Bug fix: assigning init-op param its default value as instance got lost #1578
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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 <lg@larrygritz.com>
|
@lkerley @sandipshukla This is the weird bug we talked about a couple days ago. |
|
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.
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Sep 13, 2022
…st (AcademySoftwareFoundation#1578) 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 <lg@larrygritz.com> Signed-off-by: Larry Gritz <lg@larrygritz.com>
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This is a tricky situation to describe. Consider this shader:
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:
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).
!!!
Reading the patch should be self-explanatory for what the bug is and how we fix it.
Signed-off-by: Larry Gritz lg@larrygritz.com