The flash.geom package contains classes that define geometric
objects such as points, rectangles, and transformation matrixes.
These classes don’t necessarily provide functionality by themselves;
however, they are used to define the properties of objects that
are used in other classes.
All the geometry classes are based around the notion that locations
on the screen are represented as a two-dimensional plane. The screen
is treated like a flat graph with a horizontal (x) axis and a vertical
(y) axis. Any location (or
point
) on the screen can be represented
as a pair of x and y values—the
coordinates
of that location.
Every
display object, including the Stage, has its own
coordinate space
.
The coordinate space is an object’s own graph for plotting the locations
of child display objects, drawings, and so on. The
origin
is
at coordinate location 0, 0 (where the x and y-axes meet), and is
placed at the upper-left corner of the display object. While this
origin location is always true for the Stage, it is not necessarily
true for other display objects. Values on the x-axis get bigger
going toward the right, and smaller going toward the left. For locations
to the left of the origin, the x coordinate is negative. However,
contrary to traditional coordinate systems, Flash runtime coordinate
values on the y-axis get bigger going down the screen and smaller
going up the screen. Values above the origin have a negative y coordinate
value). Since the upper-left corner of the Stage is the origin of
its coordinate space, most objects on the Stage have an x coordinate
greater than 0 and smaller than the Stage width. And the same object
has a y coordinate larger than 0 and smaller than the Stage height.
You can use Point class instances to represent individual points
in a coordinate space. You can create a Rectangle instance to represent
a rectangular region in a coordinate space. For advanced users,
you can use a Matrix instance to apply multiple or complex transformations
to a display object. Many simple transformations, such as rotation,
position, and scale changes, can be applied directly to a display
object using that object’s properties. For more information on applying transformations
using display object properties, see
Manipulating display objects
.
Important concepts and terms
The following
reference list contains important geometry terms:
-
Cartesian coordinates
-
Coordinates are commonly written as a pair of number (like
5, 12 or 17, -23). The two numbers are the x coordinate and the
y coordinate, respectively.
-
Coordinate space
-
The graph of coordinates contained in a display object, on which
its child elements are positioned.
-
Origin
-
The point in a coordinate space where the x-axis meets the
y-axis. This point has the coordinate 0, 0.
-
Point
-
A single location in a coordinate space. In the 2-d coordinate
system used in ActionScript, the location along the x-axis and the
y-axis (the point’s coordinates) define the point.
-
Registration point
-
In a display object, the origin (0, 0 coordinate) of its coordinate
space.
-
Scale
-
The size of an object relative to its original size. When
used as a verb, to scale an object means to change its size by stretching
or shrinking the object.
-
Translate
-
To change a point’s coordinates from one coordinate space
to another.
-
Transformation
-
An adjustment to a visual characteristic of a graphic, such
as rotating the object, altering its scale, skewing or distorting
its shape, or altering its color.
-
X-axis
-
The horizontal axis in the 2-d coordinate system used in
ActionScript.
-
Y-axis
-
The vertical axis in the 2-d coordinate system used in ActionScript.
