'\" t
.\"     Title: glBeginQuery
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: 05/21/2015
.\"    Manual: [FIXME: manual]
.\"    Source: [FIXME: source]
.\"  Language: English
.\"
.TH "GLBEGINQUERY" "3G" "05/21/2015" "[FIXME: source]" "[FIXME: manual]"
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.SH "NAME"
glBeginQuery \- delimit the boundaries of a query object
.SH "C SPECIFICATION"
.HP \w'void\ glBeginQuery('u
.BI "void glBeginQuery(GLenum\ " "target" ", GLuint\ " "id" ");"
.HP \w'void\ glEndQuery('u
.BI "void glEndQuery(GLenum\ " "target" ");"
.SH "PARAMETERS FOR GLBEGINQUERY"
.PP
\fItarget\fR
.RS 4
Specifies the target type of query object established between
\fBglBeginQuery\fR
and the subsequent
\fBglEndQuery\fR()\&. The symbolic constant must be one of
\fBGL_SAMPLES_PASSED\fR,
\fBGL_ANY_SAMPLES_PASSED\fR,
\fBGL_ANY_SAMPLES_PASSED_CONSERVATIVE\fR,
\fBGL_PRIMITIVES_GENERATED\fR,
\fBGL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN\fR, or
\fBGL_TIME_ELAPSED\fR\&.
.RE
.PP
\fIid\fR
.RS 4
Specifies the name of a query object\&.
.RE
.SH "PARAMETERS FOR GLENDQUERY"
.PP
\fItarget\fR
.RS 4
Specifies the target type of query object to be concluded\&. The symbolic constant must be one of
\fBGL_SAMPLES_PASSED\fR,
\fBGL_ANY_SAMPLES_PASSED\fR,
\fBGL_ANY_SAMPLES_PASSED_CONSERVATIVE\fR,
\fBGL_PRIMITIVES_GENERATED\fR,
\fBGL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN\fR, or
\fBGL_TIME_ELAPSED\fR\&.
.RE
.SH "DESCRIPTION"
.PP
\fBglBeginQuery\fR
and
\fBglEndQuery\fR()
delimit the boundaries of a query object\&.
\fIquery\fR
must be a name previously returned from a call to
\fBglGenQueries\fR()\&. If a query object with name
\fIid\fR
does not yet exist it is created with the type determined by
\fItarget\fR\&.
\fItarget\fR
must be one of
\fBGL_SAMPLES_PASSED\fR,
\fBGL_ANY_SAMPLES_PASSED\fR,
\fBGL_PRIMITIVES_GENERATED\fR,
\fBGL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN\fR, or
\fBGL_TIME_ELAPSED\fR\&. The behavior of the query object depends on its type and is as follows\&.
.PP
If
\fItarget\fR
is
\fBGL_SAMPLES_PASSED\fR,
\fIid\fR
must be an unused name, or the name of an existing occlusion query object\&. When
\fBglBeginQuery\fR
is executed, the query object\*(Aqs samples\-passed counter is reset to 0\&. Subsequent rendering will increment the counter for every sample that passes the depth test\&. If the value of
\fBGL_SAMPLE_BUFFERS\fR
is 0, then the samples\-passed count is incremented by 1 for each fragment\&. If the value of
\fBGL_SAMPLE_BUFFERS\fR
is 1, then the samples\-passed count is incremented by the number of samples whose coverage bit is set\&. However, implementations, at their discression may instead increase the samples\-passed count by the value of
\fBGL_SAMPLES\fR
if any sample in the fragment is covered\&. When
\fBglEndQuery\fR
is executed, the samples\-passed counter is assigned to the query object\*(Aqs result value\&. This value can be queried by calling
\fBglGetQueryObject\fR()
with
\fIpname\fR\fBGL_QUERY_RESULT\fR\&.
.PP
If
\fItarget\fR
is
\fBGL_ANY_SAMPLES_PASSED\fR
or
\fBGL_ANY_SAMPLES_PASSED_CONSERVATIVE\fR,
\fIid\fR
must be an unused name, or the name of an existing boolean occlusion query object\&. When
\fBglBeginQuery\fR
is executed, the query object\*(Aqs samples\-passed flag is reset to
\fBGL_FALSE\fR\&. Subsequent rendering causes the flag to be set to
\fBGL_TRUE\fR
if any sample passes the depth test in the case of
\fBGL_ANY_SAMPLES_PASSED\fR, or if the implementation determines that any sample might pass the depth test in the case of
\fBGL_ANY_SAMPLES_PASSED_CONSERVATIVE\fR\&. The implementation may be able to provide a more efficient test in the case of
\fBGL_ANY_SAMPLES_PASSED_CONSERVATIVE\fR
if some false positives are acceptable to the application\&. When
\fBglEndQuery\fR
is executed, the samples\-passed flag is assigned to the query object\*(Aqs result value\&. This value can be queried by calling
\fBglGetQueryObject\fR()
with
\fIpname\fR\fBGL_QUERY_RESULT\fR\&.
.PP
If
\fItarget\fR
is
\fBGL_PRIMITIVES_GENERATED\fR,
\fIid\fR
must be an unused name, or the name of an existing primitive query object previously bound to the
\fBGL_PRIMITIVES_GENERATED\fR
query binding\&. When
\fBglBeginQuery\fR
is executed, the query object\*(Aqs primitives\-generated counter is reset to 0\&. Subsequent rendering will increment the counter once for every vertex that is emitted from the geometry shader, or from the vertex shader if no geometry shader is present\&. When
\fBglEndQuery\fR
is executed, the primitives\-generated counter is assigned to the query object\*(Aqs result value\&. This value can be queried by calling
\fBglGetQueryObject\fR()
with
\fIpname\fR\fBGL_QUERY_RESULT\fR\&.
.PP
If
\fItarget\fR
is
\fBGL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN\fR,
\fIid\fR
must be an unused name, or the name of an existing primitive query object previously bound to the
\fBGL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN\fR
query binding\&. When
\fBglBeginQuery\fR
is executed, the query object\*(Aqs primitives\-written counter is reset to 0\&. Subsequent rendering will increment the counter once for every vertex that is written into the bound transform feedback buffer(s)\&. If transform feedback mode is not activated between the call to
\fBglBeginQuery\fR
and
\fBglEndQuery\fR, the counter will not be incremented\&. When
\fBglEndQuery\fR
is executed, the primitives\-written counter is assigned to the query object\*(Aqs result value\&. This value can be queried by calling
\fBglGetQueryObject\fR()
with
\fIpname\fR\fBGL_QUERY_RESULT\fR\&.
.PP
If
\fItarget\fR
is
\fBGL_TIME_ELAPSED\fR,
\fIid\fR
must be an unused name, or the name of an existing timer query object previously bound to the
\fBGL_TIME_ELAPSED\fR
query binding\&. When
\fBglBeginQuery\fR
is executed, the query object\*(Aqs time counter is reset to 0\&. When
\fBglEndQuery\fR
is executed, the elapsed server time that has passed since the call to
\fBglBeginQuery\fR
is written into the query object\*(Aqs time counter\&. This value can be queried by calling
\fBglGetQueryObject\fR()
with
\fIpname\fR\fBGL_QUERY_RESULT\fR\&.
.PP
Querying the
\fBGL_QUERY_RESULT\fR
implicitly flushes the GL pipeline until the rendering delimited by the query object has completed and the result is available\&.
\fBGL_QUERY_RESULT_AVAILABLE\fR
can be queried to determine if the result is immediately available or if the rendering is not yet complete\&.
.SH "NOTES"
.PP
If the query target\*(Aqs count exceeds the maximum value representable in the number of available bits, as reported by
\fBglGetQueryiv\fR()
with
\fItarget\fR
set to the appropriate query target and
\fIpname\fR\fBGL_QUERY_COUNTER_BITS\fR, the count becomes undefined\&.
.PP
An implementation may support 0 bits in its counter, in which case query results are always undefined and essentially useless\&.
.PP
When
\fBGL_SAMPLE_BUFFERS\fR
is 0, the samples\-passed counter of an occlusion query will increment once for each fragment that passes the depth test\&. When
\fBGL_SAMPLE_BUFFERS\fR
is 1, an implementation may either increment the samples\-passed counter individually for each sample of a fragment that passes the depth test, or it may choose to increment the counter for all samples of a fragment if any one of them passes the depth test\&.
.PP
The query targets
\fBGL_ANY_SAMPLES_PASSED\fR, and
\fBGL_TIME_ELAPSED\fR
are availale only if the GL version is 3\&.3 or higher\&.
.PP
The query target
\fBGL_ANY_SAMPLES_PASSED_CONSERVATIVE\fR
is available only of the GL version is 4\&.3 or higher\&.
.SH "ERRORS"
.PP
\fBGL_INVALID_ENUM\fR
is generated if
\fItarget\fR
is not one of the accepted tokens\&.
.PP
\fBGL_INVALID_OPERATION\fR
is generated if
\fBglBeginQuery\fR
is executed while a query object of the same
\fItarget\fR
is already active\&.
.PP
\fBGL_INVALID_OPERATION\fR
is generated if
\fBglEndQuery\fR()
is executed when a query object of the same
\fItarget\fR
is not active\&.
.PP
\fBGL_INVALID_OPERATION\fR
is generated if
\fIid\fR
is 0\&.
.PP
\fBGL_INVALID_OPERATION\fR
is generated if
\fIid\fR
is the name of an already active query object\&.
.PP
\fBGL_INVALID_OPERATION\fR
is generated if
\fIid\fR
refers to an existing query object whose type does not does not match
\fItarget\fR\&.
.SH "VERSION SUPPORT"
.TS
allbox tab(:);
lB cB s s s s s s s s s s s
lB cB cB cB cB cB cB cB cB cB cB cB cB.
T{

T}:T{
\fBOpenGL Version\fR
T}
T{
\fBFunction / Feature Name\fR
T}:T{
\fB2\&.0\fR
T}:T{
\fB2\&.1\fR
T}:T{
\fB3\&.0\fR
T}:T{
\fB3\&.1\fR
T}:T{
\fB3\&.2\fR
T}:T{
\fB3\&.3\fR
T}:T{
\fB4\&.0\fR
T}:T{
\fB4\&.1\fR
T}:T{
\fB4\&.2\fR
T}:T{
\fB4\&.3\fR
T}:T{
\fB4\&.4\fR
T}:T{
\fB4\&.5\fR
T}
.T&
l c c c c c c c c c c c c
l c c c c c c c c c c c c.
T{
\fBglBeginQuery\fR
T}:T{
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T}:T{
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T}:T{
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T}
T{
\fBglEndQuery\fR
T}:T{
✔
T}:T{
✔
T}:T{
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T}
.TE
.sp
.SH "SEE ALSO"
.PP
\fBglBeginQueryIndexed\fR(),
\fBglDeleteQueries\fR(),
\fBglEndQuery\fR(),
\fBglGenQueries\fR(),
\fBglGetQueryObject\fR(),
\fBglGetQueryiv\fR(),
\fBglIsQuery\fR()
.SH "COPYRIGHT"
.PP
Copyright
\(co
2005 Addison\-Wesley\&. Copyright
\(co
2010\-2014 Khronos Group\&. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1\&.0, 8 June 1999\&.
\m[blue]\fBhttp://opencontent\&.org/openpub/\fR\m[]\&.
.SH "COPYRIGHT"
.br
Copyright \(co 2005 Sams Publishing
.br
Copyright \(co 2010-2014 Khronos Group
.br