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Experimental QML support is inflexible and inefficient
Closed, WontfixPublic


The current QVTKQuickItem implementation uses the Qt Quick integration approach of painting the VTK scene to the screen before the QSG[1]. This has a few significant drawbacks:

  • You must remember that Qt Quick stacking order does not apply to QVTKQuickItem instances in your Qt Quick application. So doing something as simple as drawing a solid black rectangle for the application background no longer works.
  • No item properties (other than x, y, width, height) can be applied or animated via Qt Quick. So fading out a view port during layout changes or animating a left-right or top-bottom flip of the viewport are not possible.
  • The QSG optimizations to repaint items only when necessary cannot be applied to QVTKQuickItem instances. So if you have, say, a pulsing animation that is not superimposed over any VTK viewport, the QSG will still re-render all the VTK viewports for every frame of the 60 FPS pulsing animation.


Event Timeline

I have a work-in-progress solution here that addresses this issue by rendering VTK to an OpenGL Framebuffer Object (FBO) and sharing that FBO with Qt Quick using QQuickFramebufferObject:

This is working well except for:

  • It has only been extensively tested on a v2014.09-based version of MITK. I rebased the changes to the current MITK master on Sep 19, and was seeing some weird rendering issues when rendering to both 2D renderers and 3D renderers.
  • There is a memory leak when changing the slice of a 2D renderer on the order of about 1MB per 2D renderer slice change. I haven't been able to track this one down yet, but I have one good lead: the memory leak only happens when you also have a 3D renderer.

One additional note: Run applications with environment variable QML_BAD_GUI_RENDER_LOOP=1 in order to use single-threaded Qt Quick rendering so that you don't need to worry about the thread safety problems, which is a separate issue (T18394)

Is anyone still working on this?

I'm not working on it, but I know there are several stakeholders who are very much still interested in it.

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