Updating Displayed Normals ?

[eloop]

I've written a SOP that defines a fixed number of points, then depending on the input parameters moves these points around and builds a new set of primitives. For efficiency I don't gdp->clearAndDestroy() each time, instead I delete all the primitives and define a new bunch on top of the existing points. This works except that when displaying, the resulting surface normals (opengl display only, ie not attributes) aren't being recalculated properly. Simply appending a Facet SOP with no operations selected is enough to get things displaying correctly again. So I'm guessing the clearAndDestroy() is clearing some cached values, how can I do it manually ?

Thanks,

Drew

[sibarrick]

Doing

gdp->normal();

will recompute the normals, is that all you need?

Si

[eloop]

Yep, that fixed it. I'd trawled across a lot of examples, docs and headers and hadn't run into it ...

Thanks.

Doing

gdp->normal();

will recompute the normals, is that all you need?

Si

[eloop]

Oops, it didn't fix it. This actually adds a normal point attribute.

-Drew

Yep, that fixed it. I'd trawled across a lot of examples, docs and headers and hadn't run into it ...

Thanks.

[sibarrick]

Oops, it didn't fix it. This actually adds a normal point attribute.

-Drew

duplicate answer in another thread.

Sorry, I assumed you must have point normals coming in, i've never seen a problem with building geometry with no normals where it shaded wrong. I tend to just do a test for N, if it exists I recalculate them if it doesn't I leave them alone. Odd....

[eloop]

For the record the following solution for this was provided by MarkE on the devkit list ...

For OGL display, we compute normals into an "internal" attribute. You

probably just want to clear that.

You can do that by:

gdp->destroyPointAttrib("internalN", sizeof(UT_Vector3), GB_ATTRIB_MIXED);

and in a similar vein over on the sidefx forums, Ondrej gave this solution to another similar sounding situation. I wonder if I should really be doing this, probably more expensive operation, instead ? Without knowing whats going on underneath it's hard to know the correct answer.

You'll probably want to call gdp->notifyCache(GU_CACHE_ALL) to ensure that any caches (including display caches) are rebuilt.

-Drew