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Efficient Implementation of the PHIGS Pipeline for Area-Type Primitives

IP.com Disclosure Number: IPCOM000100262D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 93K

Publishing Venue

IBM

Related People

Einkauf, MA: AUTHOR [+3]

Abstract

A method is disclosed in which area-type graphics primi- tives may be processed more efficiently in a PHIGS compatible 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 52% of the total text.

Efficient Implementation of the PHIGS Pipeline for Area-Type Primitives

       A method is disclosed in which area-type graphics primi-
tives may be processed more efficiently in a PHIGS compatible
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 outputs 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 area-type primitives (as opposed to line-type) so only
the "Area Pipeline" will be discussed.  The processing of lines is
also described by the PHIGS Pipeline, but does not include such steps
as lighting and culling.

      The standard PHIGS Area Pipeline describes the transformation,
culling, lighting and clipping operations which must be performed on
area-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 Area Pipeline is shown below:
Transform -> Area -> Lighting -> Transform -> View -> Map ->
Transform to WC      Cull    Calculation    to VRC     Clip    to to
DC NPC
    Fig 1.  Standard PHIGS Area 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.

      In PHIGS, the View Volume to which clipping is performed can be
either a frustum (truncated pyramid), for a perspective view, or a
skewed p...