Blackmagic Forum

I have a long line of Simple Expression code in a parameter that would be much shorter if I could store the interim result in a custom variable.

Can you create a variable in a parameter's Simple Expression? If not, can you create a variable in a node's Frame/Start Render Script field and then access it in its parameters' Simple Expression code?

Thanks in advance.

Yes, but I'm not sure how far you can take it if things start getting complex. For example, a simple expression to display the current frame position in seconds for a Text+ control might look like this:

Code: Select all

os.date("%M:%S",time/24)

where the frames per second value is hard-coded to 24. (If you are not familiar with the other expressions, os.date() is a Lua method for formatting a time value and time is a built-in variable which returns the current frame number)

You can instead name a variable to hold the fps value, but there are some rules:

• the variable name must be preceded by a colon where it is declared
• the variable declaration must be separated from the remaining code by a semi-colon
• you have to add a return statement to make the whole thing work

Same example using a variable:

Code: Select all

:fps=24; return os.date("%M:%S",time/fps)

This stuff is seriously badly documented - maybe others can improve or expand on this?

Thank you. Worked like a charm.

Do you know by any chance if there's a way to create variables in Frame/Start Render Script and use them from parameters?

Sorry, that’s beyond what little I know about scripting. You might get better luck asking the question in the Fusion forum.

bobosola wrote:Yes, but I'm not sure how far you can take it if things start getting complex. For example, a simple expression to display the current frame position in seconds for a Text+ control might look like this:

Code: Select all

os.date("%M:%S",time/24)

where the frames per second value is hard-coded to 24. (If you are not familiar with the other expressions, os.date() is a Lua method for formatting a time value and time is a built-in variable which returns the current frame number)

You can instead name a variable to hold the fps value, but there are some rules:

• the variable name must be preceded by a colon where it is declared
• the variable declaration must be separated from the remaining code by a semi-colon
• you have to add a return statement to make the whole thing work

Same example using a variable:

Code: Select all

:fps=24; return os.date("%M:%S",time/fps)

This stuff is seriously badly documented - maybe others can improve or expand on this?

Just a bit of nit picking, about the colon: Reason really is that any multi-statement expression needs to be preceded with a colon, it's not so much about the variable declaration. So, for instance, the following works

Code: Select all

:a=1; b=2; return a+b;