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Thread: ILDA show frames and animation

  1. #1
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    Default ILDA show frames and animation

    I have a decent understanding of the ILDA format and I understand how frames are stored. However, one thing that puzzles me is how framerate is controlled. Let's say you create and animation that consists of 100 frames and you want to play it back in a nice fluid motion. But what if the frames have different numbers of points so that some are slow to draw and some are fast? Do you make the fast ones repeat? How does that work?

  2. #2
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    Default Re: ILDA show frames and animation

    Quote Originally Posted by carmangary
    I have a decent understanding of the ILDA format and I understand how frames are stored. However, one thing that puzzles me is how framerate is controlled. Let's say you create and animation that consists of 100 frames and you want to play it back in a nice fluid motion. But what if the frames have different numbers of points so that some are slow to draw and some are fast? Do you make the fast ones repeat? How does that work?
    It doens't work in my opinion. I think you just need to add some points to balance the 'weight' of the frames. The ilda format is just purely based on point output speed and not frame based (for output at least).

  3. #3
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    Default

    There is some info here

    Jim

  4. #4
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    Default

    You're right, the framerate is left as an exercise for the reader

    The most common way is to use a variable frame rate, you can see these on most older ILDA files... A good example are ILDA files output from the old QM32 board. You can still select this mode on the QM2000 as an option when generating ILDA files.

    The newer way is using preset fixed framerates, these have a problem in that if you are scanning at 30kpps, then the max number of points in the frame at 30fps is 1000 points! At 15fps, then the max number of points is 2000 points...

    A good example of a fixed framerate shows is the all-frames demo provided by Laser Action (http://www.laseraction.ru/Download/frames.zip)

    And as shown by many shows, it is quite possible to have 3000 points displayed with minimal flickering by using (abusing) how our persistance of vision works.... So many people also implement variable framerates along a minimum framerate,
    which can be seen as a new option in the Pangolin QM2000 boards.

    In terms of aethetics, variable framerates based on number of points are the most attractive, but is harder to synchronise to in software.

    The fixed (and variable w/ min) framerates are much easier to deal with, but can lead to millisecond timing shifts which need to be compensated for in software based on the actual length of the frames...

    So in truth, there isn't a right answer... just whatever you choose and the ability to user other formats if necessary.

    (And yes, with a fixed framerate, you let the frame repeat if it is to short, but you should always let a frame finish for visual continuity. You can do a blanking line from the current point in the frame to the first point in the next frame, but that creates "hot" lines which may or may not matter depending on your situation. The way to see if you need to repeat is
    by looking at the number of points in the next frame, seeing how long it will take (multiply by 1/30000 sec), see if there
    is enough time after displaying the current frame to display it, and repeat if there is... Use of nearest frame rounding
    can help the worst case timing issues which arise from frame based display. )

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