I am having a bit of difficulty with the $SF variable which needs to appear in the Output File parm of a custom ROP OTL that has a Dynamics ROP inside of it. I am trying to link the Dynamics ROP's Output File parm (dopoutput) to the top level of the OTL, but Houdini refuses to recognize $SF in that context.

Consequently, the $SF evaluates to an empty string and so the dopoutput path of the Dynamics ROP inside the OTL ends up with no frame token. The expression in the Dynamics node's dopoutput parm is chs(“../dopoutput”).

Is there a way to get Houdini to recognize $SF at the top level of an OTL so that it evaluates properly in the Dynamics ROP inside? Preferably without a bunch of string replacement voodoo in the expression inside. That tends to be fragile given all the unpredictable ways a path can be constructed/expressed on the top-level dopoutput parm.

Thanks!

I don't think $SF exists at the upper level. So you may want to try and add it as a detail attribute from within DOPs network when it does exist. Then fetch that value, via an import, and route it to an upper level user defined parameter that you can copy and use in an expression.

Just guessing though…

Well, $SF exists at the top level of a Dynamics ROP because you can, and must, use it in the dopoutput (“Output File”) parm if you want the “Output Every Sim Frame Using $SF” checkbox to have any effect.

My expectation is that if $SF exists at the top level of a Dynamics ROP, then there ought to be a way (for SideFX) to make it available at the top level of a custom ROP OTL that contains one, so that the dopoutput parm can be promoted to the OTL's interface and work accordingly.