Use Offset instead of ConstOffset for GLSL function textureGatherOffset (#5426)

* Use Offset instead of ConstOffset for GLSL function textureGatherOffset

This commit changes to use `Offset` option on OpImageGather instruction
when translating `textureGatherOffset` to SPIR-V code.

Interestingly GLSL allows the offset value to be a variable not
constant just for the function `textureGatherOffset` while all other
offset variants of texture sampling functions require the offset to be a
constant value.

From a few experiments, I found that the spirv-optimizer changes
`Offset` to `ConstOffset` if the offset is a compile-time value. I also
found that when the offset value is zero, it changes to `None` with no
offset value.

0 files changed, 0 insertions, 0 deletions