Occlusion queries track the number of samples that pass the per-fragment
tests for a set of drawing commands.
As such, occlusion queries are only available on queue families supporting
graphics operations.
The application can then use these results to inform future rendering
decisions.
An occlusion query is begun and ended by calling vkCmdBeginQuery
and
vkCmdEndQuery
, respectively.
When an occlusion query begins, the count of passing samples always starts
at zero.
For each drawing command, the count is incremented as described in
Sample Counting.
If flags
does not contain VK_QUERY_CONTROL_PRECISE_BIT
an
implementation may generate any non-zero result value for the query if the
count of passing samples is non-zero.
![]() | Note |
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Not setting |
When an occlusion query finishes, the result for that query is marked as
available.
The application can then either copy the result to a buffer (via
vkCmdCopyQueryPoolResults
) or request it be put into host memory (via
vkGetQueryPoolResults
).
![]() | Note |
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If occluding geometry is not drawn first, samples can pass the depth test, but still not be visible in a final image. |