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glBeginQuery — delimit the boundaries of a query object
void glBeginQuery(GLenum target, GLuint id);
target
Specifies the target type of query object established between
glBeginQuery and the subsequent glEndQuery.
The symbolic constant must be GL_SAMPLES_PASSED.
idSpecifies the name of a query object.
void glEndQuery(GLenum target);
target
Specifies the target type of query object to be concluded.
The symbolic constant must be GL_SAMPLES_PASSED.
glBeginQuery and glEndQuery delimit the
boundaries of a query object. If a query object with name id does not yet exist it is created.
When glBeginQuery is executed, the query object's samples-passed counter is reset to 0. Subsequent
rendering will increment the counter once for every sample that passes the depth test. 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.
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.
If the samples-passed count exceeds the maximum value representable in the number of available bits, as reported by
glGetQueryiv with pname
GL_QUERY_COUNTER_BITS, the count becomes undefined.
An implementation may support 0 bits in its samples-passed counter, in which case query results are always undefined and essentially useless.
When SAMPLE_BUFFERS is 0, the samples-passed counter will increment once for each fragment that passes
the depth test. When 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.
glBeginQuery and glEndQuery
are available only if the GL version is 1.5 or greater.
GL_INVALID_ENUM is generated if target is not GL_SAMPLES_PASSED.
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 glBeginQuery or
glEndQuery is executed between the execution of
glBegin and the corresponding execution of
glEnd.
Copyright © 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/.