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Efficient Implementation of the Phigs Pipeline for Line-Type Primitives

IP.com Disclosure Number: IPCOM000100089D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 120K

Publishing Venue

IBM

Related People

Einkauf, MA: AUTHOR [+3]

Abstract

A method is disclosed in which line-type graphics primitives may be processed more efficiently in a PHIGS com- patible computer graphics system. Complete compatibility with the "standard" PHIGS graphics pipeline is maintained while providing significantly increased performance.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 47% of the total text.

Efficient Implementation of the Phigs Pipeline for Line-Type Primitives

       A method is disclosed in which line-type graphics
primitives may be processed more efficiently in a PHIGS com- patible
computer graphics system.  Complete compatibility with the "standard"
PHIGS graphics pipeline is maintained while providing significantly
increased performance.

      The "Programmer's  Hierarchical Interactive Graphics System"
(PHIGS) describes a programming interface to a complete computer
graphics system.  The interface consists mainly of "primitive"
(Polyline, Circle, Polygon, Triangle Mesh, etc.) and "attribute"
(Line Color, View Volume description, Shading Method, etc.) commands.
 A system which supports the PHIGS interface must process primitives
and attributes in the manner prescribed by PHIGS, so that the
primitive commands produce identical output on all PHIGS-compatible
systems.

      The manner in which primitives must be processed is commonly
referred to as the "PHIGS Pipeline".  This invention applies to the
processing of line-type primitives (as opposed to areas, such as
polygons), so only the "Line Pipeline" will be discussed here.  The
processing of areas is also described by the PHIGS Pipeline, but
includes such steps as shading and culling, which are not applicable
to lines (and are therefore not part of this discussion).

      The standard PHIGS Line Pipeline describes the transformation
and clipping operations which must be performed on line-type
primitives.  The following terminology is used:  Modelling
Coordinates (MC), World Coordinates (WC), View Reference Coordinates
(VRC), Normalized Projection Coordinates (NPC), and Device
Coordinates (DC).  The primitive is described in MC, and various
attributes control the transformations, clipping, and mapping which
determine the appearance of the primitive on the screen (i.e., in
DC).  The standard PHIGS Line Pipeline is shown below:
   Transform -> Transform -> View -> Map to -> Transform
    to WC        to VRC     Clip     NPC        to DC
            Fig 1. Standard PHIGS Line Pipeline

      Note that the standard PHIGS Pipeline has a final step called
the "workstation clip", which is to be performed in NPC.  In the
invention described here, it is assumed that this clip region
includes all of NPC space.  Therefore, the workstation clip is
omitted from this discussion.

      A  standard practice in computer graphics is to combine
adjacent transormations, using principles of linear algebra. This
allows multiple transformations to be done by a single transformation
matrix, which is a concatenation of several matrices.  Therefore, the
standard pipeline readily reduces to these steps:
                      1) Transform from MC to VRC
                      2) Clip in VRC
                      3) Map to NPC
                  ...