Abstract: A graphics processor uses a line draw facility to receive first and second values indicative of the coordinates of respective first and second end points of a line. The reception of the second value is sensed by the line draw facility and line data is generated responsive to the sensing of the second value.

Abstract: A graphics device includes first and second endpoint memories where coordinates of a line can be stored. State logic within the graphics device calculates line parameters from the first and second endpoints. The calculated line parameters include a line error term which can be stored in an error term memory. The error term memory is writeable from a source external to the graphics device, such as the CPU of a computer system, so that the external source can modify the contents of the error term register.

Abstract: Line draw circuitry receives parameters defining first and second endpoints of a line and calculates line parameters based on the first and second endpoints. The line parameters are then stored in a memory. A "calculate-only" control signals determines whether a line is drawn immediately after calculation (and storing) of the end parameters or whether the line is drawn responsive to a subsequent "start" signal. If the line is to be drawn responsive to the start signal, the line parameters may be modified prior to drawing the line.

Abstract: A graphics processor uses a line draw facility to receive first and second values indicative of the coordinates of respective first and second end points of a line. The reception of the second value is sensed by the line draw facility and line data is generated responsive to the sensing of the second value.

Abstract: Circuitry for drawing lines includes a video memory for storing pixel data and circuitry for generating a sequence of addresses defining a line of pixels in the video memory. A first memory stores a sequence of pattern units corresponding to the generated sequence of addresses. A second memory stores a value indicating a current pattern unit. Writing circuitry writes to the video memory at a generated address responsive to a current pattern unit. A third memory stores a control value which is accessed by update circuitry for updating the second memory to indicate the next pattern unit. The update circuitry may selectively update the second memory to the sequential pattern unit or reset the second memory to a predetermined pattern unit.

Abstract: In a line generator and a method for determining the individual pixels to be plotted for a line to be drawn in a display system, coded representations of a plurality of lines are stored in a line definition table. The coded representation of each individual line is a string of data items representing the transitions between adjacent pixels to be plotted for drawing the individual line. Preferably, only coded representations of lines up to a predetermined size (i.e. the length of the line in the case of a straight line) are stored in the line definition table. Strings of data items for representing the pixels to be plotted for longer lines to be drawn are still calculated as in the prior art. In this case, control logic determines whether there are coded representations of a line to be drawn in the line definition table, or not, and passes control to appropriate processing logic for determining the pixels to be plotted.

Abstract: In a method of storing characters in a display system having a display device with an orthogonal matrix of addressable points, each character is represented as a succession of strokes each constrained to lie in one of the eight fundamental directions of the matrix and, except for the first stroke, each starting at the end of the previous stroke. Each such stroke is stored in a binary coded form which includes a first binary number (direction code) defining the angular direction of the stroke, a second binary number (length code) defining a number of matrix steps from one addressable point to the next along the stroke in that direction, and a third binary number (move/draw code) defining the visibility of the stroke. In order to facilitate character rotation by any multiple of 45.degree. the direction code defining each fundamental direction corresponds to the addition modulo 2.sup.n of a binary constant to the direction code which defines the fundamental direction of 45.degree.

Abstract: The invention concerns a graphics display system of the kind having a refresh raster display device, a line clipping mechanism for clipping line primitives for viewing in a selected rectangular viewport having horizontal and vertical edges parallel to the X and Y axes respectively of the display area of the display device, and a vector-to-raster converter for converting the clipped lines to patterns of discrete pels in a refresh buffer, the vector-to-raster converter including an incremental line drawing mechanism responsive to line information supplied by the clipping mechanism to draw the line starting at one endpoint and proceeding towards the other.

Abstract: An improved method and apparatus are disclosed for generating circular arcs of any arc length greater than zero up to and including a full circle of 360 degrees. The method and apparatus can locate nonsymmetrical closest points for noninteger radius and arc center values. The method and apparatus is capable of generating the incremental move commands for drawing an arc either in the clockwise or counter clockwise direction which is a distinct advantage when used to drive a pen type electromechanical plotter. By dividing the generation of a 360 degree arc into eight octants, only two of the original eight directions need to be considered as candidate directions toward the next integer display matrix value to be displayed. The method and apparatus employ a novel initialization which provides a simple stopping test for any circular arc of arbitrary length and direction. Only simple addition and sign testing is used to display the circular arc.