glBeginQuery â 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.
+
id+ Specifies 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 GL_SAMPLE_BUFFERS is 0, the samples-passed counter 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.
+
+ 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/. +