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 Name

     ANGLE_timer_query

 Name Strings

     GL_ANGLE_timer_query

 Contributors

     Contributors to ARB_occlusion_query

     Contributors to EXT_timer_query

     Contributors to ARB_timer_query

     Ben Vanik, Google Inc.

     Daniel Koch, TransGaming Inc.

 Contact

     Ben Vanik, Google Inc. (benvanik 'at' google 'dot' com)

 Status

     Draft

 Version

     Last Modified Date: Apr 28, 2011

     Author Revision: 1

 Number

     OpenGL ES Extension #??

 Dependencies

     OpenGL ES 2.0 is required.

     The extension is written against the OpenGL ES 2.0 specification.

 Overview

     Applications can benefit from accurate timing information in a number of

     different ways.  During application development, timing information can

     help identify application or driver bottlenecks.  At run time,

     applications can use timing information to dynamically adjust the amount

     of detail in a scene to achieve constant frame rates.  OpenGL

     implementations have historically provided little to no useful timing

     information.  Applications can get some idea of timing by reading timers

     on the CPU, but these timers are not synchronized with the graphics

     rendering pipeline.  Reading a CPU timer does not guarantee the completion

     of a potentially large amount of graphics work accumulated before the

     timer is read, and will thus produce wildly inaccurate results.

     glFinish() can be used to determine when previous rendering commands have

     been completed, but will idle the graphics pipeline and adversely affect

     application performance.

     This extension provides a query mechanism that can be used to determine

     the amount of time it takes to fully complete a set of GL commands, and

     without stalling the rendering pipeline.  It uses the query object

     mechanisms first introduced in the occlusion query extension, which allow

     time intervals to be polled asynchronously by the application.

 IP Status

     No known IP claims.

 New Procedures and Functions

     void GenQueriesANGLE(sizei n, uint *ids);

     void DeleteQueriesANGLE(sizei n, const uint *ids);

     boolean IsQueryANGLE(uint id);

     void BeginQueryANGLE(enum target, uint id);

     void EndQueryANGLE(enum target);

     void QueryCounterANGLE(uint id, enum target);

     void GetQueryivANGLE(enum target, enum pname, int *params);

     void GetQueryObjectivANGLE(uint id, enum pname, int *params);

     void GetQueryObjectuivANGLE(uint id, enum pname, uint *params);

     void GetQueryObjecti64vANGLE(uint id, enum pname, int64 *params);

     void GetQueryObjectui64vANGLE(uint id, enum pname, uint64 *params);

 New Tokens

     Accepted by the <pname> parameter of GetQueryivANGLE:

         QUERY_COUNTER_BITS_ANGLE                       0x8864

         CURRENT_QUERY_ANGLE                            0x8865

     Accepted by the <pname> parameter of GetQueryObjectivANGLE,

     GetQueryObjectuivANGLE, GetQueryObjecti64vANGLE, and

     GetQueryObjectui64vANGLE:

         QUERY_RESULT_ANGLE                             0x8866

         QUERY_RESULT_AVAILABLE_ANGLE                   0x8867

     Accepted by the <target> parameter of BeginQueryANGLE, EndQueryANGLE, and

     GetQueryivANGLE:

         TIME_ELAPSED_ANGLE                             0x88BF

     Accepted by the <target> parameter of GetQueryivANGLE and

     QueryCounterANGLE:

         TIMESTAMP_ANGLE                                0x8E28

 Additions to Chapter 2 of the OpenGL ES 2.0 Specification (OpenGL ES Operation)

     (Modify table 2.1, Correspondence of command suffix letters to GL argument)

     Add two new types:

     Letter Corresponding GL Type

     ------ ---------------------

     i64    int64ANGLE

     ui64   uint64ANGLE

     (Modify table 2.2, GL data types) Add two new types:

     GL Type       Minimum Bit Width   Description

     -------       -----------------   -----------------------------

     int64ANGLE    64                  Signed 2's complement integer

     uint64ANGLE   64                  Unsigned binary integer

 Additions to Chapter 5 of the OpenGL ES 2.0 Specification (Special Functions)

     Add a new section 5.3 "Timer Queries":

     "5.3  Timer Queries

     Timer queries use query objects to track the amount of time needed to

     fully complete a set of GL commands, or to determine the current time

     of the GL.

     Timer queries are associated with query objects.  The command

       void GenQueriesANGLE(sizei n, uint *ids);

     returns <n> previously unused query object names in <ids>.  These

     names are marked as used, but no object is associated with them until

     the first time they are used by BeginQueryANGLE.  Query objects contain

     one piece of state, an integer result value.  This result value is

     initialized to zero when the object is created.  Any positive integer

     except for zero (which is reserved for the GL) is a valid query

     object name.

     Query objects are deleted by calling

       void DeleteQueriesANGLE(sizei n, const uint *ids);

     <ids> contains <n> names of query objects to be deleted.  After a

     query object is deleted, its name is again unused.  Unused names in

     <ids> are silently ignored.

     If an active query object is deleted its name immediately becomes unused,

     but the underlying object is not deleted until it is no longer active.

     A timer query can be started and finished by calling

       void BeginQueryANGLE(enum target, uint id);

       void EndQueryANGLE(enum target);

     where <target> is TIME_ELAPSED_ANGLE.  If BeginQueryANGLE is called

     with an unused <id>, that name is marked as used and associated with

     a new query object.

     If BeginQueryANGLE is called with an <id> of zero, if the active query

     object name for <target> is non-zero, if <id> is the name of an existing

     query object whose type does not match <target>, or if <id> is the active

     query object name for any query type, the error INVALID_OPERATION is

     generated.  If EndQueryANGLE is called while no query with the same target

     is in progress, an INVALID_OPERATION error is generated.

     When BeginQueryANGLE and EndQueryANGLE are called with a <target> of

     TIME_ELAPSED_ANGLE, the GL prepares to start and stop the timer used for

     timer queries.  The timer is started or stopped when the effects from all

     previous commands on the GL client and server state and the framebuffer

     have been fully realized.  The BeginQueryANGLE and EndQueryANGLE commands

     may return before the timer is actually started or stopped.  When the timer

     query timer is finally stopped, the elapsed time (in nanoseconds) is

     written to the corresponding query object as the query result value, and

     the query result for that object is marked as available.

     If the elapsed time overflows the number of bits, <n>, available to hold

     elapsed time, its value becomes undefined.  It is recommended, but not

     required, that implementations handle this overflow case by saturating at

     2^n - 1.

     The necessary state is a single bit indicating whether an timer

     query is active, the identifier of the currently active timer

     query, and a counter keeping track of the time that has passed.

     When the command

          void QueryCounterANGLE(uint id, enum target);

     is called with <target> TIMESTAMP_ANGLE, the GL records the current time

     into the corresponding query object. The time is recorded after all

     previous commands on the GL client and server state and the framebuffer

     have been fully realized. When the time is recorded, the query result for

     that object is marked available. QueryCounterANGLE timer queries can be

     used within a BeginQueryANGLE / EndQueryANGLE block where the <target> is

     TIME_ELAPSED_ANGLE and it does not affect the result of that query object.

     The error INVALID_OPERATION is generated if the <id> is already in use

     within a BeginQueryANGLE/EndQueryANGLE block."

 Additions to Chapter 6 of the OpenGL ES 2.0 Specification (State and State

 Requests)

     Add a new section 6.1.9 "Timer Queries":

     "The command

       boolean IsQueryANGLE(uint id);

     returns TRUE if <id> is the name of a query object.  If <id> is zero,

     or if <id> is a non-zero value that is not the name of a query

     object, IsQueryANGLE returns FALSE.

     Information about a query target can be queried with the command

       void GetQueryivANGLE(enum target, enum pname, int *params);

     <target> identifies the query target and can be TIME_ELAPSED_ANGLE or

     TIMESTAMP_ANGLE for timer queries.

     If <pname> is CURRENT_QUERY_ANGLE, the name of the currently active query

     for <target>, or zero if no query is active, will be placed in <params>.

     If <pname> is QUERY_COUNTER_BITS_ANGLE, the implementation-dependent number

     of bits used to hold the query result for <target> will be placed in

     <params>.  The number of query counter bits may be zero, in which case

     the counter contains no useful information.

     For timer queries (TIME_ELAPSED_ANGLE and TIMESTAMP_ANGLE), if the number

     of bits is non-zero, the minimum number of bits allowed is 30 which

     will allow at least 1 second of timing.

     The state of a query object can be queried with the commands

       void GetQueryObjectivANGLE(uint id, enum pname, int *params);

       void GetQueryObjectuivANGLE(uint id, enum pname, uint *params);

       void GetQueryObjecti64vANGLE(uint id, enum pname, int64 *params);

       void GetQueryObjectui64vANGLE(uint id, enum pname, uint64 *params);

     If <id> is not the name of a query object, or if the query object

     named by <id> is currently active, then an INVALID_OPERATION error is

     generated.

     If <pname> is QUERY_RESULT_ANGLE, then the query object's result

     value is returned as a single integer in <params>. If the value is so

     large in magnitude that it cannot be represented with the requested type,

     then the nearest value representable using the requested type is

     returned. If the number of query counter bits for target is zero, then

     the result is returned as a single integer with the value zero.

     There may be an indeterminate delay before the above query returns. If

     <pname> is QUERY_RESULT_AVAILABLE_ANGLE, FALSE is returned if such a delay

     would be required; otherwise TRUE is returned. It must always be true

     that if any query object returns a result available of TRUE, all queries

     of the same type issued prior to that query must also return TRUE.

     Querying the state for a given timer query forces that timer query to

     complete within a finite amount of time.

     If multiple queries are issued on the same target and id prior to 

     calling GetQueryObject[u]i[64]vANGLE, the result returned will always be

     from the last query issued.  The results from any queries before the

     last one will be lost if the results are not retrieved before starting

     a new query on the same <target> and <id>."

 Errors

     The error INVALID_VALUE is generated if GenQueriesANGLE is called where

     <n> is negative.

     The error INVALID_VALUE is generated if DeleteQueriesANGLE is called

     where <n> is negative.

     The error INVALID_OPERATION is generated if BeginQueryANGLE is called

     when a query of the given <target> is already active.

     The error INVALID_OPERATION is generated if EndQueryANGLE is called

     when a query of the given <target> is not active.

     The error INVALID_OPERATION is generated if BeginQueryANGLE is called

     where <id> is zero.

     The error INVALID_OPERATION is generated if BeginQueryANGLE is called

     where <id> is the name of a query currently in progress.

     The error INVALID_OPERATION is generated if BeginQueryANGLE is called

     where <id> is the name of an existing query object whose type does not

     match <target>.

     The error INVALID_ENUM is generated if BeginQueryANGLE or EndQueryANGLE

     is called where <target> is not TIME_ELAPSED_ANGLE.

     The error INVALID_ENUM is generated if GetQueryivANGLE is called where

     <target> is not TIME_ELAPSED_ANGLE or TIMESTAMP_ANGLE.

     The error INVALID_ENUM is generated if GetQueryivANGLE is called where

     <pname> is not QUERY_COUNTER_BITS_ANGLE or CURRENT_QUERY_ANGLE.

     The error INVALID_ENUM is generated if QueryCounterANGLE is called where

     <target> is not TIMESTAMP_ANGLE.

     The error INVALID_OPERATION is generated if QueryCounterANGLE is called

     on a query object that is already in use inside a

     BeginQueryANGLE/EndQueryANGLE.

     The error INVALID_OPERATION is generated if GetQueryObjectivANGLE,

     GetQueryObjectuivANGLE, GetQueryObjecti64vANGLE, or

     GetQueryObjectui64vANGLE is called where <id> is not the name of a query

     object.

     The error INVALID_OPERATION is generated if GetQueryObjectivANGLE,

     GetQueryObjectuivANGLE, GetQueryObjecti64vANGLE, or

     GetQueryObjectui64vANGLE is called where <id> is the name of a currently

     active query object.

     The error INVALID_ENUM is generated if GetQueryObjectivANGLE,

     GetQueryObjectuivANGLE, GetQueryObjecti64vANGLE, or

     GetQueryObjectui64vANGLE is called where <pname> is not

     QUERY_RESULT_ANGLE or QUERY_RESULT_AVAILABLE_ANGLE.

 New State

     (Add a new table 6.xx, "Query Operations")

     Get Value                      Type    Get Command              Initial Value   Description              Sec

     ---------                      ----    -----------              -------------   -----------              ------

     -                              B       -                        FALSE           query active             5.3

     CURRENT_QUERY_ANGLE            Z+      GetQueryivANGLE          0               active query ID          5.3

     QUERY_RESULT_ANGLE             Z+      GetQueryObjectuivANGLE,  0               samples-passed count     5.3

                                            GetQueryObjectui64vANGLE

     QUERY_RESULT_AVAILABLE_ANGLE   B       GetQueryObjectivANGLE    FALSE           query result available   5.3

 New Implementation Dependent State

     (Add the following entry to table 6.18):

     Get Value                      Type    Get Command      Minimum Value      Description           Sec

     --------------------------     ----    -----------      -------------      ----------------      ------

     QUERY_COUNTER_BITS_ANGLE       Z+      GetQueryivANGLE  see 6.1.9          Number of bits in     6.1.9

                                                                                query counter

 Examples

     (1) Here is some rough sample code that demonstrates the intended usage

         of this extension.

         GLint queries[N];

         GLint available = 0;

         // timer queries can contain more than 32 bits of data, so always

         // query them using the 64 bit types to avoid overflow

         GLuint64ANGLE timeElapsed = 0;

         // Create a query object.

         glGenQueriesANGLE(N, queries);

         // Start query 1

         glBeginQueryANGLE(GL_TIME_ELAPSED_ANGLE, queries[0]);

         // Draw object 1

         ....

         // End query 1

         glEndQueryANGLE(GL_TIME_ELAPSED_ANGLE);

         ...

         // Start query N

         glBeginQueryANGLE(GL_TIME_ELAPSED_ANGLE, queries[N-1]);

         // Draw object N

         ....

         // End query N

         glEndQueryANGLE(GL_TIME_ELAPSED_ANGLE);

         // Wait for all results to become available

         while (!available) {

             glGetQueryObjectivANGLE(queries[N-1], GL_QUERY_RESULT_AVAILABLE_ANGLE, &available);

         }

         for (i = 0; i < N; i++) {

             // See how much time the rendering of object i took in nanoseconds.

             glGetQueryObjectui64vANGLE(queries[i], GL_QUERY_RESULT_ANGLE, &timeElapsed);

             // Do something useful with the time.  Note that care should be

             // taken to use all significant bits of the result, not just the

             // least significant 32 bits.

             AdjustObjectLODBasedOnDrawTime(i, timeElapsed);

         }

         This example is sub-optimal in that it stalls at the end of every

         frame to wait for query results.  Ideally, the collection of results

         would be delayed one frame to minimize the amount of time spent

         waiting for the GPU to finish rendering.

     (2) This example is basically the same as the example above but uses

         QueryCounter instead.

         GLint queries[N+1];

         GLint available = 0;

         // timer queries can contain more than 32 bits of data, so always

         // query them using the 64 bit types to avoid overflow

         GLuint64ANGLE timeStart, timeEnd, timeElapsed = 0;

         // Create a query object.

         glGenQueriesANGLE(N+1, queries);

         // Query current timestamp 1

         glQueryCounterANGLE(queries[0], GL_TIMESTAMP_ANGLE);

         // Draw object 1

         ....

         // Query current timestamp N

         glQueryCounterANGLE(queries[N-1], GL_TIMESTAMP_ANGLE);

         // Draw object N

         ....

         // Query current timestamp N+1

         glQueryCounterANGLE(queries[N], GL_TIMESTAMP_ANGLE);

         // Wait for all results to become available

         while (!available) {

             glGetQueryObjectivANGLE(queries[N], GL_QUERY_RESULT_AVAILABLE_ANGLE, &available);

         }

         for (i = 0; i < N; i++) {

             // See how much time the rendering of object i took in nanoseconds.

             glGetQueryObjectui64vANGLE(queries[i], GL_QUERY_RESULT_ANGLE, &timeStart);

             glGetQueryObjectui64vANGLE(queries[i+1], GL_QUERY_RESULT_ANGLE, &timeEnd);

             timeElapsed = timeEnd - timeStart;

             // Do something useful with the time.  Note that care should be

             // taken to use all significant bits of the result, not just the

             // least significant 32 bits.

             AdjustObjectLODBasedOnDrawTime(i, timeElapsed);

         }

 Issues from EXT_timer_query

     (1) What time interval is being measured?

     RESOLVED:  The timer starts when all commands prior to BeginQuery() have

     been fully executed.  At that point, everything that should be drawn by

     those commands has been written to the framebuffer.  The timer stops

     when all commands prior to EndQuery() have been fully executed.

     (2) What unit of time will time intervals be returned in?

     RESOLVED:  Nanoseconds (10^-9 seconds).  This unit of measurement allows

     for reasonably accurate timing of even small blocks of rendering

     commands.  The granularity of the timer is implementation-dependent.  A

     32-bit query counter can express intervals of up to approximately 4

     seconds.

     (3) What should be the minimum number of counter bits for timer queries?

     RESOLVED:  30 bits, which will allow timing sections that take up to 1

     second to render.

     (4) How are counter results of more than 32 bits returned?

     RESOLVED:  Via two new datatypes, int64ANGLE and uint64ANGLE, and their

     corresponding GetQueryObject entry points.  These types hold integer

     values and have a minimum bit width of 64.

     (5) Should the extension measure total time elapsed between the full

         completion of the BeginQuery and EndQuery commands, or just time

         spent in the graphics library?

     RESOLVED:  This extension will measure the total time elapsed between

     the full completion of these commands.  Future extensions may implement

     a query to determine time elapsed at different stages of the graphics

     pipeline.

     (6) If multiple query types are supported, can multiple query types be

         active simultaneously?

     RESOLVED:  Yes; an application may perform a timer query and another

     type of query simultaneously.  An application can not perform multiple

     timer queries or multiple queries of other types simultaneously.  An

     application also can not use the same query object for another query

     and a timer query simultaneously.

     (7) Do query objects have a query type permanently associated with them?

     RESOLVED:  No.  A single query object can be used to perform different

     types of queries, but not at the same time.

     Having a fixed type for each query object simplifies some aspects of the

     implementation -- not having to deal with queries with different result

     sizes, for example.  It would also mean that BeginQuery() with a query

     object of the "wrong" type would result in an INVALID_OPERATION error.

     UPDATE: This resolution was relevant for EXT_timer_query and OpenGL 2.0.

     Since EXT_transform_feedback has since been incorporated into the core,

     the resolution is that BeginQuery will generate error INVALID_OPERATION

     if <id> represents a query object of a different type.

     (8) How predictable/repeatable are the results returned by the timer

         query?

     RESOLVED:  In general, the amount of time needed to render the same

     primitives should be fairly constant.  But there may be many other

     system issues (e.g., context switching on the CPU and GPU, virtual

     memory page faults, memory cache behavior on the CPU and GPU) that can

     cause times to vary wildly.

     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.

     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?

     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.

 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