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GLBEGINQUERY(3G)                                 OpenGL 3.3                                 GLBEGINQUERY(3G)



NAME
       glBeginQuery - delimit the boundaries of a query object

C SPECIFICATION
       void glBeginQuery(GLenum target, GLuint id);

PARAMETERS
       target
           Specifies the target type of query object established between glBeginQuery and the subsequent
           glEndQuery(). The symbolic constant must be one of GL_SAMPLES_PASSED, GL_ANY_SAMPLES_PASSED,
           GL_PRIMITIVES_GENERATED, GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN, or GL_TIME_ELAPSED.

       id
           Specifies the name of a query object.

C SPECIFICATION
       void glEndQuery(GLenum target);

PARAMETERS
       target
           Specifies the target type of query object to be concluded. The symbolic constant must be one of
           GL_SAMPLES_PASSED, GL_ANY_SAMPLES_PASSED, GL_PRIMITIVES_GENERATED,
           GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN, or GL_TIME_ELAPSED.

DESCRIPTION
       glBeginQuery and glEndQuery() delimit the boundaries of a query object.  query must be a name
       previously returned from a call to glGenQueries(). If a query object with name id does not yet exist
       it is created with the type determined by target.  target must be one of GL_SAMPLES_PASSED,
       GL_ANY_SAMPLES_PASSED, GL_PRIMITIVES_GENERATED, GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN, or
       GL_TIME_ELAPSED. The behavior of the query object depends on its type and is as follows.

       If target is GL_SAMPLES_PASSED, id must be an unused name, or the name of an existing occlusion query
       object. When glBeginQuery is executed, the query object's 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 GL_SAMPLE_BUFFERS is 0, then the samples-passed count is incremented by 1 for each fragment.
       If the value of GL_SAMPLE_BUFFERS 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 GL_SAMPLES if any sample in the fragment is
       covered. When glEndQuery is executed, the samples-passed counter is assigned to the query object's
       result value. This value can be queried by calling glGetQueryObject() with pname GL_QUERY_RESULT.

       If target is GL_ANY_SAMPLES_PASSED, id must be an unused name, or the name of an existing boolean
       occlusion query object. When glBeginQuery is executed, the query object's samples-passed flag is
       reset to GL_FALSE. Subsequent rendering causes the flag to be set to GL_TRUE if any sample passes the
       depth test. When glEndQuery is executed, the samples-passed flag is assigned to the query object's
       result value. This value can be queried by calling glGetQueryObject() with pname GL_QUERY_RESULT.

       If target is GL_PRIMITIVES_GENERATED, id must be an unused name, or the name of an existing primitive
       query object previously bound to the GL_PRIMITIVES_GENERATED query binding. When glBeginQuery is
       executed, the query object's 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 glEndQuery is executed, the primitives-generated
       counter is assigned to the query object's result value. This value can be queried by calling
       glGetQueryObject() with pname GL_QUERY_RESULT.

       If target is GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN, id must be an unused name, or the name of an
       existing primitive query object previously bound to the GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN
       query binding. When glBeginQuery is executed, the query object's 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
       glBeginQuery and glEndQuery, the counter will not be incremented. When glEndQuery is executed, the
       primitives-written counter is assigned to the query object's result value. This value can be queried
       by calling glGetQueryObject() with pname GL_QUERY_RESULT.

       If target is GL_TIME_ELAPSED, id must be an unused name, or the name of an existing timer query
       object previously bound to the GL_TIME_ELAPSED query binding. When glBeginQuery is executed, the
       query object's time counter is reset to 0. When glEndQuery is executed, the elapsed server time that
       has passed since the call to glBeginQuery is written into the query object's time counter. This value
       can be queried by calling glGetQueryObject() with pname GL_QUERY_RESULT.

       Querying the GL_QUERY_RESULT implicitly flushes the GL pipeline until the rendering delimited by the
       query object has completed and the result is available.  GL_QUERY_RESULT_AVAILABLE can be queried to
       determine if the result is immediately available or if the rendering is not yet complete.

NOTES
       If the query target's count exceeds the maximum value representable in the number of available bits,
       as reported by glGetQueryiv() with target set to the appropriate query target and pname
       GL_QUERY_COUNTER_BITS, the count becomes undefined.

       An implementation may support 0 bits in its counter, in which case query results are always undefined
       and essentially useless.

       When GL_SAMPLE_BUFFERS is 0, the samples-passed counter of an occlusion query will increment once for
       each fragment that passes the depth test. When GL_SAMPLE_BUFFERS 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.

       The query targets GL_ANY_SAMPLES_PASSED, and GL_TIME_ELAPSED are availale only if the GL version is
       3.3 or higher.

ERRORS
       GL_INVALID_ENUM is generated if target is not one of the accepted tokens.


       GL_INVALID_OPERATION is generated if glBeginQuery is executed while a query object of the same target
       is already active.


       GL_INVALID_OPERATION is generated if glEndQuery() is executed when a query object of the same target
       is not active.


       GL_INVALID_OPERATION is generated if id is 0.


       GL_INVALID_OPERATION is generated if id is the name of an already active query object.


       GL_INVALID_OPERATION is generated if id refers to an existing query object whose type does not does
       not match target.

SEE ALSO
       glDeleteQueries(), glGenQueries(), glGetQueryiv(), glGetQueryObject(), glIsQuery()


COPYRIGHT
       Copyright (C) 2005 Addison-Wesley. This material may be distributed subject to the terms and
       conditions set forth in the Open Publication License, v 1.0, 8 June 1999.
       http://opencontent.org/openpub/.



OpenGL 3.3                                       03/08/2011                                 GLBEGINQUERY(3G)