GLBEGINQUERY(3G)						   OpenGL Manual						  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_ANY_SAMPLES_PASSED_CONSERVATIVE, 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_ANY_SAMPLES_PASSED_CONSERVATIVE, 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 pnameGL_QUERY_RESULT.

       If target is GL_ANY_SAMPLES_PASSED or GL_ANY_SAMPLES_PASSED_CONSERVATIVE, 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 in the case of GL_ANY_SAMPLES_PASSED, or if the implementation
       determines that any sample might pass the depth test in the case of GL_ANY_SAMPLES_PASSED_CONSERVATIVE. The implementation may be able to
       provide a more efficient test in the case of GL_ANY_SAMPLES_PASSED_CONSERVATIVE if some false positives are acceptable to the application.
       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 pnameGL_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 pnameGL_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 pnameGL_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 pnameGL_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 pnameGL_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.

       The query target GL_ANY_SAMPLES_PASSED_CONSERVATIVE is available only of the GL version is 4.3 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. Copyright (C) 2010-2012 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.  http://opencontent.org/openpub/.

AUTHORS

       opengl.org

opengl.org							    06/10/2014							  GLBEGINQUERY(3G)