University of Pennsylvania, CIS 560: Introduction to Computer Graphics
- Bowen Deng
A mesh editor based on half-edge structure, assembled with Maya-like features like triangulation, edge splitting, Catmull-Clark subdivision with sharp edges/vertices, and skeleton control with skin deformation.
Half-edges are directed edges that form a ring around a particular face. Each traditional edge is composed of two symmetric half-edges. A mesh based on half-edge structure includes vertices, faces, and half-edges.
In this way, adjacent information (i.e. spacial adjacent faces) is stored. Besides, each component in the structure has a fixed size.
An arbitrary 3D object can be loaded from OBJ files, and constructed as a half-edge based mesh. Once loaded, each component of it can be viewed and selected for highlight displaying.
| vertex | half-edge | face |
|---|---|---|
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The position of a selected vertex and the color of a selected face can be modified through the spin boxes.
- Edge Splitting
Split an edge by adding a midpoint onto it.
- Triangulation
Triangulate a face.
Subdivision recursively adds vertices to a mesh to smooth it. The result of subdivision converges to the form of B-spline surface with original vertices as control points. For example, a cube will become a sphere after several iterations.
| origin | after subdivision |
|---|---|
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An edge or a vertex can be marked as sharp to keep it "sharp" during the process of subdivision. For example, if we set one vertex of the cube as sharp, we will get a drop-like shape after subdivision.
Another example shows a cylinder shape by setting all edges on top and bottom faces as sharp.
Further more, semi-sharpness is allowed when the value typed into sharpness is between 0 and 1. See how the examples above changes with different sharpness configuration.
| Semi-Sharp | Sharper | Fully Sharp |
|---|---|---|
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| sharpness = 0.5 | sharpness = 0.75 | sharpness = 1 |
| Semi-Sharp | Sharper | Fully Sharp |
|---|---|---|
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| sharpness = 0.5 | sharpness = 0.75 | sharpness = 1 |
(Preview of this part is on building... Available before Nov 3)