CMSC 335 COMPUTER GRAPHICS LECTURE 12 IMPLICIT MODELING

CMSC 335 COMPUTER GRAPHICS LECTURE 12 • • IMPLICIT MODELING • PREVIEW OF TESSELLATION PROCEDURAL MODELING

IMPLICIT MODELING

IMPLICIT MODELING •

BLOBBY OBJECTS • Blobby objects are defined as distribution functions over space • An example would be defining a ball by a distance from a point scaled by that distance (think of heat radiating from the sun) • Summation or other blending techniques combine many primitive blobs into a model

CONSTRUCTIVE SOLID GEOMETRY • The process of generating a new object from two objects using a set operation is called constructive solid geometry • Union, intersection, and difference allow for various complex models to be formed • Warping is also allowed of shapes in the form of twisting, tapering, or bending

PRECISE CONTACT MODELING • Precise contact modeling is a method for deformation and contact modeling while maintaining continuity

BLOB TREE • Most of the implicit modeling approaches, including constructive solid geometry allow for combinations in a tree hierarchy to represent very complex shapes

SPACE PARTITIONING • In order to render an implicit model, it needs to be approximated by polygons • Space partitioning algorithms facilitate this • Example algorithm: (1) divide the space into a grid of voxels, (2) determine voxels intersecting model, (3) convert voxels into tetrahedrons • Extra data structures • • Binary space partitions Octtrees

PROCEDURAL MODELING

PROCEDURAL MODELING • Procedural modeling can refer to the algorithmic generation of shape data • Many methods exist and are widely used

SWEEPING ALGORITHMS • Objects with symmetry can often be specified by a 2 D shape moving through (sweeping) space • Using a parametric representation, we can generate vertex/triangle information from this • Example of a sphere and torus in Ch 6 of Computer Graphics Programming

GENERATIVE GRAMMARS • Grammars are descriptions of languages • Generative grammars describe how to expand language constructs into an infinite number of possible sentences • Shape grammars extend this idea to shapes • Applies randomness to the logical expansion rules

FRACTALS • Self-similar subset of space, exhibiting a repeating pattern at smaller and smaller scales • Defined recursively

RANDOMIZED APPROACHES • Many algorithms exist to generate random properties • Allows variance in set of generated shapes • Smoothing can become an important aspect to post process the shape

TESSELLATION

TESSELLATION OVERVIEW • Tessellation refers to the generation of a large number of primitives for rendering complex shapes • Related to the concept of tiling a flat surface with a pattern

TESSELLATION SHADER ARCHITECTURE Tessellation Control Shader • The first and third stage of tessellation is programmable • The second stage is Tessellator Tessellation Evaluation Shader synonymous to rasterizing, in that it is a fixed algorithm

TESSELLATION CONTROL SHADER • Configures what type of grid of triangles the tessellator will generate for the patch • Executes once per vertex to allow additional computations to be done per vertex (or pass data through)

TESSELLATION EVALUATION SHADER • Allows the manipulation of the grid into a specific shape • Executes once per vertex produced by the tessellator