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Dynamic Parameter's are broken

See this thread: https://forums.unrealengine.com/showthread.php?139383-Optimisation-made-to-Dynamic-Parameter-Particle-Module-has-broken-it

I haven't done any Particle FX for a while, so I have no idea how long this has been broken. I built a material using a dynamic parameter, trying to animate some properties and leave others static. In my scenario:

 Param0 - Animated with Constant Curve, 'SpawnTimeOnly' was unchecked.
 Param1 - Static with Constant, 'SpawnTimeOnly' was Checked.
 Param2 - Animated with Constant Curve, 'SpawnTimeOnly' was unchecked.
 Param3 - Static with Constant, 'SpawnTimeOnly' was Checked.

Previously this would be fine, but it doesn't work anymore (I'm using 4.15 - but this could have been broken for a while). Param0 would not animate properly unless Param2 had SpawnTimeOnly CHECKED, which makes no sense as it's a constant curve (and therefore wouldn't animate).

Changing my material so I had the following arrangement made it all work:

 Param0 - Animated with Constant Curve, 'SpawnTimeOnly' was unchecked.
 Param1 - Animated with Constant Curve, 'SpawnTimeOnly' was unchecked.
 Param2 - Static with Constant, 'SpawnTimeOnly' was Checked.
 Param3 - Static with Constant, 'SpawnTimeOnly' was Checked.

I dug into engine code a bit because this is obviously broken, and discovered that an optimization has been added whereby Dynamic Paramters don't send updates to the material unless this property is unchecked. The code is done with flags, but unfortunately it is done in such a way that it only works properly if the first set of params have it unchecked, and subsequent ones have it checked. You can't mix and match them anymore. This is a problem, because you now need to know in what order you need your params to be in - or you may have to create duplicates of materials just to have the params in the right order.

Even if this is intentional, it's behaviour is totally undocumented and I don't feel like the UI should let me do it if it's not going to work properly.

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asked Mar 31 '17 at 08:38 AM in Bug Reports

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TheJamsh
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avatar image Doug E ♦♦ STAFF Apr 03 '17 at 05:02 PM

Hey TheJamsh-

Can you provide the material setup you're using to help me test this issue on my end? Also, can you identify when the first setup was working for you if there was a change in behavior?

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Hey TheJamsh-

We have not heard back from you in a few days, so we are marking this post as Resolved for tracking purposes. If you are still experiencing the issue you reported, please respond to this message with additional information and we will follow up.

Cheers

Doug Wilson

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answered Apr 18 '17 at 04:02 PM

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