Overview

Progressive meshes are a continuous level-of-detail representation for 3D models (as opposed to discrete levels of detail). They work by iteratively removing edges from an original, detailed mesh to obtain meshes with lower and lower detail. Each time an edge is removed, information about the removal gets stored in a "vsplit" record, which can then be used to reconstruct the edge later. After a number of iterations (it is common to iterate until some criteria about the mesh are true), you are left with a coarse base mesh and many vsplit records. To construct a mesh with any level of detail between the coarse mesh and the original mesh, you simply inject edges (via vsplit records) until you achieve your desired detail level.

The original idea for this project was to write a program that would load a traditional mesh (represented as vertices and faces) from a file and output it to a progressive mesh format, allowing the user to perform a qualitative analysis of the resulting levels of detail at various distances from the camera. What I actually ended up implementing, however, falls significantly short of my original goals.

When I started implementing this project, I decided to create my own mesh data structure and functions for manipulating meshes. Dr. Wood recommended that I use an existing mesh class so I could concentrate on implementing the progressive meshes algorithm, but I stubbornly insisted on starting from scratch. This decision was what ultimately prevented me from completing the project. I spent the vast majority of my time on this project creating the mesh data structure and an edge collapse function. Due to severe time constraints, these two features were the only aspects of progressive meshes that I was able to implement before the project was due.

Features

• Load meshes in *.m format
• Toggle rendering of mesh edges
• Toggle between flat and smooth shading
• Toggle normal inversion -- this is provided because some meshes have their faces wound clockwise
• Collapse mesh edges
• Smooth mesh vertices by averaging neighbor positions

Bugs

• There are no manifold-ness checks when a mesh is loaded, or when an edge is collapsed. Sometimes an edge collapse will result in an access violation.
• Sometimes when rotating the mesh it will disappear abruptly. If this happens, use the "Reset Mesh" menu option to fix it.

Instructions

Key Commands:

• You can LEFT CLICK and move the mouse to ROTATE the mesh
• You can use your mouse's SCROLL WHEEL to ZOOM

Screenshots:

Resources:

• Progressive Meshes. Hughes Hoppe, SIGGRAPH 1996.
• Efficient Implementation of Progressive Meshes. Hughes Hoppe, 1998