This paper describes how evolutionary techniques of variation and selection can be used to create complex simulated structures, textures, and motions for use in computer graphics and animation. Interactive selection, based on visual perception of procedurally generated results, allows the user to direct simulated evolutions in preferred directions. Several examples using these methods have been implemented and are described. 3D plant structures are grown using fixed sets of genetic parameters. Images, solid textures, and animations are created using mutating symbolic lisp expressions. Genotjps consisting of symbolic expressions are presented as an attempt to surpass the limitations of fixed-length genotypes with predefine expression rules. his proposed that artificial evolution has potential as a powerful tool for achieving flexible complexity with a minimum of user input and knowledge of details. 2

Techniques are presented that are used to animate and ren-der particle systems with the Connection Machine CM-2, a data parallel supercomputer. A particle behavior language provides an animator with levels of control from kinematic spllne motions to physically based simulations. A parallel particle rendering system allows particles of different shapes, sizes, colors and transparencies to be rendered with anti-allasing, hidden surfaces, and motion-blur. One virtual pro-cessor is assigned to each primitive data element: one to each particle, and during the rendering process, one to each pixeLsized particle fragment, and to each pixel. These tools are used to model dynamic phenomena such as wind, snow, water, and fire. 2

The paper extends Lindenmayer systems in a manner suitable for simulating the interaction between a developing plant and its environment. The formalism is illustrated by modeling the response of trees to pruning, which yields synthetic images of sculptured plants found in topiary gardens.

Complex repetitive scenes containing forests, foliage, grass, hair or fur, are challenging for common modeling and rendering tools. The amount of data, the tediousness of modeling and animation tasks, and the cost of realistic rendering have caused such kind of scene to see only limited use even in high-end productions. We describe here how the use of volumetric textures is well suited to such scenes. These primitives can greatly simplify modeling and animation tasks. More importantly, they can be very efficiently rendered using ray tracing with few aliasing artifacts. The main idea, initially introduced by Kajiya and Kay [KK89], is to represent a pattern of 3D geometry in a reference volume that is tiled over an underlying surface much like a regular 2D texture. In our contribution, the mapping is independent of the mesh subdivision, the pattern can contain any kind of shape, and it is pre-filtered at different scales as for MIP-mapping. Although the model encoding is volumetric, the rendering method differs greatly from traditional volume rendering: a volumetric texture only exists in the neighborhood of a surface, and the repeated instances (called texels) of the reference volume are spatially deformed. Furthermore, each voxel of the reference volume contains a key feature which controls the reflectance function, that represents aggregate intra-voxel geometry. This allows for raytracing of highly complex scenes with very few aliasing artifacts, using a single ray per pixel (for the part of the scene using the volumetric texture representation). The major technical considerations of our method lie in the ray-path determination, and in the specification of the reflectance function.

This paper introduces a combined discrete/continuous model of plant development that integrates L-system-style productions and differential equations. The model is suitable for animating simulated developmental processes in a manner resembling time-lapse photography. The proposed technique is illustrated using several developmental models, including the flowering plants Campanula rapunculoides, Lychnis coronaria, and Hieracium umbellatum. CR categories: F.4.2 [Mathematical Logic and Formal Languages ]: Grammars and Other Rewriting Systems: Parallel rewriting systems, I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism: Animation, I.6.3 [Simulation and Modeling ]: Applications, J.3 [Life and Medical Sciences]: Biology Keywords: animation through simulation, realistic image synthesis, modeling of plants, combined discrete/continuous simulation, L-system, piecewise-continuous differential equation. 1 INTRODUCTION Time-lapse photography reveals the enormous visual appeal...

This paper addresses the problem of realistically simulating the motion of tree-branches subjected to turbulence. Since the resulting motion is random in nature, we model it as a stochastic process. We synthesize this process directly by filtering a white noise in the Fourier domain. The filter is constructed by performing a modal analysis of the tree. We use a sophisticated numerical technique which is able to compute the first few significant modes of large trees. The main advantage of our technique over previous methods is that we are able to compute complicated motions without the need to integrate dynamical equations over time. Consequently, tree-motions can be viewed and manipulated in real-time by a user. Our technique can further be extended to other flexible structures such as two-dimensional plates.

Abstract. The goal of this paper is the interactive rendering of 3D trees covering a landscape, with shading and shadows consistent with the lighting conditions. We propose a new IBR representation, consisting of a hierarchy of Bidirectional Textures, which resemble 6D lightfields. A hierarchy of visibility cube-maps is associated to this representation to improve the performance of shadow calculations. An example of hierarchy for a given tree can be a small branch plus its leaves (or needles), a larger branch, and the entire tree. A Bidirectional Texture (BT) provides a billboard image of a shaded object for each pair of view and light directions. We associate a BT for each level of the hierarchy. When rendering, the appropriate level of detail is selected depending on the distance of the tree from the viewpoint. The illumination reaching each level is evaluated using a visibility cube-map. Thus, we very efficiently obtain the shaded rendering of a tree with shadows without loosing details, contrary to mesh simplification methods. We achieved 7 to 20 fps fly-throughs of a scene with 1000 trees. Keywords: Real-time rendering, natural scenes, forests, IBR, levels of detail, billboards

We present a procedural approach to authoring layered, solid models. Using a simple scripting language, we define the internal structure of a volume from one or more input meshes. Sculpting and simulation operators are applied within the context of the language to shape and modify the model. Our framework treats simulation as a modeling operator rather than simply as a tool for animation, thereby suggesting a new paradigm for modeling as well as a new level of abstraction for interacting with simulation environments.

Extensible typesafe systems, such as Java, rely critically on a large and complex software base for their overall protection and integrity, and are therefore difficult to test and verify. Traditional testing techniques, such as manual test generation and formal verification, are too time consuming, expensive, and imprecise, or work only on abstract models of the implementation and are too simplistic. Consequently, commercial virtual machines deployed so far have exhibited numerous bugs and security holes. In this paper, we discuss our experience with using production grammars in testing large, complex and safety-critical software systems. Specifically, we describe lava, a domain specific language we have developed for specifying production grammars, and relate our experience with using lava to generate effective test suites for the Java virtual machine. We demonstrate the effectiveness of production grammars in generating complex test cases that can, when combined with comparative and variant testing techniques, achieve high code and value coverage. We also describe an extension to production grammars that enables concurrent generation of certificates for test cases. A certificate is a behavioral description that specifies the intended outcome of the generated test case, and therefore acts as an oracle by which the correctness of the tested system can be evaluated in isolation. We report the results of applying these testing techniques to commercial Java implementations. We conclude that the use of production grammars in combination with other automated testing techniques is a powerful and effective method for testing software systems, and is enabled by a special purpose language for specifying extended production grammars. 1.

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