Improvements to triplanar blending

[crydalch]

Fixes triplanar node's blending, so the corner's are not bright. Also adds a blend control for users to adjust the blending between maps. The default blend value of 1.0 matches the original behavior (apart from the brightness bug). Here is a comparison of the old triplanar (left), with the new (right):

Here are some different blend values, showing sharper or smoother blending of the maps:

Math worked out mostly by @BrianSharpe.

[jstone-lucasfilm]

@crydalch @BrianSharpe I like the overall direction of this proposed change, but I suspect there may be an error in the math, as both MaterialXView and MaterialXGraphEditor render triplanarprojection nodes as uniform black when running with this pull request.

Here's the example MaterialX file that I'm testing, which renders as expected in the main branch, but renders as uniform black with this pull request.

triplanar_example.zip

[BrianSharpe]

Here is a fix for the color3 version

NG_triplanarprojection_color3.txt

[BrianSharpe]

Also, I think the blend parameter should have a UI min/max on there
<input name="blend" type="float" value="1.0" uimin="0.0" uimax="1.0" />

[crydalch]

Thanks @jstone-lucasfilm and @BrianSharpe, I've committed a fix that seems to have things working again, and adds the UI min/max for the blend parm. I also went ahead and added those fixes to the other signatures as well.

[jstone-lucasfilm]

Thanks for this great work, @BrianSharpe and @crydalch, and I believe it's fine to allow this change in brightness as it's effectively a fix to a bug in the original node graph.

[jomaro110]

Don't know if I can comment here but this node is very basic and needs more settings.

It's missing the alpha (opacity) values for each image (X, Y, Z) and scale & rotation as well.
And it needs a projection type: (Object, World, Reference).

Thanks

[jstone-lucasfilm]

@jomaro110 This would be a great topic to bring up on the MaterialX channel of the ASWF Slack, where developers from SideFX, Autodesk, and other teams can weigh in with their thoughts.

Here is the top-level page on how to join the ASWF Slack, and you'll find the dedicated MaterialX channel there:

https://www.aswf.io/get-involved/