VTKActor not visible after render but visible on camera->resetview()

Question

I am working on a qt-vtk project. We have a line drawing function. where straight lines are created between two mouse click position. But once actor is created it is not visible. I was calling render function just after adding the actor. But it didn't work. But if i do camera->resetview() lines become visible , but entire perspective changes. Where am i doing wrong ?

thanks Rwik

Answer 1

I think that's a bit hard to help, without see the code, but have you tried using

ui->qvtkwidget->update();

, where ui is the instance of your class derived from QMainWindow?

Answer 2

This may not be relevant to you, but I had this exact same problem (in ActiViz [managed VTK]) and wrangled with it for a week, so I hope this helps someone out there. It turned out to be a problem with the location of the lines we wanted to draw on the canvas; they were too far away from the camera (on the Z axis) to be visible.

For us, we were trying to draw a cross on the viewing area wherever the user clicked. The data points were there, as were the actors and whatnot, but they would only be visible in the scene if you called resetCamera() and thusly changed the camera's configuration. Initially, I blamed the custom interactor that we had to add to cirvumvent the default interactor's swallowing of MouseUp events (intended behavior). Investigation revealed that this seemed unlikely.

After this I shifted the blame onto the camera under the suspicion that perhaps the reset call was making a call to some kind of update method which I wasn't aware of. I called resetCamera() and then reverted the camera values to what they were initially. When this was successfully done, it eventuated that the crosses would appear when the camera zoomed out and then disappear again as soon as it was set back, and it was at this point I realized that it was something to do with the scene.

At this point, I checked the methods we were using to retrieve the mouse location in 3D and realized that the z value was enormous and it was placing the points too far away as a byproduct of VTK's methods to convert 2D locations on the control to 3D locations in the scene and vice versa.

So after all that, a very mundane and avoidable mistake that originated from the methods renderer.DisplayToWorld() and WorldToDisplay(). This might not be everyone's problem, but I hope I've spared someone a week of fiddling around with VTK.