Showing papers on "Graphics published in 1998"

Linear and nonlinear mixed-effects models

Abstract: Douglas M. Bates Department of Statistics University of Wisconsin Madison Jose C. Pinheiro Bell Laboratories Lucent Technologies 1 Recent developments in computational methods for maximum likelihood (ML) or restricted maximum likelihood (REML) estimation of parameters in general linear mixed-effects models have made the analysis of data in typical agricultural settings much easier. With software such as SAS PROC MIXED we are able to handle da~ from random-effects one-way classifications, from blocked designs including incomplete blocked designs, from hierarchical designs such as splitplot designs, and other types of data that may be described as repeated measures or longitudinal data or growth-curve data. It is especially helpful that the new computational methods do not depend on balance in the data so we are able to deal more easily with observational studies or with randomly missing data in a designed experiment. We describe some of the new computational approaches and how they are implemented in the nlme3.0 library for the S-PLUS language. One of the most powerful features of this language is the graphics capabilities, especially the trellis graphics facilities developed by Bill Cleveland and his coworkers at Bell Labs. Although most participants in this conference may be more familiar with SAS, and most of the models described here can be fit with PROC MIXED or the NLiNMIX macro or new P ROC N LM IXED in SAS version 7, some exposure to the combination of graphical display and model-fitting approaches from S-PLUS may be informative. 1 Annual Conference on Applied Statistics in Agriculture Kansas State University New Prairie Press http://newprairiepress.org/agstatconference/1998/proceedings/2 2 Kansas State University We show how data exploration with trellis graphics, followed by fitting and comparing mixedeffects models, followed by graphical assessment of the fitted model can be used in a variety of situations. On some occasions, such as modeling growth curves, a linear trend or polynomial trend or other types of linear statistical models for the within-subject time dependence are just not going to do an adequate job of representing the data. In those cases, a nonlinear model is more appropriate. We show how the concept of a random coefficient model can be extended to nonlinear models so as to fit nonlinear mixed-effects models.

The office of the future: a unified approach to image-based modeling and spatially immersive displays

Abstract: We introduce ideas, proposed technologies, and initial results for an office of the future that is based on a unified application of computer vision and computer graphics in a system that combines and builds upon the notions of the CAVE™, tiled display systems, and image-based modeling . The basic idea is to use real-time computer vision techniques to dynamically extract per-pixel depth and reflectance information for the visible surfaces in the office including walls, furniture, objects, and people, and then to either project images on the surfaces, render images of the surfaces , or interpret changes in the surfaces. In the first case, one could designate every-day (potentially irregular) real surfaces in the office to be used as spatially immersive display surfaces, and then project high-resolution graphics and text onto those surfaces. In the second case, one could transmit the dynamic image-based models over a network for display at a remote site. Finally, one could interpret dynamic changes in the surfaces for the purposes of tracking, interaction, or augmented reality applications. To accomplish the simultaneous capture and display we envision an office of the future where the ceiling lights are replaced by computer controlled cameras and “smart” projectors that are used to capture dynamic image-based models with imperceptible structured light techniques, and to display high-resolution images on designated display surfaces. By doing both simultaneously on the designated display surfaces, one can dynamically adjust or autocalibrate for geometric, intensity, and resolution variations resulting from irregular or changing display surfaces, or overlapped projector images. Our current approach to dynamic image-based modeling is to use an optimized structured light scheme that can capture per-pixel depth and reflectance at interactive rates. Our system implementation is not yet imperceptible, but we can demonstrate the approach in the laboratory. Our approach to rendering on the designated (potentially irregular) display surfaces is to employ a two-pass projective texture scheme to generate images that when projected onto the surfaces appear correct to a moving headtracked observer. We present here an initial implementation of the overall vision, in an office-like setting, and preliminary demonstrations of our dynamic modeling and display techniques.

Regression Graphics: Ideas for Studying Regressions Through Graphics

Abstract: Introduction to 2D Scatterplots. Constructing 3D Scatterplots. Interpreting 3D Scatterplots. Binary Response Variables. Dimension--Reduction Subspaces. Graphical Regression. Getting Numerical Help. Graphical Regression Studies. Inverse Regression Graphics. Sliced Inverse Regression. Principles Hessian Directions. Studying Predictor Effects. Predictor Transformations. Graphics for Model Assessment. Bibliography. Indexes.

Method and apparatus for personnel detection and tracking

Abstract: Techniques from computer vision and computer graphics are combined to robustly track a target (e.g., a user) and perform a function based upon the image and/or the identity attributed to the target's face. Three primary modules are used to track a user's head: depth estimation, color segmentation, and pattern classification. The combination of these three techniques allows for robust performance despite unknown background, crowded conditions, and rapidly changing pose or expression of the user. Each of the modules can also provide an identity classification module with valuable information so that the identity of a user can be estimated. With an estimate of the position of a target in 3-D and the target's identity, applications such as individualized computer programs or graphics techniques to distort and/or morph the shape or apparent material properties of the user's face can be performed. The system can track and respond to a user's face in real-time using completely passive and non-invasive techniques.

Practical parameterization of rotations using the exponential map

Abstract: Parameterizing three degree-of-freedom (DOF) rotations is difficult to do well. Many graphics applications demand that we be able to compute and differentiate positions and orientations of articulated figures with respect to their rotational (and other) parameters, as well as integrate differential equations, optimize rotation parameters, and interpolate orientations. Widely used parameterizations such as Euler angles and quaternions are well suited to only a few of these operations. The exponential map maps a vector in R 3 describing the axis and magnitude of a three-DOF rotation to the corresponding rotation. Several graphics researchers have applied it with limited success to interpolation of orientations, but it has been virtually ignored with respect to the other operations mentioned above. In this paper we present formulae for computing, differentiating, and integrating three-DOF rotations with the exponential map. We show that our formulation is numerically stable in the face of machine precision issues, and that for most applications all singularities in the map can be avoided through a simple technique of dynamic reparameterization. We demonstrate how to use the exponential map to solve both the "freely rotating body" problem, and the important ball-and-socket joint required to accurately model shoulder and hip joints in articulated figures. Examining several common graphics applications, we explain the benefits of our formulation of the exponential map over Euler angles and quaternions, including robustness, small state vectors, lack of explicit constraints, good modeling capabilities, simplicity of solving ordinary differential equations, and good interpolation behavior.

The virtual reality modeling language and Java

Abstract: The Virtual Reality Modeling Language (VRML) and Java provide a standardized, portable and platform- independent way to render dynamic, interactive 3D scenes across the Internet. Integrating two powerful and portable software languages provides interactive 3D graphics plus complete programming capabilities plus network access. Intended for programmers and scene authors, this paper provides a VRML overview, synopsizes the open development history of the specification, provides a condensed summary of VRML 3D graphics nodes and scene graph topology, describes how Java interacts with VRML through detailed examples, and examines a variety of VRML/Java future developments. Overview. The Web is being extended to three spatial dimensions thanks to VRML, a dynamic 3D scene description language that can include embedded behaviors and camera animation. A rich set of graphics primitives provides a common-denominator file format which can be used to describe a wide variety of 3D scenes and objects. The VRML specification is now an International Standards Organization (ISO) specification (VRML 97). Why VRML and Java together? Over twenty million VRML browsers have shipped with Web browsers, making interactive 3D graphics suddenly available for any desktop. Java adds complete programming capabilities plus network access, making VRML fully functional and portable. This is a powerful new combination, especially as ongoing research shows that VRML plus Java provide extensive support for building large-scale virtual environments (LSVEs). This paper provides historical background, a detailed overview of VRML 3D graphics, example VRML-Java test programs, and a look ahead at future work.

Real time compression of triangle mesh connectivity

Abstract: In this paper we introduce a new compressed representation for the connectivity of a triangle mesh. We present local compression and decompression algorithms which are fast enough for real time applications. The achieved space compression rates keep pace with the best rates reported for any known global compression algorithm. These nice properties have great benefits for several important applications. Naturally, the technique can be used to compress triangle meshes without significant delay before they are stored on external devices or transmitted over a network. The presented decompression algorithm is very simple allowing a possible hardware realization of the decompression algorithm which could significantly increase the rendering speed of pipelined graphics hardware. CR Categories: I.3.1 [Computer Graphics]: Hardware Architecture; I.3.3 [Computer Graphics]: Picture/Image Generation— Display algorithms

Method and system for computer-mediated, multi-modal, asynchronous meetings in a virtual space

Abstract: A computer-supported collaborative work environment allows for computer-mediated, multi-modal, asynchronous meetings in a virtual space that enables, recording, reviewing and augmenting meetings that take place in the virtual environment. Meeting participants interact via avatars, i.e., graphical representations of the participants, in a place-based, multi-dimensional graphical environment. Meeting sessions are captured for future replay and augmentation in a multi-modal document. The system utilizes multiple "tracks" in the multi-modal document, such as text discussion, audio commands, graphics, and documents, which are combined into the multi-modal document to preserve a recording of the meeting for future participants. The multi-modal document of this meeting can then be replayed and augmented by future participants ad infinitum to create a single, synchronous meeting. Furthermore, using avatars enables a straightforward method for generating composite screens for multiple sessions, and alleviates privacy concerns of users.

Multiple-center-of-projection images

Abstract: In image-based rendering, images acquired from a scene are used to represent the scene itself. A number of reference images are required to fully represent even the simplest scene. This leads to a number of problems during image acquisition and subsequent reconstruction. We present the multiple-center-of-projection image, a single image acquired from multiple locations, which solves many of the problems of working with multiple range images. This work develops and discusses multiple-center-ofprojection images, and explains their advantages over conventional range images for image-based rendering. The contributions include greater flexibility during image acquisition and improved image reconstruction due to greater connectivity information. We discuss the acquisition and rendering of multiple-center-of-projection datasets, and the associated sampling issues. We also discuss the unique epipolar and correspondence properties of this class of image. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation – Digitizing and scanning, Viewing algorithms; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism; I.4.10 [Image Processing]: Scene Analysis

Computer vision for interactive computer graphics

Abstract: Vision can be a powerful interface device for computers because of its potential for sensing body position, head orientation, direction of gaze, pointing commands, and gestures. Such unencumbered interaction can make computers easier to use. We describe vision algorithms for interactive graphics and present vision-controlled graphics applications using these algorithms. Some applications employ an artificial retina chip for image detection or preprocessing.

Method and system for map display in a navigation application

Abstract: A program and method for a map display tool for use with a navigation system and used with a map database. The map display tool is adapted to render a map on a display or in a graphics buffer for a predetermined geographic region. The map display tool includes a map processing layer for performing the essential data manipulation, a graphics interface layer that maintains a series of look up tables with graphics commands, and a primitive layer customized to interact with an underlying graphics platform and the graphics interface layer. The map display tool renders a map by retrieving data items from the map database and processing each data item. Shape information is rendered on a screen or in a graphics buffer, name information is buffered and sorted to optimize filtering, prioritization, spatial conflicts resolution and other tasks prior to rendering.

Principles of Educational Multimedia User Interface Design

Abstract: This paper discusses principles of educational multimedia user interface design. The purpose of these principles is to maximize the learning effectiveness of multimedia applications. The principles are based on the results of studies in psychology, computer science, instructional design, and graphics design. The principles help user interface designers make decisions about the learning materials, learners, tasks that the learners perform, and tests for measuring learning performance.

User-friendly graphics generator using direct manipulation

Abstract: A 3D graphics generation and display application for PCs and laptops in a business environment includes an authoring mode screen which has a list (38) database elements sought to be graphically displayed, along with a list (40) of variables pertaining to the database elements. Also, the application presents a menu (42) of graphics attributes, including each of the three spatial dimensions and time, as well as various graphics object attributes, such as color, size, rotation, opacity, intensity, texture, etc. The user determines whether the graphics objects are balls for a scatter plot, bars for a bar chart, pie-shaped elements for a pie chart, or other 3D representation. By clicking on a database variable in the list (40) of variables and dragging it over an attribute on the attribute menu (42), the user can correlate the database variable with the graphics attribute. When the user correlates a variable to a graphics attribute, the correlation is noted by a legend (44) that is displayed with the menu (42) of attributes. The graphics are displayed in an animated 3D presentation with graphics attributes, including their motion over time, determined by the database variables which have been correlated to the attributes.

Real-time generation of continuous levels of detail for height fields

Abstract: Height fields play an important role in the fast growing domain of Geographic Information Systems (GIS). For exploring different kinds of geographic-based data sets on screen it is necessary to display height fields at interactive frame rates. Because of the inherent geometric complexity, this goal is often unachievable even with new generations of powerful graphics computers, unless the original height field data is approximated in order to reduce the number of geometric primitives that need to be rendered without compromising visual quality. So far most algorithms have focused on global reduction or multi-resolution techniques, which reduce resolution on the basis of surface roughness. A recent new approach called Continuous Levels of Detail [LKR+96] introduced a hierarchical quadtree technique. In order to reduce the projected pixel error, the height field is dynamically triangulated in a bottom up fashion according to the distance to the point of view. Since resolution is allowed to change smoothly, the result is a much better image quality. However, this algorithm still has a major disadvantage. With the viewpoint moving, the triangulation is continuously changing, resulting in a phenomenon called vertex popping. As the observer approaches an area with detail information, this detail will suddenly appear at a certain distance. To eliminate these artifacts we introduce a new, rapid geomorphing algorithm, which operates top down on a quadtree data structure.

Method for sorting 3D object geometry among image chunks for rendering in a layered graphics rendering system

Abstract: A pre-processing method prepares 3D objects for rendering to image layers in a layered graphics rendering pipeline. The method transforms a bounding volume for an object to a 2D bounding box in a 2D view space. It then subdivides the bounding box into blocks of image samples called chunks. To computer the portion of the object that should be rendered to each chunk, it determines which geometric primitives of the object overlap each chunk and generates a list of primitives to the rendered for each chunk.

Method and system for menu-driven two-dimensional display lesion generator

Abstract: A high frequency generator system with a computer graphic two-dimensional user-interactable interface is achieved to allow selection of menus associated with the function, state, and output parameters of the high frequency generator system. A two-dimensional graphics display is coupled directly or remotely to a high frequency power source system which is further connected to electrodes in contact or proximity to the tissue of a patient's body. A two-dimensional display allows the user to see, in a compact, convenient, and comprehensive way, selection menus for use of the high frequency generator system, control of its parameters, monitoring of its processes during clinical application, and graphics displays related to historic or current image scan data and real-time monitoring of output parameters related to the application. Pre-set or user-selectable arrays of parameters can be selected through the two-dimensional user interface to the high frequency generator system. Real-time plotting of single or multiple output parameters as a function of time course during the clinical application can be graphically displayed on the two-dimensional display. Digital displays, alphanumeric streams of information, help menus, prompts, and sequences of menus may be selected by the two-dimensional interface through actuators on the interface or on the panel of the high frequency generator system. Several forms of the interface, user actuators, screen layouts, and methods for use of this system accommodate the specific objectives.

User-friendly graphics generator including automatic correlation

Abstract: A 3D graphics generation and display application for PCs and laptops in a business environment includes an authoring mode screen which lists database elements sought to be graphically displayed, along with a list of variables pertaining to the database elements. Also, the application presents a menu of graphics attributes, including each of the three spatial dimensions and time, as well as various graphics object attributes, such as color, size, rotation, opacity, intensity, texture, etc. The user determines whether the graphics objects are balls for a scatter plot, bars for a bar chart, pie-shaped elements for a pie chart, or other 3D representation. By clicking on a database variable in the list of variables and dragging it over an attribute on the attribute menu, the user can correlate the database variable with the graphics attribute. When the user correlates a variable to a graphics attribute, the correlation is noted by a legend that is displayed with the menu of attributes. The graphics are displayed in an animated 3D presentation with graphics attributes, including their motion over time, determined by the database variables which have been correlated to the attributes. In an alternate embodiment, the user can simply select variables to be presented, and a programmatic rule interpreter receives the variables and accesses a list of conditional rules to automatically correlate the variables to graphics attributes for presentation thereof.

The Information Mural: a technique for displaying and navigating large information spaces

Abstract: Information visualizations must allow users to browse information spaces and focus quickly on items of interest. Being able to see some representation of the entire information space provides an initial gestalt overview and gives context to support browsing and search tasks. However, the limited number of pixels on the screen constrain the information bandwidth and make it difficult to completely display large information spaces. The Information Mural is a two-dimensional, reduced representation of an entire information space that fits entirely within a display window or screen. The Mural creates a miniature version of the information space using visual attributes, such as gray-scale shading, intensity, color, and pixel size, along with antialiased compression techniques. Information Murals can be used as stand-alone visualizations or in global navigational views. We have built several prototypes to demonstrate the use of Information Murals in visualization applications; subject matter for these views includes computer software, scientific data, text documents and geographic information.

Computer imaging using graphics components

Abstract: Graphics software for use in rendering an image on a computer display. The software is used in conjunction with special hardware including a high resolution computer monitor and high speed graphics imaging software. The software allows the user to create and manipulate paint objects that define the way images are modified by rendering tools such as a drawing tool or a titling tool. The attributes for a plurality of paint objects are defined in a hierarchy and can be stored on a memory device such as a computer hard drive. The organization into a hierarchy of the various attributes making up a complex object such as a paint stroke or a text body result in an ability to deal with branches of the hierarchy as persistable objects in their own right.

A shading language on graphics hardware: the pixelflow shading system

Abstract: Over the years, there have been two main branches of computer graphics image-synthesis research; one focused on interactivity, the other on image quality. Procedural shading is a powerful tool, commonly used for creating high-quality images and production animation. A key aspect of most procedural shading is the use of a shading language, which allows a high-level description of the color and shading of each surface. However, shading languages have been beyond the capabilities of the interactive graphics hardware community. We have created a parallel graphics multicomputer, PixelFlow, that can render images at 30 frames per second using a shading language. This is the first system to be able to support a shading language in real-time. In this paper, we describe some of the techniques that make this possible.

Video game system and coprocessor for video game system

Abstract: A low cost high performance three dimensional (3D) graphics system can model a world in three dimensions and project the model onto a two dimensional viewing plane selected based on a changeable viewpoint. The viewpoint can be changed on an interactive, real time basis by operating user input controls such as game controllers. The system rapidly produces a corresponding changing image (which can include animated cartoon characters or other animation for example) on the screen of a color television set. The richly featured high performance low cost system gives consumers the chance to interact in real time inside magnificent virtual 3D worlds to provide a high degree of image realism, excitement and flexibility. An optimum feature set/architecture (including a custom designed graphics/audio coprocessor) provides high quality fast moving 3D images and digital stereo sound for video game play and other graphics applications.

Multiple viewpoint rendering

Abstract: This paper presents an algorithm for rendering a static scene from multiple perspectives. While most current computer graphics algorithms render scenes as they appear from a single viewpoint (the location of the camera) multiple viewpoint rendering (MVR) renders a scene from a range of spatially-varying viewpoints. By exploiting perspective coherence, MVR can produce a set of images orders of magnitude faster than conventional rendering methods. Images produced by MVR can be used as input to multiple-perspective displays such as holographic stereograms, lenticular sheet displays, and holographic video. MVR can also be used as a geometry-to-image prefilter for image-based rendering algorithms. MVR techniques are adapted from single viewpoint computer graphics algorithms and can be accelerated using existing hardware graphics subsystems. This paper describes the characteristics of MVR algorithms in general, along with the design, implementation, and applications of a particular MVR rendering system.

Dehalftoning of digital images

Abstract: Methods and apparatus for blending graphics objects. In one aspect, a method includes receiving a first graphics object; rendering the first graphics object to produce a first pixel map having a first bit depth; increasing a bit depth of a second pixel map associated with a second graphics object that is to be blended with the first graphics object, where the second bit depth is less than the first bit depth; and blending the first and second pixel maps. The method may be implemented to blend graphics objects received by a printing device. In one embodiment, the invention features blending deep pixel data received by a printing device with corresponding shallow halftoned data stored in a shallow frame buffer. The invention may be implemented as a printer configured to receive a page description language description of a page to be printed, the printer including a dehalftone engine for deriving deep pixel data values for objects stored in a shallow frame buffer. In another aspect, the invention features using a pixelmap representative of underlying graphics data for transfer between a host and a remote device by transmitting a halftone representation of the pixelmap from the host to the remote device and reconstructing the pixelmap at the remote device from the halftone representation and a threshold matrix.

A distributed 3D graphics library

Abstract: We present Repo-3D, a general-purpose, object-oriented library for developing distributed, interactive 3D graphics applications across a range of heterogeneous workstations. Repo-3D is designed to make it easy for programmers to rapidly build prototypes using a familiar multi-threaded, object-oriented programming paradigm. All data sharing of both graphical and non-graphical data is done via general-purpose remote and replicated objects, presenting the illusion of a single distributed shared memory. Graphical objects are directly distributed, circumventing the “duplicate database” problem and allowing programmers to focus on the application details. Repo-3D is embedded in Repo, an interpreted, lexically-scoped, distributed programming language, allowing entire applications to be rapidly prototyped. We discuss Repo-3D’s design, and introduce the notion of local variations to the graphical objects, which allow local changes to be applied to shared graphical structures. Local variations are needed to support transient local changes, such as highlighting, and responsive local editing operations. Finally, we discuss how our approach could be applied using other programming languages, such as Java.

Computer-generated floral ornament

Abstract: This paper describes some of the principles of traditional floral ornamental design, and explores ways in which these designs can be created algorithmically. It introduces the idea of “adaptive clip art,” which encapsulates the rules for creating a specific ornamental pattern. Adaptive clip art can be used to generate patterns that are tailored to fit a particularly shaped region of the plane. If the region is resized or reshaped, the ornament can be automatically regenerated to fill this new area in an appropriate way. Our ornamental patterns are created in two steps: first, the geometry of the pattern is generated as a set of two-dimensional curves and filled boundaries; second, this geometry is rendered in any number of styles. We demonstrate our approach with a variety of floral ornamental designs. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation; I.3.4 [Computer Graphics]: Graphics Utilities— Picture description languages. Additional

Interactive reflections on curved objects

Abstract: Global view-dependent illumination phenomena, in particular reflections, greatly enhance the realism of computer-generated imagery. Current interactive rendering methods do not provide satisfactory support for reflections on curved objects. In this paper we present a novel method for interactive computation of reflections on curved objects. We transform potentially reflected scene objects according to reflectors, to generate virtual objects. These are rendered by the graphics system as ordinary objects, creating a reflection image that is blended with the primary image. Virtual objects are created by tessellating scene objects and computing a virtual vertex for each resulting scene vertex. Virtual vertices are computed using a novel space subdivision, the reflection subdivision. For general polygonal mesh reflectors, we present an associated approximate acceleration scheme, the explosion map. For specific types of objects (e.g., linear extrusions of planar curves) the reflection subdivision can be reduced to a 2-D one that is utilized more accurately and efficiently. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism.

Virtual studios: an overview

Abstract: Virtual studio systems began as experimental prototypes that extended traditional chromakeying. Now commercial products based on graphics supercomputers are commonly used for broadcast production. We discuss this evolution and consider extensions, alternative approaches, and issues facing broadcasters who introduce virtual studio systems.

Advanced graphics controls

Abstract: A graphics control for an interactive user interface includes a plurality of individually specified graphics components. Each graphics component has non-transparent portions and potentially also has transparent portions. In one embodiment, the graphics components include a background component, a face component, a frame component, and a focus component. The components are overlaid on each other from bottom to top, creating a layered effect. The face component is selectable by the user input to perform an action, and selecting the face component changes the appearance of the face component. Other than the background component, the components each are constructed of a texture bitmap and one or more luminance bitmaps. The texture bitmaps are tiled to conserve memory and data bandwidth. The luminance bitmaps can be supplied in a small size, and scaled using a special tiling technique.

Visualization of large nested graphs in 3D: Navigation and Interaction

Abstract: Most systems for visualizing large information structures use 2D graphics to view networks of nodes and arcs that represent data. To understand large structures it is often necessary to show both small-scale and large-scale structures. This has been called the problem of focus and context. Distortion, rapid zooming, elision and multiple windows are all techniques that have been developed to provide both focus and context within single representations. We review these techniques and argue that 3D visualization has a number of advantages. A system called NestedVision3D (NV3D) will be presented that has been developed to investigate the use of 3D visualization for understanding the structure of large computer programs. NV3D is a system for visualizing large nested graphs using interactive 3D graphics. It has been tested with graphs containing more than 35,000 nodes and 100,000 relationships. We describe NV3D and its design philosophy. Basic navigation is facilitated by a set of 3D widgets, rapid scaling and interactive elision. More experimental features include animations called snakes, which are used to trace dynamic software behavior.