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kc3-lang/angle/extensions/ANGLE_timer_query.txt
Jamie Madill
- extensions/ANGLE_timer_query.txt
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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