[vtkusers] Make 2D texts follow model

[Yifei Li]

Thank you. I tried it and it works, BUT,  vtkCaptionActor2D does not hide
annotation when the thing it annotates cannot be seen from the current view
point. Is is possible with vtkCaptionActor2D? Thanks

Yifei

On Fri, Oct 14, 2011 at 2:13 PM, Wayne Christopher <wayne at 4raccoons.com>wrote:

>  What you want is a vtkCaptionActor2D.  You give it a point in world
> coordinates and it will make a text actor that will follow that point.
>
>     Wayne
>
>
> On 10/14/11 11:09 AM, Yifei Li wrote:
>
> Hi all,
>
>  My application displays a mesh and adds annotation to its elements (i.e.,
> faces, edges and vertices).
>
>  In order to make annotations follow the elements they are annotating, I
> calculated the display coordinates of the cell centers and use those
> coordinates to set the positions of annotation actors whenever the model is
> rotated or the viewport is resized. For example:
>
>  # convert the coordinate of a cell center to display coordinate
>
> world_coord = self.m_faceCenters().GetOutput().GetPoint(k)
>
> self.m_renderer.SetWorldPoint(world_coord[0], world_coord[1], world_coord[
> 2], 1.0)
>
> self.m_renderer.WorldToDisplay()
>
> x, y, z = self.m_renderer.GetDisplayPoint()
>
>
>  # get the value in z-buffer at display coordinate (x,y)
>
> # the annotation should not be displayed if its associated cell cannot be
> seen
>
> # in theory, a cell center is seen if its z coordinate after the above
> conversion is less than or equal to the
>
> # the value in the z-buffer at (x, y).
>
> # However, due to the imprecise nature of floating-point arithmetic, I
> relaxed the criteria by adding (z-z_in_buffer <= 1e-3)
>
> z_in_buffer = self.m_renderer.GetZ(x,y)
>
> if z <= z_in_buffer or z-z_in_buffer <= 1e-3:
>
>    actor.SetPosition(x,y)
>
>
>  My strategy of making 2D annotations follow model ALMOST works. However,
> the annotations flickers when I rotate the model or resize the viewport, and
> I found out the reason is that renderer.GetZ(x,y) sometimes returns 0!  Do
> you have any idea why this happens? Thanks in advance
>
>
>  Yifei
>
>
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