Problem with hooks at rendering...

Hi !

I have encountered a problem using hooks.
I was trying to make a tutorial about animating grass, for someone here,
when I found this problem. The problem is explained in the Text window when you open the file.

You will see that an important deformation of the mesh can be seen
at rendering. Though, the Hook (named Empty) hasn’t been moved. it is at the place where it was when created.

The blend file can be downloaded on this page :

http://securimax.chez.tiscali.fr/starblend/grasstest.html

Thanks in advance for any help! %|

Philippe.

Works perfectly with dupliverts turned off. My guess is that dupliverts is adding an offset into the system.

Recommendation:
Adjust for the offset as a workaround (offset seems to be linear)
Bug report it at www.blender.org

Alex

Hi Alicopey158 !

Recommendation:
Adjust for the offset as a workaround (offset seems to be linear)

I didn’t understand what you mean by this sentence… I’m french, and my english is not as good as I’d wish !

The offset of what ?

I know that the problem doesn’t occurs with duplivert turned off, but when I make the blades real, the problem is still the same… %|

Philippe.

Delete the empty. Duplivert the grass first, then add the hook afterwards. Works better this way. Not sure why, though.

When parenting and using duplis, it’s a really good idea get into the habit of applying size and rotation (ctrl-A) before connecting bits together.

Your blade of grass has a 90 degree rotation in it’s X axis before being dupliverted. It’s not showing in the 3D window, but it’s recalculated on render.

Cheers.

Hi !

I have corrected the blend file after reading this :

Delete the empty. Duplivert the grass first, then add the hook afterards. Works better this way. Not sure why, though.

When parenting and using duplis, it’s a really good idea get into the habit of applying size and rotation (ctrl-A) before connecting bits together.

Sorry… but no change ! %|

If it is not possible to use hooks and duplivert at the same time, grass blades can be animated by AVK or RVK… It works well, but it is less andy.

Philippe.

Hmmm - Something odd about the way you’re hook is set up, but I can’t put my finger on it.

Here’s one I prepared earlier:

https://blenderartists.org/forum/viewtopic.php?t=33528&postdays=0&postorder=asc&start=44

Hope it helps!

OK, I think I understand the problem, though I don’t have any solution for it. If you deleted the original hook in Scene 2, selected the grass mesh , entered the edit mode and added a hook to the topmost vertex, the grass deforms with the hook, and is rendered correctly for that frame. But if you attempted to set keyframes for various positions of the hook, the grass doesn’t animate, although the hook moves. Very strange behavior indeed. But I found that if you selected the grass mesh and hit the Tab key to enter the edit mode and hit the Tab key to go back to object mode, the mesh deformation is applied. Could be a bug in the hook implementation?
After going through Ammusionist’s blend file to see what’s the difference, why his file works while this one doesn’t, the one thing I found is that in Ammusionist’s file, the grass mesh has an object IPO assigned to it. So I assigned an absolute key for your grass mesh. Then moved the hooks at various frames and assigned keyframes to it, and the animation is rendered. I think maybe the problem is that the mesh doesn’t have an IPO curve in the first place, so that the hook’s position doesn’t affect the mesh for various frames…
IMO, just adding keyframes to hooks should also automatically create an IPO curve for the mesh it controls. But this is not the case, as it seems here.

Ammusionist, I have also a problem with your Waterweed.blend file :

The rendered picture is also shifted. There is an offset between what is shown in the 3D view and what is shown in the rendered picture.

As the scene is a bit different, the blades are not distorted, but they are displaced !

I have reported the problem to the Bugtracker…

Philippe.
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