Showing papers in "ACM Transactions on Graphics in 1982"

A Reflectance Model for Computer Graphics

Abstract: This paper presents a new reflectance model for rendering computer synthesized images. The model accounts for the relative brightness of different materials and light sources in the same scene. It describes the directional distribution of the reflected light and a color shift that occurs as the reflectance changes with incidence angle. The paper presents a method for obtaining the spectral energy distribution of the light reflected from an object made of a specific real material and discusses a procedure for accurately reproducing the color associated with the spectral energy distribution. The model is applied to the simulation of a metal and a plastic.

Synthetic Image Generation with a Lens and Aperture Camera Model

Abstract: This paper extends the traditional pinhole camera projection geometry used in computer graphics to a more realistic camera model which approximates the effects of a lens and an aperture function of an actual camera. This model allows the generation of synthetic images which have a depth of field and can be focused on an arbitrary plane; it also permits selective modeling of certain optical characteristics of a lens. The model can be expanded to include motion blur and special-effect filters. These capabilities provide additional tools for highlighting important areas of a scene and for portraying certain physical characteristics of an object in an image.

An experimental system for creating and presenting interactive graphical documents

Abstract: An experimental system is described for the design, development, and presentation of computer-based documents that combine pictures and text on a high-resolution color raster display. Such documents can be used, for example, for maintenance and repair tasks, videotex databases, or computer-aided instruction. Documents are directed graphs whose nodes we refer to as pages, in analogy to the pages of a paper book. A page includes a set of simultaneously displayed pictures, actions (procedures and processes), and indexing information. Pages may be nested arbitrarily deeply in chapters that serve much the same organizing function as those of conventional books. The system is comprised of separate programs for laying out and drawing pictures, for graphically specifying the contents of pages, chapters, and their interconnections, and for displaying the document for user interaction. Examples are given from a prototype maintenance and repair manual in which emphasis was placed on designing actions that allow simple real-time animation and assist in finding one's way around the document.

A High-Level Language for Specifying Pictures

Abstract: A programming language tha t includes special constructs for drawing pictures is discussed. The language has been designed so that programs to draw pictures can reflect the structure of those pictures. Picture elements are called boxes. They are defmed by declaring algebraic relationships tha t should exist among their significant points and requesting actions to be performed at those points. The algebraic relationships are processed by an equation solver to determine the absolute location of significant points. A new mechanism of variable reference and scope makes the expression of relationships tha t should exist among picture elements more direct than it is in conventional languages. Some common picture operations--drawing lines using a pattern, filling in areas with textures, and obscuring parts of a picture by other par ts--are all expressed readily once the mechanism for defining and using boxes is in place. The language has been implemented, and used by several authors to prepare figures for their papers and books. It was also used to prepare this paper.

Using program transformations to derive line-drawing algorithms

Abstract: : A wide variety of line-drawing algorithms can be derived by applying program transformations to a simple, obviously correct algorithm. The transformations increase the algorithm's performance and eliminate the need for floating-point computations. Two familiar algorithms are derived in this way: Bresenham's algorithm and the digital differential analyzer (DDA). The transformations are then used to derive several highly parallel variants of Bresenham's algorithm, designed for use on displays that can generate more than one pixel at a time. The treatment shows a complete, extended example of the practical use of program transformations. Moreover, the transformations derive Bresenham's algorithm without recourse to complex geometric arguments.

Frame-to-frame coherence and the hidden surface computation: constraints for a convex world

Abstract: Frame-to-frame coherence is the highly structured relationship that exists between successive frames of certain animation sequences. From the point of view of the hidden surface computation, this implies that parts of the scene will become visible or invisible in a predictable fashion. In this paper the frame-to-frame coherence constraints are identified and characterized for static scenes restricted to stationary, closed, convex, nonintersecting polyhedra. The animation derives from a continuous movement of the viewer. The mathematical analysis of the constraints is geometric, and leads to a characterization of the self-occlusion relationship over a single polyhedron; and to a characterization of the occlusion or change of occlusion relationship over two polyhedra. Based on these constraints, an algorithm is presented which generates successive frames in an animation sequence.

A language for bitmap manipulation

Abstract: In this paper we propose that bitmaps, or raster images, should be given full citizen status in the world of computer science. We introduce a calculus of bitmap operations and MUMBLE, a programming language appropriate for describing bitmap computations. We illustrate the use of MUMBLE by several interesting graphical applications. We also discuss the structure of BOP, an efficient implementation of the bitmap calculus that is the underpinning of our system.

Hidden Line Elimination in Projected Grid Surfaces

Abstract: : Hidden line and hidden surface problems are often simpler when restricted to special classes of objects. An example is the class of grid surfaces, i.e. graphs of bivariate functions represented by their values on a set of grid points. Projected grid surfaces have geometric properties which permit hidden line or hidden surface elimination to be done more easily then in the general case. These properties are discussed in this paper and an algorithm is given which exploits them. (Author)

Anti-Aliasing through the Use of Coordinate Transformations

Abstract: The use of the point-line distance in evaluating the 2-dimensional anti-aliasing convolution is studied. We derive transformations of the point-spread function (PSF) that give the effective convolution in terms of the point-line distance when the class of object space primitives is limited to lines and polygons. Because the quality of filtering is embedded in a table indexed by the point-line distance, this approach allows one to use arbitrarily complex PSF's, only the width and not the shape of the PSF affects the amount of computation. We apply the CORDIC algorithm to point-line distance evaluation, and show its merits. Also, we show the more standard use of the CORDIC algorithm for coordinate rotation, polar-to-rectangular and rectangular-to-polar conversion, and calculating the norm of a vector. Rounded end points can be achieved by using the point-segment distance, computational methods are given, including CORDIC implementation. The CORDIC algorithms for the aforementioned geometric operations are prime candidates for VLSI implementation because of their inherent parallel/pipeline nature.

A Visible Polygon Reconstruction Algorithm

Abstract: An algorithm for determining visible lines or visible surfaces in polygonal form, at object resolution, is presented. The original scene must consist of non-intersecting planar polygons. The procedure relies on image coherence, since the sampling is dependent on the complexity of the image. The reconstruction method is based on an elaborate data structure, which allows the polygonal output to be easily obtained. The polygonal output is useful for smooth shaded or textured images, as well as the for creation of shadows.

Graphics Programming Using a Database System with Dependency Declarations

Abstract: This paper presents and integrates two ideas which can have a long-term impact on the ease of developing interactive computer graphics applications. The first idea is that of using a database management system (DBMS) to manage all the data in an interactive graphics application program (graphical input data, application data, and graphical output data). The second idea is that of replacing much of the traditional procedural specification of an application program with a more concise specification of the dependencies among the input, application, and output data. The underlying system performs the procedures necessary to maintain the dependencies. These two ideas are combined by using a relational DBMS to manage the data, and continuously evaluated qualified updates to specify dependencies to the DBMS. We illustrate these ideas with an example, and discuss the implementation of our system.

The Rack

Abstract: D e s c r i p t i o n : T h e rack is a modif icat ion of the two-axis t rackbal l or the two-axis n u m b e r wheel [2], and is designed to facil i tate the scaling or s t re tching of objects. Firs t the center of origin of the scaling opera t ion mus t be determined, and then the magni tude of the scale factors can be established. To locate the scaling origin, the user picks a scale origin point on the screen (the + cue in Figure 1). T h e user is then given an \" ident i ty cue\" (e) represent ing a scale of 1.0 in bo th x and y, along with the tab le t t racker (*) and the origin cue. W h e n the table t t racker is super imposed on the ident i ty cue, an ident i ty scale factor results, and the result ing objec t is the same as the original. A t rans format ion process is applied to bo th the xand y-scales of the selected object. T h e x-scale is de te rmined by X s c a l e = ( X t r a c k e r X o r i g i n ) / ( X i d e n t i t y Xor ig in} . T h e y-scale is de te rmined similarly. As the t racker is moved away f rom the ident i ty cue in an x-direction, the x-scale increases (Figure 2). As the t racker moves back towards the origin, the x-scale diminishes to 0 (Figure 3). As the t racker moves pas t the origin in a negat ive direction, the resul t is a negat ive scale increasing in magni tude (Figure 4). Th is is equivalent to reflection abou t the y-axis followed by a scaling by the absolute value of Xsca le . In this technique, the user ' s hand actions are t ight ly coupled to the scaling in the two directions.