(articolo originale : http://coding.smashingmagazine.com/2013/09/17/introduction-to-polygonal-modeling-and-three-js/)
THE MESH
The skeleton that makes up the shape of the 3-D objects we will be working with is commonly referred to as the mesh, although it is also called a wireframe or model. The mesh type typically used and the one we will use here is the polygonal model.
(Two other types of meshes are used to model 3-D objects. Curve modeling entails setting points in the scene that are connected by curves that shape the model. Digital sculpting involves using software that mimics actual substances. For instance, rather than working with shapes and polygons, it would feel more like sculpting out of clay.)
The meshes that make up a polygonal model consist of three parts:faces, edges and vertices. The faces are the individual polygons you see while viewing a mesh and that give the object its shape and structure. Edges run along the outside of the faces and are the connections between vertices. A vertex is the point where any number of these edges intersect. If the mesh is planned out and built correctly, then each vertex will be both at the intersection of edges and at the corners of the adjoining faces.
This allows the faces and edges to be pushed along with the vertices, and it explains why moving vertices in a full model is the most common and effective way to sculpt. Each of these parts is a separate and selectable entity with differing behaviors.
Faces, vertices and edges on a polygonal cube. (Larger view)
Polygonal modeling makes more sense for use in the browser than other types, not only because it is much more popular, but also because it takes the least amount of time for the computer to render. The downside to this saved speed is that polygons are planar and cannot be curved. This is why a raw 3-D model looks “blocky.”
To combat this issue, programs such as Blender, Maya and 3ds Max have a smoothing utility, used before exporting, that adds many tiny polygons to the model. Adding these polygons along a curve creates many small angles where a previously sharp angle of two large polygons used to meet, giving the illusion of smoothness.
Polygonal shape next to its smoothed counterpart. (Image: Blender | Larger view)
While using meshes, it is possible to use different materials to get different behaviors and interactions. A basic mesh and material will render as flat polygons, showing the model in flat color. Using a lambert material will keep light from reflecting off of the surface and is generally regarded as non-shiny. Many prototypes are created in lambert materials in order to focus on the structure, rather than the aesthetics. Phong materials are the opposite, instead rendering shiny surfaces. These can show some really fantastic effects when combined with the correct use of light.
In addition to these mesh materials, materials for sprites, particles and shaders can all be applied similarly.
(A polygonal model is called “faceted” because it consists of polygonal faces that define the shape of the structure.)