Your scale should be directly proportional to your z distance to
counteract projection.
-Jeremy Smoler
Eric Hawthorne wrote:
>
> I'm trying to dynamically adjust the bounds of a scene graph object so that the
> "apparent" size
> (i.e. percentage of the field-of-view i.e. span of the object in pixels)
> remains the same
> no matter what the VWorld "z" distance from the object to the eyepoint is.
>
> That is, I'm trying to "undo" the shrinkage due to perspective.
>
> Reason why is I'm trying to make a Raster Shape3D pickable.
> Now don't worry, I've got the performance aspect of this covered.
>
> I need help figuring out the amount by which I should shrink or expand the
> bounding box
> of the object as the view moves toward or away from the object.
> (I'm going to use a Billboard to make sure the boundingbox stays with a face
> facing the view.)
>
> So far, I know how to get the eyepoint position in VWorld coords, so I can
> calculate the VWorld distance from the object to the eyepoint.
> I think I also know how to calculate what the size of the bounds should be
> (in VWorld coords) if the "z" position of the object were right up forward at
> the image plate "z".
>
> Can anyone help with what function of the VWorld distance I should use
> in expanding the bounds of the object as the object recedes further into the
> scene.
> Part of what I don't understand is how the viewing projection works and what
> the
> effect of that projection on my expansion function should be.
>
> Eric
>
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