How to emulate Recompute Points Normals for digital assets?

[magneto]

Hi,

In one of my assets, I am trying to add the Recompute Point Normals after moving points via a VOPSOP, but as soon as the points are moved, the normals are updated.

Is there a way to create this behaviour for digital assets where you can leave the choice to the user?

This is just curiosity though as updating normals seems like the way to go.

Thanks

[edward]

Do you have a point attribute named "N" ? If you don't, then the normals used in the viewport will always be "computed". If you do, then offhand, I wouldn't expect the "N" attribute values to be modified unless you did so explicitly inside the VOP SOP.

[magneto]

Thanks Edward. I just tried what you said and this is what happened:

In the image showing the nodes, I added normals and then in the vopsop_points, all I did was to move a line of points (group7) on a grid using the normals as the direction multiplied by a value of 1 and adding it on point positions.

So this changed the point normals even though I didn't change the normals.

In vopsop_display, I multiplied the normals by 10 to make it easier to see. But the normals are modified when I select vopsop_points and look at the Details View.

After this, I disabled the point5 node and when I selected vopsop_points, the Details View showed no normals. It's after I started modifying them using vopsop_display they appeared in the Details View again.

But in both these tests, the final values of the normals was exactly the same as I checked them in the Details View, when I selected vopsop_display node.

So what do you think?

[edward]

Ah indeed, it's handier than I thought it would be. So if you want to NOT modify the N attribute, you can connect the the "Point Normal" output from the Global Variable VOP to the "Point Normal" input on the Output VOP.

[magneto]

Thanks Edward. I learnt so much from you

[tjeeds]

Yeah it never used to do this pre-12, there's a Compute Normals vop node to do this if you want it but it now appears to be doing it without asking. It's got to be confusing for people learning VOPs when N is the only attribute that behaves this way.

edit:

I just checked myself and perhaps it has always done this, I may have had it backwards as the Compute Normal node has an option to turn off this behavior. The real problem arises when you are just using points with a normal on them (but no geometry). In that case, when you modify P it sets your N values to [0,0,0] unless you run N through or use Compute Normal set to "No Modification to N".

Edited September 12, 2012 by tjeeds

[magneto]

Thanks Jesse. I didn't know of Compute Normals node. I guess the normals confused me a little but I thought it's done to make it less hassle to update them I guess?

Btw is this related to how if you use the Point Normals from the Globals node, it gets the correct normals if they don't exist, but using the Import Attribute node to import normals doesn't work in this case?