2005
Sams Publishing
2010-2013
Khronos Group
glBeginQuery
3G

# glBeginQuery

delimit the boundaries of a query object

## C Specification

                    void glBeginQuery
                    GLenum target
                    GLuint id

                    void glEndQuery
                    GLenum target

## Parameters for `glBeginQuery`

`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.

## Parameters for `glEndQuery`

`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 `pname` `GL_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 `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.

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 2005 Addison-Wesley. Copyright 2010-2013 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/.