movement on the touch-sensitive surface is outside the perimeter of the human-unperceivable circle at the time of the touch object movement;

produce an output signal representing no operation, if the touch object is touching the touch-sensitive surface, and if no portion of the touch object movement is outside the perimeter of the human-unperceivable circle at the time of the touch object movement; and

produce an output signal representing a mouse click operation, if the touch object is removed from the touch-sensitive surface, and if no portion of the touch object movement is outside the perimeter of the human-unperceivable circle at the time of removal.

9. The touchscreen device of claim 8 , wherein:

the radius of the human-unperceivable circle decreases at an exponential rate.

10. The touchscreen device of claim 9 , wherein:

the radius of the human-unperceivable circle decreases by an exponential factor of five over a half second.

11. The touchscreen device of claim 8 , wherein the touch object is a stylus.

12. A computer-implemented method for distinguishing touch input representing a graphical user interface drag operation and a graphical user interface click operation, the method comprising:

detecting touch input from a touch object at an initial location on a touch-sensitive surface;

determining a human-unperceivable circle in response to the touch input,

wherein the human-unperceivable circle is centered at the initial location of the initial touch input,

wherein the human-unperceivable circle has a radius of an initial value at the time that the human-unperceivable circle is determined, and

wherein, while the touch input continues to be detected, the radius decreases from the initial value over time to a value less than the initial value;

distinguishing whether the touch input represents a graphical user interface drag operation or a graphical user interface click operation, based on a movement of the touch object on the touch-sensitive surface and a perimeter of the human-unperceivable circle; and

producing an output signal, wherein the output signal represents the distinguished graphical user interface operation.

13. The computer-implemented method of claim 12 , wherein:

while the touch object is touching the touch-sensitive surface, if any portion of the touch object movement is outside the perimeter of the human-unperceivable circle at the time of touch object movement, then the distinguished graphical user interface operation represents a graphical user interface drag operation.

14. The computer-implemented method of claim 12 , wherein:

when the touch object is removed from the touch-sensitive surface, if no portion of the touch object movement is outside the perimeter of the human-unperceivable circle at the time of removal, then the distinguished graphical user interface operation represents a mouse click operation.

15. The computer-implemented method of claim 12 , further comprising:

distinguishing whether the touch input represents no operation from the graphical user interface click operation and the graphical user interface drag operation, wherein:

while the touch object is touching the touch-sensitive surface, if no portion of the touch object movement is outside the perimeter of the human-unperceivable circle at the time of the movement, then the distinguished graphical user interface operation represents no operation.

16. The computer-implemented method of claim 12 , wherein:

the radius of the human-unperceivable circle decreases at an exponential rate.

17. The computer-implemented method of claim 16 , wherein:

the radius of the human-unperceivable circle decreases by an exponential factor of five over a half second.

18. The computer-implemented method of claim 12 , further comprising:

displaying a computer-generated image on a display screen,

wherein the display screen is visually aligned with the touch-sensitive surface, and

wherein the computer-generated image is visible to a user through the touch-sensitive surface.

19. The computer-implemented method of claim 12 , wherein the touch object is a stylus.

20. A non-transitory computer-readable storage medium having computer-executable instructions for distinguishing between touch input representing a graphical user interface drag operation and a graphical user interface click operation, the computer-executable instructions comprising instructions for:

detecting touch input from a touch object at an initial location on a touch-sensitive surface;

determining a human-unperceivable circle in response to the touch input,

wherein the human-unperceivable circle is centered at the initial location of the touch input,

wherein the human-unperceivable circle has a radius of an initial value at the time that the human-unperceivable circle is determined, and

wherein, while the touch input continues to be detected, the radius decreases from the initial value over time to a value less than the initial value; and

distinguishing whether the touch input represents a graphical user interface drag operation or a graphical user interface click operation, based on a movement of the touch object on the touch-sensitive surface and a perimeter of the human-unperceivable circle; and

producing an output signal, wherein the output signal represents the distinguished graphical user interface operation.

21. The non-transitory computer-readable storage medium of claim 20 , wherein:

while the touch object is touching the touch-sensitive surface, if any portion of the touch object movement is outside the perimeter of the human-unperceivable circle at the time of touch object movement, then the distinguished graphical user interface operation represents a graphical user interface drag operation.

22. The non-transitory computer-readable storage medium of claim 20 , wherein:

when the touch object is removed from the touch-sensitive surface, if no portion of the touch object movement is outside the perimeter of the human-unperceivable circle at the time of removal, then the distinguished graphical user interface operation represents a mouse click operation.

23. The non-transitory computer-readable storage medium of claim 20 , further comprising instructions for:

distinguishing whether the touch input represents no operation from the graphical user interface click operation and the graphical user interface drag operation, wherein:

while the touch object is touching the touch-sensitive surface, if no portion of the touch object movement is outside the perimeter of the human-unperceivable circle at the time of the movement, then the distinguished graphical user interface operation represents no operation.

24. The non-transitory computer-readable storage medium of claim 20 , wherein:

the radius of the human-unperceivable circle decreases at an exponential rate.

25. The non-transitory computer-readable storage medium of claim 24 , wherein:

the radius of the human-unperceivable circle decreases by an exponential factor of five over a half second.

26. The non-transitory computer-readable storage medium of claim 20 , further comprising instructions for:

displaying a computer-generated image on a display screen,

wherein the display screen is visually aligned with the touch-sensitive surface, and

wherein the computer-generated image is visible to a user through the touch-sensitive surface.

27. The non-transitory computer-readable storage medium of claim 20 , wherein the touch object is a stylus.