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592 lines
24 KiB
592 lines
24 KiB
Name
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ANGLE_timer_query
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Name Strings
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GL_ANGLE_timer_query
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Contributors
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Contributors to ARB_occlusion_query
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Contributors to EXT_timer_query
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Contributors to ARB_timer_query
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Ben Vanik, Google Inc.
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Daniel Koch, TransGaming Inc.
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Contact
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Ben Vanik, Google Inc. (benvanik 'at' google 'dot' com)
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Status
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Draft
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Version
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Last Modified Date: Apr 28, 2011
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Author Revision: 1
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Number
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OpenGL ES Extension #??
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Dependencies
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OpenGL ES 2.0 is required.
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The extension is written against the OpenGL ES 2.0 specification.
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Overview
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Applications can benefit from accurate timing information in a number of
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different ways. During application development, timing information can
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help identify application or driver bottlenecks. At run time,
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applications can use timing information to dynamically adjust the amount
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of detail in a scene to achieve constant frame rates. OpenGL
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implementations have historically provided little to no useful timing
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information. Applications can get some idea of timing by reading timers
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on the CPU, but these timers are not synchronized with the graphics
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rendering pipeline. Reading a CPU timer does not guarantee the completion
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of a potentially large amount of graphics work accumulated before the
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timer is read, and will thus produce wildly inaccurate results.
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glFinish() can be used to determine when previous rendering commands have
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been completed, but will idle the graphics pipeline and adversely affect
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application performance.
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This extension provides a query mechanism that can be used to determine
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the amount of time it takes to fully complete a set of GL commands, and
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without stalling the rendering pipeline. It uses the query object
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mechanisms first introduced in the occlusion query extension, which allow
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time intervals to be polled asynchronously by the application.
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IP Status
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No known IP claims.
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New Procedures and Functions
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void GenQueriesANGLE(sizei n, uint *ids);
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void DeleteQueriesANGLE(sizei n, const uint *ids);
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boolean IsQueryANGLE(uint id);
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void BeginQueryANGLE(enum target, uint id);
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void EndQueryANGLE(enum target);
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void QueryCounterANGLE(uint id, enum target);
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void GetQueryivANGLE(enum target, enum pname, int *params);
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void GetQueryObjectivANGLE(uint id, enum pname, int *params);
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void GetQueryObjectuivANGLE(uint id, enum pname, uint *params);
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void GetQueryObjecti64vANGLE(uint id, enum pname, int64 *params);
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void GetQueryObjectui64vANGLE(uint id, enum pname, uint64 *params);
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New Tokens
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Accepted by the <pname> parameter of GetQueryivANGLE:
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QUERY_COUNTER_BITS_ANGLE 0x8864
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CURRENT_QUERY_ANGLE 0x8865
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Accepted by the <pname> parameter of GetQueryObjectivANGLE,
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GetQueryObjectuivANGLE, GetQueryObjecti64vANGLE, and
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GetQueryObjectui64vANGLE:
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QUERY_RESULT_ANGLE 0x8866
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QUERY_RESULT_AVAILABLE_ANGLE 0x8867
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Accepted by the <target> parameter of BeginQueryANGLE, EndQueryANGLE, and
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GetQueryivANGLE:
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TIME_ELAPSED_ANGLE 0x88BF
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Accepted by the <target> parameter of GetQueryivANGLE and
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QueryCounterANGLE:
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TIMESTAMP_ANGLE 0x8E28
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Additions to Chapter 2 of the OpenGL ES 2.0 Specification (OpenGL ES Operation)
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(Modify table 2.1, Correspondence of command suffix letters to GL argument)
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Add two new types:
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Letter Corresponding GL Type
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------ ---------------------
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i64 int64ANGLE
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ui64 uint64ANGLE
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(Modify table 2.2, GL data types) Add two new types:
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GL Type Minimum Bit Width Description
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------- ----------------- -----------------------------
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int64ANGLE 64 Signed 2's complement integer
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uint64ANGLE 64 Unsigned binary integer
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Additions to Chapter 5 of the OpenGL ES 2.0 Specification (Special Functions)
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Add a new section 5.3 "Timer Queries":
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"5.3 Timer Queries
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Timer queries use query objects to track the amount of time needed to
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fully complete a set of GL commands, or to determine the current time
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of the GL.
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Timer queries are associated with query objects. The command
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void GenQueriesANGLE(sizei n, uint *ids);
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returns <n> previously unused query object names in <ids>. These
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names are marked as used, but no object is associated with them until
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the first time they are used by BeginQueryANGLE. Query objects contain
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one piece of state, an integer result value. This result value is
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initialized to zero when the object is created. Any positive integer
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except for zero (which is reserved for the GL) is a valid query
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object name.
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Query objects are deleted by calling
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void DeleteQueriesANGLE(sizei n, const uint *ids);
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<ids> contains <n> names of query objects to be deleted. After a
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query object is deleted, its name is again unused. Unused names in
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<ids> are silently ignored.
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If an active query object is deleted its name immediately becomes unused,
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but the underlying object is not deleted until it is no longer active.
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A timer query can be started and finished by calling
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void BeginQueryANGLE(enum target, uint id);
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void EndQueryANGLE(enum target);
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where <target> is TIME_ELAPSED_ANGLE. If BeginQueryANGLE is called
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with an unused <id>, that name is marked as used and associated with
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a new query object.
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If BeginQueryANGLE is called with an <id> of zero, if the active query
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object name for <target> is non-zero, if <id> is the name of an existing
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query object whose type does not match <target>, or if <id> is the active
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query object name for any query type, the error INVALID_OPERATION is
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generated. If EndQueryANGLE is called while no query with the same target
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is in progress, an INVALID_OPERATION error is generated.
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When BeginQueryANGLE and EndQueryANGLE are called with a <target> of
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TIME_ELAPSED_ANGLE, the GL prepares to start and stop the timer used for
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timer queries. The timer is started or stopped when the effects from all
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previous commands on the GL client and server state and the framebuffer
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have been fully realized. The BeginQueryANGLE and EndQueryANGLE commands
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may return before the timer is actually started or stopped. When the timer
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query timer is finally stopped, the elapsed time (in nanoseconds) is
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written to the corresponding query object as the query result value, and
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the query result for that object is marked as available.
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If the elapsed time overflows the number of bits, <n>, available to hold
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elapsed time, its value becomes undefined. It is recommended, but not
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required, that implementations handle this overflow case by saturating at
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2^n - 1.
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The necessary state is a single bit indicating whether an timer
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query is active, the identifier of the currently active timer
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query, and a counter keeping track of the time that has passed.
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When the command
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void QueryCounterANGLE(uint id, enum target);
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is called with <target> TIMESTAMP_ANGLE, the GL records the current time
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into the corresponding query object. The time is recorded after all
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previous commands on the GL client and server state and the framebuffer
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have been fully realized. When the time is recorded, the query result for
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that object is marked available. QueryCounterANGLE timer queries can be
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used within a BeginQueryANGLE / EndQueryANGLE block where the <target> is
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TIME_ELAPSED_ANGLE and it does not affect the result of that query object.
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The error INVALID_OPERATION is generated if the <id> is already in use
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within a BeginQueryANGLE/EndQueryANGLE block."
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Additions to Chapter 6 of the OpenGL ES 2.0 Specification (State and State
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Requests)
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Add a new section 6.1.9 "Timer Queries":
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"The command
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boolean IsQueryANGLE(uint id);
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returns TRUE if <id> is the name of a query object. If <id> is zero,
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or if <id> is a non-zero value that is not the name of a query
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object, IsQueryANGLE returns FALSE.
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Information about a query target can be queried with the command
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void GetQueryivANGLE(enum target, enum pname, int *params);
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<target> identifies the query target and can be TIME_ELAPSED_ANGLE or
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TIMESTAMP_ANGLE for timer queries.
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If <pname> is CURRENT_QUERY_ANGLE, the name of the currently active query
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for <target>, or zero if no query is active, will be placed in <params>.
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If <pname> is QUERY_COUNTER_BITS_ANGLE, the implementation-dependent number
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of bits used to hold the query result for <target> will be placed in
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<params>. The number of query counter bits may be zero, in which case
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the counter contains no useful information.
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For timer queries (TIME_ELAPSED_ANGLE and TIMESTAMP_ANGLE), if the number
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of bits is non-zero, the minimum number of bits allowed is 30 which
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will allow at least 1 second of timing.
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The state of a query object can be queried with the commands
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void GetQueryObjectivANGLE(uint id, enum pname, int *params);
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void GetQueryObjectuivANGLE(uint id, enum pname, uint *params);
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void GetQueryObjecti64vANGLE(uint id, enum pname, int64 *params);
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void GetQueryObjectui64vANGLE(uint id, enum pname, uint64 *params);
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If <id> is not the name of a query object, or if the query object
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named by <id> is currently active, then an INVALID_OPERATION error is
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generated.
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If <pname> is QUERY_RESULT_ANGLE, then the query object's result
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value is returned as a single integer in <params>. If the value is so
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large in magnitude that it cannot be represented with the requested type,
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then the nearest value representable using the requested type is
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returned. If the number of query counter bits for target is zero, then
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the result is returned as a single integer with the value zero.
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There may be an indeterminate delay before the above query returns. If
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<pname> is QUERY_RESULT_AVAILABLE_ANGLE, FALSE is returned if such a delay
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would be required; otherwise TRUE is returned. It must always be true
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that if any query object returns a result available of TRUE, all queries
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of the same type issued prior to that query must also return TRUE.
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Querying the state for a given timer query forces that timer query to
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complete within a finite amount of time.
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If multiple queries are issued on the same target and id prior to
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calling GetQueryObject[u]i[64]vANGLE, the result returned will always be
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from the last query issued. The results from any queries before the
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last one will be lost if the results are not retrieved before starting
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a new query on the same <target> and <id>."
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Errors
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The error INVALID_VALUE is generated if GenQueriesANGLE is called where
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<n> is negative.
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The error INVALID_VALUE is generated if DeleteQueriesANGLE is called
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where <n> is negative.
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The error INVALID_OPERATION is generated if BeginQueryANGLE is called
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when a query of the given <target> is already active.
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The error INVALID_OPERATION is generated if EndQueryANGLE is called
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when a query of the given <target> is not active.
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The error INVALID_OPERATION is generated if BeginQueryANGLE is called
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where <id> is zero.
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The error INVALID_OPERATION is generated if BeginQueryANGLE is called
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where <id> is the name of a query currently in progress.
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The error INVALID_OPERATION is generated if BeginQueryANGLE is called
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where <id> is the name of an existing query object whose type does not
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match <target>.
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The error INVALID_ENUM is generated if BeginQueryANGLE or EndQueryANGLE
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is called where <target> is not TIME_ELAPSED_ANGLE.
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The error INVALID_ENUM is generated if GetQueryivANGLE is called where
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<target> is not TIME_ELAPSED_ANGLE or TIMESTAMP_ANGLE.
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The error INVALID_ENUM is generated if GetQueryivANGLE is called where
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<pname> is not QUERY_COUNTER_BITS_ANGLE or CURRENT_QUERY_ANGLE.
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The error INVALID_ENUM is generated if QueryCounterANGLE is called where
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<target> is not TIMESTAMP_ANGLE.
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The error INVALID_OPERATION is generated if QueryCounterANGLE is called
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on a query object that is already in use inside a
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BeginQueryANGLE/EndQueryANGLE.
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The error INVALID_OPERATION is generated if GetQueryObjectivANGLE,
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GetQueryObjectuivANGLE, GetQueryObjecti64vANGLE, or
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GetQueryObjectui64vANGLE is called where <id> is not the name of a query
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object.
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The error INVALID_OPERATION is generated if GetQueryObjectivANGLE,
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GetQueryObjectuivANGLE, GetQueryObjecti64vANGLE, or
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GetQueryObjectui64vANGLE is called where <id> is the name of a currently
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active query object.
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The error INVALID_ENUM is generated if GetQueryObjectivANGLE,
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GetQueryObjectuivANGLE, GetQueryObjecti64vANGLE, or
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GetQueryObjectui64vANGLE is called where <pname> is not
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QUERY_RESULT_ANGLE or QUERY_RESULT_AVAILABLE_ANGLE.
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New State
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(Add a new table 6.xx, "Query Operations")
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Get Value Type Get Command Initial Value Description Sec
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--------- ---- ----------- ------------- ----------- ------
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- B - FALSE query active 5.3
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CURRENT_QUERY_ANGLE Z+ GetQueryivANGLE 0 active query ID 5.3
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QUERY_RESULT_ANGLE Z+ GetQueryObjectuivANGLE, 0 samples-passed count 5.3
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GetQueryObjectui64vANGLE
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QUERY_RESULT_AVAILABLE_ANGLE B GetQueryObjectivANGLE FALSE query result available 5.3
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New Implementation Dependent State
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(Add the following entry to table 6.18):
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Get Value Type Get Command Minimum Value Description Sec
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-------------------------- ---- ----------- ------------- ---------------- ------
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QUERY_COUNTER_BITS_ANGLE Z+ GetQueryivANGLE see 6.1.9 Number of bits in 6.1.9
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query counter
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Examples
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(1) Here is some rough sample code that demonstrates the intended usage
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of this extension.
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GLint queries[N];
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GLint available = 0;
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// timer queries can contain more than 32 bits of data, so always
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// query them using the 64 bit types to avoid overflow
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GLuint64ANGLE timeElapsed = 0;
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// Create a query object.
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glGenQueriesANGLE(N, queries);
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// Start query 1
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glBeginQueryANGLE(GL_TIME_ELAPSED_ANGLE, queries[0]);
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// Draw object 1
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....
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// End query 1
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glEndQueryANGLE(GL_TIME_ELAPSED_ANGLE);
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...
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// Start query N
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glBeginQueryANGLE(GL_TIME_ELAPSED_ANGLE, queries[N-1]);
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// Draw object N
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....
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// End query N
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glEndQueryANGLE(GL_TIME_ELAPSED_ANGLE);
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// Wait for all results to become available
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while (!available) {
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glGetQueryObjectivANGLE(queries[N-1], GL_QUERY_RESULT_AVAILABLE_ANGLE, &available);
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}
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for (i = 0; i < N; i++) {
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// See how much time the rendering of object i took in nanoseconds.
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glGetQueryObjectui64vANGLE(queries[i], GL_QUERY_RESULT_ANGLE, &timeElapsed);
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// Do something useful with the time. Note that care should be
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// taken to use all significant bits of the result, not just the
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// least significant 32 bits.
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AdjustObjectLODBasedOnDrawTime(i, timeElapsed);
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}
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This example is sub-optimal in that it stalls at the end of every
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frame to wait for query results. Ideally, the collection of results
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would be delayed one frame to minimize the amount of time spent
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waiting for the GPU to finish rendering.
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(2) This example is basically the same as the example above but uses
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QueryCounter instead.
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GLint queries[N+1];
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GLint available = 0;
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// timer queries can contain more than 32 bits of data, so always
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// query them using the 64 bit types to avoid overflow
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GLuint64ANGLE timeStart, timeEnd, timeElapsed = 0;
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// Create a query object.
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glGenQueriesANGLE(N+1, queries);
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// Query current timestamp 1
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glQueryCounterANGLE(queries[0], GL_TIMESTAMP_ANGLE);
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// Draw object 1
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....
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// Query current timestamp N
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glQueryCounterANGLE(queries[N-1], GL_TIMESTAMP_ANGLE);
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// Draw object N
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....
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// Query current timestamp N+1
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glQueryCounterANGLE(queries[N], GL_TIMESTAMP_ANGLE);
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// Wait for all results to become available
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while (!available) {
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glGetQueryObjectivANGLE(queries[N], GL_QUERY_RESULT_AVAILABLE_ANGLE, &available);
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}
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for (i = 0; i < N; i++) {
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// See how much time the rendering of object i took in nanoseconds.
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glGetQueryObjectui64vANGLE(queries[i], GL_QUERY_RESULT_ANGLE, &timeStart);
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glGetQueryObjectui64vANGLE(queries[i+1], GL_QUERY_RESULT_ANGLE, &timeEnd);
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timeElapsed = timeEnd - timeStart;
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// Do something useful with the time. Note that care should be
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// taken to use all significant bits of the result, not just the
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// least significant 32 bits.
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AdjustObjectLODBasedOnDrawTime(i, timeElapsed);
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}
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Issues from EXT_timer_query
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(1) What time interval is being measured?
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RESOLVED: The timer starts when all commands prior to BeginQuery() have
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been fully executed. At that point, everything that should be drawn by
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those commands has been written to the framebuffer. The timer stops
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when all commands prior to EndQuery() have been fully executed.
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(2) What unit of time will time intervals be returned in?
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RESOLVED: Nanoseconds (10^-9 seconds). This unit of measurement allows
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for reasonably accurate timing of even small blocks of rendering
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commands. The granularity of the timer is implementation-dependent. A
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32-bit query counter can express intervals of up to approximately 4
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seconds.
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(3) What should be the minimum number of counter bits for timer queries?
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RESOLVED: 30 bits, which will allow timing sections that take up to 1
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second to render.
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(4) How are counter results of more than 32 bits returned?
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RESOLVED: Via two new datatypes, int64ANGLE and uint64ANGLE, and their
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corresponding GetQueryObject entry points. These types hold integer
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values and have a minimum bit width of 64.
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(5) Should the extension measure total time elapsed between the full
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completion of the BeginQuery and EndQuery commands, or just time
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spent in the graphics library?
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RESOLVED: This extension will measure the total time elapsed between
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the full completion of these commands. Future extensions may implement
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a query to determine time elapsed at different stages of the graphics
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pipeline.
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(6) If multiple query types are supported, can multiple query types be
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active simultaneously?
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RESOLVED: Yes; an application may perform a timer query and another
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type of query simultaneously. An application can not perform multiple
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timer queries or multiple queries of other types simultaneously. An
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application also can not use the same query object for another query
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and a timer query simultaneously.
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(7) Do query objects have a query type permanently associated with them?
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RESOLVED: No. A single query object can be used to perform different
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types of queries, but not at the same time.
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Having a fixed type for each query object simplifies some aspects of the
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implementation -- not having to deal with queries with different result
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sizes, for example. It would also mean that BeginQuery() with a query
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object of the "wrong" type would result in an INVALID_OPERATION error.
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UPDATE: This resolution was relevant for EXT_timer_query and OpenGL 2.0.
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Since EXT_transform_feedback has since been incorporated into the core,
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the resolution is that BeginQuery will generate error INVALID_OPERATION
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if <id> represents a query object of a different type.
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(8) How predictable/repeatable are the results returned by the timer
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|
query?
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RESOLVED: In general, the amount of time needed to render the same
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|
primitives should be fairly constant. But there may be many other
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|
system issues (e.g., context switching on the CPU and GPU, virtual
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|
memory page faults, memory cache behavior on the CPU and GPU) that can
|
|
cause times to vary wildly.
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|
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|
Note that modern GPUs are generally highly pipelined, and may be
|
|
processing different primitives in different pipeline stages
|
|
simultaneously. In this extension, the timers start and stop when the
|
|
BeginQuery/EndQuery commands reach the bottom of the rendering pipeline.
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|
What that means is that by the time the timer starts, the GL driver on
|
|
the CPU may have started work on GL commands issued after BeginQuery,
|
|
and the higher pipeline stages (e.g., vertex transformation) may have
|
|
started as well.
|
|
|
|
(9) What should the new 64 bit integer type be called?
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|
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|
RESOLVED: The new types will be called GLint64ANGLE/GLuint64ANGLE. The new
|
|
command suffixes will be i64 and ui64. These names clearly convey the
|
|
minimum size of the types. These types are similar to the C99 standard
|
|
type int_least64_t, but we use names similar to the C99 optional type
|
|
int64_t for simplicity.
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|
|
|
Issues from ARB_timer_query
|
|
|
|
(10) What about tile-based implementations? The effects of a command are
|
|
not complete until the frame is completely rendered. Timing recorded
|
|
before the frame is complete may not be what developers expect. Also
|
|
the amount of time needed to render the same primitives is not
|
|
consistent, which conflicts with issue (8) above. The time depends on
|
|
how early or late in the scene it is placed.
|
|
|
|
RESOLVED: The current language supports tile-based rendering okay as it
|
|
is written. Developers are warned that using timers on tile-based
|
|
implementation may not produce results they expect since rendering is not
|
|
done in a linear order. Timing results are calculated when the frame is
|
|
completed and may depend on how early or late in the scene it is placed.
|
|
|
|
(11) Can the GL implementation use different clocks to implement the
|
|
TIME_ELAPSED and TIMESTAMP queries?
|
|
|
|
RESOLVED: Yes, the implemenation can use different internal clocks to
|
|
implement TIME_ELAPSED and TIMESTAMP. If different clocks are
|
|
used it is possible there is a slight discrepancy when comparing queries
|
|
made from TIME_ELAPSED and TIMESTAMP; they may have slight
|
|
differences when both are used to measure the same sequence. However, this
|
|
is unlikely to affect real applications since comparing the two queries is
|
|
not expected to be useful.
|
|
|
|
Issues
|
|
|
|
(12) What should we call this extension?
|
|
|
|
RESOLVED: ANGLE_timer_query
|
|
|
|
(13) Why is this done as a separate extension instead of just supporting
|
|
ARB_timer_query?
|
|
|
|
ARB_timer_query is written against OpenGL 3.2, which includes a lot of
|
|
the required support for dealing with query objects. None of these
|
|
functions or tokens exist in OpenGL ES, and as such have to be added in
|
|
this specification.
|
|
|
|
(14) How does this extension differ from ARB_timer_query?
|
|
|
|
This extension contains most ARB_timer_query behavior unchanged as well
|
|
as a subset of the query support required to use it from the core
|
|
OpenGL 3.2 spec. It omits the glGetInteger(TIMESTAMP) functionality used to
|
|
query the current time on the GPU, but the behavior for all remaining
|
|
functionality taken from ARB_timer_query is the same.
|
|
|
|
(15) Are query objects shareable between multiple contexts?
|
|
|
|
RESOLVED: No. Query objects are lightweight and we normally share
|
|
large data across contexts. Also, being able to share query objects
|
|
across contexts is not particularly useful. In order to do the async
|
|
query across contexts, a query on one context would have to be finished
|
|
before the other context could query it.
|
|
|
|
Revision History
|
|
|
|
Revision 1, 2011/04/28
|
|
- copied from revision 9 of ARB_timer_query and revision 7 of
|
|
ARB_occlusion_query
|
|
- removed language that was clearly not relevant to ES2
|
|
- rebased changes against the OpenGL ES 2.0 specification
|