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[Manta] two frame lag?


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  • From: David E DeMarle < >
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  • Subject: [Manta] two frame lag?
  • Date: Thu, 4 Feb 2010 15:05:42 -0500
I think I am missing something important.

In vtkManta, the VTK thread sends transaction requests to the manta threads and uses SyncDisplay::waitOnFrameReady to wait for them to take effect before it shows the pixels to the user. My problem is that there is a two frame lag.

This is how works now, written from the vtk thread's perspective (in BASIC)

10 waitOnFrameReady()        REM now the manta threads should be "stopped" because thread 0 is,
...                                             REM process changes in vtk state by issuing transactions to let manta threads know about it.
60 displayDone()                     REM release the manta threads, I expect callbacks to be received now
70 waitOnFrameReady()         REM this frame doesn't show the changes yet
80 displayDone()                     REM let manta render the frame that has the changes
90 waitOnFrameReady()         REM now the image I get has the changes in it

The effect is to halve the framerate, since I always have to ask manta to render twice to see what I ask it to draw.

Is there some good way to obviate the need for lines 80 and 90?

David E DeMarle
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x109

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