How to get visible size of DisplayObject with perspective projection

Posted by Ain on Stack Overflow See other posts from Stack Overflow or by Ain
Published on 2010-05-02T11:38:23Z Indexed on 2010/05/02 11:47 UTC
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The following is entirely a math question.

As we know, PerspectiveProjection delivers perspective transformations in 3D represented by the interdependent values of fieldOfView and focalLength according to the following formula:

focalLength = stageWidth/2 * (cos(fieldOfView/2) / sin(fieldOfView/2)

Bjørn Gunnar Staal has prepared a good image to illustrate the situation.

Q: How to get the visible on-screen size of the DisplayObject (Cube on the above-linked image) to which PerspectiveProjection has been applied?

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