SDK: AE fails to call into third-party plugins with PF_Cmd_USER_CHANGED_PARAM for sliders

[FxFactory]

When users change the value of a slider parameter declared by a plugin with the
PF_ParamFlag_SUPERVISE flag, AE fails to notify the plugin via PF_Cmd_USER_CHANGED_PARAM.

Steps to reproduce:
- Take an existing plug-in based on the AE SDK, and make one of its slider parameters observable by setting its PF_ParamFlag_SUPERVISE flag.
- Set a breakpoint / print something to the console / beep when handling the PF_Cmd_USER_CHANGED_PARAM command.
- Apply the plugin inside any recent version of AE.
- Change the slider’s value and notice that PF_Cmd_USER_CHANGED_PARAM is never invoked.

Expected:
Plug-ins should receive a PF_Cmd_USER_CHANGED_PARAM command whenever the value assigned to a slider parameter is changed.

Notes:
Sliders can trigger a large number of changes very quickly, and it would be perfectly fine if AE were to coalesce multiple changes into one. BUT it is vital that AE issue at least one PF_Cmd_USER_CHANGED_PARAM command, when the user is done scrubbing. Ideally, it should issue multiple PF_Cmd_USER_CHANGED_PARAM at a maximum rate (2 per second?) so as to periodically give plugins a chance to respond.

[omotion]

My plugins seem to be impacted by this problem as well

[JohnColombo]

Hi @FxFactory,

Thank you for reporting this issue. Which version of the SDK are you using when you encounter this issue? We recently released a new SDK and would like to determine if this is a recent regression.

Thank you for any further insight,

- John, After Effects Engineering Team  

[FxFactory]

Hi John,

Thanks for the quick reply, always greatly appreciated! Our plugins are currently linking against the SDK that defines current API version as 234:

#define PF_AE_PLUG_IN_VERSION PF_AE234_PLUG_IN_VERSION

#define PF_AE_PLUG_IN_SUBVERS PF_AE234_PLUG_IN_SUBVERS

The problem cannot be a recent regression. I found comments in my code that date two years that document the workaround, along these lines:

Since neither After Effects or Premiere Pro are sending PF_Cmd_USER_CHANGED_PARAM for slider-based parameters, any time you receive PF_Cmd_UPDATE_PARAMS_UI, iterate over all sliders and check if some work needs to be done, i.e. should any other parameters be enabled or displayed based on the slider? (One example of such a rule: "If the strength of a glow is > 0%, enable a separate Blend Mode popup menu parameter to allow the user to control how the glow is to be composited.)

It's my fault I only filed the bug now. Sometimes when one finds a workaround that seems reasonable, you just write those few lines of code and move on. 

[FxFactory]

@JohnColombo I just made a new build of our plugins after upgrading to the latest SDK (PF_AE235_PLUG_IN_VERSION and PF_AE235_PLUG_IN_SUBVERS) and it had no side effects on the bug. Hope that helps.

[JohnColombo]

Thank you for those confirmations and details, @FxFactory! We now have a ticket filed to investigate this more deeply. If there any updates, we will update this thread (or perhaps one of the other threads on this topic).

Cheers,

- John, After Effects Engineering Team