Microsoft Technology Licensing, LLC

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Dean Dayton Ballard

Eliyezer Kohen

An improved scan converter to support the efficient and accurate display of character outlines by pixel-oriented display devices. To conserve the finite resource of memory, the improved scan converter supports an efficient use of available memory workspace by accurately determining an upper bound for the amount of memory required to support scan conversion calculations. To achieve improvements in speed and character image quality, the improved scan converter renders the spline segments of a character outline by using a second order equation to calculate an implicit function based on the control points of each segment. The improved scan converter further addresses in a systematic manner the rendering of an endpoint located on a scan line to determine whether the pixel associated with the endpoint should be activated. This decision is based upon the direction of approach to and exit from this endpoint for the pair of segments connected to the endpoint. The improved scan converter also reduces the number of calculations requiring sub-pixel precision to support the selection of a pixel located nearest the contour, thereby providing an improved solution for dropout condition.

Method for rendering endpoints of segments during scan conversion of a glyph

Laying out a paragraph using a layout services library. An entire paragraph is defined as a single text run. The text run is laid out by substituting glyphs for the characters of the text run and then positioning the glyphs. After the text run is laid out, the length of the text run is compared to the line length. If the length of the text run exceeds the line length, then the text run is divided into a parent text run and a child text run. If justification is enabled, then the parent text run is justified. If a child text run is created, then the length of the child text run is compared to the line length. If the length of the child text run exceeds the line length, then the process is repeated until the length of the last child text run does not exceed the line length. A layout services library provides text processing functions which support the paragraph layout and the justification.

Laying out a paragraph by defining all the characters as a single text run by substituting, and then positioning the glyphs

Rendering glyphs using a layout services library. A layout services library provides a set of text-processing functions for use by a client program. The text-processing functions access font information stored in the font tables insulating the client program from the details of the font table formats. The layout services library may be used to identify glyph variants and to position glyphs along a base line for a run of text. To identify glyph variants, the layout services library scans the run of text to identify the locations of characters having alternative glyph forms. The layout services library creates a list of feature parameter structures, each of which contains a count of the number of glyph alternates that apply for each identified character. The client program assembles a list of identical characters which have different parameters and presents a list of all glyph variants to the user who chooses one of the alternatives. To position glyphs, the layout services library assembles data that describes the advance of a virtual pen point from glyph to glyph along the base line, an X-placement value, and a Y-placement value. The X-placement value and the Y-placement value are used to position the glyph with respect to the virtual pen point on the base line.

Method for rendering glyphs using a layout services library

Method for estimating the memory required for scan conversation of a glyph

Method of dropout control for scan conversion of a glyph comprising a

Method for rendering a spline for scan conversion of a glyph comprising

Method for rendering a spline for scan conversion of a glyph

A system and method of rendering a curve using data look-up tables for rasterizing the curve. The curve is subdivided so that it is approximated by a series of straight line segments of approximately equal length, with no line segment exceeds two pixels in length. The system subdivides any line segment that crosses horizontal axis of two adjacent horizontal scan rows. If the line segment does not cross the horizontal axis of a scan row, the pixel does not require detailed analysis. If the line segment does cross the horizontal axis of a particular horizontal scan row, the system uses look-up tables to determine the distance from the center point of the pixel in which the line segment crosses the horizontal axis to the point at which the line segment crosses the horizontal axis. The system uses three indices as pointers to the data look-up table containing the desired data. The three indices are themselves pointers to separate index tables in which the multiplication calculations required for the data look-up table have been precalculated and are incorporated into the values stored in the index tables. The index tables also incorporate a reduction in resolution from 1/64 to 1/8 pixel resolution. The index tables are also nonlinear to allow more data entries in areas where the round off error resulting from the resolution reduction are greatest. If the line segment crosses the horizontal axis to the left of the center of a pixel, the logic state for the pixel is changed. The system can be implemented on any computer and operates with any raster scan graphics display unit.

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Dean Dayton Ballard