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The main difference between a two-dimensional (2D) object and
a three-dimensional (3D) object projected on a two-dimensional screen
is the addition of a third dimension to the object. The third dimension
allows the object to move toward and away from viewpoint of the
user.
When you explicitly set the
z
property of a
display object to a numeric value, the object automatically creates
a 3D transformation matrix. You can alter this matrix to modify
the 3D transformation settings of that object.
In addition, 3D rotation differs from 2D rotation. In 2D the
axis of rotation is always perpendicular to the x/y plane - in other
words, on the z-axis. In 3D the axis of rotation can be around any
of the x, y, or z axes. Setting the rotation and scaling properties
of a display object enable it to move in 3D space.
Important concepts and terms
The following
reference list contains important terms that you will encounter when
programming 3-dimensional graphics:
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Perspective
-
In a 2D plane, representation of parallel lines as converging
on a vanishing point to give the illusion of depth and distance.
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Projection
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The production of a 2D image of a higher-dimensional object;
3D projection maps 3D points to a 2D plane.
-
Rotation
-
Changing the orientation (and often the position) of an object
by moving every point included in the object in a circular motion.
-
Transformation
-
Altering 3D points or sets of points by translation, rotation, scale,
skew, or a combination of these actions.
-
Translation
-
Changing the position of an object by moving every point
included in the object by the same amount in the same direction.
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Vanishing point
-
Point at which receding parallel lines seem to meet when represented
in linear perspective.
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Vector
-
A 3D vector represents a point or a location in the three-dimensional space
using the Cartesian coordinates x, y, and z.
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Vertex
-
A corner point.
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Textured mesh
-
Any point defining an object in 3D space.
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UV mapping
-
A way to apply a texture or bitmap to a 3D surface. UV mapping assigns
values to coordinates on an image as percentages of the horizontal
(U) axis and vertical (V) axis.
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T value
-
The scaling factor for determining the size of a 3D object
as the object moves toward, or away from, the current point of view.
-
Culling
-
Rendering, or not, surfaces with specific winding. Using
culling you can hide surfaces that are not visible to the current
point of view.
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