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Calculating FOCA Character Positioning Metrics for non-FOCA Font Technologies Including Methods for Estimating Vertical Metrics

IP.com Disclosure Number: IPCOM000022462D
Original Publication Date: 2004-Mar-16
Included in the Prior Art Database: 2004-Mar-16
Document File: 6 page(s) / 111K

Publishing Venue

IBM

Abstract

Traditionally, print data generated in the format defined by the IBM Mixed Object Document Content Architecture for Presentation (MO:DCA-P) have been limited to fonts packaged in a format defined by the IBM Font Object Content Architecture (FOCA). Recent changes to MO:DCA-P will now allow documents to use fonts created in other font technology formats, such as TrueType, OpenType, and Adobe Type 1. This invention describes how the character metrics in these new font technologies are related to the character metrics in FOCA fonts.

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Calculating FOCA Character Positioning Metrics for non-FOCA Font Technologies Including Methods for Estimating Vertical Metrics

Main Idea

Traditionally, print data generated in the format defined by the IBM Mixed Object Document Content Architecture for Presentation (MO:DCA-P) have been limited to fonts packaged in a format defined by the IBM Font Object Content Architecture (FOCA). Recent changes to MO:DCA-P will now allow documents to use fonts created in other font technology formats, such as TrueType and Adobe Type 1.

When using these technologies and the rasterizers that support them, one cannot directly obtain character positioning metrics for the four character rotations that FOCA defines. Refer to the "Font Object Content Architecture Reference" for a detailed description of character rotation and character positioning metrics. For MO:DCA documents, these rotations provide the means to support different writing modes, such as right-to-left and vertical writing, required in certain scripts and geographies. The figure below illustrates the four ordinal rotations defined and how they are used with various inline and baseline directions to achieve different writing modes.

Without a method to calculate the character metrics for all four rotations, it would be difficult to utilize the new font technologies in the AFP environment.

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Horizontal Metrics

When a rasterizer RIPs the outline descriptions into character bitmaps, they provide metrics for positioning the bitmaps horizontally within the line of text. While the parameters returned vary by rasterizer, they invariably provide enough information to calculate the metrics defined by FOCA for 0 degree character rotation. This information includes the width and depth of the bitmap, the distance from the character origin to a corner of the bitmap, and the distance to the origin of the next character.

The figure below compares the parameters returned by a typical rasterizer to the horizontal (0 degree) metrics provide by a FOCA font.

Based on this illustration, the key FOCA metrics can be calculated as follows:

Character Increment (HCI) = Escapement A-space (HAS) = X Origin B-space (HBS) = Black Width C-space (HCS) = Escapement - A-space - B-space Baseline Extent (HBE) = Black Depth Baseline Offset (HBO) = Y Origin Character Descender (HCD) = Black Depth - Y Origin

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The FOCA metrics for 180 degrees (up-side-down) rotation have a simple relationship to those for 0 degree rotation. The A-space and the C-space metrics are reversed, as are the baseline offset and character descender metrics. The character increment, B-space, and baseline extent metrics are identical.

Vertical Metrics

Character rotations of 90 and 270 degrees are used to support vertical forms of writing. In addition to the metrics mentioned earlier, vertical positioning and character incre...