[vtkusers] how to draw overlays on a image

[永强 谭]

Hi,

I would appriciate any help on drawing overlays on a image.

How can I draw a line, a circle on a image. The lines (vtkActor from 
vtkLineSource and vtkMapper) will be covered by the image. If I make the 
image a texture and make the texture translucent, then I can see the line.
but the image looks a bit fainter after it turns translucent and I couldn't 
see both the image and the line clear.

There must be some other way to draw overlays on a image. Could someone 
help me?

Thanks.