Hello, if i want to do a rig that is a bit of xpresso and a bit of mograph i always have priority issues
Xpresso_lag.c4d (144.5 KB)
if you take a look at the file you see there is a super simple xpresso tag. i can’t in any way get rid of the lag.
am i doing something wrong? thx!
It does not seem to be a priority issue. It’s a refresh issue. If you render your spline it’s in the correct state.
If you freeze frame and get forward step-by-step tha issue remains but selecting any element in the object manager will position the spline correctly.
Sorry to oppose, but it is a priority issue.
See Maxon’s doc about priorities here.
In the diagram shown there you can see that all tags (expressions) are being executed before any generators. But in your scene you want to use the result of a generator (your matrix object) in a tag/expression (your Xpresso tag).
So leaving the random effector aside, the actual execution order is:
But what you need is this order of execution:
Fix is simple, just set the Xpresso tag to priority Generators +1 so it will be executed after the generators (especially after the matrix). C4D will make sure, the spline gets executed after the tags which are assigned to it.
In your Xpresso I was first a bit confused, as it was throwing an error (the point node highlighted yellow). I expected it to do nothing at all, but surprisingly it did quite well… The reason is, the iteration node being fed the MoData count as end of iteration. With this it actually iterates one too far and thus the point node addresses a point not existent in the spline. Fix is simple, just subtract one before feeding into the iteration node.
Here’s the scene with changed priority and xpresso fixed: cgs_xpresso_lag_2.c4d (142.1 KB)
Nice thank you very much!
So here what drives me crazy: your file in the render in always correct. BUT in the viewport you see it correctly ONLY if you have the spline selected in point mode, otherwise you see the lag.
This is very frustrating. probably i did fix it in my main setup but i didnt relise it because i was just judging the viewport. so stupid! this is defenetly a bug. maxon should fix this kind of stuff
thanks again for the explanations
The renderer sometimes does an extra round of evaluation, leading to the non laggy behavior. If we do that in the viewport everything will slow down considerably. The new core does take care of this, with scene nodes you are actualy not able to create setups that show this kind of lag.
Ooopsy, you are right.
I guess I betrayed myself with “C4D will make sure, the spline gets executed after the tags which are assigned to it.”. Obviously it was the point mode granting us the extra needed update. 
Unfortunately I have no other ideas.
Except maybe an awkward workaround, which may or may not suit your needs: The Point Cache tag.
Then at least the viewport should be exact.
Cheers
ok its all clear now, thx.
bottom line scene nodes is desperately needed, c4d feels really ancient at this point
C4D is really ancient at this point. Houdini feels like it’s already a decade ahead in workflow terms.
How many years do you think it’ll take for the WHOLE of C4D to transfer to the Scene Nodes system?
1, 2, 5 or 10 years?
I hope you’ve got some serious patience it could be a very loooong wait for those priority issues to be consigned to history.
Amen you are totally right! i am learning houdini in my free time…
frankly houdini at this point its a no brainer. it cost me 200 eur every year, c4d i think cost 600.
i cant wait to be ready to move completely to houdini. but right now i am no ready.
and another important thing is that cd4 like ae is industry standard (in certain industries) so it doesnt matter how ancient they are, sometimes the clients demand for the projects to be done in ae or c4d…