Browse Prior Art Database

Method for Incorporating Elements of the Phigs Workstation Clip into View Clip

IP.com Disclosure Number: IPCOM000100809D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 113K

Publishing Venue

IBM

Related People

Einkauf, MA: AUTHOR [+4]

Abstract

Disclosed is a method to combine the workstation clip and view clip in the standard Programmer's Hierarchical Interactive Graphics System (PHIGS) pipeline into a single clipping step. This method simplifies the clipping procedure, and increases the performance and efficiency of the transformation pipeline.

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Method for Incorporating Elements of the Phigs Workstation Clip into View Clip

       Disclosed is a method to combine the workstation clip and
view clip in the standard Programmer's Hierarchical Interactive
Graphics System (PHIGS) pipeline into a single clipping step.  This
method simplifies the clipping procedure, and increases the
performance and efficiency of the transformation pipeline.

      In the standard PHIGS pipeline, the following terminologies are
used:  Modelling Coordinate (MC), World Coordinate (WC), View
Reference Coordinate (VRC), Normalized Projection Coordinate (NPC)
and Device Coordinate (DC).  The standard PHIGS transformation
pipeline includes the following steps:
      1. Transform from MC to WC
      2. Apply view orientation matrix to transform from WC to VRC
   3. Perform view clipping against the specified view volume in VRC
      4. View mapping into NPC
      5. Workstation clip and transform into DC

      In the standard PHIGS pipeline there are two clips: a view clip
and a workstation clip.  The view clip takes place in  VRC against a
given view volume.  The workstation clip happens in NPC against the
workstation window boundaries. Clipping against some volumes is more
simple than general ones because they minimize the amount of involved
calculation.  Therefore, the given view volume should be transformed
to a canonical view volume (VRC').  The efficiency of the pipeline
will  increase if the workstation clip can be incorporated into a
view clip to form a single clip in VRC'.  Thus, when the view volume
or the workstation transformation gets updated, only the
transformation matrices are changed.  The primitives are always
clipped against the same volume independent of the given view volume.

      Transformations from VRC' to NPC and from NPC to DC include
translation and scaling.  With a given workstation window,
workstation viewport, NPC viewport, and view volume, "backmapping"
can be performed to go from DC to NPC, from NPC to VRC', and from
VRC' to VRC to obtain a corresponding view volume.

      "Backmapping" is only called whenever the view volume or
workstation transformation gets updated.  This includes the following
steps:  (see the figure):
      1.   Determine the DC intersection of the workstation viewport
and the screen.
     2.   Map the DC intersection area into the workstation window in
NPC and find the corresponding workstation window.
      3.   Find the NPC intersection of the new workstation window
and the NPC viewport.
      4.   Map t...