[vtkusers] bug in vtkOpenGLVolumeTextureMapper2D + suggestion

[Lisa S. Avila]

Hi Alex,

You caught me - I never fully implemented that code for determining the 
major viewing direction (and I forgot about it). I will look into fixing it.

Lisa

At 12:12 PM 6/12/2001, alext at win.tue.nl wrote:


>   Hello all,
>
>   I think I've discovered something that looks like a bug in the
>texture-based volume renderer (vtkOpenGLVolumeTextureMapper2D).
>Basically I tried to add a vtkVolume actor and then to set the transform of
>this actor, e.g. by using SetUserMatrix(), to some simple rotation.
>Then I started to interactively rotate the camera, by using the trackball
>interactor for example. The rendering looks ok from some angles, but TOTALLY
>wrong from other angles!
>   I have no clear idea what the problem is. However, I noticed that when the
>vtkVolume actor has no user-matrix set, or when this user-matrix is NOT a
>rotation, all seems to be ok - the volume rendering looks ok.
>   It seems to me that the problem is that the rotation of the camera and
>that of the vtkVolume object seem to interfere when computing the major
>viewing direction, or the way the texture-planes are stacked in 3D to
>produce the volume rendering. When the vtkVolume is itself rotated, it seems
>one can view it from 'bad' angles, i.e. angles from which one doesn't face
>the 2D textures anymore but looks almost parallel at them. A very clear
>example of the above is when the vtkVolume actor is rotated with e.g.
>approximately 180 degrees around some axis, for example due to an:
>
>   volume->RotateWXYZ(170,1,1,1)  //rotate volume around (1,1,1) axis with 
> 170 degrees)
>
>   It is hard to me to find an obvious solution to the above problem. First
>of all, is this a problem experienced by other users? Is this something that
>the VTK team knows about?
>
>   Regards,
>
>   Alex
>
>-----------------------------------------------------------------
>  Dr. Alexandru C. Telea      | Technische Universiteit Eindhoven
>                              |
>  E-mail   : alext at win.tue.nl | Dept. of Mathematics and
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