expression in the channel + keyframes

[ikoon]

Hello, I have a noob question. Please see the attached image:

- I have expression in the channel (sin($F*10)*2)
- There are three different types of "evaluation" ... what is the purpose of this?
 

Please, what should I search in the help file to understand it better?

[3dome]

I guess when you set the keyframes you have some keys with    sin($FF*10)*2    [from frame 1 to 121] and after that you change expression to    sin($F*10)*2

Difference between $FF and $F:
$FF: evaluates on subframes (hence the smooth curve)
$F: evaluates (as the name frame says) every frame only. that's why you get the steps in the cruve.


So typically when using DOPs you might want to use $FF to be on the save side if you later increase substeps
(For frame specific events like turning on/off some force $F is fine)

On SOP level $F is fine
(although I dont know if there is a difference later in motionblur. maybe someone else here knows this? would like to know )
 

 

oh and what you think is the third type of evaluation is just the animation editor showing you how the curve behaves before your first and after your last key as dotted line

Edited July 8, 2016 by 3dome
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[ikoon]

Wow you are right! Thank you very much. Now I understand it nice feeling.
That example was from the original help example, I don't know why they did it once $F and once $FF, never mind ...  \nodes\sop\font\BubblyFont.otl

As regards your question, I have seen this formerly, it may help you:
http://houdinitricks.com/fromthedocs-motion-blur-and-expressions/
http://houdinitricks.tumblr.com/post/139984978254/quicktip-motion-blur-in-houdini

I am still learning, so I dont know if it answers your question.

[3dome]

Glad I could help

yeah cool thanks for those links. the first one answered it for me. I already felt like for proper motion blur you need $FF but now I have it confirmed, thanks.
 

So I guess I should say that in SOP land you'll be fine wit $F for objects that you are not going to render but use $FF or $T if you plan to render them with motion blur.
But anyway, always using $FF instead of $F could save you some trouble and it won't really slow down things, so feel free to always use it.