Bug fix: assigning init-op param its default value as instance got lost

[lgritz]

This is a tricky situation to describe. Consider this shader:

shader test (float A = 0.5,
             float B = A)
{
    printf("A = %g, B = %g\n", A, B);
}

By default, A is 0.5 and B gets A's value, also 0.5. If you give A a different instance value, like 1.0, then B will also get the same value, they'll both be 1.0. If you give B an instance value, that will be used for B rather than copying A's value, like this:

$ testshade  -param B 1.0 -shader test test
A = 0.5, B = 1

But there is a corner case bug: if we assign B an instance value of 0.0, it will incorrectly fall into a special case where it thinks it gets a default value, only coincidentally because 0.0 is in an unused slot for the default value (unused because it has no default -- its default comes from "init ops", that assignment).

$ testshade  -param B 0.0 -shader test test
A = 0.5, B = 0.5

!!!

Reading the patch should be self-explanatory for what the bug is and how we fix it.

Signed-off-by: Larry Gritz [email protected]

[lgritz]

@lkerley @sandipshukla This is the weird bug we talked about a couple days ago.

[sandipshukla]

Cool. It's fixed now.

…

On Sat, 10 Sep, 2022, 4:45 pm Larry Gritz, ***@***.***> wrote: @lkerley <https://github.com/lkerley> @sandipshukla <https://github.com/sandipshukla> This is the weird bug we talked about a couple days ago. — Reply to this email directly, view it on GitHub <#1578 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AF5DLPLNIQLYR7CJNQB5YLLV5UMTJANCNFSM6AAAAAAQJRAQ3M> . You are receiving this because you were mentioned.Message ID: <AcademySoftwareFoundation/OpenShadingLanguage/pull/1578/c1242821006@ github.com>