X3D graphics principles

The educational technology and digital learning wiki
Jump to navigation Jump to search

Introduction

Principles underlying X3D graphics are similar to other 3D graphic formats and APIs. In this small tutorials we attempt to provide a simplified view useful to beginners.

Representation of an object

This is (roughly) how an object is built up:

  1. In 3D Graphics, an object is first defined by its edges (points) in a three dimensional x-y-z space.
  1. When those points a are linked together by lines we get a wireframe rendering of an object.
  1. After the frame has been created, a surface or skin is applied to the object. The surface can have many qualities: color, texture, shininess, reflectivity, etc.
  1. Finally, objects are either lit or emit light. Most objects have been lit by a light source and must be shaded. Shading is the most computer intensive task.

All surfaces can be represented as a set of polygons (that are perfectly flat). Complex Polygons are always split up into triangles by the rendering machine.

Polygons have only one side, the so-called "normal" or outside. Therefore, in X3D even flat objects (such as a sheet of paper) are always represented (as very flat) cubes. For example, a cube is composed of 12 polygons (2 triangles for each side) with their "normals" outside.

Position and orientation

  • Width (x axis) or left(-) / right(+)
  • Height (y axis) or down(-) / up(+)
  • Depth (z axis) or far(-) / close (+)

You can picture the coordinate system with the "right hand rule": "x" is your thumb, "y" the index finger, and "z" the middle finger.

The right hand rule