A conceptual model of raster graphics systems was developed. The model integrates core-like graphics package concepts with contemporary raster display architectures. The conceptual model of raster graphics introduces multiple pixel matrices with associated index tables

Foley, J. D.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19850010281 2020-03-20T20:09:41+00:00Z
tI yASA-CR-174J 48) BASIEfi GbAFHICS LXTE ►SIGHS	 b85-1E590
TC THE CG6E SYSIEB Final 6EFort, 1 bay 1981
- 15 flow. 1984 (George Nasbington Univ. )
7 p HC A02/!!F AC 1	 CSCL 09B	 UDClaf
G3/61 01407
RASTER GRAPHICS EXTENSIONS
TO THE CORE SYSTEM
Final Report to NASA Langley Research Center
James J. Foley
Principal Investigator
Department of Electrical Engineering and Computer Science
The George Washington University
Washington, D.C. 20052
NASA Research Grant NAG-1-185
May 1, 1981 to November 15, 1984
z	 -1Vr--
3
3I
Significant Accomplishments
under
NASA Grant NAG-1-185
to
The George Washington University
J. Foley, Principal Investigator
1983-84
During the first year of the
nodel of raster graphics systems.
graphics package concepts with
architectures.
The model captures the wide range ofraster system cap-
abilities. Output primitives are passed through a window to
viewport transformation into one of several normalized device
coordinate (NDC) spaces. Each primitive in NDC space is then scan
converted into a pixel matrix. The application program can also
read/write arbitrary parts of pixel matrixes. RasterOps may be
performed to transfer parts of one pixel matrix to another, or to
a different area in the same pixel matrix. A view maps selected
pixels from a pixel matrix window to a screen viewport on the
viewsurface, where they are combined according to a composition
rule and displayed.
The concepts of a window on a world coordinate space and a
viewport in a normalized device coordinate space are exactly the
same as in the conceptual model of vector graphics. The raster
model also includes all the functions of our initial raster
extensions with one minor modification: whereas in the current
Core System output primitives that have passed through the
viewing pipeline are scan-converted and displayed directly; they
are now scan-converted into an intermediate pixel matrix. A
pixel matrix is a two-dimensional array of pixel values. Height,
width and bits/pixel are static attributes of a pixel matrix,
defined when it is created and remaining unchanged until it is
deleted. A distinct pseudo-display file as in the Core System is
associated with each pixel matrix and contains the output prim-
itives, arranged by segments that are scan converted into the
pixel matrix.
Associated with each pixel matrix is an index table which
specifies the color or intensity corresponding to each possible
pixel value in that pixel matrix. Thus the same pixel value in
different pixel matrixes can represent a different color in each
of them. In addition, each pixel matrix has dynamic attributes
which specify individual transparency values, and erasability.
The transparency of a pixel value indicates that pixels with that
value are not to be displayed, and thus do not obscure other
pixels they overlap. Any number of pixel values may be trans-
parent. The erasability attribute is used to allow a pixel matrix
to be unaffected by a newframe.
grant we developed a conceptual
The model integrates Core-like
contemporary raster display
•	
Ar^.aL^
'RasterOps' are defined as operations on pixel matrixes. A
RasterOp moves an arbitrary rectangular array of pixels from a
specified location in a source pixel matrix to a location in a
destination pixel matrix. The source and destination may be the
same pixel matrix. Rotation and scaling transformations may be
applied as part of Rasterop and scaling transformations may be
applied as part of Rasterop. An application program may transfer
pixels directly between a pixel n.atrix and an appropriately
formatted 2-D array of pixel val •les, thus entirely bypassing the
viewing process and segmented pse'ulo-display file of the vector
graphics systems. Pixels are rendered in temporal priority and
may overwrite images already in the pixel matrix.
A window defined on the world and an associated viewport
defined on NDC space specify a viewing transformation through
which real objects are mapped into NDC space. In the same way, a
pixel matrix window and screen viewport define another trans-
formation called a view which maps pixel matrix images onto the
viewsurface. All parts of a pixel matrix appearing in the pixel
matrix window are mapped into the screen viewport. Any number of
views may be defined on a pixel matrix. Because a view is
defined as a transformation from one raster coordinate space (the
pixel iratrix) to another (the viewsurface), the pixel matrix
window and screen viewport are defined in logical raster co-
ordinates, as are the pixel matrixes and viewsurface. The
resolution of the viewsurface in logical raster coordinates is
set by the application program at initialization time, and the
mapping to physical device coordinates is performed, if needed; a
uniform integer replication to use the maximum screen area. The
use of logical device coordinates for both pixel matrixes and
viewsurfaces all a programmer to work entirely with raster
graphics concepts, if the Core system capabilities themselves are
unneeded.
The final visible picture on the viewsurface is a com-
bination of some or all of the views and is created by a process
called view composition. A composition is specified by a com-
position frame and a composition expression. The composition
frame is a rectangular region defined on the view-surface. Only
those views or parts of views that fall within a composition
frame are composed using its composition expression. The com-
position expression defines how several overlapping images from
different views are to be rendered on the viewsurface. The
composition expression includes conditional, boolean and arith-
metic operators on any number of pixel matrixes and is applied to
all non-transparent pixel values. The full set of 16 boolean
operations is supported. Thus, for example, the final picture
may by the sum of all images in a composition frame, or it may be
an arrangement with higher-priority images obscuring lower
priority ones. Any number of composition frames ma y
 be in effect
-2-
^. Wit3-
V
at a time. Where composition frames overlap, the visible images
are in strict temporal priority of composition frame creation-the
most recently created takes precedence. Similarly, although the
aspect ratios of composition frames or their composition-rules
may be changed arbitrarily, the more recently modified com-
positions will have priority over eerlier ones.
In summary, the conceptual model of raster graphics intro-
duces multiple pixel matrixes with associated index tables,
RasterOp operations on them and new, raster oriented, viewing
transformations called views which can be combined to form a
final image on the viewsurface.
During the second half of the grant period we have con-
centrated on developing key concepts needed in a graphics
programming language. The overall structure consists of geo-
metric modeling, viewing, interaction management, and display
management subsystems. Within each area, wfe have been developing
descriptions of the semantic capabilities required. Many of
these semantics are included in our 1984 report.
Several important themes run through these capabilities. The
themes are important because they will form the basis foY
constructs in the programming language. One of the themes is
that of dynamic links. Links maintain fependencies between data
variables (which might include graphic/geometric cbjects). Thus
when variable A changes, so too do the other variables which have
functional dependencies on A.
Another theme is that of coordinate system. 	 It seems
natural that a graphics language deal with coordinate systems,
but none have. We will have named coordinate systems, and
declare an object's coordinate system as one of its attributes.
We then use another theme, that of a transformer, to relate one
coordinate system to another. Transformers are useful in input
(to relate the coordinate system of a mouse or tablet to the
world coordinate system), in modeling (to relate objects to
subobjects), and in viewing (to relate world coordinates Ln the
screen).
Another concept used is that of additional dimensions as a
means of specifying attributes. The intensity of a point, for
example, is just another (non-geometrical; coordinate of the
point. By treating attributes in this way, the attribute values
can be operated on by transformers: a separate language con-
struct is not needed.
Separately, we have started implementing the look-up table
compiler for composing separate images into a single view. The
concepts of composition, composition frames and image priority
are all working.
-3-
BIBLIOGRAPHY OF PAPERS & REPORTS
Acquah, J.B., J.D. Foley, J.L. Sibert, and P. Wenner, "A Con-
ceptual Model of Raster Graphics Systems," Computer Graphics 16,
3, July 1982, (Proceedings of 1982 SIGGRAPH Conference) pp.
321-328.
Abstract
In this paper we present a conceptual model of raster graphics
systems which integrates, at a suitable level of abstraction, the
major features found in both contemporary and anticipated
graphics systems. These features are the refresh buffer; the
image creation !scan-conversion) system; the single address-space
architecture which integrates the address space of the refresh
buffer with those of the image creation system and the associated
general-purpose computer; the Raster-Op or BitBlt instructions
found in some single address-space architectures; the video
look-up }able, and refresh buffer to screen transformations. Also
included are the major components from the conceptual model of
vector graphics systems which are embodied in the
ACM/SIGGRAPH/GSPC Core System. Using the conceptual model as a
base we proceed to sketch out the capabilities we have defined in
a substantial addition to the core system. The capabilities are
currently being implemented as part of the George Washington
University Core System.
;Acquah, J.B., J. D. Foley, and P. Wenner, Reference Manual for
Advanced Raster Graphics Extensions to ACM/SIGGRAPH Core System.
IIST Report 82-21, Department of Elf:ctrical Engineering and
Computer Science, The George Washington University, Washington,
D.C. , March 1982.
Abstract
This reference manual contains detailed functional descriptions
of advanced raster graphics extensions developed for the
ACM/SIGGRAPH Core Graphics System. It should be read in con-
junction with the paper describing the philosophy behind these
extensions: "A Conceptual Model of Raster Graphics Systems" by
Jame3 Acquah, James Foley, John Sibert and Patricia Wenner.
(GWU/EE/CS/IIST Report 81-29, November 1981). The original
specification for the Core Graphics System is found in "Report of
the Graphics Standards Planning Committee", published by Assoc-
iation for Computing Machinery, special Interest Group in
-4-
wGraphics. (Computer Graphics, Vol 13, No 4, August 1979). The
section headings and numbering are a continuation of that
document and are therefore not necessarily sequential.
Acquah, J.B., J.D. Foley, and C.F. McMath, Graphics Programming
Language Research. IIST Report 84-49, Department of Electrical
Engineering and Computer Science, The George Washington Uni-
versity, Washington, D.C., July 1984.
Abstract
This report describes the state of our graphics programming
language research. The work covers two areas: 'look-up table'
compilers, and general graphics programming languages. We have
refined our earlier look-up table language, and are now preparing
to implement it. We have developed the basic concepts needed in
a graphics programming language. Both efforts are described
herein.
Acquah, J.B., The IMAGYS Graphics Programming Language:
Description and Anal_ l sis. IIST Report 84-50, Department of
Electrical Engineering and Computer Science, The George
Washington University, Washington, D.C., November 1984.
Abstract
Imaqys (Interactive Modelling And Graphics system) is a high-
level modelling and graphics programming language being developed
at GWU. The language is designed to considerably reduce the
difficulty of writing highly interactive engineering-oriented
graphics programs, and is based on the paradigms of object-
oriented systems and functional, or value-oriented systems.
Although these are generally considered alternative approaches to
designing languages, they are combined in Imagys to produce a
language which we believe combines the best features of both and
has few of the drawbacks of either.
Data abstraction in general, and object-oriented systems in
particular, are naturally suited to uny system that creates a
model of real-world entities and processes. The principle of
hiding irrelevant details and encapsulating system-dependent
features is an extremely powerful tool. of even greater impor-
tance in a language for graphics is that such languages are
extensible, adapting to meet new requirements and demands.
Value-oriented computation is adopted in Imagys for two reasons.
Firstly, many graphics programs involve considerable amounts of
numerical computation, especially for geometric transformations.
Concurrency is the key to high-speed computation. With any given
-5-
hardware technology, massive increases in computing speed can
only be achieved by operating multiple processors in parallel.
This is Greatly facilitated by a language that permits the
greatest degree of concurrency to be extracted from a program.
such languages must be free from side effects and must have no
sequencing requirements not derived from data dependencies in the
program. Functional, or applicative languages which perform all
numerical computation by t'e application of functi ,)ns to values
have such properties.
But in an interactive graphics language there is an additional
reason for developing a language which imposes no superfluous
sequencing constraints on an algorithm. Human factors con-
siderations require that a system be as flexible as possible in
order to accomodate different user preferences and stylee. A
non-procedural or declarative style of programming is the one
best-suited to these requirements.
This paper presents an introduction to the Imagys base language.
A companion report (Standard Graphics and Modelling Classes of
the Imagys Language (IIST 84-51)) describes in detail how the
language is extended for high-level graphics.
-6-


Raster graphics extensions to the core system

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server