Apparatus for and method of generating a straight line of pixels in a discrete coordinate system

An apparatus for drawing a straight line having a start point and an end point in a discrete coordinate system comprising:

• (a) means for receiving X coordinate values and Y coordinate values of the start point and the end point of the line;
• (b) means for computing an X difference value and an X difference absolute value and a Y difference value and a Y difference absolute value of the start point and the end point of the line;
• (c) means for computing a region code defining a region obtained by dividing a range of 360 degrees in accordance with the X difference value, the Y difference value and a ratio of the X and Y difference absolute values;
• (d) means for computing an initial error term value based on a ratio of the X difference absolute value and the Y difference absolute value;
• (e) means for computing a positive added value which is added to the error term value when the error term value is positive;
• (f) means for computing a negative added value which is added to the error term value when the error term value is negative;
• (g) means for storing and repetitively performing incrementing and decrementing operations of X and Y coordinates specified by a combination of the region code and a sign of the error term value;
• and
• (h) means for repetitively and selectively adding either of the positive added value and the negative added value to the error term value on the basis of the sign of the error term value.

A method of drawing a straight line having a start point and an end point in a discrete coordinate system, comprising the steps of:

• (a) reading X coordinate values and Y coordinate values of the start point and the end point of the line;
• (b) computing an X difference value and an X difference absolute value and a Y difference value and a Y difference absolute value of the start point and the end point of the line;
• (c) computing a region code defining a region obtained by dividing a range of 360 degrees in accordance with the X difference value, the Y difference value and a ratio of the X and Y difference absolute values;
• (d) computing an initial error term value based on the ratio of the X difference absolute value and the Y difference absolute value;
• (e) computing a positive added value which is added to the error term value when the error term value is positive;
• (f) computing a negative added value which is added to the error term value when the error term value is negative;
• (g) selecting X and Y coordinates and repetitively incrementing and decrementing these coordinates according to the combination of the region code and the error term value;
• (h) repetitively and selectively adding either of the positive added value and the negative added value to the error term value on the basis of a sign of the error term value.

A straight line generator for drawing a straight line in a discrete coordinate system comprised of pixels, each pixel having a first coordinate and a second coordinate, said straight line having a slope, a start pixel and an end pixel, said generator determining the coordinates for intermediate pixels between the start and end pixels and comprising:

• means for storing the first and second coordinates of at least a current intermediate pixel;
• a region code register for storing a region code indicative of a relation of the coordinates of the end pixel to the coordinates of the start pixel and of the slope of said straight line;
• an error register for storing an error term obtained using a Bresenham algorithm;
• a first register for storing a first error update value;
• a second register for storing a second error update value;
• an adder for selecting an error update value from the first and second registers and for adding the selected error update value to the error term in the error register;
• control logic for successively updating the current first and second coordinates in the means for storing on the basis of said region code and said error term and for controlling the selection of error update values by said adder.

A straight line generator for drawing a straight line in a discrete coordinate system comprised of pixels, each pixel having a first coordinate and a second coordinate, said straight line having a start pixel and an end pixel, said generator determining the coordinates for intermediate pixels between the start and end pixels and comprising:

• means for storing the first and second coordinates of at least a current intermediate pixel;
• a region code register for storing a region code indicative of a region of a circle in which at least a portion of the straight line is located, said circle having a center defined by a pixel of said straight line;
• an error register for storing an error term obtained using a Bresenham algorithm;
• a first register for storing a first error update value;
• a second register for storing a second error update value;
• an adder for selecting an error update value from the first and second registers and for adding the selected error update value to the error term in the error register;
• control logic for successively updating the current first and second coordinates in the means for storing on the basis of said region code and said error term and for controlling the selection of error update values by said adder.

A method of drawing a straight line having a slope, a start point and an end point, each point having coordinates in a discrete coordinate system by use of a Bresenham algorithm, comprising:

• computing a region code indicative of the slope of the straight line, and a relation of the coordinates of the end point to the coordinates of the start point;
• computing an error term using the Bresenham algorithm;
• providing an error adjustment term;
• repetitively incrementing and decrementing the coordinates of one of the start point and the end point to generate coordinates of points intermediate the start point and the end point, the incrementing and decrementing being performed on the basis of the error term, the region code and the error update value;
• and displaying a line in accordance with the coordinates generated.

An apparatus for drawing a straight line having a start point and an end point in a discrete coordinate system comprising:

• (a) means for receiving X coordinate values and Y coordinate values of the start point and the end point of the line;
• (b) means for computing an X difference value and an X difference absolute value and a Y difference value and a Y difference absolute value of the start point and the end point of the line;
• (c) means for computing a region code defining a region obtained by dividing a range of 360 degrees in accordance with the X difference value, the Y difference value and a ratio of the X and Y difference absolute values;
• (d) means for computing an initial error term value based on the ratio of the X difference absolute value and the Y difference absolute value;
• (e) means for computing a positive added value which is added to the error term value when the error term value is positive;
• (f) means for computing a negative added value which is added to the error term value when the error term value is negative;
• (g) means for storing and repetitively performing incrementing and decrementing operations of X and Y coordinates specified by a combination of the region code and a sign of the error term value to generate coordinates of points for the line;
• (h) means for repetitively and selectively adding either of the positive added value and the negative added value to the error term value on the basis of the sign of the error term value;
• and
• (i) means for displaying the line in accordance with the coordinates generated by the means for performing incrementing and decrementing operations.

A method of drawing a straight line having a start point and an end point in a discrete coordinate system, comprising the steps of:

• (a) reading X coordinate values and Y coordinate values of the start point and the end point of the line;
• (b) computing an X difference value and an X difference absolute value and a Y difference value and a Y difference absolute value of the start point and the end point of the line;
• (c) computing a region code defining a region obtained by dividing a range of 360 degrees in accordance with the X difference value, the Y difference value and a ratio of the X and Y difference absolute values;
• (d) computing an initial error term value based on the ratio of the X difference absolute value and the Y difference absolute value;
• (e) computing a positive added value which is added to the error term value when the error term value is positive;
• (f) computing a negative added value which is added to the error term value when the error term value is negative;
• (g) selecting X and Y coordinates and repetitively incrementing and decrementing these coordinates according to a combination of the region code and the error term value to generate coordinates of points on the line;
• (h) repetitively and selectively adding either of the positive added value and the negative added value to the error term value on the basis of a sign of the error term value;
• and
• (i) displaying the line in accordance with the generated coordinates.