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.

COPYRIGHT

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. m[blue]http://opencontent.org/openpub/m[].