Browse Prior Art Database

Computer Graphics - Swath Approach to Virtualizing the Z-buffer

IP.com Disclosure Number: IPCOM000101292D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Albaugh, V: AUTHOR [+2]

Abstract

Disclosed is a method to reduce three-dimensional (3D) graphics adapter cost by limiting the amount of required memory on the graphics adapter required for depth sorting of surfaces yet maintaining good performance. The approach is an alternative to the concept of virtualizing the Z-buffer as a single scan line. The single scan line approach imposes severe performance limitations due to the per scan line processing it requires. Z-buffers are used in graphics adapters to store the depth value of pixels and to provide hidden surface removal. The pixel data is developed for all surfaces intersecting a given pixel; however, it is only written to the frame buffer if it is closer (test on current z value) than the existing pixel.

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Computer Graphics - Swath Approach to Virtualizing the Z-buffer

       Disclosed is a method to reduce three-dimensional (3D)
graphics adapter cost by limiting the amount of required memory on
the graphics adapter required for depth sorting of surfaces yet
maintaining good performance.  The approach is an alternative to the
concept of virtualizing the Z-buffer as a single scan line.  The
single scan line approach imposes severe performance limitations due
to the per scan line processing it requires.  Z-buffers are used in
graphics adapters to store the depth value of pixels and to provide
hidden surface removal.  The pixel data is developed for all surfaces
intersecting a given pixel; however, it is only written to the frame
buffer if it is closer (test on current z value) than the existing
pixel.  For the resolution desired in sorting the depth, as much or
more memory is commonly required for storing z values as is required
for the actual display (color) data.  Eliminating the need for this
much memory could provide a considerable reduction to the cost of the
adapter.  It is possible to virtualize the Z-buffer.  This is done by
implementing a partial Z-buffer and mapping it at various times to
different sections of the frame buffer until eventually all areas of
the frame buffer have been covered.  This is really only practical
for delayed mode graphics language interfaces, such as PHIGS, where
all of the primitives for a display frame are received prior to any
drawing.  It is not practical for immediate mode interfaces that
require primitives to be drawn in the order they are issued.  For
delayed mode interfaces the primitives can be sorted into buckets
that correspond to the various mappings of the virtual Z-buffer.  The
primitives in a given bucket (frame area) can then all be processed
through the same area with only one mapping.  Immediate mode
interfaces may require a constant remapping of the frame buffer for
each primitive and thus s...