Apparatus and method for identifying next matrices for vector drawing

Apparatus for vector to pixel conversion in which each pixel of a display screen is organized into one of a plurality of separate matrices each having a given number of pixels in an x coordinate direction and a selected number of pixels in a y coordinate direction, each said matrix being located on said screen at a fixed location relative to all other ones of said matrices, such conversion defining which pixels must be "on" in order to draw a first vector from a first pixel to a last pixel on said screen, a current matrix being one of such matrices during such conversion thereof, a matrix prior to said current matrix being one of said matrices that is adjacent said current matrix in a direction toward said first pixel, an exit side of one of said matrices being a side of said matrix that is intersected by said vector as said vector extends from said current matrix to a next matrix, each said matrix having a first decision point located therein at a selected location, comprising:

• means responsive to first input signals defining the x and y coordinates of the first pixel of said vector for producing X and Y matrix address signals that define the respective X and Y matrix addresses of a first matrix that contains said first pixel of said vector;
• said producing means also being responsive to said first input signals and second input signals defining the x and y coordinates of said last pixel for producing delta X and delta Y signals indicating how many matrices in each of the x and y coordinate directions there are from said first matrix to a last matrix that contains said last pixel;
• said producing means also being responsive to said first and second input signals for producing a first directional signal representing a first directional characteristic of said vector and a first intercept signal representing the intersection of said vector with the exit side of the matrix prior to said current matrix;
• said producing means also being responsive to said first and second input signals for producing a major signal representing a second directional characteristic of said vector;
• current address means responsive to said matrix address signals for generating current matrix address signals to indicate the address of said current matrix;
• next matrix means responsive to said first intercept signal for generating a second intercept signal representing the relationship of said first decision point to the location at which said vector exits said current matrix, said next matrix means also being responsive to said first intercept signal and to said first directional signal for generating next matrix signals that indicate the direction of the next matrix through which said vector extends, said direction being one of the x coordinate direction or the y coordinate direction or both of said x and y coordinate directions;
• said current address means being responsive to said next matrix signals to change said current matrix address signals to the address of said next matrix;
• counter means responsive to said delta X and delta Y signals and cycled in response to said next matrix signals for producing vector end signals indicating said first and last matrices;
• said next matrix means being interrupted in response to one of said vector end signals that indicates that said current matrix is said last matrix;
• means responsive to said first intercept signal for said matrix prior to said current matrix for generating a third intercept signal representing the intersection of said vector with an entrance side of said current matrix through which said vector enters said current matrix;
• means responsive to the sign of said first directional signal, to said first and third intercept signals and to said major signal for generating pixel write enable signals that define these pixels within said current matrix that are to be "on" to draw said vector;
• and
• means responsive to said current matrix address signal for said current matrix and responsive to said pixel write enable signal for said current matrix for storing, at an address related to said matrix address, data representing said "on" pixels of each said current matrix through which said vector extends.

A method of converting a vector to pixel enable data for displaying said vector on a display screen having pixels extending in x and y coordinate directions, said vector being defined by a first pixel having a first x and y coordinate address on said screen and by a last pixel having a last x and y coordinate address, said vector having a directional characteristic, which comprises:

• organizing all of said pixels on said screen into selected separate matrices, each said matrix being at a different fixed location on said display screen and having a given number of pixels in said x coordinate direction and a selected number of pixels in said y coordinate direction;
• converting said x,y coordinates of said first pixel that defines one end of said vector into matrix coordinates that define the location of a first matrix in which said first pixel is located;
• determining first and second quantities equal respectively to the number of said matrices in each of said x and y coordinate directions that are between said first matrix and a last matrix in which said last pixel is located, said last pixel defining the end of said vector;
• determining the locations of said vector with respect to opposite sides of a given pixel in a current one of said matrices as said vector extends from said current matrix into a next matrix;
• identifying the direction of said next matrix through which said vector extends upon exiting said current matrix according to said locations of said vector relative to decision points positioned at a predetermined location on each of said opposite sides of said given pixel;
• reducing said first quantity by one if said next matrix is in said x coordinate direction and reducing said second quantity by one if said next matrix is in said y coordinate direction;
• and
• for each matrix through which said vector extends, defining which pixels are to be enabled in order to display said vector.