[vtkusers] QVTKWidget signal/slot question

Clinton Stimpson clinton at elemtech.com
Wed Mar 18 18:30:38 EDT 2009

Perhaps moving the mouse in the graphics window to change window level 
skips levels that your QSlider approach doesn't skip.  Are you doing 
tracking with the QSlider with a high number of ticks forcing the render 
window to go through each level?

Consider doing some of the following if you aren't already.
Call QVTKWidget::update() instead of vtkRenderWindow::Render() in your slot.
Reduce the number of ticks on your QSlider to a practical number (for 
example, more ticks than your screen resolution probably isn't a good idea).
Turn tracking off and connect to the valueChanged() signal.

Or maybe its only a compiz related problem like others are warning about.


John Eke wrote:
> Hi,
> I currently have a Qt dialog with a slider. The valueChanged signal 
> from this slider is connected to a slot in my QVTKWidget subclass 
> which performs some Window-Level modifications on a vtkImageActor 
> inside the renderer.
> In the vtk example (Examples/GUI/Qt/ImageViewer) dragging the mouse 
> across the image is fast enough. So why does it get ridiculously slow 
> when I send the commands through a slot? Is there a way I can speed it up?
> - John E
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