ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Working in three dimensions (3D)
A cube has sides not visible from the current viewpoint
So, the Graphics.drawTriangles() method has a fourth parameter to establish a culling value:
public function drawTriangles(vertices:Vector., indices:Vector. = null,
uvtData:Vector. = null, culling:String = "none"):void
The culling parameter is a value from the TriangleCulling enumeration class: TriangleCulling.NONE,
TriangleCulling.POSITIVE, and TriangleCulling.NEGATIVE. These values are dependent upon the direction of
the triangle path defining the surface of the object. The ActionScript API for determining the culling assumes that all
out-facing triangles of a 3D shape are drawn with the same path direction. Once a triangle face is turned around, the
path direction also changes. At that point, the triangle can be culled (removed from rendering).
So, a TriangleCulling value of POSITIVE removes triangles with positive path direction (clockwise). A
TriangleCulling value of NEGATIVE removes triangles with a negative (counterclockwise) path direction. In the case
of a cube, while the front facing surfaces have a positive path direction, the back facing surfaces have a negative path
direction:
A cube “unwrapped” to show the path direction. When “wrapped”, the back side path direction is reversed.
To see how culling works, start with the earlier example from “UV mapping” on page 364, set the culling parameter of
the drawTriangles() method to TriangleCulling.NEGATIVE:
container.graphics.drawTriangles(vertices, indices, uvtData, TriangleCulling.NEGATIVE);
Notice the “back” side of the image is not rendered as the object rotates.
Last updated 6/6/2012
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