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Browse Prior Art Database

Screen Transforms

IP.com Disclosure Number: IPCOM000111400D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 164K

Publishing Venue

IBM

Related People

Lucus, B: AUTHOR

Abstract

Disclosed is a means, called screen transforms, in a computer graphics system to represent and display objects that remain aligned with the final picture (or display screen) regardless of their position in space.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 34% of the total text.

Screen Transforms

      Disclosed is a means, called screen transforms, in a computer
graphics system to represent and display objects that remain aligned
with the final picture (or display screen) regardless of their
position in space.

      In a typical computer graphics system, an object to be
displayed on the screen is represented by a hierarchy of parts
related by coordinate transformations.  For example, a car might be
represented as a hierarchy consisting of a body and four tires:
where the four Transform Nodes xforml, xform2, xform3, and xform4
express the four different relationships between the coordinate
system of a prototype tire and the four real tires of a car.  In
addition, the xform0 Transform Node expresses the relationship
between the coordinate system of the assembled car and the "world
coordinates" which is viewed.  Changing xform0 changes the apparent
position of the car in space.  (Note: these Transform Nodes are not
Screen Transform, although they play a similar role.)

      Sometimes it is desirable to attach an object, such as a
caption, to a particular point on another object, such as a car, such
that a reference point on the caption remains attached to the car no
matter how the car is oriented in space, say by changing xform0
above, but such that the caption itself is not rotated in space by
xform0, that is the caption always remains facing the camera.  On the
other hand, it is sometimes desirable to attach a caption to an
object so that the caption appears to be part of the object to which
it is attached and remains oriented in space in a fixed relation to
the object as the object is rotated in space.  In a typical graphics
system this is accomplished by defining two kinds of caption objects
for the two different behaviors; in some systems these two kinds of
objects are referred to as annotation and geometric text
respectively.  Such an object might be incorporated into a scene as
follows:

      The subject of this disclosure is a means of generalizing this
distinction by abstracting out the concept of an object (text or
otherwise) whose reference point remains attached to the object but
whose orientation and/or size remains fixed relative to the viewer.
Such an object is represented by a Screen Transform applied to a
basic object, such as text.  The Screen Transform plays a role in
such a system that is similar to the role played by Transform Nodes
xform0 through xform4 in the examples above, in that it specifies how
the object that it controls is finally to be positioned, oriented,
and scaled before being displayed.

      For example, suppose there is a basic text object that plays
the same role as the geometric text object in the example above; that
is, it represents a caption that is to remain fixed with respect to
position, orientation, and size on the object that it is part of.  A
car with a text caption would then be represented by

      On the other hand, if one wishes...