Controlling an output device
A method for generating a series of digitized control values for an output device to represent a continuous series of source data, comprising the steps of: storing in a single register a first digitized control value and an indication of deviation between that value and the source data; and repeatedly adding an increment to the register to generate a further digitized control value and simultaneously update the indication of deviation.
1. A method for generating a series of digitised control values for an output device to represent a continuous series of source data, comprising the steps of:
storing in a single register a first digitised control value and a second value indicating a deviation between the first value and the source data; and
repeatedly adding a single incrementing value to the register to generate a further digitised control value and simultaneously update the second value indicating the deviation;
wherein the single incrementing value comprises a first portion for incrementing the control value and a second portion for incrementing the second value indicating the deviation.
2. A method as claimed in claim 1 , wherein the register comprises a first set of adjacent bits holding the control value and a second set of adjacent bits holding the second value indicating the deviation.
3. A method as claimed in claim 2 , wherein the second set of bits are the most significant bits of the register.
4. A method as claimed in claim 1 , wherein the increment is of a third value if the second value indicating the deviation is less than a predetermined value, and otherwise the increment is of a fourth value.
5. A method as claimed in claim 1 , wherein the step of adding an increment comprises determining whether the second value indicating the deviation is greater or less than a predetermined value, and the increment that is added to the register depends on the result of that determination.
6. A method as claimed in claim 4 , wherein the predetermined value is 0.
7. A method as claimed in claim 4 , wherein the step of adding an increment comprises generating a mask as a function of the second value indicating the deviation and generating the increment by masking a predetermined increment value with the mask.
8. A method as claimed in claim 1 , wherein the output device is a video display device having a plurality of pixels at digitised positions.
9. A method as claimed in claim 8 , wherein the digitised control values represent values for controlling activation of pixels of the display.
10. A method as claimed in claim 1 , wherein the step of repeatedly adding, an increment to the register is stored as a set of instructions for a data processing apparatus and the set of instructions includes no branch instructions.
11. A process for performing Bresenhamt's algorithm comprising a method as claimed in claim 1 .
12. A method as claimed in claim 1 , wherein the second value indicating the deviation represents a discriminator.