Abstract: A trajectory and a footprint of a hypothetical pen are each divided into sequences of segments, each segment having a slope associated therewith. The segments of the footprint form a closed sequence and those of the trajectory form a sequence with a beginning and an end. Each of the two approximate envolvents of the thick line are calculated in the same way, from the trajectory segments and the footprint segments. An envolvent is initialized to include the first segment of the trajectory starting at an appropriate offset from the trajectory start point, followed by zero or more footprint segments and then followed by the next trajectory segment until each of the trajectory segments are concatenated. In determining how many footprint segments to concatenate before concatenating the next trajectory segment, the slopes of the last concatenated trajectory segment and the next trajectory segment are compared to the slopes of the footprint segments.

Abstract: A method and apparatus for converting multi-level raster shapes into bi-level raster shapes while preserving as much of the visual character of the shape is disclosed. The method and apparatus solve two main problems arising in the task: that of broken continuity (drop-outs) and that of large changes in the width of horizontal and vertical lines on the bi-level raster shape as a result of minute changes on the multi-level shape (stem width aliasing). Drop-outs are handled by identifying certain boundaries between pixels as drop-out warnings. Pixels adjacent to dropout warnings have their coverage values converted from multi-level to bi-level by a process that guarantees that at least one of them will be rounded up. Dropout warnings are found from the outline of the ideal shape used to generate the multi-level shape and represent an approximation to said outline.

Abstract: A method of synthesizing multi-level raster shapes directly from outlines describing ideal shapes is disclosed. A raster shape suitable for approximating the ideal shape in a raster display device is synthesized by dividing a plane into a plurality of pixel areas according to a pixel grid, then by representing the shape as one or more arcs in the plane, where the arcs collectively, and in conjunction with an insideness criterium, divide the plane into an inside region and an outside region, and then by separating the pixels into inside pixels, outside pixels, and boundary pixels. The raster shape comprises coverage values assigned to each pixel in the plane, where inside pixels are assigned a coverage value of 1, outside pixels a coverage value of 0 and the boundary pixels a coverage value between 0 and 1 approximating the degree to which the boundary pixel is covered by the inside of the outline.

Abstract: A method and apparatus is described which fills in the pixels missed when drop-out occurs during the fill process of character contours. The character contour is decomposed into a series of rook moves. The pixel selected is the one more covered by the actual shape of the portion of the curve where the rook moves are coincident and dropout occurs. This is dependent upon the slope of each of the curves at the location of dropout. Preferably the length of the sequence of colinear consecutive rook moves is used to approximate the slopes of the curves. The target pixel of the longest sequence of colinear rook moves is more covered than its opposite pixel and therefore the target pixel is set. The target pixel for a rook move is the pixel in the winding direction (i.e., left or right direction) along the rook move. Thus the target pixel of the stronger rook moves will be set and added to the bit map image generated using a outline fill process.

Abstract: Disclosed is a page printing system which uses virtual (logical) memory for mapping images. Physical memory which is used for creating a page image bitmap for synthetic graphics is to be allocated as patches. A path in general corresponds to a rectangular area of a page when the page exists in bitmap form. Each patch is represented by a set of non-contiguous segments of logical memory which, when mapped to physical memory, are contiguous.