Fix Storm code generation from USD PreviewSurface for GLSL bindings to primvars

[marktucker]

Description of Change(s)

Fix code generation for GLSL bindings to primvars. This type of binding was missing the definition of HdGetScalar_name to call HdGet_name.

I'm fairly out of my depth with this change, so I'm not sure if this is the right approach. But in the specific case of opacity reported in issue #1862, this change fixes the code generation and the material works as expected.

Fixes Issue(s)

• Storm shader compile error with a primvar reader connected to opacity #1862

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[jilliene]

Filed as internal issue #USD-7375

[davidgyu]

Thanks, Mark! This fix looks good to me, and thank you for the test case in #1862 We'll make sure to add a case for this to our test suite and get the fix merged.