Simple expression for strobing makes node turn red?

Hi Im an editor and have not used fusion that much. But I like to create an expression that is going a brightness/contrast node. The expression will be on the gain slider.

The expression is designed to create a strobing effect that starts with more frequent black frames and gradually decreases the frequency of these black frames over time.

Below is the expression but it does not work, it turns the brightness/contrast node red and also the output node. But I guess is because it after the node that failed.

frame = time; duration = 100; intensityStart = 25; fadeRate = 0.5; currentIntensity = math.max(0, intensityStart - (frame / duration) * fadeRate); if frame % math.max(1, math.floor(currentIntensity)) == 0 then 0 else 1 end

Do you se what is causing the node to go red? Thanks! /Joel

In simple expressions you need to use

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iif

instead of

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if

Personally I'd always try to do this with modifiers and other calculations first, before writing such a lot of code. For example a Shake or Perturb modifier with values that change over time, gives you much more interactive control, without having to type things over and over again.

Thanks for your input Sander de Regt, it did not help in this case but still it was very kind of you share your thoughts and knowledge. Thank you!

I think Im starting to se the problem. It's because I created an adjustment layer on the edit page to be more flexible. So I need to reconstruct the expression to alter abit since it does not have any media input file.

For a multi-line expression, you have to start it with a colon : and you have to deliberately use the return keyword to send the value out to the input.

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:frame = time; duration = 100; intensityStart = 25; fadeRate = 0.5; currentIntensity = math.max(0, intensityStart - (frame / duration) * fadeRate); if frame % math.max(1, math.floor(currentIntensity)) == 0 then return 0 else return 1; end


I have not evaluated the expression to know if it does what you want or not, but that ought to at least get it to evaluate successfully.