Browse Prior Art Database

Pixel Scrolling Technique for Personal Computers

IP.com Disclosure Number: IPCOM000110765D
Original Publication Date: 1994-Jan-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Kerr, DA: AUTHOR [+3]

Abstract

Described is a software implementation for Personal Computers (PCs) to provide smooth character scrolling using pixel manipulation instead of the text line smoothing techniques.

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

Pixel Scrolling Technique for Personal Computers

      Described is a software implementation for Personal Computers
(PCs) to provide smooth character scrolling using pixel manipulation
instead of the text line smoothing techniques.

      Typically, a raster display shows all items as a series of
dots, or pixels.  Character scrolling is an essential part of PC
operation and requires that the scrolling be smoothed out; otherwise,
the scrolling would appear in a jerk fashion.  In prior art, to
attain smooth character scrolling, hardware implementations were
generally employed.  The concept described herein uses software to
attain smooth scrolling of textual characters on a raster display.

      Generally, every character on the display has a distinct height
and width.  The height is a value calculated by adding the base
height plus the ascender, as in the top of a "d", plus the maximum
descender, as in the bottom of a "g".  Each of the values is a number
of pixels high.  The sum is the maximum height of a character.  Since
video displays have different characteristics, the values of the
pixel height must be computed.  The objective is to scroll characters
upwards, appearing from the bottom of the screen and disappearing at
the top.  The main body of the software algorithm is as follows:

o   The main idea:

    -   Draw each line of text "number of pixels high" times,
        scrolling the displayable area up by one each time, and each
        time offsetting the text drawing location up by one.  After
        "number of pixels high" times, change the text in the buffer
        and do it all again.  As this goes on and the displayable
        area is filled, the text will smoothly, pixel by pixel,
        scroll off the top as well.

o   The pseudocode:

    -...