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Generating Tri-Plane (Anti-Aliased) Text Using Colour Comparison

IP.com Disclosure Number: IPCOM000101325D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 94K

Publishing Venue

IBM

Related People

O'Hara, JMP: AUTHOR

Abstract

This article describes a fast software technique of translating tri-plane anti-aliased font definitions into four- or more-plane bitmaps of the required colour for stage in the VRAM font buffer. Existing hardware is more efficiently employed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Generating Tri-Plane (Anti-Aliased) Text Using Colour Comparison

       This article describes a fast software technique of
translating tri-plane anti-aliased font definitions into four- or
more-plane bitmaps of the required colour for stage in the VRAM font
buffer.  Existing hardware is more efficiently employed.

      Tri-plane symbol set definitions, used for anti-aliased text,
are traditionally held in memory as three separate single-plane
bitmaps, which define a three-plane image of the character, giving
eight possible colours per pixel. This colour-independent three-plane
definition is then translated into the final required text colour to
be displayed on a display of four or more planes.  These may be put
into a cache, or into the final position on the visible display.

      This disclosure uses the built-in colour comparison logic, and
BitBlt capability of a display adapter to achieve more efficient,
faster translation than existing methods. The process for a
four-plane display differs slightly, and is described separately.
The process as described for an eight-plane display is effective for
eight or more planes.

      Description: For an eight-plane display, a two-stage process is
used.  For a four-plane display, an extra intermediate stage is
necessary.

      Stage 1 Stage 1 produces an intermediate image consisting of
eight different pixel values using three BitBlts from the character
font definition to a VRAM character buffer area. Stage 1, four planes

      A tri-plane character image in a font consists of three
monochrome (bit per pixel) images which are translated into a
four-plane deep image (Fig 1), with pixel values 0 to 7, by means of
three patterned rectangular area fills. Stage 1, eight planes

      Stage 1 for eight planes is virtually identical to Stage 1 for
four planes except that the pixel values generated are in the range N
+ 0 to N + 7.  N is a number less than 248, and divisible
by 8, such that none of the eight numbers N + 0 to N +
7 occur as entries in the text colour index table.  The text colour
index table is eight entries lon...