Magnum::GL::TimeQuery class

Query for elapsed time.

Queries timestamp after all previous OpenGL calls have been processed. It can query either duration of sequence of commands or absolute timestamp. Example usage of both methods:

GL::TimeQuery q1{GL::TimeQuery::Target::TimeElapsed},
              q2{GL::TimeQuery::Target::TimeElapsed};

q1.begin();
// rendering...
q1.end();

q2.begin();
// another rendering...
q2.end();

UnsignedInt timeElapsed1 = q1.result<UnsignedInt>();
UnsignedInt timeElapsed2 = q2.result<UnsignedInt>();
GL::TimeQuery q1{GL::TimeQuery::Target::Timestamp},
              q2{GL::TimeQuery::Target::Timestamp},
              q3{GL::TimeQuery::Target::Timestamp};

q1.timestamp();
// rendering...
q2.timestamp();
// another rendering...
q3.timestamp();

UnsignedInt tmp = q2.result<UnsignedInt>();
UnsignedInt timeElapsed1 = tmp - q1.result<UnsignedInt>();
UnsignedInt timeElapsed2 = q3.result<UnsignedInt>() - tmp;

Using the latter results in fewer OpenGL calls when doing more measures.

Base classes

class AbstractQuery
Base class for queries.

Public types

enum class Target: GLenum { TimeElapsed = GL_TIME_ELAPSED, Timestamp = GL_TIMESTAMP }
Query target.

Public static functions

static auto wrap(GLuint id, Target target, ObjectFlags flags = {}) -> TimeQuery
Wrap existing OpenGL time query object.

Constructors, destructors, conversion operators

TimeQuery(Target target) explicit
Constructor.
TimeQuery(NoCreateT) explicit noexcept
Construct without creating the underlying OpenGL object.
TimeQuery(const TimeQuery&) deleted
Copying is not allowed.
TimeQuery(TimeQuery&&) noexcept defaulted
Move constructor.

Public functions

auto operator=(const TimeQuery&) -> TimeQuery& deleted
Copying is not allowed.
auto operator=(TimeQuery&&) noexcept -> TimeQuery& defaulted
Move assignment.
void timestamp()
Query timestamp.

Enum documentation

enum class Magnum::GL::TimeQuery::Target: GLenum

Query target.

Enumerators
TimeElapsed

Elapsed time. Use result<UnsignedLong>() or result<Long>() to retrieve the result.

Timestamp

Timestamp. For use with timestamp() only, use result<UnsignedLong>() or result<Long>() to retrieve the result.

Function documentation

static TimeQuery Magnum::GL::TimeQuery::wrap(GLuint id, Target target, ObjectFlags flags = {})

Wrap existing OpenGL time query object.

Parameters
id OpenGL time query ID
target Query target
flags Object creation flags

The id is expected to be of an existing OpenGL query object. Unlike query created using constructor, the OpenGL object is by default not deleted on destruction, use flags for different behavior.

Magnum::GL::TimeQuery::TimeQuery(Target target) explicit

Constructor.

Creates new OpenGL query object. If ARB_direct_state_access (part of OpenGL 4.5) is not available, the query is created on first use.

Magnum::GL::TimeQuery::TimeQuery(NoCreateT) explicit noexcept

Construct without creating the underlying OpenGL object.

The constructed instance is equivalent to moved-from state. Useful in cases where you will overwrite the instance later anyway. Move another object over it to make it useful.

This function can be safely used for constructing (and later destructing) objects even without any OpenGL context being active.

void Magnum::GL::TimeQuery::timestamp()

Query timestamp.

Use result<UnsignedLong>() or result<Long>() to retrieve the result.