SubgroupLocalInvocationId
SubgroupLocalInvocationId
Decorating a variable with the SubgroupLocalInvocationId builtin
decoration will make that variable contain the index of the invocation
within the subgroup.
This variable is in range [0,SubgroupSize-1].
If VK_PIPELINE_SHADER_STAGE_CREATE_REQUIRE_FULL_SUBGROUPS_BIT is
specified,
full subgroups are enabled for that pipeline stage.
When full subgroups are enabled, subgroups must be launched with all
invocations active, i.e., there is an active invocation with
SubgroupLocalInvocationId for each value in range
[0,SubgroupSize-1].
There is no direct relationship between SubgroupLocalInvocationId and
LocalInvocationId or LocalInvocationIndex.
If the pipeline
or shader object
was created with full subgroups applications can compute their own local
invocation index to serve the same purpose:
index = SubgroupLocalInvocationId + SubgroupId ×
SubgroupSize
If full subgroups are not enabled, some subgroups may be dispatched with inactive invocations that do not correspond to a local workgroup invocation, making the value of index unreliable.
Valid Usage
VUID-SubgroupLocalInvocationId-SubgroupLocalInvocationId-04380
The variable decorated with SubgroupLocalInvocationId must be
declared using the Input Storage Class
VUID-SubgroupLocalInvocationId-SubgroupLocalInvocationId-04381
The variable decorated with SubgroupLocalInvocationId must be
declared as a scalar 32-bit integer value