Mixing
ARB shader ballot : not coherent between false and true?
I am wondering why ballotARB(false) returns always 0 and not return the bitfield where the corresponding bits are set for all active invocations in the sub-group.
Because of that, I do not see how can I use ballotARB fonction in my program.
Is my understanding of this function false?
opengl glsl vulkan
asked Jan 2 at 21:26
Antoine MorrierAntoine Morrier
2,102721
add a comment |
I am wondering why ballotARB(false) returns always 0 and not return the bitfield where the corresponding bits are set for all active invocations in the sub-group.
Because of that, I do not see how can I use ballotARB fonction in my program.
Is my understanding of this function false?
opengl glsl vulkan
asked Jan 2 at 21:26
Antoine MorrierAntoine Morrier
2,102721
add a comment |
I am wondering why ballotARB(false) returns always 0 and not return the bitfield where the corresponding bits are set for all active invocations in the sub-group.
Because of that, I do not see how can I use ballotARB fonction in my program.
Is my understanding of this function false?
opengl glsl vulkan
asked Jan 2 at 21:26
Antoine MorrierAntoine Morrier
2,102721
I am wondering why ballotARB(false) returns always 0 and not return the bitfield where the corresponding bits are set for all active invocations in the sub-group.
Because of that, I do not see how can I use ballotARB fonction in my program.
Is my understanding of this function false?
opengl glsl vulkan
opengl glsl vulkan
asked Jan 2 at 21:26
Antoine MorrierAntoine Morrier
2,102721
asked Jan 2 at 21:26
Antoine MorrierAntoine Morrier
2,102721
asked Jan 2 at 21:26
Antoine MorrierAntoine Morrier
2,102721
asked Jan 2 at 21:26
Antoine MorrierAntoine Morrier
2,102721
asked Jan 2 at 21:26
Antoine MorrierAntoine Morrier
2,102721
2,102721
add a comment |
add a comment |
1 Answer
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What should ballotARB(false) return, if not 0?
It does return the count of the true votes in the local subgroup. Since all your invocations vote false no matter what, the result must be 0. This is even explicitely stated in the ARB_shader_ballot extension spec:
The following trivial assumptions can be made:
ballotARB(true)returnsbitfieldwhere the corresponding bits are set for all active invocations in the sub-group.
ballotARB(false)returns zero.
So to make use of the votes, you should use it on an experession which is actually not dynamically uniform.
answered Jan 2 at 21:56
derhassderhass
31.7k22743
Okay I misexplain my problem. If I have 25 invocations that votetrueand 7 that votefalse. A thread that votetruewill get thebitfield where the corresponding bits are set for all active invocations in the sub-group.. However in my understanding ofthe spec, if a thread vote false, it will get always 0 even if other invocation vote true
– Antoine Morrier
Jan 2 at 22:40
1
Ah okay. These 2 assumptions are made only for the case where we wrote explicitely true or false. Thanks !
– Antoine Morrier
Jan 2 at 22:43
add a comment |
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1 Answer
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active
oldest
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1 Answer
1
active
oldest
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active
oldest
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votes
What should ballotARB(false) return, if not 0?
It does return the count of the true votes in the local subgroup. Since all your invocations vote false no matter what, the result must be 0. This is even explicitely stated in the ARB_shader_ballot extension spec:
The following trivial assumptions can be made:
ballotARB(true)returnsbitfieldwhere the corresponding bits are set for all active invocations in the sub-group.
ballotARB(false)returns zero.
So to make use of the votes, you should use it on an experession which is actually not dynamically uniform.
answered Jan 2 at 21:56
derhassderhass
31.7k22743
Okay I misexplain my problem. If I have 25 invocations that votetrueand 7 that votefalse. A thread that votetruewill get thebitfield where the corresponding bits are set for all active invocations in the sub-group.. However in my understanding ofthe spec, if a thread vote false, it will get always 0 even if other invocation vote true
– Antoine Morrier
Jan 2 at 22:40
1
Ah okay. These 2 assumptions are made only for the case where we wrote explicitely true or false. Thanks !
– Antoine Morrier
Jan 2 at 22:43
add a comment |
What should ballotARB(false) return, if not 0?
It does return the count of the true votes in the local subgroup. Since all your invocations vote false no matter what, the result must be 0. This is even explicitely stated in the ARB_shader_ballot extension spec:
The following trivial assumptions can be made:
ballotARB(true)returnsbitfieldwhere the corresponding bits are set for all active invocations in the sub-group.
ballotARB(false)returns zero.
So to make use of the votes, you should use it on an experession which is actually not dynamically uniform.
answered Jan 2 at 21:56
derhassderhass
31.7k22743
Okay I misexplain my problem. If I have 25 invocations that votetrueand 7 that votefalse. A thread that votetruewill get thebitfield where the corresponding bits are set for all active invocations in the sub-group.. However in my understanding ofthe spec, if a thread vote false, it will get always 0 even if other invocation vote true
– Antoine Morrier
Jan 2 at 22:40
1
Ah okay. These 2 assumptions are made only for the case where we wrote explicitely true or false. Thanks !
– Antoine Morrier
Jan 2 at 22:43
add a comment |
What should ballotARB(false) return, if not 0?
It does return the count of the true votes in the local subgroup. Since all your invocations vote false no matter what, the result must be 0. This is even explicitely stated in the ARB_shader_ballot extension spec:
The following trivial assumptions can be made:
ballotARB(true)returnsbitfieldwhere the corresponding bits are set for all active invocations in the sub-group.
ballotARB(false)returns zero.
So to make use of the votes, you should use it on an experession which is actually not dynamically uniform.
answered Jan 2 at 21:56
derhassderhass
31.7k22743
What should ballotARB(false) return, if not 0?
It does return the count of the true votes in the local subgroup. Since all your invocations vote false no matter what, the result must be 0. This is even explicitely stated in the ARB_shader_ballot extension spec:
The following trivial assumptions can be made:
ballotARB(true)returnsbitfieldwhere the corresponding bits are set for all active invocations in the sub-group.
ballotARB(false)returns zero.
So to make use of the votes, you should use it on an experession which is actually not dynamically uniform.
answered Jan 2 at 21:56
derhassderhass
31.7k22743
answered Jan 2 at 21:56
derhassderhass
31.7k22743
answered Jan 2 at 21:56
derhassderhass
31.7k22743
answered Jan 2 at 21:56
derhassderhass
31.7k22743
31.7k22743
Okay I misexplain my problem. If I have 25 invocations that votetrueand 7 that votefalse. A thread that votetruewill get thebitfield where the corresponding bits are set for all active invocations in the sub-group.. However in my understanding ofthe spec, if a thread vote false, it will get always 0 even if other invocation vote true
– Antoine Morrier
Jan 2 at 22:40
1
Ah okay. These 2 assumptions are made only for the case where we wrote explicitely true or false. Thanks !
– Antoine Morrier
Jan 2 at 22:43
add a comment |
Okay I misexplain my problem. If I have 25 invocations that votetrueand 7 that votefalse. A thread that votetruewill get thebitfield where the corresponding bits are set for all active invocations in the sub-group.. However in my understanding ofthe spec, if a thread vote false, it will get always 0 even if other invocation vote true
– Antoine Morrier
Jan 2 at 22:40
1
Ah okay. These 2 assumptions are made only for the case where we wrote explicitely true or false. Thanks !
– Antoine Morrier
Jan 2 at 22:43
Okay I misexplain my problem. If I have 25 invocations that vote
true and 7 that vote false. A thread that vote true will get the bitfield where the corresponding bits are set for all active invocations in the sub-group.. However in my understanding ofthe spec, if a thread vote false, it will get always 0 even if other invocation vote true– Antoine Morrier
Jan 2 at 22:40
Okay I misexplain my problem. If I have 25 invocations that vote
true and 7 that vote false. A thread that vote true will get the bitfield where the corresponding bits are set for all active invocations in the sub-group.. However in my understanding ofthe spec, if a thread vote false, it will get always 0 even if other invocation vote true– Antoine Morrier
Jan 2 at 22:40
1
1
Ah okay. These 2 assumptions are made only for the case where we wrote explicitely true or false. Thanks !
– Antoine Morrier
Jan 2 at 22:43
Ah okay. These 2 assumptions are made only for the case where we wrote explicitely true or false. Thanks !
– Antoine Morrier
Jan 2 at 22:43
add a comment |
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